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Li u tin chng em xin chn thnh cm n s dy d , hng dn tn tnh ca

thy L Nht Tm hin ang cng tc ti Vin Cng Ngh Sinh Hc V Thc Phm

trng i Hc Cng Nghip TPHCM . Chng em xin gi li cm n chn thnh n

trng i Hc Cng Nghip TPHCM to dng c mt mi trng lm vic rt

khoa hc v thun li cho cng vic ging dy ca ging vin v nghin cu ca sinh

vin nh trng. Cm n Vin Cng Ngh Sinh Hc Thc Phm trang b cho emnhng kin thc qu bu v b ch v b mn phn tch thc phm v ngoi ra em cng

xin cm n th vin trng i hc Cng Nghip TPHCM, c bit l phng a phng

tin to iu kin thun li trong cng vic tm kim t liu lm bi, th vin cung

cp mt h thng ti liu b ch gip chng em lm vic c hiu qu hn v gii quyt

c nhng kh khn, b tc trong sut qu trnh lm tiu lun .

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Phng php o ph hp th nguyn t l mt k thut phn tch ha l v

ang c pht trin v pht trin rng ri trong nhiu ngnh khoa hc k thut , trong

sn xut nng nghip , cng nghip , y dc , a cht , ha hc . Nht l cc nc

nc pht trin , phng php phn tch theo ph hp th nguyn t l mt phng

php tiu chun phn tch lng vt kim loi trong nhiu i tng mu khc nhau

nh : t , nc , khng kh , thc phm

nc ta k thut phn tch bng ph hp ph nguyn t AAS cng c ch

v pht trin trong nhng nm gn y c bit l trong cc trng i hc vin nghin

cu hu nh c trang b kh tt nhng thit b ny phc v cho nghin cu ging

dy v dch v phn tch .

Hin nay trong thc phm , phng php ny l mt trong nhng cng c c lc

xc nh hm lng cc kim loi v nhng nguyn t c hi c trong thc phm.

Kin thc l v tn , hin gi chng em cng cha nng lc tm hiu su hn

v ti cho nn trong bi tiu lun ny khng trnh khi nhng sai st mong thy v

cc bn gp hon thin bi hn . Chng em chn thnh cm n !

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NHN XT CA GIO VIN HNG DN

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NHN XT CHUNG :

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NI DUNG1. C s ca phng php ph hp th nguyn t:

1.1. Nguyn tc :

Trong iu kin bnh thng nguyn t khng thu v cng khng pht ra nng

lng di dng cc bc x. Lc ny nguyn t tn ti trng thi c bn. l trng

thi bn vng v ngho nng lng nht ca nguyn t. Nhng khi nguyn t trng thi

hi t do, nu ta chiu mt chm tia sng c nhng bc sng (tng s) xc nh vo

m hi nguyn t , th cc nguyn t s hp thu cc bc x c bc sng nht nh

ng ng vi nhng tia bc x m n c th pht ra c trong qu trnh pht x ca n.

Lc ny nguyn t nhn nng lng ca cc tia bc x chiu vo n v n

chuyn ln trng thi kch thch c nng lng cao hn trng thi c bn. l tnh chtc trng cu nguyn t trng thi hi. Qu trnh c gi l qu trnh hp thu nng

lng ca nguyn t t do trng thi hi v to ra ph nguyn t cu nguyn t . Ph

sinh ra trong qu trnh ny gi l ph hp thu nguyn t.

Mun c ph hp thu nguyn t trc ht phi to ra c m hi nguyn t t

do, v sau chiu vo n mt chm tia sng c nhng bc sng nht nh ng ng

vi cc tia pht x nhy ca nguyn t cn nguyn cu. D vo mi quan h gia cng

ca vch ph hp thu v nng ca nguyn t trong m hi ta c th xc nhc nng ca nguyn t cn phn tch.

Da vo phng trnh c s ca php o nh lng cc nguyn t theo ph hp

thu nguyn t, xc nh nng cht cn phn tch.

Da= a.Cb

C : Nng ca nguyn t phn tch c trong dung dch mu.

b : Hng s bn cht, ph thuc vo tng vch ph ca tng nguyn t, 0


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1.2. Qu trnh nguyn t ha mu:Nguyn t ha mu phn tch l mt cng vic ht sc quan trng ca php o ph

hp th nguyn t, bi v ch c cc nguyn t t do trng thi hi mi cho ph hp th

nguyn t, ngha l s nguyn t t do trong trng thi hi l yu t quyt nh cng

vch ph hp th v qu trnh nguyn t ha mu thc hin tt hay khng tt u c nhhng trc tip n kt qu phn tch mt nguyn t. Chnh v th ngi ta thng v qu

trnh nguyn t ha mu l hot ng tri tim ca php o ph hp th nguyn t.

Mc ch ca qu trnh ny l to ra c m hi cc nguyn t t do t mu

phn tch vi hiu sut cao v n nh php o t kt qu chnh xc v c lp li

cao. p ng mc ch , nguyn t ha mu phn tch, ngy nay ngi ta thng

dng hai k thut. Th nht l k thut nguyn t ha mu trong ngn la n kh. K

thut ny ra i u tin cng vi s ra i ca php o ph hp th nguyn t. Nhng kthut ny c nhy khng cao, thng l trong vng 0,05 - 1 ppm . Sau l k thut

nguyn t ha khng ngn la.

K thut ny ra i sau, nhng li c nhy rt cao t n 0,1ng v hin nay li

c ng dng nhiu hn k thut nguyn t ha mu bng ngn la. Chnh v c hai k

thut nguyn t ha mu khc nhau nn chng ta cng c hai php o tng ng. l

php o ph hp th nguyn t trong ngn la (F-AAS: Flame Atomic Absorpt Ion

Spectrophotometry) v php o ph hp th nguyn t khng ngn la (Electro-ThermalAtomizat Ion Atomic Absorpt Ion Spectrophotometry: ETA- AAS).

1.2.1. Nguyn t ha mu bng ngn la

Theo k thut ny ngi ta dng nng lng nhit ca ngn la n kh ha hi

v nguyn t ha mu phn tch. V th mi qu trnh xy ra trong khi nguyn t ha mu

l ph thuc vo cc c trng v tnh cht ca ngn la n kh. Nhng ch yu l nhit

ca ngn la. N l yu t quyt nh hiu sut nguyn t ha mu phn tch.

Ngn la n kh mun dng vo mc ch ho hi v nguyn t ha mu phn

tch n cn phi tha mn mt s yu cu nht nh sau y:

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Ngn la n kh phi bao qut v cp nhit u c mu phn tch.

Nng lng ( nhit )ca ngn la phi ln v c th iu chnh c

ty theo tng mc ch phn tch mi nguyn t . ng thi li phi n nh theo

thi gian v c th lp li c trong cc ln phn tch khc nhau m bo cho

php phn tch t kt qu ng n.

Ngn la phi thun khit . Ngha l khng sinh ra cc vch ph ph lm

kh khn cho php o hay to ra ph nn qu ln gy nhiu cho php o.

Qu trnh ion ha v pht x phi khng ng k.

Ngn la phi c b dy ln lm tng nhy ca php oTrong cc

my hin nay, b dy ny c th thay i c t 2cm n 10cm.

Tiu tn t mu phn tch.

to ra ngn la , ngi ta c th t chy nhiu hn hp kh khc nhau, bao gm

mt kh oxy ha v mt kh chy .

Trong h thng nguyn t ha mu c hai b phn chnh l du t ( Burnerhead )

v bung phun sng p lc aerosol ha ( nebulizer)

to cc ht sol kh t dung dch mu ngi ta dng cc k thut khc nhau nh

k thut phun kh mao dn (pneumatic ) v k thut siu m ( ultrasonic ). Thng ch

khong 10% dung dch mu c to thnh bi kh vi kch tht t yu cu khong t5 7 m , ti a l 20m.

Trong k thut phun kh dung dch mu c nh mnh to thnh cc ht bi nh

li ti bi mt qu bi v cnh qut ri trn u vi hn hp kh t v a ln bung t

nguyn t ha .

Trong k thut ny tc dn mu nh hng nhiu ti cng ca vch ph v

ph thuc vo nht ca dung dch mu.

Tuy vy thng thng nu tng tc dn n qu gii hn >6ml/ph th cng vch ph s khng tng tuyn tnh na c th dn n hin tng nhiu ha hc.

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1.2.2. Nguyn t ha khng ngn l

1.2.2.1. c im v nguyn tc

K thut ny cung cp cho php o AAS c nhy rt cao (mc nanogam ppb);

c khi gp hng trm n hng nghn ln php o trong ngn la. y l u im chnh

ca k thut nguyn t ha khng ngn la. Do , khi phn tch lng vt cc kim loitrong nhiu trng hp khng cn thit phi lm giu s b cc nguyn t cn xc nh.

c bit l khi xc nh cc nguyn t vi lng trong cc loi mu ca y hc, sinh hc,

dc phm, thc phm, nc gii kht, mu, srum.

Tuy c nhy cao nhng trong mt s trng hp, n nh ca php o

khng ngn la thng km php o trong ngn la, nh hng ca ph nn thng rt

ln. l c im v cng l nhc im ca php o ny. V th cc h thng my o

ph hp th theo k thut khng ngn la ca nhng nm 1980 lun lun c km theo h

thng b chnh nn v n nh ca n cng khng km cc h thng ca php o trong

ngn la v m bo nhy cao c ppb i vi nhiu nguyn t. c im na ca

php o khng ngn la l i hi mt lng mu tng i nh. Thng thng mi ln

o ch cn lng mu t 20 n 50 L. Do khng cn nhiu lng mu phn tch.

V nguyn tc, k thut nguyn t ha khng ngn la l qu trnh nguyn t ha

tc khc trong thi gian rt ngn nh nng lng ca dng in cng sut ln v trong

mi trng kh tr. Qu trnh nguyn t ha xy ra theo ba giai on k tip nhau: sy

kh, tro ha luyn mu, nguyn t ha o ph hp th v cui cng l lm sch cuvet.

Trong hai giai on u l chun b cho giai on nguyn t ha t kt qu tt.

Nhit trong cuvet graphit l yu t chnh quyt nh mi s din bin ca qu trnh

nguyn t ha mu.

1.2.2.2. Sy kh mu

thc hin qu trnh sy tt, i vi mi mt loi mu cn phi tin hnh nghin

cu, pht hin v chn nhit v thi gian sy cho ph hp. Nhit v thi gian sy

kh ca mi loi mu ph thuc vo bn cht ca cc cht trong mu v dung mi ho

tan n. Thc nghim cho thy rng, da s cc mu v c trong dung mi nc nm trong

khong t 100 - 150oCtrong thi gian t 25-40 giy

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1.2.2.3. Tro ho luyn mu

y l giai on th hai ca qu trnh nguyn t ha mu. Mc ch l tro ha

(t chy) cc hp cht hu c v mn c trong mu sau khi sy kh, ng thi nung

luyn mt nhit thun li cho giai on nguyn t ha tip theo t hiu sut cao v

n nh, tro ha mu t t v nhit thp hn nhit gii hn th php o lun luncho kt qu n nh, v mi nguyn t u c mt nhit tro ha luyn mu gii hn

(Tr.) trong php o ETA- AAS.

1.2.2.4. Nguyn t ho

y l giai on cui cng ca qu trnh nguyn t ha mu, nhng li l giai

on quyt nh cng ca vch ph. Song n li b nh hng bi hai giai on trn.

Giai on ny c thc hin trong thi gian rt ngn, thng thng t 3 n 6 giy, rt

t khi n 8-10 giy.

Nhng tc tng nhit li l rt ln t ngay tc khc n nhit

nguyn t ha v thc hin php o cng vch ph. Tc tng nhit thng l

t 1800 - 2500oC/giy, thng thng ngi ta s dng tc ti a. nguyn t ha

ca mt nguyn t rt khc nhau .

ng thi mi nguyn t cng c mt nhit nguyn t ha gii hn Ta ca n.

