phân tích nitrate, nitrite

8/10/2019 Phn Tch Nitrate, Nitrite

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SVTH :

Nguyn Vn ThiPhng Hng MnhNguyn Phng TngSn Th Thanh TuynTrn Th Bch ThnhNguyn Th Thu Tm


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Tng quan v Nit v cc hp cht ca Nit

Trong t nhin tn ti ch yu di dng N2 kh ph bin v chim trn 78% th tch khng

kh

trong phn t N2, nit lin kt bng 3 lin ktha tr

Nit l kh c tnh tr v mt ha hc Phn ln cc sinh vt khng hp thu nit trc

tip c


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Nitrate trong nc v thc phm

Nitrat v nitrit c t nhin trong thcphm v nc

Trong CNTP nitrit c s dng nhiunhm bo v cc loi thc phm

Nitrat v nitrit thng tn ti trong ncdo ngun nc ngm b nhim


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Nitrate trong nc v thc phm


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Tnh c hi

Nitrite c hi hn so vi cc hp chtcha Nit

Nitrite +hemoglobin methaemoglobin

(lm gim qu trnh vn chuyn oxi trong mu)

Khi nitrite vo d dy nitrite c chuynthnh axit nitr

axit nitr+ amin hoc amit nitroamin(nitroamin, y l hp cht dn n ung th.)


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c tnh ca Nitrit

iu kin xy raphn ng : -Nhit nu qu cao

-Khi phi kh v khi hung khi cc loi lng thc

-Khi p tht vi loi mui Nitrate

-Khi tiu ho cc loi lng thc c cha Nitrite


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c tnh ca Nitrit

C ch gy c: NO3

-NO2

- di tc dng ca men tiuha trong c th

Nitrite +hemoglobin methaemoglobin

4HbFe2++ 4 NO2-+ 2 H2O ----> 2 HbFe

3++ OH-+ 4 NO3-+ O2


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c tnh ca Nitrit

NO2-+ amin nitrosamine

(mt hp cht tin gy ung th)

amin bc hai +axit nitrhp cht nitroso

nitrosamine

amin bc hai thng xut hin trong qu trnhnu rn thc phm giu protein hay qu trnh lnmen


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QUY NH V HM LNG NITRATTRONG THC PHM

Theo Q chung ca th gii, c gil rau qu sch, ti phi c lng nitratethp va phi

Q T chc Y t th gii (WHO) : nitrate trong nc ung l 50 mg/l Nitrate trong l rau 300 mg/kg rau ti


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QUY NH V HM LNG NITRATTRONG THC PHM

Loicy Hm lngNO3 Loicy Hm lngNO3

Dahu 60 Hnh ty 80

Dab 90 C chua 150

Mpngt 200 Dachut 150

Mngty 200 Khoai ty 250

uqu 200 C rt 250

Ng rau 300 Hnh l 400

Cibp 500 Bub 400

Su ho 500 C tm 400

Su l 500 X lch 1500


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Phng php nghin: dch nghin c munh hng n php xc nh nitrat.

Phng php ngm chit: thi gian lu,ko di qu trnh phn tch.

Phng php chit dng nng lng visng: thi gian chit tng i nhanh,dch chit khng mu, hiu sut chitcao.


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Phng php phn tch th tch

Nguyn tc: Phn tch chun l o th tch cadung dch cht chun ( bit chnh xc nng ) vcht chun phn ng hon ton vi dung dch t

mu thc phm cn tch.


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Phng php phn tch th tch

Tin hnh : da trn phn ng kh NO3-v cc trng thi oxi ho thp hn bngcc cht kh thch hp

Chun ngc : Cc phn ng xy ra nh sau:

NO3-+ 3Fe2++ 4H+ NO + 3Fe3++ 2H2O2

Fe2++ Cr2O72++ 14H+ 6Fe3++ 2Cr3++ 7H2O


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Phng php o mu

Nguyn tc : Chuyn cht cn xc nh thnh mt hp

chtc mu. oshpthnh sng cadung dchmu

ny hocso snh cngmu cadung dchphn tch

vicngmu cadung dchbittrcnng.

