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TRN TH VINHHm lng thuc tr su gc clo hu c v Poly Clorua Biphenyl (PCBs) trong thu sn v sn phm thu sn - Phng php nh lng bng sc k kh

A. T VN

Trn th gii c rt nhiu cht ang gy nhim mi trng. Trong s c 12 nhm cht hu c c bit nguy hi vi mi trng, 9 trong s l cc loi thuc tr su, mt cht dung trong cng nghip (PCB) v hai nhm cht sinh ra ngoi mun (PCDD v PCDF). Chng c gi chung l cc hp cht hu c nhim kh phn hy, vit tt l POPs.im ng ch l nng nh chng cng c kh nng gy ung th. Chng c kh nng pht tn hng ngn km so vi ngun thi. Con ngi tng sn xut cc thuc tr su dng POP v PCB vi khi lng ln, trc khi bit tc hi ca chng.

Chng bn vng trong mi trng, thi gian bn phn hy t vi nm n hn 100 nm ty vo iu kin mi trng. m u cho ti ny, chng ta bt u t vic tm hiu: Th no l PCBs?

Cc ng dng ca PCBs trn th gii c tnh ca PCBs?

Phn tch PCBs trong thy sn v sn phm thy sn_ Phng php nh lng bng sc k kh.B. PCBs L G?1. Khi nim PCBs

PCBs l hp cht hu c c tn l PolyChlorinated Biphenyl.

PCBs thuc nhm cht hu c nhim kh phn hy, POPs

Cng thc:

Cc PCBs trong t nhin c chu k bn hy hang trm nm (rt bn, bn hn c DDT). PCBs l nhm hp cht m trong phn t ca chng cha 2 nhm phenyl c clo ha, c pht hin trong chui thc n lin quan n cc thu vc (sng, h) nh trong bn lng, cy c, sinh vt ph du, c, ng vt thn mm, cc loi chim sng quanh thu vc v l d nhin c cc m m ca nhng ngi c s dng tm, c lm thc phm trong ba n.Cc nh khoa hc cho bit, hm lng clo (Cl) trong PCB cng cao th hp cht cng c. PCB nh hng n h thn kinh, gan v c kh nng gy ung th. phn hu cc PCB ngi ta phi nung vt liu cha PCB n nhit cao, trn 12000C. Tuy nhin khi nung, PCB c th bc theo khi, ng thi c th chuyn ha thnh cc cht c khc.Phng php ny va tn km, va mt cng li khng an ton. Do , ngy nay h dng phng php mi gi l phn gii ha hc c kh. Ngi ta dng lc c kh lm cho phn ng xy ra, c th l dng nhng ht st p v cc cht c v bin chng thnh cht hon ton khng c hi.

2. Cc ng dng, tc hi ca PCBsng dng Cht lng cch in trong bin th v t in Cht lm mt trong vic truyn nhit nng Cht dung mi trong mc lm giy than copy Du bi trn Keo dn Cht xc tc trong cng nghip ha cht Ph gia trong sn Cht ph b mtTc hi V d in hnh

Nhim c PCBs, Dioxin trong du n V n KanemiQua trn, chng ta c th thy PCB c rt nhiu ng dng. V vy, lng pht thi hng nm trn th gii cng nh Vit Nam cng s rt ln.

3. Hin trng PCBs ti Vit Nam

Ti nc ta hin cn lu mt khi lng kh ln cc cht hu c nhim kh phn hy (POPs) tch t tp trung hoc phn tn trong mi trng t, c bit t thi k chin tranh.Cc cht hu c nhim kh phn hu (POPs) s dng cho nng nghip ch yu l DDT v HCB, hin nm ri rc cc kho a phng ch c x l, cn trong cng nghip phn ln l PCB, trong cc lnh vc nh: Du bin th v t in cng sut cao, cht lng truyn nhit v h thng thy lc, ch to du bi trn v du ct gt, cht ho do cho sn, dung mi cho mc in ca giy copy khng cha cc bon, cht kt dnh, cht chng bt chy v cht do.Theo cc s liu cng b, Vit Nam cn khi lng du c cha PCB c th ln ti 19000 tn, ch yu t cc my bin th in kiu c.4. Gii php x l PCBs tn d