Nhit Ta ny ph thuc vo bn cht ca mi nguyn t v cng ph thuc trong mc

nht nh vo trng thi v thnh phn ca mu m n tn ti, nht l cht nn ca

mu nguyn t ha v cng vch ph ca cc nguyn t

1.2.2.5. Cc yu t nh hng .

Trc ht l mi trng kh tr thc hin qu trnh nguyn t ha. Kh tr thng

c dng lm mi trng cho qu trnh nguyn t ha l argon (Ar), nit (N2) v hai

(He), ngha l qu trnh nguyn t ha thc hin trong mi trng khng c oxy. Do

khng xut hin hp cht bn nhit loi MeO hay MeOX.

Nhng bn cht, thnh phn v tc dn kh tr vo trong cuvet graphit u

nh hng n cng ca vch ph v nhit trong cuvet graphit

Yu t th hai l cng sut t nng cuvet Nhn chung, khi tng cng sut t

nngcuvet th cng vch ph tng theo Nhng s ph thuc ny cng ch trong mt

gii hn nht nh, khi cng sut t nng cuvet nh hn 6 KW.

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Cn khi t nng cuvet cng sut ln hn 7 KW th hu nh cng vch ph

khng tng na. Yu t th ba l tc t nng cuvet. Tc t nng cuvet v thi

gian nguyn t ha t l nghch vi nhau. Nu o din tch ca lc th yu t ny hu nh

khng nh hng, nhng nu o chiu cao ca lc th li rt khc nhau Ni chung chiu

cao ca lc t l vi tc t nng cuvet.cc qu trnh xy ra trong cuvet ty thuc vo:

+ iu kin nguyn t ha mu (ch yu l nhit ).

+ Tnh cht nhit ha ca cc hp cht mu ,

+ nh hng thnh phn nn ca mu, v

+ Mi trng tin hnh nguyn t ha mu.

+ Cht nn ca mu, cht ph gia thm vo.

1.2.2.6. Ti u ha cc diu kin cho php o khng ngn la mu.

C th vi php o ETA-AAS bao gm nhng iu kin nguyn t ha mu :

+ Thi gian, nhit nung nng cuvet ca cc giai on sy mu, tro ha luyn

mu v nguyn t ha o cng vch ph

+ Kh mi trng cho qu trnh nguyn t ha mu (tc , loi khi)

+ Cng sut, tc t nng cuvet graphit nguyn t ha mu;

+ iu kin lm sch cuvet graphit;

+ Lng mu v cch a vo cuvet nguyn t ha cho php o.

Cht nn ca mu phn tch v cc mu chun cn phi c pha ch v chun

cho ng nht. Mi trng axit v loi axit pha ch mu v lm mi trng cho dung

dch mu chun v mu phn tch.

Cc yu t nh hng sau y cng cn c xem xt.

Trong mt php o c th cc yu t nh hng cn phi xem xt l:

+ Cc nh hng v ph;+ Cc nh hng v vt l;

+ Cc nh hng ha hc ca cc Cation v Anion c trong mu;

+ V nh hng ca thnh phn nn ca mu.

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1.3. Cc yu t nh hng trong php o AAS:

1.3.1 Khi qut chung

Cc yu t nh hng n kt qu phn tch trong php do ph hp th nguyn t

rt a dng v phc tp, c khi xut hin v cng c khi khng xut hin, c nh hng

hay khng l ty thuc vo thnh phn ca mu phn tch v matrix ca n. Nhng nghin cu mt cch ton din, chng ta im qua tt c cc yu t nh hng c th c

trong php o ny.

Cc yu t c th c chia thnh 6 nhm sau:

Nhm l: Cc thng s ca h my o ph. Cc thng s ny cn c kho st v

chn cho tng trng hp c th. Thc hin cng vic ny chnh l qu trnh ti u ha

cc thng s ca my o cho mt i tng phn tch.

Nhm 2: Cc iu kin nguyn t ha mu. Cc yu t ny th hin rt khc

nhau ty thuc vo k thut c chn thc hin qu trnh nguyn t ha mu v n

c nghin cu k trong chng II.

Nhm 3: K thut v phng php c chn x l mu. Trong cng vic ny nu

lm khng cn thn s c th lm mt hay lm nhim bn thm nguyn t phn tch vo

mu. Do kt qu phn tch thu c khng ng vi thc t ca mu. V th, vi mi

mt loi mu ta phi nghin cu v phi chn mt quy trnh x l ph hp nht, c

c ng thnh phn ca mu v khng lm nhim bn mu. Vn ny s c

nghin cu trong mt chng ring.

Nhm 4. Cc nh hng v ph.

Nhm 5. Cc yu t nh hng vt l.

Nhm 6. Cc yu t ha hc.

1.3.2. Cc yu t v ph

1.3.2.1. S hp th nn

Yu t ny c trng hp xut hin r rng, nhng trong nhiu trng hp khng

xut hin. iu ny ph thuc vo vch ph c chn o nm trong vng ph no.

s hp th nn cn ph thuc rt nhiu vo thnh phn nn ca mu phn tch, c bit l

matrix ca mu, ngha l nguyn t c s ca mu.. loi tr ph nn, ngy nay ngi

ta lp thm vo my quang ph hp th nguyn t h thng b chnh nn.

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1.3.2.2. S chen ln ca vch ph

Yu t ny thng thy khi cc nguyn t th ba trong mu phn tch c nng

ln v thng l nguyn t c s ca mu. Tuy nguyn t ny c cc vch ph

khng nhy, nhng do nng ln, nn cc vch ny vn xut hin vi rng ln, nu

n li nm cnh cc vch phn tch th cc vch ph ny s chen ln cc vch phn tch,lm cho vic o cng vch ph phn tch rt kh khn v thiu chnh xc, nht l i

vi cc my c phn gii khng cao. V th, trong mi mc ch phn tch c th cn

phi nghin cu v chn nhng vch phn tch ph hp loi tr s chen ln ca cc

vch ph ca nguyn t khc.

1.3.2.3. S hp th ca cc ht rn

Trong mi trng hp th, c bit l trong ngn la n kh, nhiu khi cn c

cha c cc ht rn nh li ti ca vt cht mu cha b ha hi v nguyn t ha, hay cc

ht mui cacbon ca nhin liu cha c t chy hon ton. Cc ht loi ny thng

c th c lp v ca ngn la. Cc ht ny hoc hp th hoc chn ng i ca chm

sng t n HCL chiu vo mi trng hp th.

Yu t ny c gi l shp th gi, do cng gy ra nhng sai s cho kt qu

o cng vch ph thc. Yu t ny th hin rt r khi chn khng ng chiu cao

ca n nguyn t ha mu v khi hn hp kh chy khng c t chy tt, hay do

thnh phn ca hn hp kh chy khng c chn ph hp (thng l qu d axetylen).

1.3.3. Cc yu t vt l

1.3.3.1 nht v sc cng b mt ca dung dch mu

Trong php o AAS, vi k thut nguyn t ha mu trong ngn la, yu t ny

nhhng nhiu n tc dn mu vo bung aerosol ha v hiu sut aerosol ha ca

mu v t m nh hng n kt qu phn tch. Ni chung, tc dn mu t l

nghch vi nht ca dung dch mu.

Chnh s khc nhau v nng axit, loi axit, nng cht nn ca mu, thnh

phn ca cc cht c trong dung dch mu l nguyn nhn gy ra s khc nhau v nht

ca dung dch mu. V th, trong mi qu trnh phn tch mt nguyn t, nht thit phi

m bo sao cho mu phn tch v cc mu u lp ng chun phi c cng nng

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axit, loi axit v thnh phn ha hc, vt l ca tt c cc nguyn t khc, nht l cht nn

ca mu.. loi tr nh hng ny chng ta c th dng cc bin php sau y:

+ o v xc nh theo phng php thm tiu chun,

+ Pha long mu bng mt dung mi hay mt nn ph hp,

+ Thm vo mu mt cht m c nng ln, ng nht nht,+ Dng bm y mu vi mt tc xc nh m chng ta mong mun.

1.3.3.2 Hiu ng lu li

Yu t ny th hin r rng c bit trong php o ph hp th khng ngn la

v cng ln khi cht phn tch c nng ln, ng thi cng ph thuc vo bn cht

ca cc nguyn t, hp cht n tn ti trong mu, cng nh loi cuvet graphit c

dng nguyn t ha mu. Ni chung, cc nguyn t kh bay hi v d sinh ra hp

cht bn nhit lun lun gy ra nh hng ny.

Cc cuvet c ch to t graphit hot ha thng hn ch c hiu ng ny.

Hn na, b mt bn trong ca cuvet cng l mt yu t ng gp vo hiu ng ny,

ngha l b mt cng mn th nh hng cng nh, b mt cng xp th nh hng cng

ln. Do tnh cht ny m khi nguyn t ha mu o cng vch ph th mt lng

nh ca nguyn t phn tch khng b nguyn t ha, chng c lu li trn b mt

cuvet v c th tch t li qua mt s ln nguyn t ha mu.

Nhng n mt ln no th n li b nguyn t ha theo v do to ra s

nguyn t t do ca nguyn t phn tch tng t ngt khng theo nng ca n trong

mu, ngha l lm tng cng ca vch ph v dn n lm sai lc kt qu phn tch.

V th cn phi loi tr nh hng ny. loi tr nh hng ny chng ta c th theo

cc cch sau:

+ Lm sch cuvet sau mi ln nguyn t ha mu, lm bay hi ht cc cht

cn li trong cuvet. Tt nhin phi thc hin nhit cao hn nhit nguyn t ha

nguyn t phn tch;

+ Dng cc loi cuvet c ch to t cc loi graphit c hot ha ton

phn, c b mt chc v mn;

+ Khi phn tch nn o cc mu c nng nh trc;

+ Thm vo mu nhng cht m c nng ph hp;

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+ Trng b mt trong ca cuvet graphit bng mt lp cc hp cht bn nhit.

Tt nhin y ch l nhng nguyn tc chung. Cn trong thc t phi ty tng trng hp

c th m chn cc bin php ph hp nht.

1.3.3.3. S Ion ha ca cht phn tch

y l yu t vt l th ba nh hng n kt qu phn tch, v qu trnh Ion hathng lm gim s nguyn t t do ca nguyn t phn tch trong mi trng hp th

to ra ph, do lm gim cng vch ph hp th, nu nguyn t phn tch b Ion

ha cng nhiu. Nhng mc b Ion ha ca mi nguyn t l khc nhau, v cn ph

thuc vo nhit ca mi trng hp th.

Vi mt nguyn t, th khi nhit ca mi trng hp th cng cao, nguyn t

cng b Ion ha nhiu hnThc t cho thy rng, qu trnh Ion ha thng ch c

ngha i vi cc kim loi kim v sau l cc kim loi kim th, cn i vi cc

nguyn t khc s Ion ha khng ng k trong mi trng hp th ca php o ph hp

th nguyn t (F-AAS hay ETA-AAS). loi tr s Ion ha ca mt nguyn t phn

tch chng ta c th dng cc bin pht sau y:

+ Chn iu kin nguyn t ha c nhit thp ph hp, m trong iu kin

nguyn t phn tch hu nh khng b Ion ha.

+ Thm vo mu phn tch mt cht m cho s Ion ha. l cc mui halogen

ca cc kim loi kim c th Ion ha thp hn th Ion ha ca nguyn t phn tch vi

mt nng ln ph hp. Nh vy trong iu kin nguyn t phn tch s khng b

Ion ha na.

