phan tich sac ki khi th vung

7/28/2019 Phan Tich Sac Ki Khi Th Vung

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Bi Xun Vng C s phn tch sc k

Chng 1: C SL THUYT CHUNG V TCH SC K

1.1. Gii thiu phng php

1.1.1nh ngha sc k (Chromatography)

nh ngha ca Mikhail S. Tsvett (1906):

Sc k l mt phng php tch trong cc cu t ca mt hn hp c tch trn mtct hp tht trong mt h thng ang chy.

nh ngha ca IUPAC (1993):

Sc k l mt phng php tchtrong cc cu tc tch c phn b gia hai pha,mt trong hai pha l pha tnh ng yn cn pha kia chuyn ng theo mt hng xcnh.

1.1.2. Phn loi Ngi ta phn loi cc phng php sc k da vo c ch hot ng sc k: hp ph,phn b, trao i ion v vo tnh cht ca pha tnh cng nh phng php th hin sck. V d:

- Phng php sc k lng rn trn ct, phng php sc k phn b kh lngtrn ct.

- Phng php sc k phn b lng lng trn bn phng hai chiu.- Phng php sc k phn b lng lng pha ngc p sut cao trn ct

Cch sc k c nhiu nhng thc hin qu trnh sc k th ch c hai dng: dng ctv dng bn phng (bn knh, polime, kim loi, giy).

Trong sc k ct, pha tnh c gi trong mt ct ngn v pha ng c cho chuynng qua ct bi p sut hoc do trng lc. Trong sc k bn mng, pha tnh c phtrn mt mt phng thy tinh hoc kim loi.

Thng n gin ha, tuy khng chnh xc ngi ta gi tt cc phng php sc k:sc k kh, sc k lng, sc k lng cao p, sc k lp mng, sc k gel

Trong scc phng php sc k c bit, quan trng nht l sc k hp ph, sc k phnb v sc k trao i ion. Di y s gii thiu ba phng php sc k ny nhm vo haimc ch: chun b mu cho cht phn tch v phn tch mt hn hp cht.

Bng 1: Phn loi cc phng php sc k ct

Phn loi chung Phng php c th Pha tnh Kiu cn bngSc k lng (LC)(Pha ng : lng)

- Lng- lng hoc phnb- Pha lng lin kt

- Lng-rn hochp phtrao i ion

- Lng c ph trnmt cht rn- Cht hu c c gntrn mt b mt rn- RnNha trao i ion

- Phn b

- Phn b gia chtlng v b mt lin kt- Hp phTrao i ion


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Sc k kh (GC)(pha ng: Kh)

- Kh-lng

- Kh - pha lin kt

- Kh - rn

- Lng c ph trnmt cht rn- Cht hu c c linkt trn mt b mt rn

- Rn

- Phn b gia kh vlng- Phn b gia lng vb mt lin kt

- Hp phSc k lng siuti hn

Pha lng: cht lng siuti hn (supercriticalfluid)

Cht hu cc linkt trn mt b mt rn

Phn b gia cht lngsiu ti hn v b mtlin kt

Hnh 1.1: S nguyn tc a) sc k ct b) sc k bn mng

1.2. C sl thuyt chung ca phng php sc k

1.2.1 Qu trnh sc k

Sc k l mt k thut tch trong cc cu t cn tch trong mt hn hp mu c vnchuyn bi pha ng i qua pha tnh. Mu i vo tng ng c mang theo dc hthng sc k (ct, bn phng) c cha pha tnh phn bu khp.

Pha ng c th l pha lng hoc kh, pha tnh c th l mt lp phim c ph trn bmt ca cht mang tr hoc mt b mt rn. Stng tc xy ra gia cc cu t vi phatnh nh cc cu t s phn b gia pha ng v pha tnh.

Pha ng

M u

Pha tnh Hng chypha ng

S c k

Detector

Cc c u tgii tch ra

Pha ng

Lp mng pha tnh Bn mng tr

Cc c u

t tch ra

Hng chypha ng

M u (A+B+C)

Xut pht

i m ndung mi

N ng ca B


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S i lc khc nhau ca cc cht tan trn pha tnh lm chng di chuyn vi nhng vn tckhc nhau trong pha ng ca h thng sc k. Kt qu l chng c tch thnh nhngdi trong pha ng v vo lc cui ca qu trnh cc cu t ln lt hin ra theo trt ttng tc vi pha tnh.

Cu t di chuyn chm (tng tc yu) ra trc, cu t blu gi mnh hn ra sau didng cc nh (pic) tch ring r (hoc bc thang) ty thuc vo cch tin hnh sc k vc hin thdi dng sc k .

Hnh 1.1 minh ha mt qu trnh tch mt hn hp n gin gm hai cht A v B (lc tng tcvi pha tnh ca A < B) theo thi gian.

Mu cha A v B c tim vo ct. Khi cho mt cht ra gii bt u chy qua ct,phn ca mu c ha tan trong pha ng c di chuyn ti phn u ca ct (ti thiim to). y cc cu t A v B t phn b gia hai pha. Tip tc cho pha ng i qua ct th n sy phn ha tan ny chy xung di v mts phn b mi gia pha ng v pha tnh s xy ra (thi im t1). ng thi s phn bgia dung mi mi v pha tnh cng din ra ti v tr ca mu lc u.

Vic thm tip dung mi s mang cc phn t ha tan chy xung ct trong mt lot lintip cc chuyn bin gia hai pha. Bi v s di chuyn ca cht tan ch xy ra trong phang, nn tc trung bnh ca s di chuyn cht tan ph thuc vo phn thi gian chttan y nm trong pha . Phn thi gian ny l nhi vi cht tan blu gi mnh bipha tnh (cu t B trong v d trn) v ln i vi cht tan (cu t A) c slu gi trongpha ng mnh hn. Sau mt thi gian cc phn t cht A v B dn dn c tch khinhau.

Nu t mt detect c khnng pht hin c cc cht tan (cu t A v B) ti cui cttch v tn hiu ca n c v li nh mt hm ca thi gian (hoc thtch c thm

vo) th mt lot pic i xng sc ghi li v c gi l sc k . V tr ca cc pic theo thi gian c dng nhn din nh tnh v din tch ca pc

c dng cho php phn tch nh lng ca cu tang xt.


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Hnh 1.2: Qu trnh tch sc k trn ct ca hai cht A v B

1.2.2. Cc phng php tin hnh tch sc k

thc hin tch sc k ngi ta c th s dng mt trong ba phng php sau:

1.2.2.1.Phng php ra gii

K thut ny c s dng rng ri nht trong cc phng php sc k hin nay. Mt lng nh hn hp mu c gii thiu vo ct vi pha ng c i lc vi pha tnh

b hn so vi bt k cu t cn tch c trong mu. V th cc cu t cn tch di chuyn

M u

Ctnhi

Pha ng

Detector

S c k

Thi gian


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vi tc chm hn so vi cht ra gii. Tc ny c xc nh bi i lc tng ica mi cu t ln pha tnh so vi pha ng, chnh l h s phn b K = Csp/Cmp. y Csp, Cmp l nng ca cu tang xt trn pha tnh v trong pha ng. Cc cu tc ra gii theo trt t i lc ca chng nhng tc di chuyn tng ica chng ph thuc vo tng tc 3 thnh phn gia chng vi pha ng, vi pha tnhv gia pha ng vi pha tnh. Bi v cc cu tc tch khi nhau vi mt vng phang gia chng nn phng php ny c s dng trong cc php tch vi mc chphn tch.

Pha ng c thkhng thay i thnh phn dung mi trong sut qu trnh ra gii; c ththay i dung mi ra gii sau mt thi gian nh trc (ra gii theo tng giai on);cng c thkhng thay i cc dung mi to nn pha ng nhng thay i nng cacc thnh phn c trong pha ng sau mt thi gian nh trc (ra gii gradient).

1.2.2.2.Phng php tin lu

Hn hp cn tch gm cc cht A, B v C c cho chy lin tc vo phn trn ca ct,trong A l cu t c i lc yu nht vi pha tnh.

Do cc cu t A, B v C blu gi trn ct, nn trc ht t ct chy ra ch c dung mi.A do c lc tng tc trn ct yu nht s di chuyn xung di cn cc cu t c i lcmnh hn A b pha tnh giphn trn ca ct.

Do dung dng c hn ca pha tnh nn khi vt dung lng ny th cu t A s dichuyn dc theo ct v ra khi ct dng nguyn cht sau l hn hp ca cc thnhphn tip theo A+B ri A+B+C.

Phng php tin lu t c dng do khng thc hin c vic tch hon ton cc cut, c bit khi s dng s tch sc k vo mc ch phn tch.

1.2.2.3.Phng php thy:

Mu c cho vo ct, dng dung mi ra gii c i lc vi pha tnh mnh hn bt kmt cu t no ca hn hp tch y cc cu t cn tch thot ra khi ct.

Cu t thot ra khi ct u tin l cu ttng tc yu nht vi pha tnh, sau n cccu t khc c i lc vi pha tnh tng dn.

Phng php ny to nn cc di ra gii khng hon ton c tch khi nhau: c dithu c cht nguyn cht nhng c di gia cc di nguyn cht th gm hn hp cachng.

Trong thc hnh phng th nghim tch cc hn hp phc tp ngi ta thng hay dng hncl phng php ra gii.


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Hnh 1.3: Cc phng php ra gii, tin lu, thy

1.2.3. c tnh sc k ca cht tan

1.2.3.1. Tnh cht lu gi

Tnh cht lu gi phn nh s phn b ca cht tan gia pha tnh v pha ng v c biu thbng cc i lng thtch lu hay thi gian lu.

Thtch lu VR l thtch pha ng cn thit vn chuyn cht tan i t thi im amu vo, i qua ct v n detect (trn sc k l im cc i ca pic).

Thi gian lu tRi l thi gian t lc cht tan i c np vo ct tch b phn tim mucho n lc cht ra khi ct thi im c nng cc i.

Dung mi ra gii (E)

Pha tnh

Ra gii Ti n lu Th y

n Detector

Tn hiuDetector

Th tch dungmi ra gii


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Thtch lu c th nhn c trc tip t thi gian lu tRtrn sc k bng cch nhnvi tc th tch dng Fc (th tch ca pha ng trn mt n v thi gian):

VR = tR. Fc

Tc dng c tnh theo cc thng s ca ct nh sau:

M

tc

ct

LdF

4

2

y:

dcl ng knh ca ct, L l chiu di ct, t l rng ton phn ca cht nhi ct ( rng ca cht nhi ct biu

th t s th tch k hca cht nhi v th tch khi ton phn ca n: ivi cht nhi rn = 0.35 - 0.45, cht nhi xp = 0.70 - 0.90, ct mao qun= 1.0),

Vc l th tch bn trong ct.

Tc tuyn tnh trung bnh u ca s dch chuyn cht tan l:Rt

Lu

Tc tuyn tnh trung bnh u ca pha ng l:Mt

Lu

ytMhay tol thi gian khng blu gi ca cht tan (thi gian cht tan lu trong pha ng).

Trong sc k kh, tMc ly bng thi gian cn thit cho CH4 di chuyn i qua ct.Tng ng tMhay tocth tch VM(hoc Vo) biu th th tch trng ca ct (bao gm c th tchca b phn tim mu (injector), thtch cc on ng ni, th tch rng ca chnh ct v th tchdetect).

Thtch lu hiu chnh VRhoc thi gian lu hiu chnh tRc cho bi:VR = VR VM hoc tR = tR tM

(thi gian khng blu gi ca cht tan gn ng c xem nh l thi gian lu ca pha ng).


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Hnh 1.4: Sc k minh ha cc thi gian lu t (hoc th tch lu) v rng ca y pic W ca cht tankhng blu giM v ca 2 cht blu gi1 v 2

1.2.3.2. H sphn bK (Partition coefficient)

Mi cu t hoc cht tan c phn b gia 2 pha vi mt cn bng c thit lp v ttc cc qu trnh tch sc k c da trn s khc nhau v khnng phn b ca cht tangia pha ng v pha tnh.

Khi cht tan i vo h thng sc k, n ngay lp tc phn b gia cc pha ng v phatnh. Gi thit nu pha ng dng li vo bt k mt thi gian no, cht tan c mt sphn b cn bng gia hai pha, v nng ca cht tan trong mi pha c cho bi hs phn b nhit ng:

M

s

CCK

y Cs v CM l nng cht tan trong pha tnh v pha ng tng ng.

Trng hp khi K= 1 th cht tan c phn b bng nhau gia hai pha.

H s phn bxc nh tc trung bnh ca mi vng cht tan (chnh xc l tm vng)do pha ng vn chuyn khi n i qua ct.

i vi pic i xng, khi cc i pic xut hin li ra ca ct, mt na lng cht tan c ra khi ct trong thtch lu VR v mt na cn li c phn b gia th tch phang VMv th tch pha tnh Vs:

VRCM= VMCM + VsCs

hay VR = VM+ KVs

hay VR VM= KVs

Tim m u

Cng tnhiu Detector

Thi gian (th tch)


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Phng trnh ny ng vi ct phn b lng, cn i vi ct hp ph, Vs phi thay bngSs l din tch b mt ca cht hp th.

1.2.3.3. H sdung lng k (The capacity factor)

H sdung lng k l thng s thc nghim quan trng trong sc k ct c s dngrng ri m t cc tc dch chuyn ca cc cht tan trn ct.

Cho mt cht tan, h sdung lng k c nh ngha nh l t s mol cht tan trongpha tnh v s mol cht tan trong pha ng:

k =M

s

MM

ss

V

VK

VC

VC T sVM/Vsc gi l t s th tch pha

H sdung lng cn c nh ngha l t s gia thi gian ca cht tan lu li trn phatnh v thi gian cn cht tan di chuyn trong pha ng sut chiu di ca ct nukhng blu gitM.