Trn th gii c rt nhiu cng ngh c p dng ti cc quc gia, trong s c 9 cng ngh, theo tng kt nh gi ca UNEP, l mang tnh thn thin mi trng v gi thnh hp l hn c, l: s dng l t c chng, l t xi mng, kh bng ho cht pha hi, kh bng cht xc tc, kh bng kim, xi ho in ho trung gian, xi ho mui nng chy, xi ho siu ti hn v Plasma.

nc ta cng c mt s m hnh th im hoc c trin khai. Trong hi tho Gii thiu v tham vn la chn cng ngh x l ho cht POPs tn lu ti Vit Nam din ra ngy 09/08/2007, do Cc Mi trng t chc, c 4 m hnh cng ngh c gii thiu. l cc cng ngh: s dng l thiu t nhit thp (Trung tm cng ngh x l mi trng - B t lnh Ho hc), s dng l t xi mng nhit cao (Cng ty Holchim th im ti Hn Chng), s dng l t 2 cp c can thip lm lnh cng bc (Cng ty Mi trng Xanh thc hin ti cc khu cng nghip) v Cng ngh phn hu sinh hc (Vin Cng ngh Sinh hc phi hp mt s n v khc thc hin).C. PHNG PHP PHN TCH PCBs TRONG THY SN V SN PHM THY SN1. Phm vi p dng

1.1 Tiu chun ny qui nh phng php xc nh hm lng cc thuc tr su gc Clo hu c v Poly Clorua Biphenyl (sau y gi tt l PCBs) trong thu sn v sn phm thu sn bng h thng sc k kh (sau y gi tt l GC).

1.2 Gii hn pht hin ca phng php i vi:-BHC l 1,0g/kg;-BHC l 4,5g/kg;g-BHC l 0,7g/kg; heptaclo l 1,0g/kg; alrin l 1,5g/kg; ielrin l 2,5g/kg; enrin l 5,0g/kg; DDT l 1,5g/kg v cloan l 1,0g/kg.

2. Phng php tham chiu

Tiu chun ny c xy dng da theo phng php 'Rapid determination of chlorinated pesticides, polychlorinated biphenyls', Mitt.Lebendsmittelunters. Hyg. 65:131-150 (1974) v phng php s S9 nu trong S tay hng dn phn tch d lng thuc tr su ca Cng ho lin bang c (nm 1987).

3. Nguyn tc

3.1 Thuc tr su nhm clo hu c bao gm cc hp cht chnh hay ng phn ca chng nh sau: alrin;-cloan;-cloan; oxi-cloan; p,p' DDD; p,p' DDE; o,p' DDT; p,p' DDT; ielrin;-endosulfan; enrin; heptaclo, heptaclo epoxit; hexaclobenzen (HCB);-hexacloxyclohexan (-HCH);b-hexacloroxyclohexan (-HCH);-hexacloxyclohexan (-HCH); isorin, trans-nonaclo;-hexachloro-cyclohexan (-HCH).

3.2 Cc hp cht nhm PCBs bao gm: 4-PCB (CB3); 2,4,4'-PCB (CB28); 2,2',4,4'-PCB (CB47); 2,2',5,5'-PCB (CB52); 2,2',5,6'-PCB (CB53); 2,2',4,5,5'-PCB (CB101); 2,3,4,4',5'-PCB (CB114); 2,3',4,4',5'-PCB (CB118); 2,3,3',4,5'-PCB (CB122); 2,2',3,3',4,4'-PCB (CB128); 2,2',3,4,4',5'-PCB (CB138); 2,3,3,4',5',6'-PCB (CB149); 2,2',4,4',5,5'-PCB (CB153); 2,2',4,4',6,6'-PCB (CB155); 2,3,3',4,4',5'-PCB (CB156); 2,3,3',4,4',5'-PCB (CB157); 2,3',4,4',5'-PCB (CB167); 2,2',3,3',4,4',5'-PCB (CB170); 2,2',3,4,4',5,5'-PCB (CB180); 2,2',3,3',4,5,5',6-PCB (CB198).3.3 Trong mu thy sn cc hp cht trn c chit tch ra bng dung mi pentan. Dch chit c lm sch bng phng php chit pha rn (SPE) trn florisil sau c tch lm 2 phn on trn ct silicagel. Phn on A cha cc PCB (tr CB3), HCB, alrin, isorine, heptaclo v p,p' DDE. Phn on B cha CB3, p,p' DDE v cc thuc tr su gc clo cn li. Hm lng cc thuc tr su gc clo hu c v PCBs trong cc phn on chit c xc nh trn my sc k kh vi u d bt gi in t (sau y gi tt l ECD).4. Thit b, dng c, ho cht, dung dch chun v dung dch th4.1 Thit b v dng c