1.3.3.4 S pht x ca nguyn t phn tch

Yu t ny xut hin thng lm gim nng ca cc nguyn t trung ho c

kh nng hp th bc x trong mi trng hp th, do cng lm gim cng ca

vch ph hp th. Ni chung cc nguyn t c th kch thch ph pht x thp thng b

nh hng nhiu.

ng thi mi trng hp th c nhit cng cao th nh hng ny cng ln

Nhng trong nhit ca php o AAS, th s kch thch ph pht x thng ch xy ra

mnh ch yu i vi cc kim loi kim v sau l cc kim th, v cc nguyn t ny

c th kch thch ph pht x tng i thp

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loi tr nh hng ca s pht x ca nguyn t phn tch chng ta c th dng cc

bin php sau y:

Chn nhit nguyn t ha mu thp ph hp m ti nhit s kch thch

ph pht x l khng ng k hoc khng xy ra i vi nguyn t phn tch.

Thm vo mu cc cht m hn ch s pht x ca nguyn t phn tch.

chnh l cc mui halogen ca cc kim loi kim, c th kch thch Trn y l mt s

yu t vt l c th c xut hin trong php o AAS v c th nh hng n kt qu

phn tch. Nhng mc xy ra l rt khc nhau trong mi trng hp c th, c khi c,

c khi khng. Mc ny xut hin ln hay nh l c ph thuc vo nhit ca mi

trng hp th, tnh cht ca nguyn t phn tch, v thnh phn ca mu phn tch. Do

cn phi xem xt tm bin php loi tr khi chng xut hin.

1.3.4. Cc yu t ha hc

Trong php o ph hp th nguyn t cc nh hng ha hc cng rt a dng v phc

tp, n xut hin cng rt khc nhau trong mi trng hp c th v cng nhiu trng

hp khng xut hin. Cc nh hng ha hc thng c th dn n kt qu theo bn

hng sau y:

Lm gim cng ca vch ph ca nguyn t phn tch, do s to thnh cc

hp cht bn nhit, kh ha hi v kh nguyn t ha, v d nh nh hng ca cc

Ion silicat, sunfat, photphat, florua.

Lm tng cng ca vch ph, do s to thnh cc hp cht d ha hi v d

nguyn t ha, hay do hn ch c nh hng ca s Ion ha v s kch thch ph

pht x ca nguyn t phn tch. chnh l tc dng ca mt s hp cht, ch yu l

mui halogen ca kim loi kim v kim th hay lantanClorua.

S tng cng vch ph khi nguyn t phn tch tn ti trong nn ca mu lnhng hp cht d ha hi. Lc cc cht nn ny c tc dng nh l mt cht mang

cho s ha hi ca nguyn t phn tch v lm cho n c ha hi hiu sut cao hn.

S gim cng ca vch ph khi nguyn t phn tch tn ti trong nn ca

mu l nhng hp cht bn nhit, kh ha hi. Lc ny cc nguyn t nn km hm s

ha hi ca nguyn t phn tch. Cc cht nn ny thng l nhng hp cht bn nhit

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ca cc nguyn t, nh Al, t him, v.v...

V th vic nghin cu cc nh hng ha hc c trnh by trong chng ny c

tnh cht khi qut chung tt c cc loi c th c chng ta lu khi ng dng php o

ph hp th nguyn t, vi mc ch bit v loi tr cc nh hng ha hc nu chng

xut hin. Cc yu t nh hng v mt ha hc c th c sp xp theo cc loi sauy, d xem xt v tm cch loi tr:

1.3.4.1 Nng axit v loi axit trong dung dch mu

Nng axit trong dung dch mu lun lun c nh hng n cng ca

vch ph ca nguyn t phn tch thng qua tc dn mu, kh nng ha hi v

nguyn t ha ca cht mu. nh hng ny thng gn lin vi loi Anion ca axit. Ni

chung, cc axit cng kh bay hi v bn nhit, cng lm gim nhiu cng vch ph

hp th ca nguyn t phn tch. Cc axit d bay hi gy nh hng nh.

iu ny c th thy r rng khi xc nh Ca lc o vch ph Ca-422,7 nm trong

cc mi trng ca cc axit HClO4, CH3COOH, HCl, HNO3, H2SO4, H3PO4, HF vi

cng mt nng l 2% Ni chung, cc axit lm gim cng vch ph theo th t:

HClO4 < HCl: 209HNO3 < H2SO4 < HaPO4 < HF, ngha l axit HClO4 < HCl v

HNO3 gy nh hng nh nht trong vng nng nh. Chnh v th trong thc t phn tch

ca php o ph hp th nguyn t (AAS) ngi ta thng dng mi trng l axit HCl

hay HNO3 1 hay 2%. V nng nh th nh hng ca hai axit ny l khng ng

k (nh hn 5%).

1.3.4.2 V nh hng ca cc Cation c trong mu:

Dung dch mu phn tch, ngoi nguyn t cn xc nh, thng cn cha cc

nguyn t khc. Cc nguyn t ny tn ti di dng cc Cation hay Anion tan trong

dung dch mu. Cc Ion ny c th lm tng, cng c th lm gim, hoc cng c th

khng gy nh hng g n cng vch ph ca nguyn t phn tch. Khi c nh

hng th mc nh hng ca mi Ion cng rt khc nhau

Loi l: Khi nng ca Ion gy nh hng ln hn C2 th n khng lm tng

cng vch ph ca nguyn t phn tch na, nh hng ny c s dng tng

nhy ca phng php phn tch mt nguyn t, khi thm vo mu nguyn t nh hng

c nng ln hn C2.

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Loi 2: Ti nng C1 ca nguyn t gy nh hng, cng vch ph ca

nguyn t phn tch t gi tr cc i. V th nh hng ny cng c dng tng

nhy ca phng php phn tch. Nhng phi gi (khng ch) nng ca nguyn t gy

nh hng gi tr khng i C1.

Loi 3: Trong trng hp ny cng vch ph gim lin tc theo ng congli, khi nng nguyn t nh hng tng dn u.

Loi 4: Cc Cation ch gy nh hng n cng vch ph ca nguyn t phn

tch khi nng ca n ln hn gi tr C2. Do vy, nu nng ca cc Cation

trong mu nh hn gi tr C2 th khng phi quan tnm n tm bin php loi tr.

Loi 5: Trong trng hp ny cng vch ph ca nguyn t phn tch li b

gim lin tc theo ng cong lm, khi nng Cation gy nh hng trong dung dch

mu tng dn v y nht thit phi tm bin php loi tr nh hng ny.

Loi 6: Khi nng ca cc Cation khc trong mu ln hn gi tr C2 th chng

khng lm thay i cng vch ph ca nguyn t phn tch. Do , nu khng tm

c bin php loi tr ph hp th chng ta thm vo mu Cation gy nh hng vi

nng ln hn gi tr C2, a nh hng gim thnh mt gi tr hng s cho tt c

cc mu phn tch v mu chun. Nh th cng loi b c nh hng ny. Nhng tt

nhin l ta lm gim nhy ca phng php phn tch i mt t.

Loi 7: y cc Cation l lm gim lin tc cng vch ph ca nguyn t

phn tch theo chiu tng dn nng ca n mt cch tuyn tnh Do cng cn phi

tm bin php ph hp loi tr nh hng ny, hoc gi cho cc Cation l c nng

nht nh v khng i trong tt c cc mu chun v cc mu phn tch.

loi tr nh hng ca cc Cation n cng vch ph ca nguyn t phn

tch chng ta c th s dng mt s bin php sau y hoc ring bit, hoc t hp ca

chng vi nhau:

+ Chn iu kin x l mu ph hp loi cc nguyn t nh hng ra khi

dung dch mu phn tch o ph.

+ Chn cc thng s ca my o thch hp.

+ Thay i hay chn vch ph khc, c th km nhy mt cht.

+ Chn cc iu kin nguyn t ha mu thch hp v chn lc.

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+ Vi tt c cc bin php trn m khng c, th bin php cui cng l bt buc

chng ta phi tch loi b cc Cation c nh hng

1.3.4.3 nh hng ca cc an Ion c trong mu

Cng vi cc Cation, cc Anion cng nh hng n cng vch ph ca

nguyn t phn tch nh hng ny v tnh cht tng t nh nh hng ca cc loi axit.Ni chung, cc Anion ca cc axit d bay hi thng gim t cng vch ph. Ch

ring c hai Anion ClO4 v CH3COO l gy hiu ng dng (lm tng), tc l lm

tng cng vch ph ca nguyn t phn tch trong mt s trng hp mt vng

nng nht nh. Cc Anion khc thng gy hiu ng nm (lm gim).

Do thc t nn trong mi php o phi gi cho nng ca cc Anion trong

mu phn tch v mu chun l nh nhau v mt gi tr nht nh khng i. Mt khc

cng khng nn chn axit H2SO4 lm mi trng ca mu cho php o AAS m ch nn

dng axit HCl hay HNO3 vi nng di 2%

1.3.4.4 Thnh phn nn ca mu

Yu t nh hng ny ngi ta quen gi l matrix effect. Nhng khng phi lc

no cng xut hin, m thng ch thy trong mt s trng hp nht nh. Thng

thng l nhng mu c cha cc nguyn t nn di dng cc hp cht bn nhit,

kh bay hi v kh nguyn t ha.

V d: Khi xc nh cc tp cht lng vt trong cc mu oxit t him, oxit kim

loi kim th, oxit nhm, oxit zircon, cc mu mui NaCl, th cc nn ny s kh cng

ca vch ph ca nguyn t phn tch, qua lm gim nhy ca phng php

phn tch.

Trong nhiu trng hp, yu t ny lm gim hng chc ln, thm ch c trng

hp hng trm ln cng ca vch ph (bng 10.4). Nguyn nhn chnh ca nh

hng ny l s tn ti ca cc hp cht bn nhit trong mi trng hp th. Cc hp

cht ny lm kh khn, cn tr qu trnh ha hi v nguyn t ha ca cc nguyn t

phn tch

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1.3.4.5 nh hng ca dung mi hu c

Trong php o ph hp th nguyn t, c bit l i vi k thut nguyn t ha

mu trong ngn la, s c mt ca dung mi hu c trn ln vi nc trong dung dch

mu phn tch, hay mu phn tch ha tan trong dung mi hu c thng lm tng cng

ca vch ph hp th nguyn t ca nhiu nguyn t ln nhiu ln y l mt phngphp tng nhy.

V th, khi phn tch cc nguyn t c nng rt nh st gii hn di ca

php o, chng ta c th thm vo mu phn tch mt dung mi hu c c nng ph

hp th c th tng nhy ca phng php phn tch ln n hai hay i khi n ba ln

so vi khi ch dng dung mi nc. Song dung mi hu c thm vo phi trn u

c vi nc v phi c tinh khit cao.

Nu dung mi hu c tan trong nc th ngi ta thm vo dung dch mu phn

tch mt nng dung mi hu c thch hp tng nhy ca phng php phn tch.

Nu dung mi hu c khng tan trong nc th ngi ta chit cht phn tch

dng hp cht phc ca n vi mt thuc th thch hp vo dung mi hu c . Nh th

va tng nhy, va loi tr c cc Ion cn tr.

1.4. My quang ph hp th nguyn t

1.4.1. Phn loi

1.4.1.1.My quang ph hp th mt chm tia

Ngun sng (t n Catot rng hoc n EDL) pht bc x mt ph c trng cho tng

nguyn t truyn xuyn qua bung mu i vo my n sc

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Ngun pht tia bc x phi cung cp c mt chm tia pht x thun khit ch

bao gm mt s vch nhy c trng ca nguyn t phn tch. Ph nn ca n phi khng

ng k. C nh th mi hn ch c nhng nh hng v vt l v v ph cho php o

AAS.

Chm tia pht x n sc do ngun cung cp phi c cng cao, nhng li

phi bn vng theo thi gian v phi khng b cc yu t vt l khc nhiu lon, t b nh

hng bi cc dao ng ca iu kin lm vic.