M

MR

M

MR

M

R

V

VV

t

tt

t

tk

''

Khi k cho mt cht tan nhhn 1 nhiu, s ra gii xy ra rt nhanh nn vic xc nhthi gian lu l rt kh. Cn khi k khong 20 n 30 th thi gian ra gii s b ko di.

V vy cc php tch nn c thc hin nhng iu kin m cc k ca cc cht tannm trong khong gi tr t1 n 5.

Gi tr k trong sc k kh c thc thay i bi vic thay i nhit v cch nhict. Cn trong sc k lng, k thng c iu khin cho php tch tt hn bi thay

i thnh phn pha ng v pha tnh.

1.2.3.4. H schn lc (The selectivity factor)

Khnng ca mt pha tnh tch 2 cu t A v B (B l cu t blu gi mnh hn) cxc nh bi t s phn btng i ca chng v cng l nhng h slu gi ca chngi vi mt pha tnh cho.

H s chn lc l mt hm ca slu gitng i ca mi cu t trn pha tnh:

A

B

A

B

R

R

K

K

k

k

t

t ''

'1

'2


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H s chn lc ca mt cp di (pic) gn nhau l mt hm ph thuc vo loi pha tnhc s dng, pha ng v nhit ca ct. cho mt s tch c tt th nn c gatr ln hn 1. Hai cht cn tch cng tch ra xa khi nhau khi cng ln nhng nu quln th thi gian phn tch cng ko di, nn trong khong t 1,05 n 2,0.

1.2.3.5. Nhng yu tnh hng n slu gi

Tc di chuyn ca mt di cht tan qua mt ct hay mt a sc k lp mng ph thuc vo sphn b ca cc phn t cht tan gia pha tnh v pha ng. Nhng nhn tnh hng n sphn b hay slu gi l:

Thnh phn v tnh cht ca pha ng Kiu v tnh cht ca pha tnh Cc lc tng tc cc phn t gia cc cu t ca pha ng v pha tnh Nhit

Hai yu t gp phn tch tt cc hp cht bi sc k l:

S khc nhau v thi gian phn b ca chng trong 2 pha: nu s khc nhau cng ln ths tch chng cng tt.

dong rng ca cc pic nu cng rng th s tch chng cng km.1. 3. Sdong rng ca pic v hiu lc tch

1.3.1. Mu

Hiu lc ca mt ct tch chu tc ng bi ln ca s dong rng pic xy ra khi mtcht chuyn ng dc theo ct.

Cht tan khi chy dc theo ct c khuynh hng phn bnh mt hnh phn b chunGaussian vi lch chun (hnh 5).

Nu cht tan tiu tn nhiu thi gian khi dch chuyn dc xung ct th pic cng b dongrng. dong rng ca mt pic thng c biu din thng qua cc gi tr: W1/2l rng ca ca pic c o chiu cao ca pic, Wl rng ca y pic c xc nh ti hai im ct ca hai ng tip tuyn ca

hai bn thn pic vi ng nn.


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Hnh 1.5: S ca mt di cht tan v snh gi ca di sc k cho hiu lc ct.

1.3.2. Skhuch tn

Nguyn nhn chnh dn n s dong rng ca pic l s khuch tn. H s khuch tn Do tc J ti mt cht di chuyn mt cch ngu nhin t mt vng c nng caon vng c nng thp.

dx

dcD

sm

molJ )

.(

2

D l h s khuch tn c l nng xl di di chuyn

S khuch tn trong cht lng thp hn trong cht kh khong 104 ln, cn cc phn tl

n th khuch tn ch

m hn cc phn tnh

t

10

n 100 ln.

rng ca di sc k do khuch tn c biu din qua phng trnh sau:)4/(2

4Dtxe

Dt

mc

y:

lch chu n ca di

Ti m m u Chi u cao pic

Chi u

cao pic

Trc thi gian


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c l nng (mol/cm3), tl thi gian, x l khong cch di chuyn c dc theo ct, D l h s khuch tn, m l s mol cht tan dch chuyn qua mt n v din tch tit din ngang ca ct.

Phng trnh trn cho bit lch chun ca di sc k: Dt2 1.3.3. Chiu cao a l thuyt H

Chiu cao a l thuytHl mt hng s gia phng sai 2 ca di cht tan v khongcch x m n di chuyn. Tn gi ny l t l thuyt chng ct trong s tch c thchin trong nhng giai on ri rc c gi l a tch.

H = 2/L

ViL l chiu di ca ct nhi

C th ginh ct sc k c chia thnh N phn mng hay N lp hay N a tch. mia s phn b cht tan vo hai pha li t n mt trng thi cn bng mi (sc k l mtqu trnh ng, thc ra pha ng chy lin tc v thi gian khng thit lp trngthi cn bng).

Chiu cao ca a tch cng c gi l chiu cao a l thuyt. Mc d trong ct sc kkhng c cc a thc nhng ngi ta vn s dng khi nim ny ch mi quan hgia rng ca di sc k v khong cch dch chuyn dc theo ct sc k.

Nu chiu cao a l thuyt cng nh (tc sa l thuyt cng nhiu) th rng hay sdong rng ca pic cng nh. Khnng tch cc cu t ca mt hn hp ca mt ct c ci thin nu gim chiu cao

mt a l thuyt. Cc cht tan khi dch chuyn qua cng mt ct tch c chiu cao a lthuyt khc nhau bi v chng c h s khuch tn khc nhau.

Chiu cao mt a l thuyt khong t0.1 n 1 mm trong sc k kh v khong 10 mtrong sc k lng hiu nng cao v nhhn 1m trong sc k in di mao qun.

1.3.4. Sa l thuyt N

N= 2

2

LHL y L l chiu di ct, vi

Rt

WL

4

nn:


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N= 2

216

W

tR

Hay N =2

2/1

254.5

W

tR

Vi:

tR l thi gian lu ca pic, Wl rng ca pic y, W1/2 l chiu rng ca pic o na chiu cao tnh n y pic.

Cng thc ny c s dng xc nh thc nghim sa l thuyt ca mt ct tch.

Hiu lc ca ct tch stng ln khi sa l thuyt cng ln v khi chiu cao a cng nh.

1.4. Cc yu tnh hng n hiu lc tch ca ct

1.4.1. nh hng ca tc ca pha ng

Mc nh hng ng hc ln hiu lc ca mt ct r rng ph thuc vo di thigian ca pha ng tip xc vi pha tnh tc ph thuc vo tc pha ng.

Nghin cu v hiu lc ct ni chung c thc hin bi vic xc nh chiu cao H nhl mt hm ph thuc vo tc pha ng.

Kt qu cho thy c sc k kh ln sc k lng u c chiu cao a l thuyt t cc tiu trong vng tc dng thp ca pha ng v ni chung tc ca sc k lng thp

hn so vi sc k kh.

1.4.2. L thuyt v sdong rng pic

Hn 40 nm qua, rt nhiu cng trnh nghin cu v thc nghim ln l thuyt v miquan hnh lng gii thch nh hng ca cc thng snh: vn tc tuyn tnh capha ng, h s khuch tn trong pha ng v trong pha tnh, t s phn b, ng knhca ht nhi, b dy ca lp cht lng ph trn ht n chiu cao a l thuyt cho ccloi ct khc nhau.

Nhng yu tnh hng ny c phn nh qua phng trnh ca Van Deemter nh sau:uCuC

u

BAH Ms

y:

Hl chiu cao a l thuyt (cm); u l vn tc tuyn tnh ca pha ng (cm/s);


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A l h s m tnh hng n H ca s khuch tn xoy; B l h s khuch tn di; Cs v CM l cc h s chuyn khi ca pha tnh v pha ng.

Hnh 1.6: ng cong H-u (Van Deemter) cho mt ct sc k kh

1.4.2.1 Skhuch tn xoy:

Thnh phn A m t s khuch tn xoy ca cc cu tv cc ng i khc nhau capha ng chy xuyn qua pha tnh c nhi trong ct. V th cc cu t phi di chuynvi nhng khong cch ng i khc nhau qua mt n v chiu di ca ct.

S hng A c lp vi tc ca pha ng nhng ph thuc vo: ng knh ht nhi trong pha tnh dp, Cch chng c nhi trong ct hoc c ph trn bn mng c biu din qua

l hm s ph thuc vo ng th ca cht nhi, dng hnh hc v kch thcca ct:

A = .dp

Mt s phn t cht tan c ng i gn vi thnh ct s di chuyn nhanh hn so vinhng phn t khc do mt nhi tng i thp, tc nhanh hn. Cc phn t

i theo ng ngn hn c ra gii ra trc nhng phn ti theo nhng ng quanhco di hn dn n dong rng pic ca mi cht tan.

Mt stch v rng ca pic ti thiu st c nu dng cc ht nhi c ng knhtrung bnh nhv c nhi ng th vo trong ct. Tuy nhin, ht cng nh th psut cn pha ng dch chuyn qua ct cng cao, c bit s gp kh khn nhi ctng th. Trong sc k kh ct nhi ngi ta nhi ct vi cc ht c kch thc ti u

ng H = f(u)

S hng B

S hng Cs

S hng CM

S hng A

Vn t c tuy n tnh trung bnh u


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khong 0.15 m. Trong sc k kh lng khi s dng mng mng trn thnh ct maoqun th s hng A = 0.

Hnh 1.7: nh hng ca khuch tn xoy (a), khuch tn dc (b) struyn khi (c) n phng trnh VanDeemter.

1.4.2.2. Skhuch tn dc

Khuch tn l qu trnh cht di chuyn tni c nng cao n ni c nng thphn vi tc t l vi s chnh lch nng v h s khuch tn ca cht ang xt.

Trong sc k, khuch tn dc c dng m t s khuch tn din ra dc theo trc cact v song song vi ng i ca pha ng. N dn n s dch chuyn ca cht tan t

trung tm nng ca mt di cht tan n nhng vng long hn vhng pha trchoc sau ca dng chy.

Khuch tn dc l mt ngun ca s dong rng ca pic trong sc k kh do tc khuch tn cao trong pha kh. Hin tng ny t hn trong sc k lng. ln ca B

Pha

ng

Ht pha tnhTng tc ch t tan vi ht pha tnh

N ng ca di

S khuch tn ratrc v sau ca di

Pha

ng

Di ch t tan

Pha

ng

Pha tnh

Di chuy n khi pha tnh

Di chuy n vo pha tnh

Ch t tan b gi trong pha tnh


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trong phng trnh Van Deemter c xc nh phn ln bi h s khuch tn DM cacht phn tch trong pha ng v t l thun vi hng s ny:

B = 2. DM

y

:

l h s trkhng ca cht nhi ct n khuch tn dc, DM l h s khuch tn ca cht tan trong pha ng. Trong cc ct mao qun th c gi tr bng 1 cn trong ct nhi th khong 0.7.

B nh hng ln trong phng trnh V-D khi tc pha ng thp nn trong sc k lngnh hng ny t hn nhiu bi vpha ng c tc thp hn nhiu so vi ca sc kkh.

1.4.2.3. Struyn khi trong pha tnh

Khi pha tnh l cht lng: h s truyn khi Cs t l thun vi bnh phng chiu dyca lp phim trn b mt cht mang v t l nghch vi h s khuch tn Ds ca cht tantrong lp phim.

Gii thch: vi lp phim dy cc phn t cht tan phi di chuyn trung bnh xa hn tin n b mt, v vi h s khuch tn nhhn, chng s di chuyn n chm hn. Huqu l tc truyn khi chm hn v chiu cao a l thuyt tng ln.

Khi pha tnh l mt b mt rn: h s truyn khi pha tnh Cs t l thun vi thi gianc i hi cho nhng cu t b hp ph hoc gii hp, hay t l nghch hng s tc bc nht ca cc qu trnh ny.

S

chuyn

ng c

a phn t

trong pha tnh ti

u t

n m

t thi gian di hn, trong khinhng phn t khc chuyn ng vpha trc cng vi pha ng, s dn n pic s

dong rng. Pha ng i qua ct cng nhanh v tc truyn khi trong pha tnh cngnh th pic cng dong rng hn.

Khc phc: nhng cht lng t nht hn c thc chn lm pha tnh tng h skhuch tn. C th gim chiu dy ca pha tnh nhng dung lng ca ct s b gimxung.

1.4.2.4. Struyn khi trong pha ng

Cc qu trnh truyn khi trong pha ng rt phc tp. S hiu bit tt v mt nh tnhca nhng yu t tnguyn nhn ny tc ng n s dong rng ca pic dn n s cithin ln lao trong tt c cc loi ct sc k.

H s truyn khi trong pha ng CM: t l nghch vi h s khuch tn ca cht tan trong pha ng DM t l thun vi bnh phng ng knh ca ht nhi, t l thun vi bnh phng ca ng knh ct v tc chy ca pha ng.


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17


S dong rng ca di trong pha ng l do mt phn vo sng cc ng i nhmt phn t hoc ion c th tm c cch ca n i qua ct nhi. Trn b mt capha tnh c th cha cc lkhch thc khc nhau nn mt s cc phn t cht tan c thchuyn ng vo ra cc l ny dn n s b chm so vi nhng phn t khc. Cc dngcht lng ca pha ng gn cc ht chuyn ng chm hn dng cht lng giakhong cch cc ht. Nh vy thi gian lu trong ct cho cc phn t ca cng mt cht cng khc nhau. Ccphn t ny i n ct qua nhng khong thi gian khc nhau dn n s dong rng pic.nh hng ny thnh thong c gi l khuch tn xoy, c lp vi tc ca dungmi.