4.1.1 Ct sc k thy tinh (c van kho), kch thc L x ID l 500 x 20 mm v 500 x 8mm.

4.1.2 H thng c quay chn khng.

4.1.3 H thng chit mu soxhlet.

4.1.4 My nghin ng th tc 10000 vng/pht.

4.1.5 My lc

4.1.6 T sy

4.1.7 L nung

4.1.8 Cn phn tch c chnh xc 0,0001g.

4.1.9 Ct mao qun (cho my GC): loi SPBTM- SUPELCO, kch thc L x ID = 30 m x 0,32mm hoc tng ng.4.1.10 My sc k kh vi u d ECD.

4.1.11 H ng soxhlet: cc ng soxhlet c lm sch bng cch chng ct vi pentan hay diclormetan trn h thng soxhlet trong 4 gi.

4.1.12 Ci s.4.1.13 B siu m

4.1.14 Bnh thu tinh, bnh tam gic dung tch 50ml.4.2 Ho cht

4.2.1 Ete ietyl loi dng cho HPLC.

4.2.2 Pentan loi dng cho HPLC.

4.2.3 Sulfat natri khan tinh khit c lm sch bng iclometan trn h thng soxhlet, sau nung nhit 5000C trong 4 gi v gi trong chai thu tinh.

4.2.4 Isooctan loi dng cho HPLC.

4.2.5 Kh mang: Heli (loi dng cho GC).

4.2.6 Florisil c ht t 60 n100 mesh c lm sch bng h thng soxhlet v nung nhit 4500C trong 18 gi, sau cho vo chai thu tinh c ph bng giy nhm v c gi nhit 1200C trong t sy.

4.2.7 Florisil c hot ho: ly mt lng florisil (4.2.6) t t sy trc tip qua phu vo mt bnh y trn (erlenmeye) c nt nhm. Thm vo bnh 3 % nc theo t l trng lng (w/w), sau lc hn hp khong 30 pht bng my lc v yn khong 1 gi trc khi s dng.

4.2.8 Bng thu tinh c lm sch bng pentan hay iclometan trn h thng soxhlet v kh trn ming giy nhm t trong t ht.

4.2.9 Ct sch c nung nhit 5000C trong 3 gi, cho ngui trn giy nhm sau gi trong chai c np vn.

4.2.10 Silicagel c ht t 70 n 140 mesh.

4.2.11 Silicagel c hot ho: ly silicagel (4.2.10), ra sch bng iclometan ri cho vo trong chn s v trong t sy nhit 1200C trong vng 12 gi. Sau , dng giy thic bc kn ming chn s v li vo t sy nhit 1200C trc khi s dng.

4.3 Dung dch chun v dung dch th

4.3.1 Dung dch ra gii: hn hp dung dch iclometan v pentan (4.2.2) theo t l v th tch l 2:8, c pha trc khi s dng.

4.3.2 Chun b cc dung dch chun thuc tr su gc clo v PCBs trong isooctan c nng : 0,0g/l; 2,5g/l; 5g/l; 10,0g/l; 20,0g/l t cc ng chun. Tu theo nng thuc tr su c trong ng chun, dng bnh nh mc v lng isooctan thch hp.