Ngun pht tia bc x n sc phi bn lu, khng qu t tin v khng qu

phc tp cho ngi s dng.

Xut pht t nhng nhim v v yu cu phi tha mn, hin nay trong php o phhp th nguyn t, ngi ta thng dng ch yu ba loi ngun pht tia bc x n sc.

l:

+ n catot rng (HCL - Hollow Cathode Lamp),

+ n phng in khng in cc (EDL- Electrodeless Discharge Lamp),

+ n pht ph lin tc c bin iu (D2-lamp, W-lamp).

+ Cc loi ngun n sc khc.

1.4.2.1.1. n catot rng (HCL)

n pht tia bc x n sc c

dng sm nht v ph bin nht

trong php o S l n catot rng

(HCL). n ny ch pht ra nhng

tia pht x nhy ca nguyn t kim

loi lm catot rng. Cc vch pht

x nhy ca mt nguyn t thng

l cc vch cng hng. V th n catot rng cng c gi l ngun pht tia bc x

cng hng. N l ph pht x ca cc nguyn t trong mi trng kh km.

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Khi di tc dng ca nhit trong n HCL ang c t nng , cc

nguyn t kim loi ny b kch thch v pht ra ph pht x ca n. chnh l ph vch

ca chnh kim loi lm catot rng.

Nhng v trong iu kin c bit ca mi trng kh tr c p sut rt thp, nn

ph pht x ch bao gm cc vch nhy ca kim loi m thi. chnh l s phtx ca kim loi trong mi trng kh km. Chm tia pht x ny l ngun tia n sc

chiu qua mi trng hp th thc hin php o AAS.

Cc n catot rng c cu to nh m t trn l nhng n HCL n nguyn

t, ngha l mi n HCL ch phc v cho phn tch mt nguyn t. Ngy nay ngoi

cc n HCL n, ngi ta cng ch to c mt s n kp i, kp ba hay kp su

nguyn t. V d cc n kp i l (Ca+Mg), (Cu+Mn), (Cu+Cr), (Co+Ni), (K+Na),

(Cu+Pb); cc n kp ba nh (Cu+Pb+Zn) v n kp su l (Cu+Mn+Cr+Fe+Co+Ni).

1.4.2.1.2. n phng in khng din cc (EDL)

Ngun pht tia bc x

n sc th hai c dng trong

php o ph hp th nguyn t

l n phng in khng in

cc.Loi n ny cng nh

n HCL u c nhim v cung

cp chm tia pht x c trng

ca nguyn t phn tch, c bit l cc kim, th n EDL cho nhy cao hn, n nh

hn n HCL.

V cu to, n EDL thc cht cng l mt ng phng in trong mi trng kh

km c cha nguyn t cn phn tch vi mt nng nht nh ph hp to ra cchm tia pht x ch bao gm mt s vch ph nhy c trng ca nguyn t phn tch.

n EDL cng gm cc b phn:

Thn n: Mt ng thch anh chu nhit, di 18 - 15 cm, ng knh 6 - 5 cm. Mt

u ca n EDL cng c ca s S. Ca s cho chm sng i qua cng phi trong sut

vi chm sng .

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Ngoi ng thch anh l cun cm bng ng. Cun cm c cng sut t 800 - 400

W ty loi n ca tng nguyn t, v c ni vi ngun nng lng cao tn HF ph

hp nui cho n EDL lm vic . Ngoi cng l v t chu nhit.

Cht trong n l vi miligam kim loi hay mui kim loi d bay hi ca nguyn

t phn tch, lm sao khi ton b cht ha hi bo m cho p sut hi ca kim loi trong n iu kin nhit t 800 550o C l khong t 1 - 1,5 mmHg.

Cht ny thay cho catot trong n HCL, n l ngun cung cp chm tia pht x ca

nguyn t phn tch, khi chng b kch thch, trong qu trnh n EDL hot ng.

Kh trong n. Trong n EDL cng phi ht ht khng kh v np thay vo l

mt kh tr Al, He hay Nit c p sut thp, vi mmHg khi u cho s lm vic ca

n EDL.

Ngun nui n lm vic. Ngun nng lng cao tn nui n EDL lm vic

c ch to theo hai tn s. Tn s sng ngn 450 MHz v tn s sng raio 27,12 MHz,

c cng sut di 1 kW.

Do ngun nui l nng lng cm ng in t vi hai tn s khc nhau nn n

EDL cng c chia thnh hai loi:

n EDL sng ngn, ngun nui tn s 450 MHz,

n EDL sng raio, ngun nui tn s sng raio 27,12 MHz.

Cng vch ph v vng tuyn tnh ca As-193,7 v Se-196,1 i vi hai loi

n HCL v EDL. Khi n lm vic, di tc dng ca nng lng cao tn cm ng n

c nung nng , kim loi hay mui kim loi trong n c ha hi v b nguyn t

ha. Cc nguyn t t do c sinh ra s b kch thch v pht ra ph pht x ca n

trong iu kin kh km di tc dng nhit khi n lm vic. chnh l ph vch cakim loi cha trong n EDL.

Ngoi u im v nhy v gii hn pht hin, n EDL ca cc kim hay bn

kim thng c bn cao hn n HCL. ng thi vng tuyn tnh ca php o mt

nguyn t khi dng n EDL thng rng hn so vi vic dng n HCL .

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Ngy nay cc hng sn xut my o ph hp th nguyn t sn xut c n

30 loi n EDL cho 30 nguyn t. Nhng tt v c dng nhiu ch c 12 nguyn t

kim v bn kim l As, Bi, Cd, Hg, P, Pb, Se, Sn, Te, TI v Zn. Cc n EDL ca cc

nguyn t ny u c bn theo cc my ca hng. Nhng n EDL ca cc nguyn t

khc cn li t c s dng, v n khng u vit hn n HCL, m gi thnh li t hn.Ngoi n catot rng v n phng in khng in cc, ngi ta cng ch to

ra c nhiu loi n pht tia bc x n sc ca cc nguyn t, nh n catot rng

cng cao (trnh intensity cmiss Ion lamp - HIEL), n gradient nhit (controlled

temperature-gradient lamp - CTGL), n phng in c chi sng cao (glow-discharge

lamp - GDL). Cc loi kin ny c u im hn n HCL mt cht v nhy, v vng

tuyn tnh, v gii hn pht hin. Nhng cc n loi ny li kh ch to v t tin, mt

khc li km bn vng. V th n t c dng v khng c bn ngoi th trng, ch

yu ch c ng trong nghin cu l thuyt v ph.

1.4.2.1.3. n ph lin tc c bin iu:

Trong khong vi nm li

y, mt loi ngun pht x ph lin

tc cng c dng lm ngun pht

bc x cng hng cho php oAAS. l n hydrogen nng (D2-

lamp), cc n xenon p sut cao

(Xe-lamp), cc n hot ca kim loi

W. l cc loi n pht ph lin

tc trong vng t ngoi v vng kh kin (UV-VIS). Cc tc gi Fassel, Ivanop, Gibson,

Mc G, Winerfordner l nhng ngi u tin nghin cu v s dng cc loi n ny

lm ngun pht bc x cng hng cho php o AAS.n ny tuy pht ra ph lin tc, nhng nh h thng bin iu v h lc giao thoa,

nn chm sng pht x b bin iu v lng t ha thnh chm sng khng lin

tc c ph dng rng ca, mi rng ca cch nhau 0,2 nm, nn mi rng ca c coi

nh l 1 tia n sc h my o ph hp th nguyn t dng ngun sng bc x lin tc.

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Trong ngun sng c t trc h thng bin iu v b lc giao thoa. Chm

sng ny khi i qua h thng bin iu v b lc giao thoa s b bin iu theo nhng

di sng nht nh dao ng vi bin nh nhau. Sau cng c chiu vo mi

trng hp th l ngn la hay cuvet graphit.

Cc nguyn t t do trong mi trng hp th s hp th mt phn nng lng cachm sng ng vi mt di bin iu ca vng ph. Phn cn li s i vo b n sc

v detector pht hin v o cng sau khi qua b khuych i bng sng theo di

ph ca n nn li tn s. Tip cng vch ph hp th cng c o v ch th

theo cc cch bit, nh hin s digital, ghi pic trn recorder, hay dng printer in ln

bng giy.

Ngun pht ph lin tc c u im l d ch to, r tin v c bn tng i

cao, v ch cn mt n c th thc hin c php o AAS i vi nhiu nguyn t

trong mt vng ph UY hay VIS. Do n rt u vit i vi cc my ph hp th nhiu

knh v xc nh ng thi hay lin tip nhiu nguyn t trong cng mt mu phn tch,

m khng phi thay n HCL cho vic o ph mi nguyn t.

Vi n ny, vng tuyn tnh rng, li khng c hin tng t hp th ring (t

o). Song v n sc v chn lc hay nhy, th ni chung trong nhiu trng

hp cn km cc n HCL hay n EDL nhng li u vit v d dng i vi qu trnh

phn tch t ng hng lot trong cc my o ph hp th nhiu knh.

Chnh v th m trong khong nm nm li y cc loi n ph lin tc c

pht trin, ci tin v bt u c s dng rt nhiu trong php o AAS v nhiu h

thng my o ph hp th vi ngun pht ph lin tc cng c bn trn th trng

th gii.

1.4.2.1.4. Cc loi ngun n sc khc :

Ngoi ba loi ngun pht bc x n sc ch yu c trnh by trn, trong

php o ph hp th nguyn t, ngi ta cng s dng mt vi loi ngun pht tia bc x

n sc khc na nh n catot rng c di cao, ng pht x c bit, tia laze. Nhng

nhng loi ny ch ch yu dng trong nghin cu l thuyt vt l.

1.4.2.2. H thng nguyn t ha mu :

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nguyn t ha mu, trong php o ph hp th nguyn t ngi ta thng dng

hai k thut khc nhau. l k thut nguyn t ha bng ngn la ca n kh v k thut

nguyn t ha khng ngn la. ng vi hai k thut nguyn t ha c hai loi dng c

nguyn t ha mu.

H thng nguyn t ha mu bng ngn la gm hai phn chnh:

+ Bung aerosol ha (Nebulizer system), to th si kh mu,

+ n nguyn t ha mu (burner head).

Kh to ra ngn la nguyn t ha mu thng hay c dng l hn hp ca 2

cht kh (1 cht oxy ha v 1 cht chy), v d nh hn hp khng kh nn vi axetylen

hay kh N2O vi kh axetylen. i khi cng dng hn hp ca kh hydro vi axetylen hay

khng kh v kh propan. H thng nguyn t ha khng ngn la. H thng ny gm ba phn chnh l:

+ Cuvet graphit hay thuyn Ta cha mu, nguyn t ha.

+ Ngun nng lng nung cuvet hay thuyn Ta.

+ B iu khin thc hin vic nguyn t ha mu theo cc giai on ca

mt chng trnh ph hp.

Mun thc hin php o ph hp th

nguyn t (F-AAS), trc ht phi chun b mu

phn tch trng thi dung dch. Sau dn

dung dch mu vo ngn la n kh ha hi

v nguyn t ha mu phn tch v thc hin

php o. Qu trnh nguyn t ha trong ngn

la gm hai bc k tip nhau. Bc mt l

chuyn dung dch mu phn tch thnh th cc

ht nh nh sng m trn u vi kh mang v

kh chy. l cc ht sol kh (th aerosol). Qu

trnh ny c gi l qu trnh aerosol ha hay

nebulize ha. K thut thc hin qu trnh ny v hiu sut ca n nh hng trc tip n

kt qu ca php o AAS.

