L 4.6 Gidi tbieu mot so HCTS-eaphotpho tbiidng diin g:
1.5.3. Phiidng phap pban tich ton liidng
1.5.3.1. Phiidng phap lay mau ton liidng.
Do chinh xac ciia phitong phap lay mau tang len theo kich thudc mau va tinh chat phiic tap cua sd dd lay man. Ve nguyen tac cd hai sd dd lAy man : Lay mau ngan nhien va lay mau he thdng. Cd hai loai mau : Mau ddn va m a n tong hdp. Gia tri ton lUdng HCBVTV trong man ddn c6 the dao dong rat Idn, vdi he sd bien dong khoang 100%. Vi vay sd litdng man phai lay phan tich de dat dUdc do tin cay can thiet la rat Idn. Do dd viec nghien citu ton lUdng trd nen ton kem. Khi lay mau tdng hdp thi sU bien dong se giam di neu tang kich thude mau. Do dd so' lan phan tich de dat do tin cay can thiet se it hdn tritdng hdp tren nhieu va gia t h a n h nghien ciiu se giam. Vi vay man tdng hdp thUdng dUde lay de ngliien ciiu ton lUdng. Viec lay mau ngau nhien ddi hdi phai cd qui trinh lay m a u dUdc tliiet ke rat can than va viec thUc hien ciing khd khan. Viec lay mau he thdng theo thii tU thdi gian hay khdng gian deu dan thi ddn gian, t h u a n tien, it gay sai so hdn nen hay dUdc ung dung trong nghien cUu ton lUdng [32,90]. Mot vai thi du xac dinh vi tri lay m a u he thd'ng : cd the lay m^u theo (a), (b), (c) hoac (d) [1()0|.
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Hinh 4 : Sd do lay m a u he thd'ng trong khao sat ton litdng HCBVTV.
1.5.3.2. Danh gia ket qua
Cac phitdng phap thdng ke so'lieu chi diing vdi phan bd chuan, vi vay clii iing dung ditdc vdi phan bd gan chuan. Trong nghien ciiu ton lUdng HCBVTV cd the thay rkng neu kich thUdc m a n tdng hdp cang Idn thi phan bd ton lUdng cang gan vdi phan bd chuan. (]ac thii ngliiem cho thay m a n tdng hdp cd kich thUdc bang 5 cd the dUdc ling dung de tinh thdng ke. Tang kich tliUdc m a n t ^ 5 den 10 lam ket qua tot hdn mot each ro ret. Trong nghien citu ton lUdng ngUdi ta thitdng dimg man tdng hdp cd kich thUdc tit 7 den 20 m a u ban dau [32,100].
1.5.3.3. Phiidng phap chiet tach, tinh che HCBVTV trong mau phan tich.
PhUdng phap phan tich ton lUdng H(]^BVTV trong mdi trUdng Cling mot nguyen tac chung eiia phUdng phap phan tich vet, bao gdm viec chiet tach HCIBVTV ra khoi mau, lam giau mau, tinh che loai cae
tap chat lAn theo va cudi ciing la dinh litdng cac chat can phan tich [2,20,39].
1.5.3.3.1. PhUdng phap chiet tach.
Phan Idn HCBVTV deu tan trong cac dung mdi hUu cd. Do dd ngUdi ta thUdng dung cac dung mdi hUu cd n h u hexan, benzen, ete, axeton, axetonitrin... de chiet cac HCTS, cac chat diet cd, cac chat trit nam... ra khoi m a u thUc pham, nUdc, dat, man, nitdc tieu... Tuy theo dd'i tUdng mau phan tich ma chon cac dung mdi va cac phUdng phap chiet tach khac n h a u [1,39].