My o mu


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Phng php o mu

Tin hnh :

Cc phng php so mu cng c dng xc nh NO3-da trn ba loi phn ng sau:

Nitrat ho cc hp cht phenolic. Oxi ho cc hp cht hu c c nhm mang

mu c trng.

kh NO3-

thnh NO2-

hoc NH3ri xc nhchng theo phng php thch hp. Trong phng php nitrat ho ch yu c

s dng xc nh NO3- vi thuc th thng

dung l axit phenol isunfonic


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Phng php o mu

Tin hnh :

Khi s dng thuc th axit phenol 2,4 isunfonic,ion NO3

- phn ng vi axit ny to thnh axit

nitro phenol isunfonic. Trong mi trng kim,axit nitro phenol isunfonic to thnh mt muic mu vng cho hp th quang cc i bc sng 410nm.

My o mu v dd chun


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Phng php o mu

Tin hnh :

xc nh nng ca cht nghin cu, phi omt quang D ca dung dch th v dung dchchun bit nng .


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Phng php o mu

Tin hnh :

Tnh ton kt qu: Cx= (Dx/Dch).Cch

Vi Dx/Dch: mt quang dung dch th / dungdch chun

Cx/Cch: nng dung dch th / dung dch

chun Lp ng chun, dng th vi trc tung Y l

mt quang D o c, trc honh X l nng C

T th s tnh c hm lng NO3-


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Phng php o mu

Phng php ny n gin v cho nhy kh cao(0,05ppm).

khi c mt cc cht hu c,clorua, NO2-, cc ion c mu

s gy nh hng n kt qu phn tch

S dng axit sunfamin, ur, hay thiur tchNO2-, Cl-c loi b bng cch cho phn ng vi Ag2SO4.

Loi tr nh hng ca cc hp cht hu c bng cchoxi hobng H2O2hay s dng than hot tnh.


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Phng php o kh

Phn ng xy ra : 2KNO2+ CO(NH2)2+ 2HCl 2N2+ CO2+ 3H2O + 2KCl

KNO2+ HSO3 N2+ KHSO4+ H2O

Sau , un nng dung dch v to mi trngaxit mnh th nitrate s phn ng to thnh kh

N2O 2KNO3 + CO(NH2)2+ 2HCl 2N2O + CO2+ 3H2O + 2KCl

2KNO3+ HSO3NH2 + HCl N2O + H2SO4+ H2O + KCl


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Phng php o kh

Kh N2v N2O c gi li trong trc mk bng dung dch KOH trn 50%.


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Mt s phng php xc nhnitrit

Phng php th tch : Phng php ny c th xc nh c nitrite da

trn c s oxi ho nitrite thnh nitrate khi dngthuc th KMnO

4 Phng trnh chun : 2MnO4

-+ 5NO2-+ 6H+ 2Mn2++ 5NO3

-+ 3H2O

Trong mi trng axit ion NO2-b phn hu thnh NO

v NO2theo phng trnh: NO2

-+ H++ HNO2 NO + NO2+ H2O

Phng php ny c nhy khng cao v tnh chnlc km v trong dung dch c nhiu ion c kh nng b

MnO4-oxi ho


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Phng php cc ph

Nitrite l anion c hot tnh cc ph.

xc nh nitrite bng cc ph dng nn LaCl3

2%v BaCl22% th nitrit cho sng cc ph 1,2V so vi anot thu ngn.

Nu dng nn l hn hp m xitrate 2M c pH= 2,5 th gii hn pht hin l 0,225 ppm NO2-


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Phng php cc ph

Khi xc nh NO2-trong mu ngi ta thm 5mldung dch nn

Dd nn gm :4,86g KSCN v 17,2ml HClO470% trong mt lt nc ctv 1,25mliphenylamin v 20ml mu

iu chnh pH t 1- 2 bng axit HClO4 nu cn

Th nh pic xut hin - 0,52V.