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Sau dn hn hp aerosol cng hn hp kh t vo n (burner head)

nguyn t ha. Kh mang l mt trong hai kh t chy to ra ngn la. Thng thng

ngi ta hay dng kh oxy ha (khng kh nn hay kh N2O). Hai giai on trn c

thc hin bng mt h thng trang b nguyn t ha mu . H thng ny gi l Nebulizer

System, gm hai phn chnh: n nguyn t ha mu

(burner head). Cc n ny thng c

hai dng khc nhau, hoc hnh trn c

nhiu l hay hnh mt khe hp c

rng t 0,5 - 1,0 mm v chiu di 5 cm

hay 10 cm.

Loi khe di 10 cm cho hn hp

kh t axetylen v khng kh nn; loi

khe di 5 cm l cho hn hp kh t

axetylen v kh N2O Cn loi ming trn ch thch hp cho php o ph pht x.

Bung aerosol ha mu.

l bung iu ch cc ht

sol kh ca mu vi kh mang. thc hin cng vic ny

ngi ta p dng hai k thut

theo nguyn l khc nhau. l

k thut pneumatic-mao dn

(phun kh) v k thut ultrasonic

(siu nm). Do cng c hai

loi h trang b khc nhau

iu ch sol kh ca mu.

a. Aerosol ha mu theo k

thut pneumatic-mao dn.

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Theo cch ny ngi ta dng h thng nebulize v kh mang to ra th si kh ca mu

phn tch nh hin tng mao dn .

Trc ht nh ng mao dn S v dng kh mang K m dung dch mu c dn

vo bung aerosol ha. Trong bung ny, dung dch mu c nh tung thnh th bi

(cc ht rt nh) nh qu bi E v cnh qut Q, ri c trn u vi hn hp kh t vc dn ln n nguyn t ha (burner head).

Khi hn hp kh t chy burner head s to ra ngn la, di tc dng ca nhit

ca ngn la cc phn t mu th si kh s b ha hi v nguyn t ha to ra cc

nguyn t t do ca cc nguyn t c trong mu phn tch.

l nhng phn t hp th nng lng v to ph hp th nguyn t ca nguyn

t cn nghin cu.

Nhng cn ch rng, ngoi nh hng ca thnh phn kh t v tc dn hn

hp kh n cng vch ph, th tc dn dung dch mu vo bung aerosol ha

cng nh hng ng k n cng vch ph .

Ngha l tc dn mu V ph thuc vo cc tham s r, P, L v . Nhng trong

mt h thng my th r v L thng l c nh, P c gi khng i, cho nn V ch cn

ph thuc ch yu vo nht ca dung dch mu .

b. Aerosol ha mu bng siu nm.Theo k thut ny, aerosol ha mu phn tch

ngi ta dng h thng siu nm c tn s t 1-4,5 MHz. Lc siu nm c th c truyn

qua tng rn hay qua th lng n dung dch mu thc hin vic aerosol ha mu,

ngha l di tc dng ca lc siu nm, mu dung dch cng c phn tn (nh ti)

thnh nhng ht rt nh v trn uvi hn hp kh dn ln n (burner head) nguyn

t ha.

Nh vy, mun c cc ht aerosol nh th phi s dng tn s siu nm cao. Tn s

v cng sut ca my pht siu nm u nh hng n kch thc ca ht aerosol. Trong

hai k thut aerosol ha, th k thut pneumatic l n gin, trang b r tin, khng phc

tp nh k thut siu nm.

Nhng k thut siu nm c u im cho nhy cao hn. V kch thc cc ht

sol kh kh nh, hiu sut to sol kh cao v qu trnh aerosol t ph thuc vo kh mang

v qu trnh dn mu. c bit l vic aerosol ha cc dung dch mu c nng mui

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cao th n u vit hn k thut pneumatic. Mt khc, s aerosol ha bng siu nm thng

cho lp li tt hn

1.4.2.3. H thng n sc my quang ph hp th nguyn t

H thng n sc chnh l h thng thu, phn li, chn v pht hin vch ph hp

th cn phi o. Trong php o ph hp th nguyn t h thng n sc ny l mt myquang ph c phn gii tng i cao c th l h my mt chm tia hay h my 2

chm tia. Cu to ca n gm ba phn chnh:

- H chun trc, chun trc chm tia sng vo;

- H thng tn sc (phn li) phn li chm sng a sc thnh n sc;

- H bung ti (bung nh) hi t, hi t cc tia cng bc sng li.

c trng cho h quang ca my AAS l cc thng s.

+ tn sc gc;

+ tn sc di;

+ phn gii (tn sc);

+ Vng ph lm vic ca h.

Bn thng s ny cng l cc yu t xem xt cht lng ca mt my quang

ph AAS.

Trc h chun trc l khe vo ca chm sng a sc v sau h bung nh l khe

ra ca chm tia n sc cn o.s quang hc, nguyn tc ca h thng my quang ph

hp th nguyn t. Theo s ny, chm tia pht x cng hng ca nguyn t cn

nghin cu c pht ra t n catot rng sau khi qua mi trng hp th, s c hng

vo khe my v vo h chun trc, ri vo b phn tn sc, vo h hi t chn 1 tia cn

o.

Nh vy chm sng a sc c chun trc, c phn li v sau ch mt vch

ph cn o c chn v hng vo khe o tc dng vo nhn quang in (detector-

photomultiveler) pht hin v xc nh cng ca vch ph hp th .

Mun h thng my quang ph hp th nguyn t cho c kt qu tt th h

thng tn sc phi bo m c mt s yu cu bt buc sau y:

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N phi c tn sc ln c th tch v c lp c tt cc vch ph cn o,

trnh s quy ri, s chen ln ca cc vch ph khc bn cnh. Trong cc my hin nay,

b phn ny thng l mt h cch t c hng s t 1200 n 2400 vch/mm.

Phi khng gy ra bt k mt hin tng sai lch no lm mt nng lng ca

chm sng trong my, nh s hp th, s tn x, s khuych tn ca cc b phn cu

to thnh my. c bit l cc h thng gng, cc thu knh, khe vo, khe ra ca chm

sng. Cc thu knh phi trong sut trong vng ph lm vic ca my.

Khe vo v khe ra ca my phi c m chnh xc v phi iu chnh c cho

ph hp vi tng vch ph v c lp li cao trong mi php o.

Detector pht hin cng vch ph phi c nhy cao. C nh th mi cth pht hin c s thay i nh trong qu trnh hp th ca vch ph ca mi nguyn

t. l cc iu kin ti thiu ca h quang hc trong my ph hp th nguyn t. Vi

s pht trin ca khoa hc v k thut, ngy nay ngi ta c th tha mn c tt c cc

yu cu . Chnh v th hin nay c rt nhiu my o ph hp th nguyn t c cht

lng cao c bn trn th trng quc t. l cc my o ph hp th nguyn t

ca hng Perkin Elmer, Varian, Becman, Philips Pye Unicam, Wet Zeiss, Shimadu, Instr,

Lad, Alpha,...

H tn sc. l mt h thng lng knh hay mt tm cch t. H ny c nhim v

phn li (tn sc) chm sng a sc thnh cc tia n sc, tc l phn li mt ngun sng

phc tp nhiu bc sng khc nhau thnh mt di ph ca chng theo tng sng ring

bit lch i nhng gc khc nhau.

Nu h tn sc c ch to bng lng knh th chng ta c my quang ph lng

knh. V ngc li, nu h tn sc l cch t ta c my quang ph cch t. Trong my

lng knh, tia sng ngn s b lch nhiu, sng di lch t, cn trong my cch t th ngc

li.

Lng knh l mt b phn quan trng ca my quang ph lng knh. N quyt nh

kh nng, tnh cht phn li nh sng ca my quang ph. Lng knh l mt mi trng

trong sut, ng nht v ng hng trong mt vng ph nht nh.

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Vt liu lm lng knh cng phi trong sut, ng nht v ng hng trong

mt vng ph nht nh. N phi bn vi nhit v nh sng. Chit sut phi hu nh

khng ph thuc vo nhit v m.

Trong vng kh kin, ch to lng knh ngi ta thng dng mt vi loi thy

tinh, nh thy tinh flin nng, flin nh, thy tinh krau. Trong vng t ngoi ngi tathng dng thch anh. Nu c vng ph (UY + VIS) phi dng thy tinh c bit.

nh gi cht lng, hiu qu v kh nng s dng ca mt my quang ph,

ngi ta thng dng ba thng s c trng c bn l tn sc gc, tn sc di v

phn gii.

a. tn sc gc. Trong mi my quang ph, s bin thin ca gc lch D theo

di sng ca tia sng l mt c trng quan trng. N ni ln kh nng tn sc gc ca

mt my quang ph v c gi l tn sc gc ca my quang ph .

Trong cc my quang ph lng knh, lng knh thng c t v tr cc tiu

i vi tia sng trung tnm ca mt vng ph ca my. V th tn sc gc s c tnh

theo cng thc:

Nu my quang ph c m lng knh

nh nhau trong h tn sc, th tn sc ca my s bng m ln ca my 1 lng knh.

Cn nu cc lng knh c gc nh A khc nhau, th tn sc chung s l tng ca tn

sc tng lng knh theo cch b tr. Ngha l tn sc gc chung bng tng tn sc

gc ca tng lng knh c trong h tn sc ca my quang ph.

Nh vy, theo cc biu thc trn, chng ta thy tn sc gc ca mt my quang

ph lng knh ph thuc vo cc yu t sau:

S lng knh c trong h tn sc.

Gc nh A ca lng knh.

Chit sut ca vt liu lm lng knh.

Bin thin theo bc sng (sng ngn lch nhiu, sng di lch t).

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V th, mun tng tn sc gc ca mt my quang ph lng knh ngi ta phi ch

to h tn sc c nhiu lng knh ghp li vi nhau. Trong thc t ngi ta thng ghp

hai hoc ba lng knh. Bin php th hai l chn nhng vt liu c chit sut ln ch

to lng knh v ch to cc lng knh c gc nh A ln.

Nhng bin php ch to gc A ln cng ch thc hin c trong mt mc nhtnh, thng thng n 90 l ln nht. V khi tng gc nh A ca lng knh th hin

tng phn x ton phn mt bn ca lng knh s nhanh chng xut hin, lm mt phn

chm sng s khng ra khi lng knh, v ta b mt chm tia .

b. tn sc di. tn sc gc ch cho bit s khc nhau v gc lch ca 2 tia sng,

ngha l tia sng b lch i ni gc ln bao nhiu sau khi phn li, m cha ch ra

c hai vch ph gn nhau s cch nhau l bao nhiu trn mt phng tiu (hay knh nh).

Do , trong thc t, nh gi kh nng tn sc ca mt my quang ph ngi ta

cn phi s dng thm c tn sc di. Nhng tn sc di ph thuc vo tn sc

gc v tiu c ca thu knh bung nh f2, v n c tnh theo cng thc:

c. Nng sut phn li.

Nng sut phn li (kh nng phn gii) ca mt my quang ph trong mt vng no

c biu th bng t s:

Nu my quang ph c h tn sc gm m lng knh

nh nhau th Rt= mRi

Cng thc ny cho ta thy nng sut phn li ca mt my quang ph lng knh ph thuc

vo nhiu yu t, nh:

S lng knh trong h tn sc (m);

Chit sut ca vt liu lm lng knh (n);

Sin ca 1/2 gc nh ca lng knh (A/2)

ng knh ca thu knh bung nh (d2);

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S bin thin ca chit sut theo bc sng (dn/d)

1.4.2.4. Detector :

Detector l mt loi dng c quang hc dng thu nhn v pht hin tn hiu

quang hc theo hiu ng quang in ca n. Trc y thu nhn cng ca

chm sng ngi ta thng dng knh nh hay phim nh sau l t bo quang in.

l cc dng c c in c nhy km, nht l knh nh, v knh nh c nhiu nhc

im, nh kh bo qun, d b nh hng bi m, nhit , thi tit.