De tach DDT, HCH, HCB... ra khdi m^u khi ngUdi ta cho thoi qua etilengiicol hoac silicagel de t h u giU chiing. De tach chiing ra khdi man nude, ngUdi ta cho chay qua cac chat hap phu khac n h a u nhu ambelit XAD2, poliuretan xd'p hoac l^c chiet vdi n-hexan [115]. Ddi vdi cac mail thUc pham, m a u dat chii yen ngUdi ta sii dung dung mdi liiiu cd (n-hexan, axetonitrin, axeton...) de cliiet tach cac hdp chat trii" sau ra khdi man, PhUdng phap chiet tach HCBVTV trong dat b^ng thiet bi soxlet vdi hdn hdp dung mdi thich hdp dUdc coi la phUdng phap chuan ddi vdi mau dat, m a u khd va m a u thUc pham chita nhieu dau md [1,100].
1.5.3.3.2. Tinh che
Qua trinh tinh che hay qua trinh lam sach m a n la mot bUdc quan trong trong phan tich vi lUdng^vi sau khi cliiet, ch^ng nhUng HCBVTV ma mot lUdng Idn tap chat trong cay va dat ciing di vao dich chiet, lam a n h hUdng den qua trinh dinh htdng sau nay. Tap chat cd the bao gdm cac amin, cac phenol, axit hUu cd, ditdng, dau thitc vat, sap, diep luc va cac chat m a u khac. Qua trinh lam sach thitdng dUdc tien h a n h qua 2 bude : sac ki phan bo long - long va s^c ky cot [32,100].
S^c ki phan bd long - long : Trong phUdng pha]) nay , neu
dung mdi chiet tan trong nUdc (nhit axetonitrin, axeton...) thi ngitdi ta dung hexan va nitdc de tao nen 2 he dung mdi khdng tron lan vao nhau. Khi dd cac chat trit sau cd clo dUdc keo vao ldp hexan, cac tap chat phan cUc laxit hUu cd, amin, axit amin, dUdng...), chat beo nam lai trong pha phan cUc nUdc : axetonitrin hoac nUdc : axeton. Nhd each nay ngUdi ta loai dUdc cac tap chat phan cUc va chat beo ra khdi cac hdp chat trii sau hUu cd. Diing pheu chiet ta de dang tach dUde ldp dung mdi chiia cac hdp chat trit sau hUu cd. Sau khi cat dudi phan Idn dung mdi, phan cdn lai cd the dem tinh che tiep de loai cac chat mau va lUii huynh (nhieu m a u dat cd chiia lUu huynh tU do). De loai cac chat man ngUdi ta thudng diing axit sunfuric d a c , de loai lUu huynh ngudi ta diing dong 1dm loai [20,107].
S^c ky cot: Phan Idn cac qui trinh phan tich ton lUdng HCBVTV, sau khi lam sach b^ng each phan bd Idng - long, dich chiet cudi cimg dUdc lam sach bkng each cho di qua cot hap phu. Nhieu loai chat hap phu dUdc san xuat tren thi trUdng, nhUng chi cd nhUng chat hap phu on dinh ve cac tinh chat nhU kicli thUdc cd hat dong n h a t (khoang 0,1- 0,2 mm), hoat do chinh xac theo Brockeman va de thay ddi bang each dieu chinh ty le nUdc cho vao thi mdi dUdc dung de lam sach trong phan tich ton lUdng [79,88,107].
FlorisU PR, silicagel G, silicagel Woelm [2], Kieselgel Merck, nhdm oxit Woelm [37] dUdc dung trong sac ki cot de lam sach dich chiet HC]BVTV. T h a n boat tinh - dat diatomit - magie oxit ciing ditdc dung de lam sach dich chiet nhitng phai tiian theo (iiii trinh xit ly nghiem ngat de dam bao dn dinh tinh hap phu cua chiing [32]. Tuy
titng dieu kien cu the ma ngitdi ta lUa chon cliat hap phu de lam sach dich chiet trong sac ky cot.