4.3.3 Dung dch chun thu hi: pha cc chun ca CB3, CB198 vd-HCH trong dung mi isooctan c hm lng l: 2,0g CB3/g isooctan; 0,2g CB198/g isooctan v 0,2g-HCH/g isooctan.

4.3.4 Dung dch chun kim tra: pha chnh xc hn hp dung dch chun kim tra gm p,p DDE v p,p DDT trong isooctan vi hm lng ca mi cht trong khong t 5 n 20ng/ml isooctan.

5. Phng php tin hnh

5.1 Xc nh hm lng cht bo trong mu th

5.1.1 Nghin u 250,0g mu thy sn trn my nghin ng th (4.1.4). Dng cn phn tch (4.1.8) cn chnh xc 10,0g mu (m) nghin cho vo trong ng soxhlet sch (4.1.11) c ph bng bng thu tinh (4.2.8). Chit mu vi 150,0ml pentan trong 3 gi trn h thng chit mu soxhlet (4.1.3).

5.1.2 C c dch chit trn my c quay chn khng (4.1.2) n khong 20ml. Sau , c tip ch chn khng cho n khi ch cn khong 1,0ml.

5.1.3 Chuyn dch c vo mt chn cn bit trc khi lng, dng giy nhm ph ln chn cn ri qua m trong t ht. Sau , chn cn c lm kh n khi lng khng i nhit 700C trong t sy (s thay i ca chn cn khng vt qu 0,0005g) ri ngui ti nhit phng trong bnh ht m. Phn thu c em cn l lng cht bo c trong mu.

5.2 Chun b mu th

5.2.1 Cn chnh xc 10,0g mu (m) nghin cho vo ci s (nu lng cht bo trong 10,0g mu ln hn 0,8g th gim lng mu m bo c ti a 0,8g cht bo trong lng mu em th nghim). Thm 10,0g ct sch (4.2.9) v 4,0g sunfat natri khan (4.2.3) ri nghin u bng ci s (4.1.12). Hn hp c a vo trong ng soxhlet sch (4.1.11), c ph bng bng thu tinh (4.2.8). Sau , hn hp c chit vi 150,0ml pentan trong 3 gi trn h thng chit mu soxhlet (4.1.3).

5.2.2 Nu mu cha nc, sn phm chit phi c lc qua sunfat natri khan ri c ra li bng 25,0ml pentan. Sn phm chit c c c trn my c quay chn khng (4.1.2) n khong 20ml. Sau , c tip vi ch chn khng nhit 40oC cho n khi ch cn khong 1,0ml. Thm vo dch thu c 2,0ml isooctane ri lm sch dch chit theo qui nh ti iu 5.5.

5.3 Chun b mu trng

Mu trng c nh ngha l mu thy sn c xc nh khng c thuc tr su gc clo hu c v PCBs. Tin hnh chun b mu trng ging nh chun b vi mu th theo qui nh ti iu 5.2.

5.4 Chun b mu xc nh thu hi

Thm 2,0ml dung dch chun c hm lng 5,0(g/l (4.3.2) vo 10,0g mu trng. ng nht mu bng my nghin ng th (4.1.4). Tin hnh chun b mu ging nh chun b vi mu th theo qui nh ti iu 5.2.

5.5 Lm sch dch chit

5.5.1 Chun b ct

5.5.1.1 Cn 25,0g florisil hot ho ri cho vo cc thu tinh c m cha 50,0ml dung mi pentan (4.2.2). Sau rt t t dung dch vo trong ct sc k thu tinh (4.1.1) kho van v nhi mt t bng thu tinh (4.2.8) di y ct.

5.5.1.2 yn ct cho lng, sau tho van rt dung mi pentan ra khi ct cho n khi mc dung mi trong ct cao hn mc florisil khong 1,0cm. Thm mt t bng thy tinh ln pha trn lp florisil trnh xo trn tinh th khi c dng dung dch vo.