1.4.2.5. Cc phng php gim sdong rng pic

Hai yu t quan trng nh hng n hiu qu ca ct l ng knh ca cc ht nhi vng knh ca ct:

Nu s dng cc ht nhi c ng knh cng nh th cng gim chiu cao a lthuyt.

Trong khi li dng nh hng ca ng knh ct, cc ct ngy cng hp hnc s dng trong nhng nm gn y.

Vi pha ng kh, tc ca khuch tn dc c thc gim mt cch ng k bi hthp nhit v nh vy lm gim h s khuch tn DM. iu ny dn n chiu cao al thuyt s nhhn ti nhit thp. nh hng ny khng ng k trong trng hpsc k lng bi v s khuch tn l chm nn s khuch tn dc c nh hng rt nhn chiu cao a l thuyt.

i vi pha tnh lng, chiu dy ca lp cht lng hp th nn cng mng cng tt bi vCstrong phng trnh Van-Deemter t l thun vi bnh phng ca i lng ny.

1.5. phn gii ca ct (Column resolution)

1.5.1. nh ngha

Trong sc k, phn giiRs ca hai pic c xc nh nh sau (hnh 8):Rs =

2

12

12

WW

tt

W

V

W

t RR

av

R

av

R

y :

o tR vVR l hiu ca thi gian hoc thtch lu gi ca hai pic,o Wavl rng trung bnh ca hai pic.


18/97

18


Hnh 1.8: Sphn gii pic.

Tim m u Thi gian

phn giikm, chnlc ti

phn giikm, chnlc tt nhngthi gianphn tch di

phn gii km, chn lc tt v thigian phn tch hp l

phn giikm, chnlc tt nhngthi gian phntch qu di,

pic b dongrng


19/97

19


phn gii ca mt ct tch cho bit khnng tch hai cht phn tch bi ct. Nu cttch c phn gii khong 1.5 th php tch A v B gn nh hon ton (s xen ph chcn khong 0.3%), trong khi nu phn gii 0.75 th khng tch c cn phn giibng 1 th s xen ph ca hai pic cn khong 4%.

phn gii cho mt pha tnh chn c thc ci thin bi tng chiu di ca cttch (tc tng sa l thuyt N ca ct tch) nhng nh vy s lm ko di thi gianphn tch.

1.5.2. Cc yu tnh hng n phn gii

Mi quan h gia sa l thuyt v phn gii l:T

M

MR

t

ttk

'

'1

'2

k

k

2

216W

tN R

Rs =

212

12

WW

tt RR

Rt ra:

phn gii Rs = )1

)(1

(4 '2

'2

k

kN

y: N l sa l thuyt,

k2 l h sdung lng ca cu t th hai, = '1

'2

k

k

Nu sa l thuyt ca 2 pic khng ging nhau th thay th N bng 21NN v thay k2 bng

kav.

Ci thin Rs nhchiu cao a l thuyt


20/97

20


Mt chi tit quan trng trong phng trnh trn l phn gii t l thun vi N . Vvy nu tng gp i chiu di ct th tng phn gii ln 2 ln.

Tuy nhin khi tng sa l thuyt ln do tng chiu di ct th qu trnh sc k phi tiutn nhiu thi gian hn tr khi stng sa l do gim chiu cao mi a v khng tng

chiu di ca ct, nhit ca ct (cho trng hp sc k kh) v chiu dy ca lp phim(cho sc k lng). Vic ti u ha tc pha ng cng c ch.

Ci thin Rs nhh schn lc

Khi tng hay khi tng t s phn b th phn gii cng tng theo. Cch thay i l thay i pha tnh hoc thay i c pha tnh ln pha ng trong sc k lng bi v thayi bn cht ca cc pha s dn n thay i .

Khi t s phn b =2 th m bo cho s phn gii tt. Tuy nhin s ti u ny l cho mtcp cu t. Trong trng hp hn hp cha nhiu cu t th cn phi thay i k c s

phn tch gia cc cu t. Trong sc k kh, gi tr ti u ha ca k c tht c bng chng trnh ha nhit cn trong sc k lng th bng chng trnh ha thnh phn pha ng tc thay i t lgia cc dung mi ca pha ng.

Ci thin Rs nhh sdung lng

Thng s tch c thc ci thin mt cch ng k bng vic thay i h s dunglng k. Ni chung, stng gi trk lm tng phn gii. xc nh khong ti uca gi trk, phng trnh c vit di dng:

'1'k

kQRs y Q cha phn cn li ca phng trnh.

Thng gi tr ca k > 10 nn trnh v d tng ln cht t phn gii nhng thi giani hi cho stch tng ln rt ng k. Gi tr ti u ca k trong khong t1 n 5.

Cch d nht ci thin phn gii l ti u ha k: i vi pha ng l kh, k thng c thc ci thin bi sthay i nhit . Cc phng php gim chiu cao ca a l thuyt nh c cp trong mc 4,

bao gm gim kch thc ht nhi, ng knh ca ct


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21


Bi tp

Cu 1.1: Trnh by nh ngha ca cc khi nim sau: (2 im)

a) S ra giib) Pha ngc) Pha tnhd) H s phn be) Thi gian luf) H sdung lngg) chn lch) Chiu cao a l thuyt

Cu 1.2: Trnh by cc yu t lm dong rng cc pic (1.5)

Cu 1.3: M tphng php xc nh sa l thuyt ca mt ct sc k.

Cu 1.4: Trnh by s khc nhau gia

a) Sc k kh-lng v sc k kh-rnb) Sc k lng-lng v sc k lng-rn

Cu 1.5: Trnh by cc phng php ci thin phn gii ca hai cht trn mt ct sc k.

Cu 1.6: Trong mt php phn tch sc k tinh du chanh, pic ca limonene c thi gian lu l8.36 min vi rng y pic bng 0.96 pht. Terpinene ra gii 9.54 pht, vi rng

y pic l 0.64 pht. Tnh phn gii ca 2 pic trn? (Ans: 1.48)

Cu 1.7: a) Trong mt php phn tch sc k cc axit c trng lng phn t thp, butyric acidra gi thi gian lu l 7.63 pht. Thi gian khng lu gi TM ca ct l 0.31 pht.Tnh h sdung lng ca butyric acid. (Ans: 23.6)

b) Thi gian lu ca isobutyric acid l 5.98 pht. Hi chn lc ca isobutyric acid vbutyric acid? (Ans: 1.29)

Cu 1.8: Trong mt php phn tch sc k thuc trsu c clo Dieldrin cho mt pic vi thi gianlu l 8.68 pht v rng y pic l 0.29 pht. Hi c bao nhiu a l thuyt lin quan

n php tch ny ? Cho chiu di ct l 2.0 met, Tnh chiu cao mt a l thuyt?(Ans:0.14 mm)

Cu 1.9: Mt hn hp benzene, toluene, v methane c tim vo mt my sc k kh. Methanecho mt pic sc nhn 42s, trong khi benzene v toluene c thi gian lu 251 s v 333s.Tnh thi gian lu hiu chnh v h sdung lng cho mi cht tan. Tnh chn lcgia benzene v toluene. (Ans: = 1.39)


22/97

22


Cu 1.10: Cc s liu sau y thu c t php tch 4 cu t trong ct mao qun di 20-m.Compound tr (min) w (min)

A 8.04 0.15

B 8.26 0.15C 8.43 0.16(a) Tnh sa l thuyt ca mi hp cht v sa l thuyt trung bnh ca ct.(b) Tnh chiu cao trung bnh ca mt a l thuyt.(c) Gii thch ti sao mi hp cht c th c sa l thuyt khc nhau.

Cu 1.11:Moody nghin cu hiu lc tch ca php tch sc k kh 2-butanone trn ctdinonyl phthalate . nh gi chiu cao a l thuyt nh m t hm ca tc dng phang theo phng trnh van Deemter vi A l 1.65 mm,B l 25.8 mm x mLx min1, andC l 0.0236 mm x min x mL1.(a) V th biu din H theo u (tc dng) trong khong 5120 mL/min.

(b) Khong gi tr no ca tc dng pha ng cho mi gi tr ca A, B v C c nhhng ln nht.(c) Gi tr ti u ca tc dng v chiu cao ca a l thuyt ti gi tr(d) i vi ct mao qun mth gi trA bng 0. Nu B vC vn khng thay i th tc dng ti u l bao nhiu v chiu cao a l thuytgi tr ny?


23/97

23


Chng 2: SC K KH

2.1. Mu

2.1.1 Khi nim

C s tch bng sc k kh l s phn b ca mu th gia hai pha: pha tnh c b mttip xc ln, pha ng l kh thm qua ton b mt tnh .

Nu pha tnh l rn th gi l sc k kh-rn. Cht rn nhi ct thng l silicagel, ryphn t hoc than hot tnh. Qu trnh ny ch yu l hp ph.

Nu pha tnh l lng, ta c sc k kh-lng. Cht lng bao bc quanh b mt mt cht rntr, gi l cht mang, to nn mt lp phim mng. C scho s tch y chnh l sphn b ca mu trong v ngoi lp phim mng ny.

2.1.2 Vi nt lch s

1905 Ramsey tch hn hp kh v hi da trn c shp ph ca than hot. 1906 Tswett tch cc sc t thc vt trn ct v gi qu trnh tch l sc k 1941 Martin v Synge (gii thng Nobel) trnh by l thuyt a trong chng ct v

chit sut ngc dng. Trn c s James v Martin xut ra sc k kh-lng (1952) T n nay GC ngy cng hon thin. n nm 1968 c khong 18000 cng trnh

v GC. Nhng nm gn y c s h trca cng nghin t v tin hc, GC tc nhiu thnh tu hn na.

2.2.Thit b

2.2.1. Gii thiu

Hin nay, hn 30 nh sn xut cung cp ra th trng khong 150 mu khc nhau cathit b sc k kh.

Trong thp nin 70, cc b tch phn kin t v x l s liu da trn my tnh trnnthng dng.

Thp nin 80 xut hin cc thit b sc k kh vi cc thng snh nhit ca ct,tc dng, tim mu, c iu khin bng my tnh vi gi c va phi; v c l quan

trng nht l s pht trin ca cc ct c khnng tch nhng mu phc tp c chanhiu cu t trong mt khong thi gian ngn.

Nhng thnh phn chnh ca thit b sc k kh c m t trong hnh 2.1.


24/97

24


Hnh 2.1: S khi ca mt my sc k kh

Hnh 2.2: Mt sc k tiu biu tch cc este bo ha bi sc k khi-lng1. methyl formate 2. methyl acetate 3. ethyl formate4. ethyl acetate 5.n-propyl formate 6. iso-propyl acetate7.n-butyl formate 8.sec-butyl acetate 9. iso-butyl acetate10.n-butyl acetate

2.2.2 H thng cung cp kh mang

Cc kh mang phi tr v mt ha hc nh He, Ar, N2, CO2 v H2 v vic chn la khmang thng c quyt nh bi loi detector s dng. H thng cung cp kh mang bao gm cc biu chnh p sut (pressure regulators), ccthit bo p sut (gauges), v thit bo tc dng.

H thng kh mang cn cha mt h thng lc phn ttch nc v cc cht nhimbn khc.

Tc dng c kim sot bi cc biu chnh p sut hai giai on c lp vo ccbnh cha kh mang.

Bi u dng

Bi u p B ti m m u

Bnh kh

pa ng

L

Ct tch

Tim m u Thi gian

Thi t bo t c dng

Lp mcao su

silicon


25/97

25


p sut ca kh vo thit b nm trong khong t10 n 50 psi c tc dng tkhong 30 n 150 ml/ph i vi ct nhi v khong t1 n 25 ml/ph i vi ct maoqun. Ni chung, nu p sut i vo thit bkhng i th tc dng skhng i. o tc dng kh ngi ta dng thit bo tc dng (flowmeter) vi bt x phng vng h bm giy.

Kh mang

gim p sut t l vi nht kh mang nn cn chn kh mang c nht thp cho ct maoqun v ct nhi cht. Bng sau dn ra mt sc tnh c bn ca mt s kh mang

Kh dn in ,10-4 cal/cm.oK

nht 1 atm50oC 100oC 200oC 300oC

ArgonHeli

Nito

Hydro

0.524.080.37

5.47

242208188

94

271229208

103

321270246

121

367307

-

139

Khi la chn cn ch n detector ang s dng nh sau:

Detector o dn cn phi s dng kh mang c dn cao nh H2, He. Kh He c uim khng nguy him.

Detector ion ha ngn la thng s dng kh mang N2 do r v khng nhuy him nhngtrong trng hp ghp ni vi cc thit b khc, v d ghp ni vi khi ph phi dngkh mang l heli.

Detector cng kt ngn la thng dng kh mang l N2.Sau y l c im ca mt s kh mang thng dng:

Kh H2 khi s dng lm kh mang cn dng kh nit lm kh bo v thi qua ct trc.Trong cc phng th nghim ngi ta dng ph bin my sn xut kh hydro vi cngsut t125 ml/ph n 225 ml/ph. Khi dng H2 trong phng th nghim phi c my dch hH2 v cm la. Kh He, argon l kh tr ha hc rt thch hp cho sc k nhit cao.

Kh nit do khng nguy him, gi r v d dng lm tinh khit nn N2c dng nhiucho sc k kh. Cn ch y l dn nhit ca N2 rt gn vi dn ca nhiu kh v hinhiu cht hu c nn c trng hp pic sc k c th bngc.

