Mac dii, cac phuong phap phan tich hoa hoc cho do chinh xac cao khi phan tich lugng Idn, nhung do nhay va do lap lai thlp. Do do phan tich lugng nhd thudng phai diing den cac phuong phap cong eu [5].
F.S. Grimaldi va R.C. Wells da xay dung phuong phap trac quang xac dinh nhanh lugng nho Mo trong W va quang Mo bang each sau khi loai Fe va cac thanh phan chinh khac. phirc MoOiSCN):; dugc phat trien trong dung dich nudc-axeton sir dung amoni xitrat dc lam giam anh hucmg cua W [47]. Hoac nhu khir W(VI) bang CuCl vdi moi trudng nudc-axeton roi cho tao phirc Mo(V)-SCN va xac dinh Mo bang trac quang... [68. 110].
Lazareb Ạ Ị, Lazareba V. Ị da xac dinh lugng nho Mo (0.01°o) trong natrivonframat hoac axit vonframic [150] bang each bo sung dung dich axit limonie 60% vao dung dich nghien cirụ Tron. lam lanh \a them KSCN. them H:S04 1:1 rli lam lanh tilp va them axit ascorbic, them nircVc den \ ach mire va do do hap thu quang sau 15 phiit. Dung dich so sanh chira tat ca chat phan irng trir ion molipdat.
Ị P. Kharlamov va Z. P. Korobova da su dung axil tatric dong thoi \di tia cue tim lam tac nhan khu Mo(VI) hoan toan xuong Mo(\') trong phuong phap rodanit a pH ^ 5. Phirc mau phat trien hoan toan qua ^o" \a ben 24h. W
va Re (vdi lugng gap 10 lin) cd mat ding thai trong dung djch khong bj khir va khong anh hudng din viec xac dinh Mo [166].
De lam tang do nhay cua phep xac djnh va do bin cua phirc. ngudi ta da sir dung mot s6 dung moi hiru co cho viec ehilt phirc lien hgp Mo(V)-SCN khoi W hoac khdi cac nguyen t l di kem. Brawn (1863) da cho thay phirc mau Mo-SCN hinh thanh trong khi khir Mo(VI) bang Zn ehilt dugc bang dietv letẹ nhung khong chiet duge bang clorofooc va CS:. Sau d6 King da ehilt phirc Mo(V)-SCN bang dietyl ete va phan tich lugng nho Mo trong W va WO;,. [88, 110, 150].
Chiet Mo(V)-SCN trong phan tich da co nhieu tac gia nghien ciru vai nhieu dung moi va hon hgp dung moi khac nhau nhu diet\ 1 ete [ 150] hon hgp dietyl ete va ete dau mo, butylaxetat, amylaxetat, diisopropylic etẹ etvlaxetat. butanol, isobutanol, rugu isoamylic. hon hcrp nrgu isoamylic va tetracloruaeacbon, cyelohexanol. clorofooc ... [47. 1 10. 122. 150]. Iv le dung moi, chat trg chiet [138]. dieu kien chiet toi uụ pH. budc song cue daị do hap thu quang eiia phirc cung da duge nghien cirụ
Chgn N-benzylanilin trong hon hgp clorofooc-mgu isoamvlic lam tac nhan ehilt chgn Ige phirc Mo(V)-SCN trong moi tnrdng H:S04 1.8 .\1 hoac HCI 2,8 M, Khosia va Rao [68] da xac dinh dugc Mo trong cac hon hop tong hgp da dang ma khong bi nhilu cac cation va anion anh huong nhu nhirng phuong phap thioxianat thong thircmg. Khoang tuan theo dinh luat Beer la 0-
50 pg Mo/ml. Do hip thu moi cua phirc do-da cam la 16380 - 90.
Trong nhom N-alk\lphenothiazines. methotrimeprazine (l-;iO-[3- dimetylamino-2-met\Ipropyl]-2-methox\ [phenothiazine - MlAl) hinh thanh phirc da bac vdi Mo o nhiet do phimg trong axit HCI chira thioxianat |24].
Phirc bac ba cua Mo ehilt dugc \ao clorofooc \a do do hap thu quang o 4h5
do 5-40°C. Vdi dilu kien nay co thi xac dinh Mo trong hgp kim thep va quang, lugng du W 100 Ian, cac kim loai kilm va anion co mat Idn hon khong anh hudng.
Mot vai phuong an chilt-trac quang vdi SCN" xac dinh Mo trong W kim loai va trong cac vat lieu chira W ciing duge nghien cim. Vi dụ xac djnh tuang dii chinh xac va nhanh g^n 1% Mo trong thep chira Nị Cr. W va kim loai khac sau khi ehilt Mo(V)-SCN bang dietyletẹ W bj giir lai trong dung djch nude bang each them axit tatric hoac limoniẹ Tuong tụ xac dinh Mo trong quang W diing tac nhan chiet la butylaxetat. W dugc giir trong pha nude bang each them NaF...[ 88, 96, 110, 111, 150].