Trong tritdng hdp mau chua mot lUdng chat mau va nhUng chat beo khdng xa phdng hoa, viec tinh die bo sung tot n h a t dUdc tien h a n h bang s^c ky hap phu tren cot nhdi cac chat hap phu khac nhau : silicagel [100], florisil [95]. Sau dd rUa giai b^ng dung mdi n-hexan hoac hon hdp ciia nd vdi diclometan.
Viec tinh che bo sung tren sac ky cot khdng nhiing chi de loai cac tap chat cdn lai ma trong nhieu trUdng hdp cdn cd tac dung phan tach hdn hdp cac HCBVTV t h a n h nhitng phan doan liep, giiip cho viec dinh lUdng cluing d giai doan tiep theo dUdc de dang.
Nliin chung, cac phUdiig phap phan tich ton lUdng HCBVTV khdng cd nhiing thay ddi Idn d nhUng giai doan chiet tach va tinh che. Su thay ddi can ban thudc ve sU ket thiic phan tich vdi viec tim n h a n va dinh lUdng cluing. Neu vai chuc n a m tritdc day ngUdi ta chi cd the xac dinh iihUng lUdng nhd den microgam thi ngay nay cung vdi sU tien bo ciia khoa hoc ky t h u a t cd the xac dinh ton lUdng HCBVTV trong mdi trudng (dat, nUdc, khdng khi, tliUc pham, trong cd the con ngitdi va dong vat) d miic nanogam, picrogam hoac thap hon nUa [20].
1.5.3.3.3. Cac phUdng phap phan tich ton lUdng HCBVTV.
Sau khi tinh che HCBVTV trong m a n nghien citu, ngUdi ta cd the xac dinh chiing bang nhieu phUdng phap : phUdng phap hoa hoe [39, 44], phUdng phap sinh hoc [77] , phUdng phap sac ki khi. [80, 87] sac ki long cao ap [91, phUdng phap danh dau dong vi phdng xa.
a) Dinh litdng DDT : DDT ditdc nitro hoa bang kali nitrat va axit sunfuric, rdi cliiet bAng benzen. Hdp chat tao t h a n h cd man xanh tim vdi dung dich natri metylat.
Do mat do quang tren quang ke d bUdc sdng 590 nm. Do nhay cua phUdng phap la 5 microgam [1,39]
CCI3 xN02 ^ N02 C > / \ c - \ ^ ^ - € l ^ 2K2SO4 +4H2O+CI- CCI3 -iKNOii+ll-^SiM 1^02^ (A) (B) NOOK NOOK (B) + 2 K 0 H > H O — / T ^ CH ^ \ ^ OH CCl;j NOo NO2
Pliiic chat m a u xanh tim b) Dinh lUdng HCH : Cd the xac dinh HCH dUa tren cd sd declo hoa tao benzen, rdi tien hanh nitro hoa tao metadinitrobenzen trong dung dich kiem manh, chat nay cho m a n tim dd vdi metyletylxeton. Do mat do quang tren quang ke d bUde sdng 600 nm. Do nhay cua phUdng phap 5 microgam [1].
c) Dinh lUdng 2,4 - D va cac chat cung loai. 2,4- D tac dung vdi axit cromotropic trong axit sunfuric dac cho san p h a m m a n xanh tim. (Phan ling nay rat nhay nhUng chi thich hdp vdi 2,4-D va 2,4,5-T). Sau dd do m a t do quang d bitde sdng 600 nm. Do nhay cua phUdng phap la 1 microgam [39].
d) Dinh lUdng wofatox va thiophot : Nhdm nitro trong wofatox va tliiophot dUdc khii hoa t h a n h nhdm amino (bang hot kem trong mdi trUdng axit elohidric). Dung dich chiia nhdm amino phan itng vdi dung
dicli phenol va cloramin tao t h a n h san pham mau xanh. Do mat do quang d bUdc sdng 630 nm. Do nhay ciia phUdng phap 5 microgam [39]