2.2.3 H thng tim mu


26/97

26


Cch thng dng nht a mu vo ct l s dng mt bm tim mu vi lng(microsyringe) tim mt mu lng hoc kh qua mt m cao su silicon (septum) chunhit vo mt bung ha hi (injector). Bung ny c t nng vi nhit thch hpv c ni vi ct tch (hnh 3).

i vi cc ct tch thng thng, cmu thng thay i t mt vi n 20l. Ct maoqun i hi lng mu a vo nhhn nn trong trng hp ny h thng chia dngmu c thit k trong b injector c s dng ch giao mt phn nh lng muc tim i vo ct, phn cn li c thi ra ngoi.

Kthut sdng bm tim

Ht dung dch mu vo bm tim v iu chnh dung dch n vch ri ko ngc pittng ra sau lng mu chuyn ht vo thn bm tim (u kim rng).

Sau khi xuyn kim qua lp m cao su silic ca injector yn khong 3 n 5 giy kim c cn bng nhit trong injector ri mi y pittong.

Cch ny gip trnh mt s cu tkh bay hi cn ng li u kim gy sai skhi nhlng nhng cu t ny.

Tim mu c chia dng (Split injection)

Thch hp cho mu c cc cu t phn tch c nng ln hn 0.1% mu. Vi cc phn tch c phn gii cao, cc kt qu tt nht thu c cho lng nh nht

ca mu ( 1l) tim vo c thc d tm khong 1ng cho mi cu t. Vic tim ton b mu s lm qu ti ct c ng knh 0.32 mm hoc nhhn. Trong

khi tim mu c chia dng ch gii thiu vo ct khong 0.2 n 2% lng mu.

Mu c tim nhanh (< 1s) qua lp m cao su silic (septum) vo vng ha hi ca hthng tim mu (injector) c ginhit cao (v d350oC) qu trnh bay himu c din ra nhanh (hnh 4).

Mt dng chy mnh ca kh mang li ko mu qua bung trn, c sha hi honton v ha trn tt.

Ti im chia dng, mt phn nh ca hi i vo trong ct sc k cn phn ln i qua vanchia dng n l thng kh thi. T l ca mu khng c gii thiu vo ct c gi lt s chia dng (split ratio) c gi tr t50:1 n 600:1. Sau khi mu b sc ra khi bungtim mu (khong 30 s), van chia dng ng li v kh mang c gim tng ng.

Mt l cht lng c tim vo s to khong 0.5 ml th tch kh v nhanh chng lmy bung tim mu. Vi kh c th thot ra trli theo ng ca m cao su silicon.

Cc cu t c nhit si thp sthot ra u tin ri n cc cu t c nhit si caohn. Nhit ca bung tim mu nn ln gim thiu phn mt ny ca mu. Tuynhin nu nhit qu cao, s phn hy mu c th xy ra.

Trong sut qu trnh tim mu v sc k, c dng kh 1ml/ph lm sch lp m cao susilicon tch hi mu d v cc kh thot ra t lp m cao su ny (septum purge).


27/97

27


Tim mu khng chia dng (splitless injection)

Thch hp cho phn tch lng vt nhng cu t c nng nhhn 0.01% mu v cchtim ny c khong 80 % mu c gii thiu vo ct.

.H thng tim mu tng tnh trng hp tim mu chia dng (hnh 2), nhng ngthy tinh trong bung tim mu l thng, trng v khng c bung trn mu. Mt th tch ln (khong 2 l) ca dung dch c pha long trong dung mi c nhit si thp c tim chm (khong 2s) vo trong ng thy tinh ca bung tim mu vi lthot chia dng bng.

Nhit ca bung tim mu cho ch khng chia dng gi thp hn (khong 220oC)so vi ch chia dng v mu blu gilu hn trong bung tim mu v trnh mu bphn hy nhit.

Hnh 2.3: H thng tim mu c chia dng, khng chia dng v tim mu vo ct

2.3. Ct sc k

2.3.1. Gii thiu

Trong thc t c nhiu dng ct tch khc nhau nhm tha mn cc mc ch nghin cu.Ni chung, ct tch sc k cn tha mn cc yu cu sau:

m bo trao i cht tt gia pha ng v pha tnh nhvic ti u ha cc thng s caphng tr

nh Van Deemter.

thm cao tc c gim p sut nh vi mt tc kh mang nht nh. Khnng ti trng cao ca ct. C khong nhit s dng rng v chu c nhit cao.

2.3.2. Ct nhi

2 mL/min

1 mL/min

Dng lm

sch septum

Van chia

dng

Ct tchNhi b ngnhit banu ca l

Tim m u chia dng Tim m u khng chia dng Tim m u vo ctj


28/97

28


Ct thng c lm bng thp khng r, nicken, thy tinh vi ng knh khong t 3n 6 mm v chiu di khong t1 n 5 m.

Ct nhi cha cc ht cht mang rn c ph mt lp pha tnh lng hoc bn thn htrn l pha tnh. Cht mang rn thng l diatomite c silan ha gim lin kthydro vi cc cht phn cc:

- Si - O - Si - +(CH ) SiNHSi(CH ) - Si - O - Si - + NH

OH OH ( CH ) SiO OSi(CH )

3 3 3

3 3 3 3

33

Kch thc ht ng nht s lm gim chiu cao ct v tng phn gii. Cht nh s

lm gim thi gian cn bng ha tan nhvy lm ci thin hiu qu ca ct. Tuy nhin,nu kch thc ht cng nh th cng t khng gian trng gia cc ht v p sut ppha ng qua ct phi cng cao.

Kch thc ht c biu din theo micromet hoc cmesh, tc l cli m ht c thi qua hoc b gi li trn sng. V d cc ht c80/100 mesh i qua c csng 80mesh (170m) nhng khng iqua c c100 mesh (150 m).

Yu cu ca cht mang rn l khng tham gia vo s tch v c khnng gic phatnh (khng t hn 10 %).

Mt s loi cht mang rn:

C hai iu quan trng cn ch khi chn mt cht mang l: cu trc v c tnh b mt.

Cu trc gp phn vo hiu qu ca cht mang, trong khi cc c trng b mt chi phis tham gia ca cht mang vo kt qu ca vic tch.

Cc cht mang phi l cc cht tr v mt ha hc vi tt c cc loi mu. N nn c dintch b mt ln pha lng c th tri thnh mt lp phim mng v cu trc b mt phithch hp lu gi lp phim mng . Tuy nhin, din tch b mt ln khng l ium bo ct hiu qu.

Hu ht cc cht mang trong sc k ct nhi c to t diatomite. Loi cht mang u tin dngtrong sc k kh do hng Johns Manville ch to c tn thng mi l Chromosorb. Sau y lmt s loi cht mang thng dng.

Chromosorb A dng qui m iu ch, c khnng gi tt pha lng (ti a n 25%), ccu trc kh b ph vv c b mt kh tr. Thng c sn xut kch thc 10/20,20/30 v 30/40 mesh. S dng cho nhng ct di, chnh lch p sut thp.

Chromosorb G dng tch cc hp cht phn cc. Nhc din tch b mt thp, cng, t trng cao nn n c s dng cho cc trng hp tm pha lng hm lng thp.Tm 5% trn Chromosorb G tng ng vi tm 12 % trn Chromosorb W.


29/97

29


Chromosorb P c ch to t gch chu la C-22 c mu hng (nn c k hiu P-pink)v tng i cng. B mt t hp thhn so vi cc loi Chromosorb khc, c dngcho nhng vic tch hydrocacbon.

Chromosorb W c ch to t Celite 545, mu trng v d vhn so vi loi G. B mttng i khng hp thv c dng tch cc hp cht hu c phn cc.

C hai vn chung ca cc cht mang:

Th nht, tng tc b mt cht mang (hp ph hoc xc tc) chnh l nguyn nhn gyra nhng pic c ui hoc bin dng. Chnh nhng nhm -OH hay oxit trn b mt chtmang l nguyn nhn ca nhng tng tc . C th che cc nhm ny bng mt lngnh pha lng phn cc. Nhng cch tt nht hin nay l silan ha vi cc thuc thDMCS (dimethyl dichorosilan) hoc HMDS (hexamethyl disilazane).

Thhai, kch thc ht cng nh th s hng A trong phng trnh Van Deemter cngnh, nhng s chnh lch p sut trong ct stng vt khi gii hn lm vic thc t.

Hiu sut ct ch c th ci thin nu dng cc ht c kch thc nh nhau.

T l phn trm pha lng

Lng cht lng cn phi bao bc cc ht bng mt lp mng ng nht. Pha lngqu nhiu sng li nhng ch trng gia cc ht lm gim hiu sut ct. Trn chtmang Chromosrb khi t l pha lng ln hn 30% hiu qu ca ct gim i rt nhiu.Trc y ngi ta hay tm 15-30% cht lng, nhng hin nay c khuynh hng ch tm2-10%.

V thi gian lu t l vi lng pha lng trong ct nn php phn tch cng nhanh khi ctc lng pha lng ph ln cng nh. Khi ti cht lng qu thp s xut hin nhng tmhp ph trn cht mang. Mun trnh iu ny cn phi dng nhng cht mang tr.

bay hi ca mu th cng phi tnh n khi chn lng pha lng. Cc cht kh bayhi nh steroit cn phi c phn tch trong nhng ct c ti thp (khong 3% hay thphn). Cc cht rt dbay hi nh cc hydrocacbon nh th cn c ct ti cao (20-30%) vlng cht lng cng nhiu thi gian cc cht c trong pha lng cng lu, s phn bcng tt.

Mt nhi

Mt nhi c mt snh hng r rt n slu gi trn pha tnh. Pha tnh c phtrn mt cht mang trn c sphn trm trng lng, trong khi vt liu nhi c ttrong ct trn c sth tch. Nu mt nhi ca cht mang tng ln, khi lng tngca pha tnh trong ct tng ln.

Chun b pha tnh v nhi ct:


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Tm pha tnh ln cht mang c nhiu cch, mt trong s l dng my ct quay chnkhng.

Ly mt lng pha tnh tnh ton sn ha tan vo trong mt dung mi thch hp trongmt bnh y trn, cho tip cht mang rn vi lng tnh ton thch hp vo. Lp bnh

vo my ct quay. Quay bnh cho n khi dung mi bay ht. un nng bnh bng cchthy hoc bng n hng ngoi.

Ly on ng thng c chiu di v ng knh mong mun, nt mt u bng bng thytinh, u kia lp mt ci phu, y cht mang tm pha lng vo phu. Lc ct bngmy lc hoc p nh vo ct n khi khng thy gim th tch cht mang trn phu nath ct np y. Nt u cn li bng bng thy tinh v cun ng li cho thch hp vil n nhit ca my GC.

Luyn ct:

Ct cn phi t t nht 2 gi25o

C trn nhit ti a m ct s s dng nhng khngc qu gii hn trn ca nhit bay hi ca pha lng. Mt lung kh mang nh (5-10 ml/ph) c cho qua ct. u ra ca ct hkhng ni vi

detector trnh lm bn n.

2.3.3. Ct mao qun

a s cc php phn tch trong sc k kh s dng cc ct mao qun di t15 n 100 mv ng knh trong rt nh t0.10 n 0.53 mm. Cc ct ny c ch to t thy tinhoxit tinh khit nu chy c mc lin kt ngang cao hn nhiu so vi thy tinh thngnn b

n v ch

u c nhi

t cao

n 350oC. Lc cng cao c

a

ng th

y tinh cho phpch to cc ct c thnh mng v d un.

Cc ct mao qun mc lp phim mng trng trn thnh ng cung cp phn gii caohn, thi gian phn tch ngn hn v nhy cao hn ct nhi nhng chng c dunglng thp hn cho cc mu. Ct mao qun mhp cung cp phn gii cao hn ctmao qun mrng hn nhng chng i hi p sut cao hn hot ng v c dunglng cho mu nhhn.

Lp phim mng lng pha tnh dy khong t0.1 n 5 m trn b mt bn trong nhc minh ha trong hnh 2.5. Nu gim dy ca lp phim ny s lm tng phngii, gim thi gian lu v gim dung lng cho mu.

Mt loi khc l cc ct mao qun c cc ht rn cht mang ph mt lp pha tnh lngc gn trn b mt bn trong ca ct. Bi v din tch b mt ca loi ny tng ln, ctny c th x l nhng mu ln hn ct ph lp phim mng trn thnh ct. Loi ct nyl trung gian gia ct mao qun ph phim mng trn thnh v ct nhi.


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Hnh 2.4: Ct mao qun c lm bng polyamide v fused silica

Hnh 2.5: Minh ha cu trc bn trong ca cc ct nhi v ct mao qun

2.3.4. Nhng yu cu v pha tnh lng

Mt pha tnh lng l tng cho sc k kh lng cn th hin chn lc v khnng hatan ca cc cu tc tch v c khong nhit lm vic rng.

N cng phi bn ha hc v c p sut hi bo ha thp ti cc nhit cao.

Ch t mang

Pha lng

Ct nh i Ct mao qun


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Nhit lm vic nh nht nn gn nhit phng, y cht lng pha tnh phi tn tidng lng ch khng phi rn.

Khi chn la pha tnh, mt s tha hip gia l thuyt v thc nghim phi c xemxt. V dtheo phng trnh Van Deemter th hiu qu tch ca ct cao hn nu ct chapha tnh lng t hn so vi ct nh vy cha pha tnh lng nhiu hn. Nhng trong thct pha tnh lng ph trn cht mang mng qu c th to nn mt s che phkhng y cc v tr hot ng trn b mt cht mang dn n sko ui ca pic, khi cntng phn trm ca pha tnh lng trn cht mang.

Cc php tch trong sc k kh lng l kt qu ca nhng tng tc pha tnh ha tan chnlc v s khc nhau ca hi bo ha ca cc cht tan. Lc tng tc chnh chu trchnhim trong tng tc ca cht ha tan vi pha tnh l phn b, cm ng, nh hng vtng tc cho nhn. Tng ca chng c o lng bi phn cc ca pha tnh ivi cht tan.