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Phng php sc k

Ion nitrite phn tch bng phng php sc k lngcao p vi pha ng l axit p - hyrobenroic 8mM vBis - Tris 3,2mM.

Hm lng nitrite c th xc nh c n 10e-8M

Ion nitrite cng c th xc nh c cng vi cc

ion khc bng phng php sc k ion.

Tuy nhin gii hn phng php ny ch xc nhc 0,1 mg NO2-/ lit.


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Phng php quang trc

s dng thuc th Griss u tin nitrite phn ng vi axit sunfanilic to

thnh mui iazo

Sau mui ny phn ng vi - naphtylaminto thnh hp cht azo c mu hng


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Phng php quang trc

Phng php c chn lc cao

khi c mt lng rt ln ca Cloramin, Clo ,

Thiosunfat , Natripolyphotphat v St (III) th sais ca phng php ny l 10%.

Ngoi ra ngi ta cn s dng dn xut ca Griss

v cng t c kt qu ng k

Vd: 4-amino benzene sunfona(NH2C6H4SO2NH2) vN-(1-Naphtyl)1,2- diamino etanhidroclorua(C10H7NH-CH2- CH2-NH2.HCl).


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Phng php quang trc

Quy trnh tm tt : a) Chun b thuc th : - Ho tan 0,6 g acid sunfanilic trong 100ml dung

dch nc - acid axetic - Ho tan 0,6 g a - Naphthilamin trong 100ml

dung dch nc - acid axetic

b)/ Chun b mu : Mu rau qu c la sch bng nc ct , ct

nh v nghin bng my nghin. Sau thm

nc v lc 30 pht . Lc bng dng c kh


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Phng php quang trc

c)Tin hnh xc nh:

Cho mu vo ng o, thm nc nvch.

-Thm 4 git thuc th A, lc u, yn1 pht.

-Thm 4 giot thuc th B, lc u. - yn 20 pht, so mu dung dch vi

bng mu chun.


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Phng php quang trc

Kt qu khi hm lng Nitrite nm trongkhong t 0,1 n 10 ppm th sai stng i l 5%


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xut

Trong nng nghip : V tr cc ngun nc ung (ging, h, ao,

sui...) phi trn vng cao, cch xa cc

chung nui sc vt Bo qun tht k cc bao phn ha hc v

cch xa ngun nc. Hng dn cho ngi dn s dng ng cch

v ng liu lng thuc thc vt Sau ht ph bin n ngi dn nim thm

canh phi phi hp vi lun canh


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xut

Trong qu trnh bo qun v ch bin :

Khng lm dng vic s dng ph gia. S dng ng ph gia cho php (theo quy nh

ca B Y t) Xem k nhn trc khi s dng

Cm quan trc khi cn, ong, o, m. S dng ng liu lng, ng k thut. Ma no loi rau ny, dng cc loi rau trng

ngoi vn.


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xut

Tr nh di 5 thng khng nn n rau bina,c ci

Nn b cc cng v cc l gi ca cc loi rau

c nhiu Nitrate.

- Nhng rau s qua nc si c th gimlng Nitrate t 30 n 50%.

- Khng nn hm nng cc mn rau (canh) cnhiu Nitrate, v khi hm li Nitrate c th b

bin i thnh Nitrite.


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Kt lun

Nitrat, nitrit rt d b nhim vo rau qu, ncngm, v mt s loi thc phm khc.

Hm lng cao nitrat, nitrit i vo c th trongthi gian di s gy ra nhiu nguy him cho sckhe ca con ngi.

V vy, kim tra ch tiu nitrat v nitrit trongthc phm l rt cn thit

phân tích nitrate, nitrite

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