Mt khc, n li l mt dng c trung gian thu nhn chm sng v sau phi

x l tip mi c c cng vch ph. Tc l o en ca knh nh b chm

sng tc dng vo. Vi s pht trin ca khoa hc v k thut, ngy nay ngi ta ch

to ra c nhiu loi detector quang hc kiu ng c th khuych i tn hiu o lnc n c triu ln. l cc ng nhn quang in (photomultivler tube).

Nhn quang in kiu ng l mt loi dng c thu nhn tn hiu quang hc c

tnh cht vn nng, n c nhy v chn lc cao. Nhiu hng ch to c cc

detector loi ny. Vng ph hot ng ca cc detector kiu ng loi ny thng l t 190

- 900 nm, c khi n 1100 nm. Tt nhin l thng s ny ph thuc vo bn cht ca

nguyn liu ch to bn catot ca n.

Nguyn tc cu to ca nhn quangin kiu ng H s khuch i ca

loi detector ny thng n 106, i

khi c loi n 107. Nguyn liu ch

to bn catot ca cc detector kiu ng

l cc hp kim ca cc kim loi kim

vi Sb, Ga hay As, v d hp kim Cs-

Sb; Ga-As; Na-K-Cs-S

1.5.Phng php nh lng bng ph AAS:

1.5.1.Phng php th chun:

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Trc ht ngi ta phi chun b mt dy mu u, dy mu chun (thng thng

l 5 mu u) v cc mu phn tch trong cng mt iu kin. V d cc mu u c nng

ca nguyn t X cn xc nh l C1, C2, C3, C4, C5, v mu phn tch l C1X, C2X,Sau

chn cc iu kin ph hp v o cng ca mt vch ph hp th ca nguyn t

phn tch trong tt c cc mu u v mu phn tch chun b trn.

Phng php ny n gin, d thc hin v thch hp vi mc ch phn tch hng

lot mu ca cng mt nguyn t, nh trong kim tra cht lng thnh phn, kim tra

nguyn liu sn xut. V mi khi dng mt ng chun chng ta c th xc nh c

nng ca mt nguyn t trong hng trm mu phn tch.

1.5.2. Phng php thm cht chunTrong thc t phn tch, c bit l xc nh lng cht kim loi, khi gp phi cc

i tng phn tch c thnh phn phc tp v khng th chun b c mt dy mu u

(mu chun) ph hp v thnh phn vi mu phn tch, th tt nht dng phng php

thm cht chun. Ch nh th mi loi tr c yu t nh hng v thnh phn ca mu.

34

hpth

Nng xc nh

hp th mu xcnh

Nng cht chunO


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Nguyn tc ca phng php ny l ngi ta dng ngay mu phn tch lm nn

chun b mt dy mu u, bng cch ly mt lng mu phn tch nht nh v cho

thm vo nhng lng xc nh ca nguyn t cn xc nh theo tng bc nng

V d: Lng thm vo l C1 , C2 , C3,.nh th chng ta s c mt dy mu

chun l: C0 = CX

C1 = ( CX + C 1)

C2 = ( CX + C2 )

C3 = ( CX + C3 )

Trong Cx l nng ca nguyn t cn xc nh trong mu phn tch. Tip

chn cc iu kin th nghim ph hp v mt vch ph ca nguyn t phn tch, tin

hnh ghi cng hp th ca vch ph theo tt c dy mu u, chng ta thu c

cc gi tr tng ng l D0 ,D1 ,D2 , D3.

Phng php ny c u im l qu trnh chun b mu d dng, khng cn nhiu

ha cht tinh khit cao chun b mu u nhn to. Mc khc loi tr c hon ton

nh hng v thnh phn ca mu cng nh cu trc vt l ca cc cht to thnh mu.

Hn ch c nhiu sai s phn tch gy ra bi nhng yu t gy nhiu do s khc nhau

v thnh phn vt l v ha hc ca mu v cht chun.

35

Nng ca cht chun thm voNng ca mu xc nhO

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1.6. i tng v u, nhc im ca phng php quang ph hp th nguyn t

AAS:

1.6.1. i tng ca phng php:

i tng chnh ca phng php l phn tch lng nh cc kim loi trong nhiu

i tng mu khc nhau ca cc cht v c v hu c v c bit l hm lng cc kimloi c trong du m v cc phn on du m

Vi cc trang thit b hin nay, bng phng php phn tch ny ngi ta c th

nh lng c hu ht cc kim loi v mt s kim n gii hn nng c ppm bng

k thut F-AAS v n nng ppb bng k thut ETA-AAS vi sai s phn tch dao

ng trong khong 3 10%

Phng php ph hp th nguyn t c s dng kh ph bin xc nh cc

kim loi trong cc mu qung, t, , nc khong, du m, cc mu y hc, sinh hc,

cc sn phm nng nghip, rau qu, thc phm, nc ung, cc nguyn t vi lng trong

phn bn, thc n gia sc.

Phng php o ph hp th nguyn t ang c pht trin rt nhanh, khng

nhng phn tch cc kim loi, m phng hng ang pht trin nht hin nay l

nghin cu xc nh cc cht hu c, nh cc hp cht halogen, lu hunh, photpho. N

cng v ang c s dng nh mt cng c phn tch cho nhiu ngnh khoa hc v

kinh t.

1.6.2. Nhng u im v nhc im ca phng php:

Php o ph hp th nguyn t c nhy v chn lc tng i cao. Gn 60

nguyn t c xc nh bng phng php ny vi nhy t 10^-4 10^-5 . c bit

nu s dng k thut nguyn t ha khng ngon la th c th t n nhy 10^-7 . Do

c nhy cao nn trong nhiu trng hp khng phi lm giu mu nguyn t cn xc

nh trc khi phn tch, do tn t nguyn liu, tn t thi gian khng cn phi dng

nhiu ha cht tinh khit cao khi lm giu mu .

Mt khc cng trnh c s nhim bn mu khi x l qua cc giai on phc tp.

Trong phng php ny cc ng tc thc hin nh nhng. Cc kt qu phn tch c th

c lu li trn my tnh . ng thi c th xc nh ng thi hoc lin tip nhiu

nguyn t trong mt mu, cc kt qu phn tch rt n nh, sai s nh

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Nhc im chnh ca phng php ny l ch cho ta bit thnh phn nguyn t ca

cht trong mu phn tch m khng ch ra trng thi lin kt ca nguyn t trong mu.

V th, n ch l phng php phn tch thnh phn ha hc ca nguyn t m thi.

2. ng dng ca phng php ph hp thu nguyn t trong thc phm:

2.1. Xc nh hm lng thu ngn trong thy sn2.1.1. Phm vi p dng

Tiu chun ny qui nh phng php xc nh hm lng thu ngn trong thu

sn v sn phm thu sn bng quang ph hp th nguyn t.

2.1.2. Nguyn tc

a. Mu thu sn c v c ho bng axit nitric (HNO3) m c trong bnh ph

mu bng nha teflon c np vn kn. Thu ngn (Hg) trong dung dch mu b hyrit ho

bng dng kh hyro. Hyrit thu ngn d bay hi b cun theo dng khi hyro v c

bm vo h thng quang ph hp th nguyn t. Ti y, hyrit thu ngn b phn hu

thnh hi thu ngn v c xc nh theo phng php quang ph hp th nguyn t

khng dng ngn la.

b. Cc phn ng xy ra trong h thng bay hi nguyn t Hyrit:

NaBH4 + HCl = NaCl + BH2 + 2H

4H + HgCl2 = HgH2 + 2 HCl

HgH2 = Hg + H2

2.1.3. Thit b, dng c, ho cht v cht chun

2.1.3.1. Thit b v dng c

a. My quang ph hp th nguyn t s dng n catt thu ngn rng vi h

thng bay hi nguyn t hyrit.

b. Bnh ph mu bng nha teflon c np vn kn dung tch 50ml.

c. T sy nhit 1500C.

d. Dng c thu tinh c ra sch bng axit nitric nng 8N v trng li

bng nc ct trc khi s dng.

e. Cn phn tch c chnh xc loi n 0,01g v loi n 0,0001g.

2.1.3.2. Ho cht v cht chun

a. Axit nitric m c

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b. Axit sulfuric (H2SO4) m c.

c. Axit clohyric (HCl) nng 1N.

d. Dung dch ho tan: Cho khong 300 - 500ml nc ct vo bnh nh mc 1000

ml, cho thm 58 ml axit nitric v 67ml axit sulfuric, sau nh mc n vch bng nc

ct.e. Dung dch hyroxit natri (NaOH) nng 0,25M: Ho tan 10,0 g hyroxit natri

trong 1000 ml nc ct.

f. Dung dch tetrahyrua boric natri (NaBH4), nng 3 %: Ho tan 1,50 g

tetrahyrua boric natri trong 10,0ml dung dch hyroxit natri.

g. Dung dch thu ngn chun

- Dung dch chun gc 1,0mg/ml: Ho tan 1,000g thu ngn trong 1000ml axit

sulfuric nng 1N.

- Dung dch chun trung gian 1mg/ml: Pha long 1ml dung dch chun gc thnh

1000 ml bng dung dch axit sulfuric nng 1N.

- Dung dch chun lm vic: Pha long dung dch chun trung gian thnh cc dung

dch chun lm vic c hm lng thu ngn ln lt l 0,0; 2,0; 4,0; 6,0; 8,0 v 10,0

mg/l bng dung dch axit nitric nng 1N.

2.1.4. Phng php tin hnh

2.1.4.1 V c ho mu

a. Cn khong 1,00g mu sao cho khi lng kh khng nhiu hn 300mg. i

vi mu c hm lng cht bo cao, lng mu dng sao cho khi lng kh khng ln

hn 200mg. Cho mu vo bnh ph mu. Thm 5,0ml axit nitric m c ri vn cht np

y kn bnh li.

b. bnh vo t sy t nhit 150 0 C trong vng 30 - 60 pht hoc cho

n khi dung dch tr nn trong.

c. Ly bnh ra khi t sy, ngui n nhit trong phng ri m np v

chuyn dung dch mu vo bnh nh mc 250 ml. Trng ra bnh ph mu bng khong

95ml dung dch ho tan (IV.3.2.d), rt nc ra vo bnh nh mc v nh mc bng

nc ct cho ti vch ri lc u.

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2.1.4.2. Chun b mu trng

Mu trng c chun b bng cch thay 1g mu bng 1ml nc ct ri tin hnh

theo cc bc nh qu trnh v c ho mu.

2.1.4.3 Tin hnh phn tch

a. Ti u ho cc iu kin lm vic ca my quang ph hp th nguyn t v hthng bay hi nguyn t hyrit.

b. Ni h thng, nhng cha ni u kh vo ca bnh un cha mu. iu chnh

lu lng khng kh u ra ca bm t c lu lng khong 2lt/pht bng cch

iu chnh tc ca bm thng qua in p k.

c. Ni hon chnh h thng thit b theo s lp t h thng quang ph hp th

nguyn t.

d. Xy dng ng chun bng cch bm cc mu chun vi hm lng thu

ngn ln lt l 0,0; 2,0; 4,0; 6,0; 8,0 v 10,0ppb ri xc nh hp th ca chng thng

qua din tch pic.

e. Khi ng chun c tuyn tnh tt, tin hnh bm cc dung dch mu th v

mu trng ri xc nh hp th ca chun thng qua din tch pic. Tnh hm lng

thu ngn trong mu thng qua ng chun sau khi tr i mu trng.

2.1.3.4 Yu cu v tin cy ca php phn tch

a. lp li ca 2 ln bm

lch chun (CVs) tnh theo hp th ca 2 ln bm lin tip ca cng mt dch

chun phi nh hn 0,5%.

b. thu hi (R) thu hi c xc nh bng cch s dng 5 mu cho vo

mt lng dung dch thu ngn chun bit chnh xc nng . thu hi tnh c phi

nm trong khong t 85% n 115%, thu hi trung bnh phi ln hn 90%.