Trong sc k kh lng, khnng chn lc ca mt ct chi phi khong trng gia cc pic v ln cc i ca pic c tch. S khc nhau v chn lc l c ngha v chng cho php victch cc cht tan c cu trc gn ging nhau bi mt pha tnh chn lc.

Cc thng ssau y nh hng n chn lc:

Bn cht ca pha tnh Nng ca pha tnh Nhit ct Vic chn la v x l s b cht mang rn hoc cht hp ph.

Mt vi loi pha tnh lng thng dng c lit k trong bng v vic chn pha tnh lng chomt i tng mu c da trn qui tc cc cht cng ging nhau th cng tan tt vo nhau.

Ct khng phn cc l tt nht cho mu phn tch khng phn cc. Cc ct c phn cc trung bnh th tt cho mu phn cc trung bnh v phn cc mnh

th tt cho mu phn cc mnh. V d tch ancol ta phi chn pha lng phn cc nh cacbowax-20, ngc li tch

hidrocacbon no mch thng phi s dng cc pha lng khng phn cc. Khi ct dng nhiu b lo ha th pha tnh bt bay mt nn cc nhm silan (Si-OH) b

l ra v cc pic bko di ui tng ln.

Nu trong ct c oxi nhit cao cng dn n s thoi ha ct v pic bko ui. gim khuynh hng pha tnh b mt nhit cao, ngi ta gn chng vo b mt phatnh silica bng cc lin kt cng ha tr.

Ngi ta chia cc pha lng v cc i tng cn tch ra nhiu nhm theo tnh phn cc ca phntnh sau:


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Nhm rt phn cc: H2O, glycol, glyxerin, poliphenol, axit dicacboxylic. Nhm phn cc: ancol mch thng, axit bo hu c, phenol, amin bc 1,2, hp cht nitrov nitril c cha hydro .

Nhm phn cc trung bnh: ete, ankanal, ankanon, este, amin bc 3, hp cht nitro vnitril khng cha hidro .

Nhm t phn cc: hidrocacbon thm, anken, hidrocacbon b halogen ha mt phn. Nhm khng phn cc: ankan, thioankanol, sunfua, ankan b halogen ha.

Cc loi pha tnh ph bin nht l Squalane, polysioxanes v polyethylene glycol.

-Squalane

CH3 CH3 CH3 CH3

HC-(CH2)3-CH-(CH2)3-CH-(CH2)4-CH-(CH2)3-CH-(CH2)3-CH

CH3 CH3 CH3 CH3

-Polysioxanes: l cc pha tnh c s dng rng ri nht cho cc ct sc k kh mao qun cngnh ct nhi. Bi v cu trc ca chng c thc gn thm mt s loi nhm chc a dngnn chng th hin tnh phn cc trong mt di rng. Cc loi silicon ny l dng gm nht nnc th ph tt trn silica v cng thch hp l tng cho ct sc k mao qun.


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Polyethylene glycol

Cc pha tnh khng cha silicon c s dng rng ri nht l cc polyethylene glycol.Chng c sn trn th trng vi mt khong rng ca trng lng phn t nhCarbowax 20M v Superox-4.

Cu trc chung ca mt polyethylene glycol c thc m tnh sau:HO-CH2-CH2-(-O-CH2-CH2-)n-O-CH2-CH2-OH

Loi pha tnh lng ny c phn cc cao, nhng cng c mt vi hn ch. V dCarbowax 20M c nhit lm vic cc i kh thp 225oC v nhit lm vic tithiu l 60oC. Hn na, nhng lng vt ca oxi v nc c nhng nh hng khng tttrn cc pha tnh lng nhng c bit khng tt cho carbowax 20M, lm tng nhanh qutrnh lo ha ca ct.


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2.3.5. Ch slu Kovats

Vic bo co cc s liu nh thi gian lu tuyt i tR l v ngha bi v hu nh mithng s sc k v bt kdao ng thc nghim lin quan u tc ng n php o thigian lu gi.

Vi vic s dng s liu thi gian lu gitng i ( = tR2/tR1) c mt vi ci thin,nhng vic thiu mt tiu chun thng nht thch hp cho mt khong nhit rng trncc pha tnh c phn cc khc nhau lm gim nhng s tin ch ca n.

Thtch lu tng i cng t c s dng v chng ph thuc vo rt nhiu thng snh chiu di ct tch, lng pha tnh, lu lng dng

Kovats v Ettre thng nht ngh chn dy ng ng n-ankan l cht chun nhm xcnh thtch lu tng i v:

Cc n-ankan khng c d t v nhm chc nhm trnh cc hiu ng lng cc-lng cc,hiu ng cm ng gia phn tlng cc trung ha.

Gia chng v pha tnh tng tc vi nhau ch theo lc khuch tn Van Der Waals nnthtch lu ca chng i vi bt c pha tnh no cng khng khc nhau nhiu hay c thxem l khng i.

Trong s tip cn ca Kovat, ch s lu I ca mt n-ankan c cng nhn mt gi trbng 100 ln s cacbon ca n. V d, cc gi tr I ca n-octan, n-decan, v n-dodecan lnlt bng 800, 1000 v 1200. Theo nh ngha I c th p dng trn bt k ct no,mao qun hhoc nhi, vi bt k pha lng v c lp vi mi iu kin sc k, bao

gm c nhit ct. i vi tt c cc hp cht khc, cc iu kin sc k nh pha tnh, nng ca n, chtmang v nhit ct nhi phi c ch r. Bi v cc ch s lu cng l phng phpthch hp cho vic bo co cc s liu lu gi vi cc ct mao qun nn pha tnh, dylp phim v nhit ct cng phi c chnh r cho nhng hp cht khc n-ankan;ngc li cc gi tr I l v ngha.

Ch s lu I ca cu tkhc c xc nh bng cch so snh thi gian lu ca n vivi thi gian lu ca hai n-ankan, trong mt cu tc ra gii ra trc cn cu tkia c ra gii ra sau cht nghin cu trong nhng iu kin sc k c th.

Ni cch khc, ch slu ca mt cht phn tch ti nhit ct ng nhit c thctnh ton tphng trnh sau:

',

'1,

',

',

loglog

)log(log100100

ZRZR

ZRxR

xtt

ttZI

y:


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tR,x l thi gian lu c hiu chnh ca cu tang xt.

tR,Z l thi gian lu c hiu chnh ca n-ankan ra gii trc cht nghin cu,

tR,Z +1 l thi gian lu hiu chnh ca n-ankan r gii sau n,

Z l s cacbon ca n-ankan c thi gian lu gi tR,Z .

Vi nhng ln chy sc k theo chng trnh ha nhit , cc thi gian lu hiu chnhtrong phng trnh trn c thay th bi cc nhit ra gii thch hp (K).

Nu s khc bit v s cacbon gia hai n-ankan trn khng phi l 1 m l 2 hoc lnhn th phn s trong phng trnh trn sc nhn vi 200 hoc mt bi s tngng ca 100.

V d: hy tnh ch slu Kovats ca hp cht X c thi gian lu tR,x =15.7 pht Bit tR(n-octan) = 14.3 v tR,(n-nonan) = 18.5 pht v tR(metan) = 0.5 pht thu c trong cngiu kin sc k xc nh. Ta c thi gian lu hiu chnh ca cc cu t:tR,x =15.7 0.5 = 15.2 pht

tR(n-octan) = 14.3 0.5 = 13.8 pht

tR,(n-nonan) = 18.5 0.5 = 18.0 pht

p dng phng trnh trn ta c:

Ix =lg15.2 lg13.8

800 100( )lg18.0 lg12.8

= 836Trong trng hp ny ta ni cu t X c s nguyn t cacbon biu kin l 8,36.

V vy ta c thnh ngha ch sKovats nh sau:chslu Kovats bng tch sca 100 visnguyn tcacbon biu kin.

Ch slu lm chun ha cc bin thit b trong sc k kh cho php cc s liu lu gic to trong nhng h thng sc k khc nhau c thso snh c. V d, isoamylacetat vi ch slu 1128 s b ra gii gia n-C11 v n-C12 di cng iu kin sc k.Nhng ch slu gi cng rt hu ch trong vic so snh trt t ra gii ca mt lot cccht tan trn mt ct c th ti mt nhit cho v trong vic so snh hai hoc nhiu

ct.

Mi lin h gia ch slu v cu trc ca cc hp cht:

Gia cu t cn xc nh v pha tnh c cc lc tng tc khc nhau:

Tng tc lng cc-lng cc Lc lin kt hydro, khnng to phc cho nhn


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Lc Van Der WaalsThng thng cc loi lc tng tc trn u xut hin ng thi, ty theo cu trc m loi lcno s tri hn cc loi lc khc. Da vo ch slu Kovats c th nghin cu mi quan h giaslu gi v cu trc ha hc ca cc cu t nghin cu cng nh pha tnh.

So snh ch slu ca hai hp cht trong cng mt pha tnh

Theo di ch slu ca mt lot hp cht c cng sC nhng khc nhm chc rt ra nhnggia sng vi thnh phn cu trc khc nhau.

V d hai hp cht hexylxiclopropan v 1-octan.

Cc ch slu ca chng 80oC trn pha tnh squalan l 913.0 v 782.7. Cc hydrocacbon no mch thng tng ng l n-nonan (I80 = 900) v n-octan (I80 = 800).

Nh vy cc gia sng vi cc nhm chc trn l +13 v -17.3.

Don ch slu ca hp cht 5-hexenylxiclopropan l = 900 + 13 17.3 = 895.7 Gi tr thc nghim o c ca hp cht ny I80 ca hp cht ny ng bng 895.7. Ldo ca s trng hp ny l hai nhm chc xa nhau nn khng c stng tc qua li.

So snh ch slu ca mt hp cht trn hai pha tnh khc nhau

minh ha ta xt mt lot gi tr ch slu ca cc hp cht c 6C nh trong bng sau:

Cu trc Tn cht IS IDC200 IPPG ICH2=CH-(CH2)3CH3

CH3-(CH2)4-CH2-Cl

CH3-(CH2)4-CHO

CH3-(CH2)3CH2-CO-CH3

O

CH3-(CH2)CH2-OH

Hexen-1

Xiclohexan

1-clohexan

Benzene

Hexanal

Hexanon-2

Xiclohexanon

Hexanol-2

584.5

674.8

829.1

651.0

741.5

726.0

831.1

798.5

591.2

672.3

851.6

692.3

790.2

781.2

893.9

891.3

610.5

699.2

922.6

767.9

899.0

891.0

1038.2

1103.8

26.0

24.4

93.5

116.9

157.5

165.0

207.1

305.3

IS = ch slu vi ct Squalan (100m x 0.25 mm), T = 100oC


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IDC200 = ch slu ct DC 200 (100m x 0.25 mm) , T = 100oC

IPPG = ch slu vi ct Polypropylenglycol (100mx0.25 mm), T = 100oC

I = IPPG - IS

Trong ba pha tnh s dng y squalan c tnh khng phn cc; popropylen c tnh phn ccmnh; cn du silicon c tnh phn cc trung bnh.

Theo nh ngha ca Kovats th n-hexan c ch slu l 600.

Cc gi tr trong bng c thc gii thch nh sau:

n-hexanol c I l ln nht v chng c tng tc lng cc-lng cc c bit mnh vis tham gia cu ni hydro gia cc nhm hydroxyl vi nguyn t oxi ca ete capolypropylenglycol. Cc amin bc mt v bc hai tng ng cn c tng tc mnh hnn

a.

Hexen-1 v xiclohexan c cc gi trI nh nht. Cc olefin c tng tc mnh hn doc cha cc in tpi cho tng tc lng cc cm ng.

Gi trI ca benzene ln hn hn so vi ca 1- hexen do c cu trc h pi lin hp. Phn t 1-clohexan c cha lng cc C-Cl nn phn tny c phn cc mnh tng

ng vi phn cc ca 3 lin kt i gp li. C ba hp cht cha nhm cacbonyl u cho cc gi trI tng ng nhau. Tuy nhin

xiclohexan ln hn r rt so vi hexanon-2 do cu trc mch vng ng mt vai tr ngk.

Qua v d trn ta thy c mt mi tng quan cht ch gia cu trc ha hc ca cc cht vi ccch slu ca chng.

2.3.5. Sphn loi cc pha tnh ca Mc Reynolds.

2.3.5.1 Cch tip cn ca Mc Reynolds

H thng c s dng rng ri nht trong phn loi cc pha tnh l h thng McReynolds.

Mc Reynolds chn 10 cht ha tan thm d c nhng chc khc nhau, mi chc cnh r o mt tng tc c th vi mt pha lng.

ng o cc gi tr I ca chng trn khong 200 pha khc nhau, bao gm Squalane, cphc vnh mt pha lng tham kho di cng mt iu kin sc k.Mc Renolds tnh ton cho mi cht gi trI: I = I liquiphase- I squalane Khi s khc nhau trong ch slu cho mt cht d trn mt pha lng cho v squalanetng ln, mc tng tc c thlin quan n cht d tng ln.

2.3.5.2. Bng cc cht d c sdng trong sphn loi cc pha tnh lng


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Trong bng ny, 5 hng su tin ca McRenolds thng c xut hin v c biudin bi cc k hiu X, Y, Z, U v S.

Mt s tip cn tng tc thc hin trc bi Rohrscheiner vi 5 cht ha tan. Mi cht d c n nh gi tr zero vi squalane nh l pha lng tham kho.

K hiu Cht d ca McReynolds Cht d caRohrschneider

Tng tc c o

X

Y

Z

U

S

H

J

K

L

M

Benzen

n-Butanol

2-Pentanone

Nitropropane

Pyridine

2-methyl 2-metanol

Iodobutan

2-octyne

1,4 dioxane

Cis-hydrindane

Benzen

Etanol

2-butanone

Nitrometan

Pyridine

-

-

-

-

-

Mt electron cho cchydrocacbon thm v olefin.