Chattopadhyay S. va cong su da chiet phirc mau vang ciia Mo(VI)-N- phenyIbenzohydroxamic axit-SCN trong moi trudng HCI 2-5M vdi Aliquat 336 trong toluen [31, 117] va do quang eiia djch chiet o 350 nm. Bang phuong phap nay cd the xac djnh duge Mo trong su co mat cua nhieu cation va anion [138].
Ngoai thuoc thu vo eo thong dung nhat de xac dinh Mo va W bang trac quang va chiet-trac quang la thioxianat [122.163]. thi mot khoi lugng Idn cac thuoc thir hiru ca cijng da duge nghien cirụ Chon loc nhat \di Mo la thuoc thu CO chira luu huynh nhu cac axit thioglycolic. mercaptopropionic (thiolaetie), unithiol. Trien vgng nhat la 8-mercaptoquinolin (thiooxin). phan img vdi Mo tao phirc khong tan chiet rat tot vao dung moi hiru cọ Khi xac djnh Mo bang chilt-trac quang vdi thiooxin. W \a rat nhieu ngu\en to khac khong gay anh hudng hoac dugc che hieu qua [163]. Toluen-3.4-ditiol tao ket
tua vdi Mo va ehilt tit vao amylaxetat trong cac dung dich axit manh. Do
nhay cao hcTn thiooxin nhung do chon loc kem hon [ 16.'^ |.
Hay thule thu triazenes khong phan ung \oi \U)(\I). nhirng I-(2- carboxy-4-sulphonatophenyl)-3-hydroxy-3-phen\ltriazene lai tao phuc \di
Mo(VI) d pH 3,0 - 4,2 va cd hip thu quang cue dai d 405 nm. W anh hudng d mire 80 ppm/ 8 ppm Mo [86].
Nhom thuoc thu hii-u co khac tao hgp chat mau vdi Mo la pyrocatechol, pyrogallol, axit gallic... va dac biet la cac dan xult thi cua fluoron chira cac nhom hydroxyl [163]. Phirc cua Mo(VI) vdi pyrocatechol trong su co mat cua chat hoat dgng be mat cationic CTMA (cetyltrimet>'lamoni), co the su dung
de phan tich dugc mot lugng nho Mo trong thep, dk va nuac bien [25,57].
Day cac oxiflavon ciing cho phan irng mau voi Mo nhu morin va quercetin (CusHioOy), dioxiquercetin de xac dinh Mo trong thep. Mo dugc tach ra bang each chiet phirc Mo-a-benzoinoxim voi clorotboc. Them dung dich rugu etylic ciia quercetin vao lop huu co va do quang phirc mau tao thanh [150, 160] .
Cac thuoc thir hiru co diing cho chiet-trac quang xac dinh rieng Mo la phenylhydrazin (xac dinh Mo trong W kim loai \a hgp chat). diphenylcacbazon, 8-oxiquinolin, 8-oxiquinolin-5-sultbnic axit (\ai cac thuoc thir nay, W(VI) khong cho hgp chat mau a nhirng dieu kien tao mau cua Mọ nhung CO mat lugng W > lOmg can tang lugng thuoc thu). limogalliol (lugng khong Idn W che bang axit tatric) [150, 157. 160. 165].
Mot lirorm nho Mo duac xac dinh sau khi done ket ma phirc cua no \ di kali tritloroetylxanthate trong moi tnrong axit pH 1.0-3.5 tren naphtalen (25% trong axeton). ehilt vao clorofooc va do do hap thu quang o 365 nm. Phuong phap nay ehi cln 0.4 g naphtalen co the tach ducTC phirc Mo ra khoi the tich
Idn dung djch. Khi ap dung cho xac djnh Mo trong hop kim thep. Fẹ Cọ Ni
va Cu thi phai ehilt phirc cua cac nguyen to na\ \oi tritloroxanthate bang clorofooc o pH 8-9 trude rli mdi xac dinh Mo pha nirov [ I "^d. I 5S|.
Lam Ngge Thu va cong sir da xac dmh \ i luong Mo irong lugng Ion W bang each ehilt phirc eua no \di clotrioxyazoben/cn trong moi tnrong axit
axetic 0,2M vao hon hgp dietyl ete 10% trong benzen. Do hap thu quang ciia pha hiru ca dugc do d 510 nm. 6 budc song nay phi hap thu eiia phirc W- clotrioxyazobenzen khong anh hudng din kit qua phan tich Mo va co thi
phan tich no khi lugng W Idn gap 2000 \kn [9].