2.1.5. Tnh kt qu

Hm lng thu ngn trong mu th thu sn c tnh theo cng thc sau:

M

xmxC

Hg

Hg

25010

3=

Trong :

- CHg l hm lng thu ngn c trong mu th (mg/g);

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- mHg l hm lng thu ngn c trong dung dch mu tnh c theo ng chun

(m g/l);

- V l th tch dung dch dng ho tan mu th (ml);

- M l khi lng ca mu th (g).

2.2. Hm lng ch trong thy sn

2.2.1. Phm vi p dng

Tiu chun ny qui nh phng php xc nh hm lng ch trong thu sn v sn

phm thu sn bng quang ph hp th nguyn t.

2.2.2. Phng php tham chiu

Tiu chun ny c xy dng da theo phng php chun s 972.23 ca Hip hi cc

nh ho hc phn tch (AOAC) cng b nm 1995.

2.2.3 Nguyn tc

Mu thu sn sau khi c tro ho trong l nung s c ho tan hon ton bng dung

dch axit clohyric long. Ch trong dung dch mu c xc nh trn my quang ph

hp th nguyn t.

2.2.4 Thit b, dng c, ho cht v cht chun

2.2.4.1.Thit b v dng c

- My quang ph hp th nguyn t c trang b n catt ch rng bc sng ci t l

283,3 nm, s dng ngn la axtylen-khng kh vi chiu rng ca u t l 4 inch.

- Chn s dung tch 50 ml, su 5 cm hoc cc thu tinh c m bng thch anh, dung

tch 100 ml.

- T sy nhit 1500 C.

- L nung kim sot c nhit trong khong t 250 n 6000 C vi sai lch khng

qu 100 C.

- Dng c thu tinh c ra sch bng axit nitric nng 8N v trng li bng nc

ct trc khi s dng.

- Cn phn tch c chnh xc loi n 0,01g v loi n 0,0001 g.

2.2.4.2 Ho Cht v cht chun

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- Dung dch axit clohyric (HCl), nng 1N: Pha long 82 ml axit clohyric m c

bng nc ct n 1000 ml.

- Dung dch axit nitric (HNO3) nng 1N.

- Axit percloric (HClO4) m c, nng 70,5 %.

- xit lantan (La2O3).- Ethylendinitrilotetraaxetat (sau y vit tt l EDTA)

- Dung dch m

+ Cho 163 g EDTA vo trong bnh nh mc 2000 ml, sau thm 200 ml nc ct v

mt lng va hyroxit amon (NH4OH) ho tan ht EDTA. Thm 8 git ch th

methyl da cam vo dung dch ETDA.

+ Cho 500 ml nc ct vo mt cc thu tinh ri t t cho thm 60 ml dung dch axit

percloric m c, khuy u ri ngui. Sau , cho 50 g xit lantan vo cc ri khuy

u ho tan ht lng xit lantan ny.

+ Rt t t dung dch xit lantan vo dung dch ETDA pha trn, va rt va khuy

mnh. Nu cn thit, thm hyroxit amon vo dung dch trn gi cho dung dch c

tnh kim i vi methyl da cam (dung dch c mu vng). nh mc n vch bng

nc ct.

- Dung dch ch chun

+ Dung dch chun gc, 1,0 mg/ml

Ho tan 1,5985 g nitrat ch chun trong khong 500 ml dung dch axit nitric nng 1N.

Sau , nh mc thnh 1000 ml bng dung dch axit nitric nng 1N trong bnh nh

mc.

+ Dung dch chun trung gian, 10m g/ml

Ly chnh xc 10 ml dung dch chun gc cho vo bnh nh mc 1000 ml, thm 82 ml

dung dch axit clohyric nng 1N vo bnh. Sau , nh mc ln bng nc ct.

+ Dung dch chun lm vic

Pha long dung dch chun trung gian thnh cc dung dch chun lm vic c hm lng

ch ln lt l 0,0; 0,2; 0,6; 1,0; 3,0; 5,0 v 10,0 m g Pb/ml bng dung dch axit clohyric

nng 1N trong cc bnh nh mc dung tch 50 ml.

2.2.5. Phng php tin hnh

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2.2.5.1 Chun b mu trng

Lm bay hi 4 ml dung dch axit nitric m c trong chn s n kh trn bp cch

thu. Ho tan cn bng 20 ml dung dch axit clohyric nng 1N v chuyn dung dch

vo bnh nh mc 25 ml. ngui bnh v nh mc ti vch bng axit clohyric nng

1N.Ch thch: Yu cu tng hm lng ch trong mu trng khng c ln hn 10 m g.

2.2.5.2 Chun b mu th

- Cn khong 25,0 g mu cho vo chn s ri sy kh trong t sy trong thi gian 2 gi

nhit t 1350 C n 1500 C. Chuyn chn s vo l nung v tng dn nhit n

5000C. Gi nhit l 5000 C trong thi gian 16 gi tro ho mu.

- Ly chn s ra ngui n nhit trong phng. Cho 2 ml axit nitric m c vo

chn ri lm bay hi dung dch trong chn va n kh trn bp cch thu. t chn s

tr li vo l nung nhit thng, sau tng dn nhit n 5000 C v gi nhit

ny trong khong 1 gi.

- Ly chn ra, ngui v lp li thao tc trn cho n khi tro c mu trng hon ton.

- Cho 10 ml dung dch axit clohyric nng 1N vo chn c tro ri ho tan tro bng

cch un nng. Chuyn gn dung dch vo bnh nh mc dung tch 25 ml.

- un nng phn tro cn li trong chn 2 ln, mi ln vi 5 ml dung dch axit clohyric

nng 1N ri rt dung dch vo bnh nh mc 25 ml ni trn. ngui v nh mc

ti vch bng axit clohyric nng 1N ri lc u.

2.2.5.3 Tin hnh phn tch

- Ti u ho cc iu kin lm vic ca my quang ph hp th nguyn t ti bc sng

cng hng 283,3 nm v t tc dng ca hn hp axtylen-khng kh theo hng

dn ca nh sn xut v iu kin lm vic chun i vi ch.

- Xy dng ng chun vi cc hm lng ca ch ln lt l 0,0; 0,2; 0,6; 1,0; 3,0; 5,0

v 10,0 m g/ml (4.2.7, c) da trn hp th ca chng. Trong trng hp tn hiu nhn

c yu, phi iu chnh khuych i c c hp th A ca dung dch chun

(hm lng 0,2 m g/ml) khng nh hn 1 %.

- Khi ng chun c tuyn tnh tt, tin hnh o hp th ca dung dch mu th

v mu trng chun b nh sau:

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+ i vi dung dch mu th trong, khng c cn lng

Tin hnh xc nh hp th 3 ln theo cc bc sau y: Bm ln lt mt dung dch

chun sau l dung dch mu th. Nu s lng mu nhiu th bm ln lt mt dung

dch chun v 3 dung dch mu th cho n khi bm ht dung dch chun, mu th v

mu trng.+ i vi cc dung dch mu th c

Thm 1 ml dung dch m vo cc dung dch mu th v mu trng chun b v cc

dung dch chun. Sau , tin hnh xc nh hp th ca cc dung dch

- Tnh hm lng ch trong mu thng qua ng chun sau khi tr i mu trng.

2.2.5.4 Yu cu v tin cy ca php phn tch

- lp li ca 2 ln bm

lch chun (CVs) tnh theo hp th ca 2 ln bm lin tip ca cng mt dch

chun phi nh hn 0,5 %.

- thu hi (R)

thu hi c xc nh bng cch s dng 5 mu cho vo mt lng dung dch ch

chun bit chnh xc nng . thu hi tnh c phi nm trong khong t 85 % n

115 %, thu hi trung bnh phi ln hn 90 %.

2.2.6 Tnh kt qu

Hm lng ch trong mu th thu sn c tnh theo cng thc sau:

2.2.6.1 i vi dung dch mu th trong, khng c cn lng

mPb

CPb= -------- x 25

M

2.2.6.2 i vi dung dch mu th c phi b sung thm dung dch m

V 25

CPb = mPb x --------------- x -------------

V - 1 M

Trong :

- CPb l hm lng ch c trong mu th (m g/g);

- mPb l hm lng ch c trong dung dch mu tnh c theo ng chun (m g/ml);

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- 25 l th tch dung dch axit clohyric nng 1N dng ho tan mu (ml);

- V l th tch dung dch mu th b sung 1 ml dung dch m phn tch (ml);

- M l khi lng mu th (g).

2.3. Xc nh hm lng As trong rau m v ci xanh bng ph-

ng php quang ph hp thu nguyn t (AAs)

Vit Nam, vn nhim asen (As) ang e da sc khe

hng triu ngi trong nhng nm qua. Kt qu phn tch mu nc

ging khoan khu vc pha Bc (H Ni, H Ty, H Nam..) cho thyhn 90% mu nc ging khoan nhim asen (As). Ti ng bng sng

Cu Long, cng pht hin nc ngm ca cc tnh nh: An Giang, ng

Thp, Sc Trng.. c mc nhim As rt cao .

c tnh v tnh linh ng ca As ph thuc rt nhiu vo dng

ha hc ca As. Trong khi As v c l cht gy ung th th As hu c:

monometyl asen (MMA) v dimetyl asen (DMA) l cht kch thch ung

th , v ctnh ca dng As(III) v c th cao hn nhiu ln so viAs(V) cng loi cng nng . V vy, vic xc nh tng dng ring

bit ca As trong mu thc phm rau l rt quan trng, gp phn

nh gi mt cch khoa hc c tnh v nguy c gy hi ca As cho

sc khe con ngi qua ngun thc phm.

Tch xc nh trc tip dng As bng quang ph hp thi nguyn

t (AAS) lin hp sc k lng cao p (HPLC) kt hp x l bng tia UV l

phng php phn tch hin i c chnh xc cao v tin cy cao

c s dng trong nghin cu ny.

2.3.1. Ha cht

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Cht chun As: NaAsO2 (As3+),Na2HAsO4.7H2O (As5+), DMA(C2H6AsO2Na)

Fluka;MMA(CH3NaHAsO3) Sigma. Ha cht khc : metanol, NH4H2PO4 v

(NH4)2HPO4,K2S2O8, HCl, NaOH Merck.

2.3.2. Thit b :

Hnh : S phn tch lin tc trc tip cc

dng As bng k thut ghp HPLC-UV-HG-

AAS

2.3.3. Chun b mu phn tch

Rau m v rau ci xanh trng trn t nhim As (35 mg/kg),

thu hoch sau 45 ngy,mu c ra sch bng nc ct loi b t

v bi bn. Dng dao nha tch ring phn r v phn l, sy kh 60oC

trong 72 gi. Tng t Nh vy hai loi rau m v ci xanh cng c trng

trn t nn khng nhim As i chng.

Quy trnh x l mu: (1) V c ha mu bng hn hp axit

HNO3:HCl (10:3), 165oC trong 5 pht trn thit b vi sng (MarsX 5

plus, CEM, M). nh lng hm lng As tng trn thit b AAS k thut

hydrua ha. (2) Tch chit dng As d tan trong t v rau [3]:

Chit dng As d tan trong t bng dung dch H3PO4 0,5 M.

Chit dng As d tan trong mu rau bng hn hp dung mi

metanol: nc (1:1), nhit 75oC, trn thit b vi sng (MarsX 5 plus,

CEM, M).

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Xc nh dng As d tan bng k thut ghp HPLC-UV-HG-AAS.