5.5.2 Lm sch dch chit

5.5.2.1 Chuyn cc dung dch thu c iu 5.2.2, iu 5.3 v iu 5.4 vo cc ct sc k chun b (5.5.1).

5.5.2.2 Cho tip 3 ln, mi ln 3,0ml dung dch ra gii (4.3.1). iu chnh kho tc ra gii t t 4 n 5ml/pht.

Ch thch: khng c kh ct trong tt c cc bc ca qui trnh.

5.5.2.3 Thu ton b dch chit i qua ct vo mt bnh thu tinh y trn ca my c quay chn khng (4.1.2). Tin hnh c dung dch thu c cho n khi ch cn khong 1,0ml. B sung thm 1,0ml isooctan vo trong bnh ri lc u ho tan ht cn bm trn thnh bnh. Lm bay hi t t bng dng kh nit cho ti khi dch kh hon ton.

5.5.2.4 Thm chnh xc 2,0ml isooctan ri lc u ho tan cn.

5.6 Phn tch thuc tr su gc clo v PCBs

5.6.1 Chun b ct

5.6.1.1 Cn chnh xc 7,0g silicagel c hot ho (4.2.11) vo trong bnh nh mc tam gic dung tch 50ml (4.1.14). Sau , cho thm khong 25,0ml pentan, lc u ri cho lng. hn hp ny vo trong ct sc k thu tinh kch thc L x ID l 500 x 8mm (4.1.1) nhi mt t bng thu tinh (4.2.8) di y ct.

Ch thch: trong qu trnh nhi ct phi lun gi mc pentan trong ct cao hn phn silicagel trong ct.

5.6.1.2 yn cho silicagel lng xung ri b sung mt lng tinh th sulfat natri (4.2.3) vo trong ct vi chiu cao khong 2cm. M kho tho bt pentan trong ct n khi mc pentan ngang bng vi mt trn ca phn tinh th sulfat natri.

5.6.2 Kim tra ct tch chit silicagel v dung mi pentan

5.6.2.1 Ly chnh xc 2,0ml dung dch chun kim tra (4.3.4) cho qua ct silicagel chun b (5.6.1). iu chnh kho tc chy khong 40 git/giy. Sau , cho t t 100,0ml pentan qua ct. Thu ln lt cc dung dch chit chy qua ct vo trong 9 bnh thu tinh (4.1.14). Bnh th nht (k hiu l E1) thu 60,0ml u, cc bnh tip theo (k hiu t E2 n E9) mi bnh thu ln lt khong 5,0ml dch chit.

5.6.2.2 C quay cc dung dch trong 9 bnh ni trn bng my c quay chn khng (4.1.2) cho n khi cn khong 1,0ml. Tin hnh phn tch trn my sc k kh (GC-ECD) theo qui nh ti iu 5.6.3.2, iu 5.6.3.3 v iu 5.7. Tnh hm lng ca p,p'-DDE v p,p'-DDT tng ng ca mi bnh theo cng thc nu ti iu 6.

5.6.2.3 Xc nh th tch pentan cn thit thu c dung dch ra gii A (k hiu l X), bng cng thc sau:

X (ml) = E1 + E2 ... + En-1

Trong :

- E l th tch dung dch ra gii thu vo bnh c s th t tng ng, tnh bng ml.

- n l s th t ca bnh m ti khng cn pht hin p,p'-DDE

5.6.2.4 Gi tr X ch ng vi cng mt l silicagel v pentan. Thng thng gi tr X nm trong khong t 60 n 90ml. Nu hai hp cht trong mu kim tra khng th phn tch c th b sung thm nc khong t 1 n 2% v khi lng vo silicagel trong ct ri tin hnh lp li cc bc kim tra qui nh ti iu 5.6.2.

5.6.3 Phn tch cc dn xut ca PCB v thuc tr su gc clo hu c

5.6.3.1 Cho ton b dch chit lm sch (5.5.2) qua ct silicagel chun b (5.6.1). iu chnh kho tc chy khong 40 git/giy. Cho t t X ml pentan (xc nh ti iu 5.6.2) qua ct thu c dung dch ra gii A. Sau , cho tip 100,0ml hn hp ete ietyl v pentan theo t l v th tch l 1:9 i qua ct thu c dung dch ra gii B. S dng 2 bnh cha khc nhau hng ring 2 dung dch A v B.

