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Almost 200 pesticides were analyzed in various systems using dichloromethane and ethyl acetate (129). These pesticides were visualized by the following selective detection methods: (a) o-tolidine-potassium iodide, (b) p-nitro-benzene-diazonium-fluoborate, (c) silver nitrate with UV irradiation, (d) p-dimethylaminobenzaldehyde, (e) bioassays with either fungispores of Aspergillus niger or an enzyme inhibition method. When horse blood serum was the enzyme source, acetylcholine iodide was its substrate in the presence of 2,6-dichloro-phenol-indophenol. Naphthyl acetate was applied as the substrate for the human blood plasma esterases. The Rf values and detection limits were also published (129).
Two-dimensional TLC was applied in the separation of about 150 pesticides. The first development was carried out with petroleum ether-ether (1:2), which separated the carbamates, carbamides, triazines, phthalimide-type compounds, OPs, and other pesticides. The more polar pesticides, having Rf0.25 or less, can be separated in the second direction with ether. When Rf was higher than 0.75, the development system was petroleum ether-ether (5:1), separating the nitro derivatives, thiocarba-mates, and some OP insecticides (130).
Another two-dimensional TLC method could resolve ╬Đ, OP, insecticides, triazines, and 2,4-D using a chloroform-ether system for polar pesticides and Ű-hexane-acetone for nonpolar pesticides in water, soil, and plant samples. The /fy-values are summarized in Table 10 (131).
Table 10 Multiresidue Methods
Linuron Triazines Atrazine Simazine Prometrine Dimethoate Malathion Chlorphenoxy carbonic acids
n-hexane:acetone (90: 10)
(1) n-hexane:acetone (150:45)
CH3COOH (50: 100:20)
Ű-heptane-acetone (90:10) Me0H-H20-NaCl (95 :5 : 1.
Heptane-acetone (90: 10) Me0H-H20-NaCl (65 :35 : 1
Toluene-ethyl acetate (80:20)
MeOH-H2O NaCl (65:35: I) n-hexane
Detection Sample Extraction Ref.
o-tolidine Water (I) Ű-hexane, pH 6-7 22
AgNO, Water (2) CHCI,, pH 6.5-7
AgNO, Water (3) CHC13, pH 2
Anisaldehyde Bromophthalein Anisaldehyde Dansyl chloride
Soil 0.05 N CaCl2-acetone 20
OP, ╬Đ, carbamates
pp'-DDT pp' -DDE Dimethoate
Silica gel KSK
Polygram Cel 300 Polygram Sil G
/│-hcxane acetone (1:9)
(1) Petroleum ether-ether (1:2) (2a) Ether
(2bI Petroleum ether-ether (5:1)
(1) CHClrether (5 : 2)
(2) n-hexane:acetone (20: I)
Cb-o-tolidine enzyme 130
Rf x 100
AgNO,. NH4OH Water 131
Soil 100 30
Plant 100 37
AgNO,-2-phenoxy- Peas 21