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Chromatographic scince series - Cazes J.

Cazes J. Chromatographic scince series - Marcel Dekker, 1996. - 1098 p.
ISBN 0-8247-9454-0
Download (direct link): сhromatography1996.pdf
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The widely used insecticide acaricide vamidothion can be made visible either with 0.5%
2,6-dibromo-W-chloro-p-benzoquinoneimine in cyclohexane solution or with palladium chloride. These detection systems were applied in metabolism studies (152). The P=S bond has a catalytic effect on the color development when iodine-azide reaction is applied. The white spots on a yellow background were better evaluated when the plates were sprayed with starch solution. The limit of the detection was in the 0.5-10-|lg range (149). Dithiophosphate insecticides give a colored complex with palladium(II) ions, KjPdCLj, with the cleavage of the P-S bond. Carbofos, phtalophos, and phosalone were evaluated by this color reaction combined with spectrophotometry (155).
The phosphorus content offers a sensitive detection mode for fensulfothion, metasystox, disulfoton, methylparathion, folithion, hinosan, malathion, dimethoate, formothion, phosphamidon, phosalone, thiometon, and quinalphos. After development, the plates were heated at 110C for 2 h, yielding inorganic phosphates. These reacted with ammonium molybdate to give phosphomolybdate. The reduction with ascorbic acid leads to a blue complex with a detection limit of 0.1-0.2 jxg (160).
The new OP pesticide BAY 93820 was detected on a silica gel G layer by two different methods, either with 4-aminoantipyrine and K3Fe(CN)6 or with K104-starch. The former color complex was quantified at 520 nm (160a). '
According to another method, the OP insecticides were detected by the Griess reaction. This method can be used for aromatic amino containing pesticides, such as ethyl parathion, methyl-para-thion, and fenitrothion. After reduction with stannous chloride, these insecticides were diazotized and coupled with 1-naphthylamines. The metabolite, p-nitrophenol, derived from fenitrothion, also gave a positive reaction (160b).
Endosulfan and phosphamidon residues were detected by cobalt acetate and o-tolidine on TLC plates with the sensitivity of 10 ng (160c).
B. Enzyme Inhibition
Enzyme inhibition methods can be classified not only as biological methods but as representative of fluorescent detection. The substrates of the acetylcholine esterases are nonfluorescent compounds, but after hydrolysis they produce fluorescent materials so the background becomes fluorescent. The sensitivities of the methods can be enhanced either by changing the enzymes or by applying the optimal substrate. The sensitivities of paraoxon detection methods when horse serum or human plasma esterases was applied in combination with substrates such as butyrylthiocholine or in-doxy lacetate were investigated (161). Carbaryl, dichlorphos, and malathion were determined in pines by this method using rat or pig liver esterases (73). Bromophos, iodophenphos, and metabolites in rainwater were separated on polyamide plates and detected by pig liver esterases with indoxyl acetate substrate (56).
According to another paper, methamidophos and phosphorus-containing insecticides were detected by beef liver esterases in Tris buffer using indoxyl acetate, K3Fe(CN)6, and IQFeCCN^. The insecticides gave white spots on a blue background with a detection limit of 15 ng/spot (162).
Pesticides
807
Azinphos-ethyl, carbophenothion, diazinon, ethion, malathion, mevinphos, parathion, and OP pesticides were detennined in fruits and vegetables by beef liver esterases and 5-bromoindoxy 1 acetate. Their TLC separation was carried out on silica gel plates developed in acetone-hexane (1:4) (163).
Organophosphates, thiocarbamates, carbamates, carbamoyloximes, dithiocarbamates, and ureas were included among 100 pesticides and metabolites detected on TLC plates by their cholinesterase inhibiting properties. After developing the plates in ether, xylene, di-n-butyl ether, -butyl acetate or methyl-isobutyl ketone, the plates were exposed to bromine vapor. The compounds were oxidized to their oxo derivatives, which exhibited more effective cholinesterase inhibitory activity. Bovine liver suspension served as enzyme source and the substrates 2-naphthyl acetate and Fast Blue salt as the chromogenic agents (163a).
Enzymes from various sources exhibit different sensitivity in the detection of cholinesterase inhibiting compounds. It is also expected that enzymes obtained by microbial synthesis would be more effective than enzymes of animal organs.
A new quantitative determination of OP insecticides was reported in which the esterase was obtained from Bacillus subtilis culture media. The substrate of this detection was 1-thionaphthyl acetate, and the post chromatographic reagent was 2,2'-azo(l-naphtol,8-chloro-3,6-disulfonic acid)-
4,4-diphenyl disulfide. The sensitivity of this detection was 0.1-5 ng for 18 OP insecticides (163b).
C. Biotests
1. Hill Reaction Inhibition
Herbicides having an inhibitory effect on photosynthesis can be detected by a simple, sensitive, and highly selective method: inhibition of the Hill reaction. These herbicides are of triazine, phenylurea, phenylcarbamate, uracyl, and acyl anilide types (164) (Table 12). The detection limit is of the same level as that of the enzyme inhibition technique used for insecticides. Spinach or bean leaf chloroplasts prepared in 0.5 M sucrose solution are suspended in glycerol-water (1:9) and mixed with a solution of an electron acceptor, 2,6-dichlorophenol-indophenol. The developed plates, sprayed with the reagent, are exposed to fluorescent light; blue inhibition spots appear in a short time on a pale yellow-green background (164). This photosynthesis reaction is completely hindered on TLC plates containing polyacrylamide binder, which cannot be used in conjunction with this detection method (165).
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