2.3.4. iu kin phn tch dng As bng phng php HPLC-UV-HG-AAS

HPLC: Ct tch sc k: Hamilton PRP- X100(250mm.4,1 mm i.d.10 m). Pha ng A : 12

mmol/l KH2PO4- K2HPO4;pH =6,5.B:2,4 mmol/l KH2PO4-K2HPO4;pH =6. Tc dng

pha ng : 1ml/min. Ha hi hidrit HG : Tc HCl 4M : 1,6 ml/min ; Tc K2S2O8: 1

ml/min; Tc kh mang Argon :50 ml/min. AAS :Bc sng 193,7 nm; khe sng : 5nm;

Cng dng en catot rng :12mA

2.3.5. KT QU V THO LUN

2.3.5.1. HPLC-UV-HG-AAS ca cc dng tn ti ca asen

Sau khi phn tch xc nh thi gian lu ca tng cht chun ring bit , tin hnh

tch phn tch hn hp 4 cht chun As (III), As (V), DMA v MMA . Th t gii hp

khi ct tch sc k ty thuc vo gi tr pKa v c kim sot bi pH ca pha ng .

Vi cc iu kin sc k nh trn

cc dng ca As s b ra gii ra

khi ct theo th t As3+, DMA,

MMA v As5+.

2.3.5.2. Dng As trong r cy

rau m v ci xanh

tr li cho cu hi As (V) t t b hp th bi cy trng s chuyn i dng

nh th no? Tin hnh xc nh dng As trong r, l rau m v ci xanh. Kt qu phn

tch trnh by trong bng

Bng : dng asen d tan trong r rau m v ci xanh

Mu Dng As(mg/kg)

As3+ DMA MMA As5+

R rau m 1,70 KPH KPH 0,06

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R ci xanh 37,00 KPH KPH 6,64

KPH :Khng pht hin Cc th hin

trn sc k hnh khng nh ch

c As dng v c trong r cy v cs kh As(V) v As (III) trong r cy

rau. Kt qu cho thy hm lng

As(III)cao hn As(V). iu ny c th

gii thch nh sau: trong t, As l mt

oxyanion AsO3-4 ng gi vai tr ca

PO3-4, cnh tranh vi photphat i vo trong r , n c vn chuyn ngang qua mng

huyt tng theo h thng vn chuyn photphat . Ti r, xy ra qu trnh kh As trongr ca hai loi rau ny rt ng k, c n 92% As trong r rau m v 82% As trong r

rau ci xanh dng As(III) so vi tng lng As c chit bng hn hp dung mi

methanol/ nc.

Nhng kt qu thu

c cn cho thy trong

khi trong r rau m hmlng As (III) cao gp 28

ln As (V) , th trong r

ci xanh ch cao hn 5

6 ln, cho d, ci xanh

hp th v tch ly As

nhiu hn rau m . iu

chng t mc khAs (V) ca rau ci thp

hn so vi rau m . Tuy

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c s khc nhau nh vy nhng quy lut trong r ca hai loi rau ny ch yu l As (III)

v c.

2.3.5.3 Dng As trong l rau m v ci xanh

Kt qu xc nh dng As trong l rau m v ci xanh trnh by bng:

Bng : dng asen d tan trong l rau m v ci xanh

Mu Dng As(mg/kg)

As3+ DMA MMA As5+

L rau m nhim 1,12 KPH KPH KPH

i chng 0,16 KPH KPH KPH

L ci xanh nhim 21,66 KPH KPH KPH

i chng KPH KPH KPH KPH

KPH: khng pht hin

T kt qu phn tch cho thy khng pht hin c qu trnh metyl ha As trong l rau

m v ci xanh nhm lm gim c tnh ca As. Da vo kt qu phn tch c th d on

: hoc c s kh hon ton As(V) thnh As(III) trong qu trnh As di chuyn t r ln

l . Hoc ch c As (III) di chuyn ln l

lm sng t d on trn tin hnh xc nh v so snh lng As d tan v tng

As c trong cy . Kt qu phn tch lng As trnh by bng :

Mu As d tan Dng khc Tng As (HNO3/HCl)

ppm % ppm % ppm

Rau m L 1,12 62 0,69 38 1,81

R 1,76 80 0,35 20 2,19

Ci xanh L 21,66 79 1,35 21 27,37

R 43,64 88 1,63 12 49,48

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Dng khc = tng As(HNO3/HCl)-As d tan.T kt qu trn cho thy , lng As d tan

trong rau m thp hn vi rau ci xanh ,c khong 79 n 88% As trong rau ci xanh l

dng d tan . Trong khi , rau m ch c t 62 n 80 %.Lng As cn li nhng dng

khng d tan chim t 12 n 38 % ty tng loi.

2.3.5.4. kt lun

1. Asen tan trong dung dch t dng v c l As(V), chng lan

truyn t mi trng t ln rau m v ci xanh trong qu trnh sinh

trng.

2. khng pht hin qu trnh metyl ho As trong t v trong cyrau. As tch ly trong r v trong l ch yu dng As(III).

3. c s kh As(V) thnh As(III) trong r rau m v ci xanh v ty

tng loi rau lng As(V) ch cn li trong r t 10 n 22%.

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4. Hp thu v tch ly As ca rau m thp hn so vi rau ci ni ln

c im sinh hc v s nhy cm ca mi loi thc vt rt khc

nhau i vi c t kim loi. Tuy vy, kh nng vn chuyn As t r

ln l cy rau m li cao hn so vi rau ci.

Phn tch thc phm l mt lnh vc quan trng trong ch bin thc phm, ngy

nay cng ngh tng cao, nhu cu i sng ca con ngi cng i hi cc nh sn xutch bin thc phm phi p ng c nhu cu v cht lng thc phm m khng gy

hi cho sc khe ngi tiu dng v gi c hp l. V vy vn s dng nhng phng

php phn tch thc phm l vn ht sc quan trng.

Hin nay phng php quang ph hp th nguyn t ng c quan tm, trong

c ph hp th nguyn t AAS v l phng php c ng dng trong thc t, trong

nhiu ngnh cng nghip c bit l ngnh cng nghip thc phm. Phng php ph

hp th nguyn t ny s gip chng ta pht hin c nhng kim loi nng c trongthc phm nh rau , c , qu , thy sn, .v kim loai nng c trong nc , t. ti

phng php ph hp th nguyn t AAS l ti mang tnh thc tin , c ng dng

trong di sng v sn xut . S dng phng php AAS s bit c hm lng v c

tnh ca kim loi , khng nhng th s bit c kh nng tan ca kim loi trong nhng

thc phm khc nhau .

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Nhng nc ta hin nay phng php ph nguyn t AAS ch pht trin trong

nhng nm gn y, c bit l trong cc trng i hc vin nhin cu ph v cho cng

vic ging day , dich v phn tch .

TI LIU THAM KHO1. H Vit Qy Phn tch ha l Nh xut bn gio dc Nm 2000

2. Nguyn Th Dung (bin son) Gio trnh phn tch bng quang ph - D n gio

dc k thut v dy ngh (VTEP) H Ni 2008

3. Phm Lun Phng php phn tch ph nguyn t - Nh xut bn i hc quc

gia H Ni 2003

4. www.google.com.vn

MC LC1.C s ca phng php ph hp th nguyn t.4

1.3.Nguyn tc ..4

1.4. Qu trnh nguyn t ha mu:..51.4.1. Nguyn t ha mu bng ngn la..5

1.4.2. Nguyn t ha khng ngn la7

1.4.2.1. c im v nguyn tc 7

1.4.2.2. Sy kh mu .7

1.4.2.3. Tro ho luyn mu ...8

1.4.2.4. Nguyn t ho ..8

1.2.2.5. Cc yu t nh hng . .8

1.4.2.6. Ti u ha cc diu kin cho php o khng ngn la mu. ..9

1.5. Cc yu t nh hng trong php o AAS:101.3.2 Khi qut chung.10

1.3.2. Cc yu t v ph ...10

1.3.2.1. S hp th nn.10

1.3.2.2. S chen ln ca vch ph ...11

1.3.2.3. S hp th ca cc ht rn11

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1.3.3. Cc yu t vt l ..11

1.3.3.1 nht v sc cng b mt ca dung dch mu ..11

1.3.3.2 Hiu ng lu li 12

1.3.3.3. S Ion ha ca cht phn tch 13

1.3.3.4 S pht x ca nguyn t phn tch 131.3.4. Cc yu t ha hc 14

1.3.4.1 Nng axit v loi axit trong dung dch mu ..15

1.3.4.2 V nh hng ca cc Cation c trong mu: ..15

1.3.4.3 nh hng ca cc an Ion c trong mu .17

1.3.4.4 Thnh phn nn ca mu ..17

1.3.4.5nh hng ca dung mi hu c

..18

1.4.My quang ph hp th nguyn t.18

1.4.1. Phn loi 18

1.4.1.1.My quang ph hp th mt chm tia...18

1.4.1.2. My quang ph hp th hai chm tia...191.5.2. Cu to my quang ph hp th nguyn t............................................................19

1.4.2.1. Ngun bc x: .....................................................................................................19

1.4.2.4.1. n catot rng (HCL) ..201.4.2.4.2. n phng in khng din cc (EDL)22

1.4.2.4.3. n ph lin tc c bin iu:...24

1.4.2.4.4. Cc loi ngun n sc khc :...25

1.4.2.5. H thng nguyn t ha mu :..25

1.4.2.6. H thng n sc my quang ph hp th nguyn t .28

1.4.2.7. Detector : ..32

1.5.Phng php nh lng bng ph AAS:..33

1.5.1.Phng php th chun:..33

1.5.2. Phng php thm cht chun34

1.6. i tng v u, nhc im ca phng php quang ph hp th nguyn t AAS:

1.6.1. i tng ca phng php:...35

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1.6.2. Nhng u im v nhc im ca phng php:.36

2. ng dng ca phng php ph hp thu nguyn t trong thc phm :..36

2.1. Xc nh hm lng thu ngn trong thy sn .36

2.1.1. Phm vi p dng.36

2.1.2. Nguyn tc 372.1.3. Thit b, dng c, ho cht v cht chun..............................................................37

2.1.3.1. Thit b v dng c .............................................................................................37

2.1.3.2. Ho cht v cht chun........................................................................................37

2.1.3. Phng php tin hnh......................................................................................................38

2.1.3.1 V c ho mu......................................................................................................38

2.1.3.2. Chun b mu trng .............................................................................................38

2.1.3.3 Tin hnh phn tch...............................................................................................38

2.1.3.4 Yu cu v tin cy ca php phn tch....39

2.1.4. Tnh kt qu....39

2.2. Hm lng ch trong thy sn...40

2.2.1. Phm vi p dng..40

2.2.2. Phng php tham chiu.40

2.2.3 Nguyn tc ..40

2.2.4 Thit b, dng c, ho cht v cht chun40

2.2.4.1.Thit b v dng c ..40

2.2.4.2 Ho Cht v cht chun 40

2.2.5. Phng php tin hnh41

2.2.5.1 Chun b mu trng...41

2.2.5.2 Chun b mu th..42

2.2.5.3 Tin hnh phn tch...42

2.2.5.4 Yu cu v tin cy ca php phn tch.43

2.2.6 Tnh kt qu..43

2.2.6.1 i vi dung dch mu th trong, khng c cn lng...43

2.2.6.2 i vi dung dch mu th c phi b sung thm dung dch m.43

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2.3. Xc nh hm lng As trong rau m v ci xanh bng phng php

quang ph hp thu nguyn t (AAs)

2.3.5. Ha cht .44

2.3.6. Thit b :..44

2.3.7. Chun b mu phn tch.45

2.3.8. iu kin phn tch dng As bng phng php HPLC-UV-HG-AAS.45

2.3.5. KT QU V THO LUN ....45

2.3.5.1. HPLC-UV-HG-AAS ca cc dng tn ti ca asen 45

2.3.5.2. Dng As trong r cy rau m v ci xanh 46

2.3.5.3 Dng As trong l rau m v ci xanh 47

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