Nng lc cho nhn proton(ancohol,axit, nitrils).

Tng tc nhn electron (ketone,ete, andehit, este).

Cc tng tc lng cc

Tng tc nhn electron mnh

Tng tc ancol c thtngtnh n-butanol.

Cc tng tc ankan phn cc

Tng tc hydrocacbon khngbo ha ging nh benzene

Tng tc nhn proton

Tng tc phn tn

ng dng:

Mt trong nhng ng dng quan trng nht ca cc hng sMcRenolds l nhn bitc nhng pha tnh ging nhau hoc tng t nhau nhm trnh c vic s dng trnglp.

Mt ng dng khc l s dng la chn cc ct tch thch hp. Ni chung gi tr hngs McRenolds cng ln th pha tnh c khnng gic cu t cn tch lu hn.

V d pha tnh cabowax 20M tch ancol thch hp hn OV-17 hoc OV-101 (gi trtng ng ca cc pha l 536, 158, 57). tch cc hp cht mang nhm chc khc nhauth d ancol khi xeton, este th gi tr X, Y, Z cn phi khc nhau xa.

Da vo hng s McRenolds ta c th don c th t ra gii ca cc cu t. Cchng s McRenolds ca cc pha tnh ph bin cho ct nhi GC c lit trong bng sau:


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Bng cc hng s McRenolds v cc pha tnh c s dng thng thng

Pha T(oC)min/max

Bn cht ha hc X Y Z U Z Cc pha c cu trctng t

SqualaneDC200

DC700

SE-30SE-54OV-1OV-3

OV-7

OV-11

OV-17OV-22

OV-25

OV-61

OV-73

OV-101

OV-105OV-202OV-210OV-215

OV-225

OV-275OV-330

OV-351

OV-1701SP 2100

SP2250SP2300SP2310

SP2330SP2340SP2401

20/1000/200

5/250

50/30050/300100/3500/350

0/350

0/350

0/3750/350

0/350

0/350

0/325

0/350

0/2750/2750/2750/275

0/265

25/2750/250

50/270

0/2500/350

0/37520/27525/275

25/27525/2750/275

ParaphinDimetyl silicon

Phenylmetyl silicon

Dimetyl5%phenyl 1% vinylDimetyl10%phenyl-phenyl metyldimetyl20%phenyl-phenyl metyldimetyl35%phenyl-phenyl metyldimetyl50% phenyl 50% metyl65%phenyl-phenyl metyldimetyl75%phenyl-phenyl metyldimetyl33%phenyl-diphenyldimetyl5.5%phenyl-diphenyldimetylDimetyl (lng)

Cyanopropylmetyl-dimetylTrifluoropropyl-metyl(lng)Trifluoropropyl-metyl(lng)Trifluoropropyl-metyl(gm)

Cyanopropylmetyl-phenylmetylDicyanoallylPhenylsilicon-cabowaxcopolimerCabowax nitroterephtalicacid polimer14%cyanopropylphenylMetyl50%phenyl50%cyanopropyl55%cyanopropyl90%cyanopropyl

100%cyanopropyltrluoropropyl

016

107

15331644

69

102

119160

178

101

40

17

36146146149

225

629222

335

6717

119316440

490529146

057

149

53725586

113

142

158188

204

143

86

57

108238238240

369

872391

552

17057

156495637

725757238

045

153

44664481

111

145

162191

208

142

76

45

95358358363

338

763273

382

15345

162446605

630659358

066

228

649965124

171

219

243283

305

213

114

67

139468468478

492

1106417

583

22867

243637840

913942468

043

190

41674288

128

178

202253

280

174

85

43

86310310315

386

849368

540

17143

202530670

778800310

SP-2100,SE-

30,OV-101,OV-1SP-2100, OV-101,OV-1SP-2100

DC-710

SP2250

SP-2100,SE-30,OV-1

SP-2401

SP2300

SP2340

SP-1000

SE-30,OV-101,OV-1OV-17OV-225

OV210

2.4. Detector


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2.4.1. Detector o dn nhit (Thermal conductivity detector)

2.4.1.1. Gii thiu

Trc y, detector o dn nhit l loi thng dng nht trong sc k kh bi v n ngin v p ng hu ht cc cht phn tch. Khng may, dn nhit khng nhy d tm nhng lng nh ca cht phn tchtch t ct mao qun mc ng knh ct nhhn 0.53 mm.

Cc detector o dn nhit vn cn s dng cho ct mao qun ng knh 0.53 mm vcho cc ct nhi.

Bng dn nhit ti 273 K v 1 atm

Kh dn nhitJ/(K.m.s)

Phn tlng

H2

HeNH3N2

C2H4O2Ar

C3H8CO2Cl2

0.170

0.1410.02150.02430.01700.02460.01620.01510.01440.0076

2

41728283240444471

2.4.1.2. Nguyn tc

dn nhit o khnng ca mt cht vn chuyn nhit t mt vng nng sang vnglnh (bng). Nhit mt i khi cc phn tkh p vo si dy t nng ri bt ra vi mtng nng ln hn.

S va chm phn t vi si t trong mt n v thi gian cng ln th tc mt nhitcng ln. S khc nhau v tnh dn nhit ca cc kh l do tnh linh ng, ngha l tc kh khuch tn ti v i khi si t.

Tc ca phn t li l hm ca trng lng phn t, do phn t cng nh tc chuyn ng cng cao, dn nhit cng tt.

Heli l kh mang thng dng c s dng cho detector o dn nhit. N cng l khc dn nhit cao th hai (sau H2), nn bt k cht phn tch no trn vi dng kh Hecng lm gim dn nhit ca dng kh.

Trong detector (hnh 5), cht ra gii t ct sc k chy qua si dy tc nung nngTungsten-Rhenium. Khi cht phn tch xut hin t ct, dn nhit ca dng kh bgim xung, si dy tc trnn nng hn nn in trca n tng ln v th p vo sidy ny thay i. Detector so sthay i th ny theo cu Wheatstone nh sau


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Hnh 2.6: Detector o dn nhit - Cu ni Wheatstone

Mt dng nhkh mang lm kh so snh i qua R1 v R2. Kh mang v mu sau khiqua ct c dn qua S1 v S2.

Khi c 4 si t S1, S2, R1, R2 cng mt nhit , chng s c cng gi trin trthcu cn bng, tn hiu ra bng khng. Nu in trS1 v S2 thay i do kh mang cuntheo cng vi cc cu t cht phn tch th cu mt cn bng, tn hiu ra xut hin.

nhy ca detector o dn nhit t l nghch vi tc dng kh. N nhy hn vitc dng thp hn. nhy tng theo khi s khc nhau v nhit gia si dy t

vi vng khi xung quanh tng ln. nhy cng tng theo bnh phng ca cng dng ca dy t.

2.4.2. Detector ion ha ngn la

2.4.2.1 Nguyn tc hot ng

Da trn s bin i dn in ca ngn la c to bi hn hp kh H2 v O2 trongkhng kh (ngun ion ha) v c t trong mt in trng (bung in cc).

Kh mang sau khi ri khi ct i qua ngun ion ha vo bung in cc. chng bbn ph bi cc chm ht electron to thnh cc ht tch in (ion dng, ion m,electron). Kt qu to thnh dng in gia hai in cc. Dng in ny i qua intro R. Sri thEo qua in trR ny sc khuch i ri a ra my ghi.

Nu chc kh mang i qua 2 bn ca in cc, dng in sinh ra gi l dng nn, gim thiu dng ny ngi ta dng mt dng in b chnh.

Khi kh mang em theo cc phn t mu, cc phn t ny b ion ha v dng in quain cc tng ln. Cc tn hiu c ghi li di dng cc pic.


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2.4.2.2. ng dng:

nhy ca detector FID cao hn rt nhiu so vi nhy ca detector TCD khong100 - 1000 ln.

Tuy nhin n ch s dng thch hp nht vi cc hp cht hu c cha cacbon. C mt s hp cht khng th pht hin bng detector ny nh: CO, CO2, axit formic,

formaldehit, NOx, NH3, hp cht halogen, CS2, H2S, H2O v bn thn cc kh cn thitdng hot ng detector ny nh H2, N2, He.

2.4.3. Detector cng kt in t(ECD)

2.4.3.1. Nguyn tc hot ng

B phn chnh ca detector ECD l bung ion ha, ni din ra cc qu trnh ion ha, btgi electron v ti lin hp.

Qu trnh ion ha: t mt ngun tia phng x63Ni c lp sn trong detector, pht ramt chm tia vi tc khong 108, 109 ht /giy. Cc ht ny s ion ha phn t khmang (N2 hoc 5% metan trong Ar) to ra cc ion dng ca phn tkh mang v in ttdo s cp. So vi cc in t ca chm tia , cc in t t do ny chm hn. Chngc gia tc nhmt in trng v chuyn dch v pha anot. Ti y chng b ly mtin tch v qua to ra dng nn ca detector.

Qu trnh cng kt in t din ra khi cc phn t cc cht phn tch vi i lc electroncao i vo detector. Chng bt mt s electron dn n detector thay i hiu th giaanot v catot duy tr dng nn khng i. Sthay i ny c ghi nhn di dng picsc k trn giy ghi hoc bng computer.

2.4.3.2. ng dng

Detector loi ny c bit rt nhy vi nhng phn t hp cht c khnng cng kt vicc in t tdo trong pha kh nh cc phn t cha halogen, cacbonyl lin hp, nitril,hp cht nitro, v hp cht c kim.

N tng i km nhy vi cc phn t hp cht hydrocacbon, cc ru v xeton.Nh vy nhy ca ECD ph thuc vo:

ln ca dng nn. Khnng i in t ca cht cn phn tch. Bn cht ca kh mang v hiu tht vo 2 bn in cc.

2.4.4. Detector khi ph

2.4.4.1. Gii thiu


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My khi ph l mt detector vn nng cho phn tch nh tnh v nh lng cc chthu c c sc k kh ln sc k lng.

Trong phng php khi ph, cc phn t kh b ion ha (thng to cation) c tngtc trong mt trng in tv sau c tch theo khi lng ca n. Qu trnh ionha thng cung cp nng lng n phn t ph vn thnh nhng mnh khcnhau.

Mt ph khi l mt biu cho thy lng tng i ca mi mnh v to ra tdetector khi ph. Trong sc k kh mi pic ca sc k tng ng vi mt cht phntch c tch ra c nhn din bi mt ph khi.

Hnh l mt ph khi ca hp cht c nhn din khi so snh vi th vin ph canhng hp cht bit. Trc honh ca ph khi l m/z, khi lng ca ion chia choin tch ca ion. Phn ln cc ion u mang in tch +1 nn m/z thng chnh l khilng ca ion (.v.C). Trc tung ch thnh phn % tng i ca cc ion so vi ion clng ln nht c qui c 100%.

Trong ph khi c mt pic quan trng ca ion phn t khng b ph vthnh cc mnh.Da vo t l ca cc ng v ca mt nguyn t trong t nhin, ta c th nhn thy t lny xut hin trong ph khi qua t l ca cc ion phn t ca cc ng v. V d ta c thhiu iu ny trong ph khi ca 1-brombutan. V t l ca nguyn t brom trong t nhinl 50.52% 79Br v 49.48% 81Br, pic ti m/z=136 ca ion phn t C4H979Br c cng ln hn mt cht so vi pic ca ion phn t ti m/z=138 ca phn t C4H981Br.

Hnh 2.7: Sc k v phMS tng ng ca 1-Butanol v 1-Bromobutane.

2.4.4.2.My khi phnam chm hnh qut

Nguyn tc hot ng vi ngun ion ha bng chm electron


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Cc phn t kh i vo ngun ion ha bng va chm electron v b bn ph bi ccelectron c nng lng ng hc khong 70 eV. Nng lng ny ln ion ha ccphn t (M + e M+ + 2e) v ph vchng thnh nhng mnh vnhhn.

Mt th hiu dng nha y (repeller plate) y nhng ion hng vng phn tchv mt th nhcc a hi t ion (ion focus plates) gia tc ion gip cc ion c vn tccao b tng khi phn y ca b phn ny v i vo ng phn tch.

ng phn tch (Analyser tube) c duy tr p sut chn khng cao (khong 10-5Pa) cc ion chuyn ng qua ng khng b lch hng bi nhng va chm vi cc phn tkh pha ng.

Cc cation di chuyn qua ng phn tch chu tc ng ca ttrng t vung gc vihng di chuyn ca chng. Trng ny shng cc cation vdetector t cui ngphn tch.

Mt khe detector ch cho nhng ion trong mt khong gi tr khi lng nhxc nhtip cn detector. Cc phn t c khi lng khng ph hp va phi cc thnh ng hoc

b loi b bi khe thot ion nn khng vn ti c detector. Ti b phn thu ion (ion collector), mi cation n b trung ha bi mt electron. Dngin i hi trung ha chm ion t l vi slng cc ion n b phn thu ion ny.

Ph khi l mt th cho thy dng in nh l mt hm ca s khi c chn bi ttrng.

Phng php ion ha bi tng tc electron (electron impact ionization) cho ph khi cnhiu mnh v. Ion phn t c thc hm lng thp thm ch b bin mt.

Nu phn t ln th vic c qu nhiu mnh vs lm cho vic gii thch ph khi ca ngp nhiu kh khn. Trong trng hp ny cc chng trnh my tnh c thc s

dng lm khp ph ca cht cha bit ny vi mt ph khi bit trong th vin phlu trong my tnh.