5.6.3.2 Thm 1,0ml isooctan vo cc dung dch ra gii A, B. Dung dch thu c c c quay bng my c quay chn khng (4.1.2) cho n khi cn khong 25,0ml. Sau tip tc c c cho n dung dch kh hon ton.

5.6.3.3 Thm chnh xc 2ml isooctan (v) v em phn tch trn my GC.

Ch thch: khng c kh ct trong tt c cc bc ca qui trnh.

5.7 Tin hnh phn tch trn GC

5.7.1 iu kin phn tch

a. My sc k kh s dng u d ECD, c kh nng chia dng, c th tu chn ch bm t ng.

b. Ch nhit ca h thng GC: Nhit ca bung tim l 2500C; nhit u d l 3000C. Chng trnh nhit (m t chi tit trong Biu 1) c th l:

- Duy tr nhit 1500C trong 1 pht.

- Tng nhit 20C/pht ln ti nhit 2200C.

- Tng nhit 200C/pht ln ti nhit 2400C.

- Duy tr nhit 2400C trong 13 pht.

- Tng thi gian l 51 pht.

c. Ct sc k

Ct mao qun khng phn cc trung bnh SPB -1TM - SUPELCO (ct methylsilicon c kh nng tch thuc tr su theo nhit si), nhit ti a 3600C, chiu di 30m, bn knh trong 0,32mm, bn knh ngoi 0,50mm, chiu di lp ph 0,25(m.

d. Kh

- Kh mang: Helip sut kh 70kpa.

- Kh lm sch: Nit 99, 9999%.

- Ch chia dng: 1:10.

5.7.2 Tin hnh phn tch

5.7.2.1 Tim cc dung dch chun (4.3.2) vo my GC theo th t t nng thp n cao. Mi dung dch tim 2 ln, tnh din tch pic trung bnh. Dng ng chun biu th mi quan h gia cc din tch pic thu c v nng tng loi thuc tr su theo quan h tuyn tnh bc 1 (phng trnh y = ax + b).

5.7.2.2 Tim dung dch mu th, dung dch mu trng, dung dch mu xc nh thu vo h thng GC. Mi dung dch mu tim 2 ln. Tnh gi tr trung bnh.5.8 Yu cu v tin cy ca php phn tch

5.8.1 lp li ca 2 ln tim

lch chun (CVS) tnh theo din tch pc sc k ca 2 ln tim cng mt dung dch chun phi nh hn 0,5%.5.8.2 thu hi (R) thu hi c xc nh bng cch s dng 10 mu c cng mt lng dung dch chun bit hm lng chnh xc. thu hi tnh c phi trong khong t 85% n 115 %, thu hi trung bnh phi ln hn 90 %.

5.8.3 ng chun phi c tuyn tnh tt, h s tng quan quy hi tuyn tnh (R2) phi ln hn hoc bng 0,99.6. Tnh kt qu

Hm lng tng loi thuc tr su c trong mu c tnh trn c s ng chun thu c (5.7.2.1). Vi ng chun dng y = ax + b, hm lng tng loi thuc tr su c trong mu c tnh theo cng thc sau:

(Y - b)

C ((g/kg) = ------------ x F

a

Trong :

- C l nng tng loi thuc tr su c trong mu, tnh theo (g/kg.

- Y l hiu s gia din tch pic ca dch chit v din tch pic c trong mu trng tim vo GC, tnh theo n v din tch.

- a, b l cc thng s ca ng chun y = ax + b, c xc nh theo iu 5.7.2.1.

- F l h s pha long mu v c gi tr bng t s gia th tch dch chit thu c sau khi lm sch (5.6.3.3) v khi lng mu m (5.2.1) s dng.

Ti liu tham kho: Th vin php lut Yeumoitruong.com http://www.sge.com/support/training/fast-gc-analysis/pcb-analysis