Nguyn tc hot ng vi ngun ion ha ha hc:

Mt k thut tinh t sn sinh ra t mnh v hn l s ion ha ha hc (chemicalionization). Trong trng hp ny, ngun ion ha c y metan p sut khong100 Pa.

Cc electron c cung cp nng lng chuyn CH4 n nhng sn phm hotng khc:

CH4 + e CH4+

+ 2e

CH4+ +CH4 CH5+ + CH3

CH5+ l cht nhng photon khi tng tc vi cht phn tch cho MH+, thng l ion chm lng ln nht trong ph khi ion ha ha hc metan (methane chemical ionizationmass spectrum).


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CH5+ + M CH4 + MH+

2.4.4.3.My khi phtcc

My khi ph nam chm hnh qut thng t c chn ghp ni vi sc k bi v ttrng khng ththay i nhanh ghi ph ca nhng di sc k hp. Loi c sdng ph bin hin nay kt ni vi sc k l my khi ph t cc (quadrupole massspectrometer).

Khi mi cht ha tan trong ct sc k c tch c th hin di dng pic. Cht c dn n bung ion ha tng tc electron c p sut chn khng, ti y cc phnt cht phn tch bcc electron c gia tc bn ph to cc ion mnh v. Cc ion nyli tip tc c gia tc bi mt th khong 5-15 V trc khi i vo b tch theo khilng t cc (quadupole mass seperator).

B tch gm 4 thanh kim loi song song vi nhau, trong mt cp sc p vo mtthkhng i v cp kia mt th hiu dao ng tn s radio. Ttrng c to ra lm

lch cc hnh trnh phc tp khi chng di chuyn t bung ion ha hng n detector vch cc ion no c t s khi lng vi in tch (m/z) chn trc mi tip cn videtector. Cc ion khc va p vo cc thanh kim loi v b mt trc khi vn ndetector.

Bng vic thay i nhanh chng th p vo, cc ion c khi lng khc nhau c chnlc c tip cn vi detector. Cc b tch khi ph t cc c qut nhanh ghihai n tm ph trong mt giy vi khong 800 n v khi.

2.5. Pht trin mt phng php phn tch bng sc k kh

Do c nhiu thng snh hng n qu trnh sc k nn c th lm bi ri cho nhngngi mi bt u lm quen vi vic chn mt th tc cho vic phn tch sc k mt i tngc thno . Ni chung, c nhiu gii php khc nhau c th tha mn. Trong phn ny s tholun cch chn mt phng php s dng. Trt t cn xem xt theo th t sau: mc tiuphn tch, chun b mu, detector, ct v bm mu.

2.5.1. Mc tiu ca php phn tch

Mc tiu ca php phn tch l phn tch nh tnh hay nh lng? C cn phi thc hin mt php tch phn gii cao mt cu t hoc ch cn mt php tch

c phn gii tt cho mt phn no thi trong sc k ? C cn hy sinh phn gii rt ngn thi gian phn tch? Cn phn tch nh lng ch mt cu t hoc nhiu cu t trong mu v c cn chnh

xc cao khng?

Cht phn tch hin din trong mu nng thch hp hoc cn c nhng k thut cbit (c mu v mt detector rt nhy) cho phn tch siu vt.


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Mi yu t cp dn n mt vi s tha hip trong vic chn cc k thut thch hp.

2.5.2. Chun b mu

Cc mu trong thc t rt phong ph v thng c thnh phn phc tp:

C mu c hm lng tng tnhau nhng cng c mu bn cnh cu t chnh mu cncha mt s cu t vi hm lng vt.

C mu c cc cu t vi nhit si khc nhau trong mt khong rng. Mu c thdng dung dch nhng cng c dng kh hoc dng rn. Mu cha nhiu cu t phn cc hoc cha nhiu cu t t hoc km phn cc.

Cha kha c mt qu trnh sc k thnh cng cho mt mu phc tp l cn phi lm schn trc khi gii thiu n vo ct.

Cc phng php nh vi chit pha rn, chit lng - lng, chit rn - lng, s gii hpnhit cc cc cu t dbay hi v nhiu phng php mi khc gip c lp nhng cu tcn phn tch trong mu phc tp t nhng cht cn tr.

Cc phng php ny gip c lp v lm giu cc cu t cn phn tch n mc c thd tm c.

Nu ta khng lm sch mu th sc k thu c s cha mt rng cc pic km phngii v cc cu tkhng bay hi s cn gi trong ct v ph hy cc ct t tin.

2.5.3. Chn detector

Giai on tip theo l chn detector cho qu trnh sc k. Vn t ra l cn bit mi thng tin

trong mu hay ch cn mt detector chuyn bit d tm mt hoc mt nhm cc cu tc bitno trong mu.

Detector c s dng rng ri nht l detector khi phnhng t tin. Detector ion ha ngn la cng l loi c dng ph bin nht nhng n chp ng tt

cho hp cht cha mch cacbon di hoc cc hydrocacbon. Loi ny khng nhy nhdetector bt electron hoc detector hunh quang. Detector ion ha ngn la i hi muphi cha ln hn 10 ppm cht cn phn tch cho phn tch tim mu chia dng.

Detector dn nhit l cch ph bin nht d tm cc cht nhng n khng nhy chonhng ct mao qun mc phn gii cao.

Cc detector nhy cho phn tch siu vt chp ng vi mt loi hp cht no thi.V d detector bt electron l loi c bit cho cc hp cht cha halogen, cacbonyl linhp, nitril, v hp cht nitro.

Nu ch cn bit nhng thng tin nh tnh nhn din cc cht ra gii, cc detectorkhi ph v hng ngoi l nhng chn la tt. Detector hng ngoi ging detector o dn nhit thng khng nhy cho nhng ct mao qun m.


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2.5.4.Chn ct

Nhng chn la chnh l pha tnh, ng knh ct v chiu di ct.

Chn pha tnh theo nguyn tc cc cht c cu to cng ging nhau th tng tc tt vi nhau.

Cc pha tnh khng phn cc c s dng nhiu. Pha tnh c phn cc trung bnh c s dng hu ht nhng php tch m pha tnhkhng phn cc khng th.

i vi nhng hp cht phn cc cao th mt ct phn cc mnh l cn thit. Cc ng phn quang hc v nhng hp cht c cu trc hnh hc gn ging nhau i hi

nhng pha tnh c bit cho php tch ny.

Gia ng knh ct v b dy ca lp phim c mi quan h trong vic nh hng n phngii.

phn gii cao nht c tht c bi nhng ct hp nht vi pha tnh mng nht. S kt hp ny lm gim thiu trkhng i vi s chuyn khi (s hn C trongphng trnh Van Deemter) trong c hai pha tnh v pha ng nhvy lm gim chiucao a l thuyt.

Cc ct hp v lp phim mng c bit thch hp cho vic tch cc hn hp ca cc chtc nhit si cao nn blu gi qu mnh trn cc ct c lp phim mng. Cc thi gianlu ngn cung cp nhng php phn tch nhanh.

Tuy nhin, cc ct hp c lp phim mng c dung lng mu rt thp, i hi nhngdetector c nhy cao (detecter ion ha ngn la c thkhng tng thch), khng lu

gi tt nhng hp cht dbay hi v c th chu nhng nh hng do nhng v tr hotng trn b mt c th b l ra. Cc ct chp c lp phim dy cung cp mt tha hip tt gia phn gii v dung

lng mu. Chng c thc s dng vi nhiu detector (nhng thng khng phi cc detector o

dn in hoc hng ngoi) v vi nhng hp cht dbay hi. Cc thi gian lu gidi hn so vi ct c lp phim mng.

Cc ct crng v c lp phim dy c i hi cho vic s dng cc detector o dnin v hng ngoi. Chng c dung lng mu cao v c th x l cc hp cht d bayhi nhng cho phn gii thp v thi gian lu gi lu.

Nu mt ct chuyn bit p ng vi hu ht nhng yu cu t ra nhng khng cung cp phn gii th ct di hn cng loi c thc s dng.

Chiu di gp i ca ct lm tng gp i sa l thuyt v theo phng trnh tnh phn gii th lm tng phn gii ln 2 ln. iu ny khng phi l cch tt nht tng phn gii bi v n lm tng gp i thi gian lu.


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Vic s dng mt ct hp hn hoc lp pha tnh mng hn slm tng phn gii mkhng ko di thi gian lu gi.

Vic thay i pha tnh lm thay i hon ton slu gitng i ca nhng hp chtkhc nhau ( trong phng trnh) v c th phn gii cc cu tang quan tm.

5.5. Chn phng php tim mu

Quyt nh chnh cui cng l lm thno tim mu.

Ch tim mu chia dng:

Tt nht cho nhng mu phn tch c nng cao hoc phn tch kh, nhng phn tchnh lng c th c cc cu tkh bay hi b mt trong sut qu trnh tim mu.

Tim mu chia dng cung cp phn gii cao v c th x l nhng mu bn nu nhivo ng trong b tim mu mt cht hp ph thch hp.

Cc hp cht khng bn nhit c th phn hy trong sut qu trnh tim mu nhit cao.

Ch tim mu khng chia dng:

c yu cu cho nhng dung dch rt long. N cung cp phn gii tt nhng trong phn tch nh lng c th c cc hp cht

km bay hi b mt trong qu trnh tim. N tt hn ch tim mu chia dng i vi nhng hp cht c bn nhit trung bnh

bi v nhit tim mu h thp hn. Tim mu khng chia dng gii thiu mu vo ct chm v vy by dung mi v by lnh

c i hi. Cc mu cha mi cht phn tch t hn 100 ppm c thc phn tch trong nhng ctc chiu dy lp phim < 1m vi ch tim mu khng chia dng. Nhng mu c micht phn tch t 100-1000 ppm i hi lp phim dy hn 1m.

Tim mu trn ct (on-column injection):

Tt nht cho phn tch nh lng v cho nhng hp cht km bn nhit. N l mt k thut c phn gii thp v khng th s dng cho nhng ct c ng

knh nhhn 0.25 mm.

N c th x l nhng dung dch c cng nh long.2.5.6. Chng trnh ha nhit v p sut

2.5.6.1.Nhng thun li ca chng trnh ha nhit ct

Ct sc k hot ng nhit khng i c mt sim bt li:


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Nu nhit c chn qu thp, nhng pic ha tan u tin s c khong cch rt gnnhau, trong khi cc cu t b lu gi mnh s c cc pic b dong rng v nm thp.Ngoi ra nu nhit ct hi thp th thi gian phn tch stng theo cp s nhn.

Khi phn tch hn hp gm cc cu t c nhit si khc nhau nm trong mt khonghp th vic chn nhit cho ct ch khng i khng thc s kh khn. Tuynhin, i vi nhng mu phc tp nhiu cu t c khong nhit si rng th khngth dng ch nhit ct khng i.

Nu chn nhit thch hp cho cc cu tc im si thp th cc cu tc im sicao s blu gi lu trong ct tch dn n pic ca chng b dong rng. Ngc li nuthc hin vic tch nhit cao th cc cu tc im si cao s ra gii nhanh v c phn gii tt, nhng cc cu tc im si thp th b tch chm v c phn giikm, thm ch nhiu pic b chp ln nhau.

Nhng cu tlu gi mnh c thc nhanh chng ra gii nu chn nhit cao hn,v cng ci thin khnng d tm chng. Tuy nhin, nu lm nh vy th cc cu t cng

b ra gii tng ln dn n cc pic cng st gn nhau v s lm mt phn gii cho ccpic u sc k . Trngi ny c thc gii quyt trong GC bng chng trnh hanhit , y nhit ca ct trong l c tng dn ti mt tc tuyn tnh sut qutrnh phn tch.

Chng trnh ha nhit c mt vi u im:

N lm gim thi gian tin hnh phn tch v ci thin khnng d tm ca cc cu t(pic s nhn hn v c cc di cch u nhau trong c sc k ).

Trong trng hp cc mu khng bit thnh phn hoc mu phc tp, nhng cu t cnhit si cao nu iu kin ng nhit c th khng ra gii c hoc khng th dtm, th c th th hin mt thi gian lu gi thch hp hn.

Chng trnh ha nhit cng c th gip ra sch mt ct b nhim bn cc cu t cnhit si cao trong nhng ln tim trc.

Chng trnh ha nhit thng thit lp nhit cho ct tch tng ng vi nhit ca cu t c nhit si thp nht, thch hp l di 90oC. Sau nhit c nngln theo tc chn trc cho n nhit cui cng tng ng vi nhit ca cu tc im si cao nht. Khi nhit ca ct tng ln th cc cu t s ln lt tch khi ctvo thi im nhit ca ct t n nhit si ca tng cu t.

C ba kiu chng trnh ha nhit c s dng trong sc k kh: kiu ng n (ballistic),kiu tuyn tnh v kiu a tuyn tnh.


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T ct

A

B C

Thi gian

Chng trnh kiu n o din ra khi mt l (oven) c duy tr ti mt nhit nhanh chng thay i n mt nhit cao hn (ng A), v thnh thong c s dngcho vic iu kin ha ct sc k kh rn sau khi n c s dng trong mt thi giandi. Tuy nhin, mt ct sc k c duy tr ti nhit cao sau nhanh chng nngnhit ln cao th lp phim pha tnh c th b ph hy do b sc nhit.

Chng trnh ha nhit c s dng rng ri nht l kiu tuyn tnh (ng B). Btu t nhit thp v c duy tr ng nhit trong mt khong thi gian no , sau nhit trong l cha ct c tng vi mt tc tuyn tnh n mt nhit cuicng c chn sn. Nhit cui cng ny cng c duy tr trong mt khong thigian c thno . Nhit ban u v tc tng tuyn tnh sau c xc nh tmt php phn tch thm d trc vi ghi ch nhng nhit ra gii. S chn lanhng iu kin ban u thch hp s cho php vic tch nhng cht c nhit si thp,trong khi nhit cui cng c chn nn ln ra gii c nhiu hn nhngcu t blu gi mnh (lu gii hn nhit cao nht ca pha tnh).

Kiu a tuyn tnh c thc hin trong mt vi trng hp d tm hoc tng cng phn gii trong mt php tch, nhng c s dng thng dng hn trong vic kthp vi tim mu trn ct.

Trong chng trnh ha nhit , nhit ca mt ct c tng sut qu trnh tch tng p sut hi ca cht ha tan v nh gim thi gian lu ca nhng cu t b ragii chm. Mt v dc trnh by trong hnh 6. Ti nhit hng nh 150 oC, cc hpcht dbay hi hn xut hin gn nhau v cc hp cht t bay hi c th thm ch khng


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b ra gii t ct. Nu nhit c cho tng t 50 oC n 250 oC vi tc tng8oC/pht, tt c cc cu tc ra gii v cc pic xut hin kh u. Cn trnh tngnhit ln qu cao ngn s phn hy nhit ca cht phn tch v pha tnh.

Hin nay, cc my sc k phn ln u c trang b cc bin t kim sot p sut cthchng trnh ha ca cc kh mang i vo ct. Stng p sut vo ct lm tng tc pha ng v nhvy lm gim thi gian lu.

Hnh 2.7: (a) tch ng nhit ca cc ankan tng t150oC. Ct 3%Apiezon-L on 100120 mesh VarAport 30. Kh mang helium 10 ml min1.(b) Mu v ct nh (a) nhng nhit tch c chng trnh ha cho thy phn gii cao hn v thigian ngn hn.

2.6. Phn tch nh tnh trong sc k kh Trong phn tch nh tnh, hai detector c th nhn din cc hp cht l detector khi ph

v detector hng ngoi chuyn ha Fourier. Mt pic c th nhn din bng cch so snhph ca chng vi mt th vin phc lu gi trong my tnh.


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Mt phng php km tinh thn l nhn din thi gian lu ca mt cht vi thi gianlu ca cht trong mt mu bit trc (mu chun) trn cc ct c phn cckhc nhau (hnh 7).

Cch ng tin cy nht l so snh cc thi gian lu trong cng mt sc k thu c bimu bit trc (mu chun) c thm mu cn d tm vo trong cng mt iu kinsc k. Nu nh cht cn d tm trng vi cht c trong mu chun th pic ca cht trong mu thm s c din tch hay chiu cao tng ln so vi khi cha thm cht chabit vo. S nhn din chmc thm d khi thc hin trn mt ct, nhng khng nhhn khi thc hin trn mt vi ct trn nhng loi pha tnh khc nhau.

Trong hnh 17 cho thy c th nhn din c cc nh 2,3,4,7 v 9 l metyl, etyl, n-propyl, n-butyl, v n-amyl alcol. Cn ch rng c th c nhng cht khc nhau nhng cthi gian lu ging hoc rt gn nhau. V vy cn xc nh trn nhiu pha tnh khc nhauhoc s dng cc detector khi ph hoc hng ngoi xc nh.

Hnh 2.8: Phn tch nh tnh bng cch so snh thi gian lu vi cht chun

2.7. Phn tch nh lng

2.7.1 Mt s nguyn nhn gy ra sai s


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Chun b mu: cng nh mi phng php khc, mu em phn tch c ly mu saoi din ng cho c l nguyn liu hay sn phm. Cc qui tc ly mu cn phi tun thcho tng loi mu. Mu cn c lm sch trc khi tim mu vo GC. Vic ny nulm khng tt c th gy nn mt cu t cn xc nh.

Tim mu: khi cht lng tim vo bung tim mu th nhit thit lp nu qu cao cth gy nn s phn hy mu, hoc mu c tham d vo mt phn ng no . K thuttim mu cng c th gy sai s.

Mu b phn hy hoc b hp ph: c nhiu trng hp c s phn hy hoc hp phtrong bung tim mu, trong ct, trong detector c thlm cho cc pic khng i dincho lng ca chng c trong mu. khc phc iu ny ta nn dng phng php lpng chun bit din tch hay chiu cao ca pic c t l tuyn tnh vi lng mu avo hay khng.

p ng ca detector: mi detector p ng khc nhau vi cc hp cht khc nhau. Vvy cn bit r cc h sp ng ny. Hn na khi iu kin lm vic thay i th p

ng ca detector cng thay i. Trong GC c th s dng phng php chun ni khc phc iu ny.

Kthut ly tch phn: trong GC c nhiu cch thit lp quan h gia thng tin nhnc t pic sc k vi hm lng ca cu t: o chiu cao pic, dng my ghi v tchphn, ct v cn giy. Cc cch ny c th c nhng sai s ring trong qu trnh x l.Ngy nay vi s ghp ni my tnh v cc phn mm h trvic tch phn ha din tchcc pic trnn d dng v thng dng. Kt quc bo co y cc thng tin ca picnh chiu cao pic, din tch pic, phn trm trong mu

2.7.2 Cc phng php tnh ton nh lng

2.7.2.1.Phng php chun ha din tch

y l phng php tnh thnh phn phn trm ca mu bng cch o din tch tng pictrn sc k . Theo cch ny em din tch pic ca cht quan tm A cho tng din tchca cc pic: %A = (din tch pic A/tng din tch cc pic)x100 %

Khi phn tch thnh phn c im si st nhau ca mt dy ng ng, phng php nyc thdng tnh t l phn trm khi lng.

Phng php ny ch ng nu tt c cc cu t u c ra gii v p ng cadetector vi mi cu t l ging nhau. Nu nhng iu kin ny tha mn th y lphng php nhanh v hiu qu.

2.7.2.2.Phng php tnh theo h shiu chnh

Nh bit detector p ng khc nhau i vi cc cht khc nhau. V vy cn phi tnhh s hiu chnh. Nhh s ny c th tnh c thnh phn phn trm ca cc cu ttrong mu.


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/ ( )%

( / ( ))i

dien tich cua A F AA

dien tichcua Ai F Ai

Cch xc nh h s hiu chnh:

- Tim dung dch chun bit nng cc cu t A, B, C vo GC- Sc k thu c c cc pic phn gii hon ton v din tch thu c tng ng

SA, SB, SC tng ng vi cc khi lng trong mu mA, mB, mC- Chn mt pic lm chun v d A c t l SA/mAc gn gi tr FA = 1- T t l SB/mB, SC/mC suy ra FB, FC

2.7.2.3.Phng php lp ng chun:

Lp cc ng chun ring ri vi tng cu t trong hn hp bng cch tim nhngth

tch b

ng nhau c

a m

t lo

t dung d

ch h

n h

p ch

t chu

n c n

ng khc nhau.

Nh vy mt lot cc nng ca cc cht chun c phn tch v din tch cachng c xc nh. Mt ng chun c dng cho mi cu t vi mt trc nng v trc kia l din tch tng ng kim tra s tuyn tnh ca p ng ca detector.

Tim cng th tch ca mu c cc cu t cn phn tch v chy sc k trong cng iukin nh khi chy chun.

T cc din tch thu c ca cc cu t cn phn tch v ng chun va thit lp suyra c nng ca chng.

2.7.2.4.Phng php dng chun ni

Phng php ny cn c gi l phng php chun ha tng i hay gin tip.

nh lng mt cu t X ta cn phi chn mt cht chun S sao cho:

Nu trn ln X vi S ta phi thu c 2 nh ring bit trn sc k . Pic ca X v S phi kh gn nhau.

Sau ta phi pha cc hn hp c t l trng lng ca X v S bit trc, chy sc k, o dintch cc pic, lp t s din tch tng ng, cui cng lp ng chun tng i.


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Sc/Ss

Wc/Ws Chun Cu t

y :

Sc/Ss l t l din tch ca cc cp cu t cn xc nh X v cht chun ni Wc/Ws l t l trng lng ca cc cp cu t cn xc nh X v cht chun niKhi phn tch mu tht, ta cho mt lng bit trc cht chun ni S vo mu ri tin hnhsc k hn hp. T t l din tch o c, bng ng chun tng i va dng ta c t ltrng lng. Vi trng lng chun S thm vo bit ta tnh c trng lng ca cht X.

Phng php ny c cc u im:

Khng cn bit n p ng ca detector Khng cn duy tr nghim ngt cc iu kin tin hnh sc k v nhng thay i c loi

tr theo cch tnh t s.


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BI TP

Cu 2.1: a) Trnh by s khc nhau gia sc k kh lng v sc k kh rn.

b) Cho bit nhng loi cu t no c thtch c bng phng php sc k kh rn v sc k

kh lngc) Ti sao sc kh kh rn hu nh khng c s dng rng ri nh sc kh kh lng

Cu 2.2: Nu cc nguyn tc hot ng ca cc loi detector c s dng trong sc k kh:

a) Detector o dn nhitb) Detector ion ha ngn lac) Detector bt electrond) Detector khi ph

Nhng u im v nhc im ca cc loi detector trn

Cu 2.3: Trnh by nh hng ca dy lp phim pha tnh ln sc k trong sc k kh

Cu 2.4: Gii thch ti sao ct mao qun mcung cp phn gii tt hn so vi ct nhi trongsc k kh?

Cu 2.5: Khi no cn s dng ch tim chia dng, khng chia dng v tim thng vo cttrong sc k kh?

Cu 2.6: Lm thno ci thin phn gii ca 2 pic qu st nhau trong sc k kh?

Cu 2.7: Trnh cc yu t

nh hng

n s

dong r

ng ca pic s

c k v nh

ng k

t lu

n c

n rt

ra gim s dong rng pic khi tin hnh sc k kh lng.

Cu 2.8: Trnh by cc phng php xc nh nh lng c s dng trong sc k kh:a) Phng php chun ha din tch

b)Phng php tnh theo h s hiu chnh

c) Phng php lp ng chund) Phng php dng chun ni

Cu 2.9: Cho bit trt t ra gii ca hexan, heptan, octan, butanol v 2-pentanone ra khi ctc pha tnh (diphenyl)0.35 (dimetyl)0.65 polysioxane. Bit ch slu Kovats ca butanol v 2-pentanone trn ct ny ln lt l 717 v 777.

Cu 2.10: Cho bit trt t ra gii ca hexan, heptan, octan, nonane, benzene, nitropropane vpyridine ra khi ct c pha tnh (diphenyl)0.05 (dimetyl)0.95 polysioxane. Bit ch slu Kovatsca benzene, nitropropane v pyridine trn ct ny ln lt l 672, 745 v 761.


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Cu 2.11: Mt hn hp cc methyl esters ca cc axit bo c sc k trn ct Carbowax 20 Mcho cc din tch pic v cc h sp ng detector nh sau:Ester Din tch pic, cm2 H sp ngmethyl-n-butyrate 2.95 0.81methyl-isovalerate 0.86 0.88

methyl-n-octanoate 1.66 0.98methyl-n-decanoate 4.52 1.00Tnh thnh phn % hn hp.

Cu 2.12: Trong mt php tch mt hn hp cc hydrocacbon, cc thi gian lu hiu chnhc o nh sau:propane 2.23 minisobutane 5.71 minbutane 6.67 minTnh ch slu Kovat ca cc hydrocacbon ny?

Cu 2.13: Mt hn hp n-heptane, tetrahydrofuran, 2-butanone, and n-propanol ra gii theotrt t ny khi s dng ct c pha tnh phn cc nh Carbowax. Trt t ra gii so ngc lichnh xc theo th t trn khi s dng pha tnh khng phn cc nh polydimethyl siloxane. Giithch trt t ra gii trong mi trng hp.

Cu 2.14: Cc s liu sau y l cc thi gian lu hiu chnh ca cc n-ankan s dng pha tnhCarbowax 20M.

trAlkane (min)Pentane 0.79hexane 1.99

heptane 4.47octane 14.12nonane 33.11Hi ch slu Kovat c thi gian lu hiu chnh l 9.36 min?

Cu 2.15: (7) Cc s liu sau y thu c khi phn tch sc k kh p-xylene v methylisobutylketone (MIBK) trn ct mao qun.

Injection tr Peak Peak WidthMode Compound (min) Area (min)split MIBK 1.878 54285 0.028

p-xylene 5.234 123483 0.044splitless MIBK 3.420 2493005 1.057

p-xylene 5.795 3396656 1.051Gii thch s khc nhau gia thi gian lu, din tch pic, v rng pick khi chuyn t tim muchia dng sang tim mu khng chia dng.


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Chng 3: SC K LNG

(LIQUID CHROMATOGRAPHY)

3.1. Mu

Sc k lng ct l mt trong nhng nhnh ca phn tch cng c pht trin nhanh nht,c p dng cho nhiu loi mu hn bt k k thut tch no v c khnngphn t chnhng hn hp mu cc k phc tp trong ha hc v trong sinh hc.

Nghin cu k thut tch bng LC l cn thit v n s tip tc ng mt vai tr quantrng trong tt c nhng lnh vc ca phn tch ha hc, mc d c nhng tin bhn

na trong cc thuc th chn lc v nhng ci tin trong cc k thut vt l o lng. Vi s pht trin trong sut nhng thp nin qua v thit b v s nhi ct, sc k lnghiu nng cao (HPLC) ni ln nh mt phng php c a thch cho k thut tch vphn tch nh lng ca rt nhiu loi mu.

Phn tch HPLC nhanh, hiu qu v c th d tm lng mu nhn 200 pg. Nhng chi p dng HPLC hu nh khng gii hn do HPLC trthnh mt cng c khng ththiu trong khoa hc v cng ngh

phan tich sac ki khi th vung

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