76 Organic compounds in soils, sediments & sludges
on the 0.5% Carbowax 20M – 5% SE-30 column closely similar to that of the
methoxime derivative of Oxamyl. To check for possible interference in the analysis for Oxamyl from some of these other pesticides, 50 µg amounts each of the
Aldicarb [2-methyl-2-(methylthio) propionaldehyde O-(methylcarbamoyl) oxime] and
Thiofanox [3,3-dimethyl-1-(methylthio)-2-2 butanone O-(methylcarbamoyl) oxime],
and their sulphoxide and sulphone metabolites, were taken separately through the
procedure. No detectable peaks were observed, indicating that these potentially interfering compounds are not eluted in the Oxamyl-containing fraction taken from the
Florisil column.
Leppert et al [93] have described a procedure for the determination of
Carbosulphan and Carbofuran (2,3-dihydro 2,2-dimethylbenzofuran-7-y1-methyl carbamate) utilising gas chromatography with a nitrogen specific detector. Extraction was
carried out using hexan-2-propanol or a methanol buffer.
Bilikova and Kuthan et al [94] developed a gas chromatographic method for
the determination of submicrogram concentrations of Carbofuran (2,3-dihydro-2,
2-dimethylbenzofuran-7-y1-methyl carbamate) in soils. Soil samples are mixed with
methanol-water (80:20) and water samples are extracted with chloroform, After separation of the chloroform and weak alkaline hydrolysis, derivatisation is performed
with 1-fluoro-2,4-dinitrobenzene. The ester produced is isolated from the benzene and
cleaned up with acetone. The acetone extract is used to determine Carbofuran by gas
chromatography with a nitrogen-specific detector.
Methomyl (S-methyl(-N methyl carbamoxy thioacetimidate or (methylthio) acetyl
oxime) has been determined in chloroform extracts of soil in amounts down to
1 µg kg
−1 by gas chromatography-mass spectrometry [95].
High performance liquid chromatography
Several workers [96–99] have applied this technique to the determination of Aldicarl
and its metabolites [98] N-methylcarbamates [96] and Benfuracarb and Carbofuran
in soils.
Extraction from the soil by methylene chloride followed by clean-up on silica gel
is commonly used in these procedures.
Miscellaneous
Singhal et al [100, 101] have described a titrimetric method for the determination of
low levels of Oxamyl residues in soils. Their investigations revealed that after hydrolysis Oxamyl gave a brown precipitate with carbon disulphide and an alkaline solution of
copper (II) sulphate. This depicted below, reaction suggested a procedure for the determination of Oxamyl by titration with ethylene diamine tetracetic acid of the copper
remaining unreacted to the 1-(2 pyridylazo)-2-naphthol end-point indicator).
Cohen and Wheals et al [88] determined hydrolysable carbamate and substituted urea herbicides in soil in amounts down to 0.001–0.05 ppm. In this method,
a solution of the herbicide-containing extract of the soil is spotted onto a silica gel G
plate and developed with hexane: acetone (5:1). The plate is sprayed with 1-fluoro1,4-dinitrobenzene in acetone and heated to 190
◦ C to produce the 2,4-dinitrophenyl
derivative of the herbicide amine moiety. Acetone extract in the areas of interest on
the plate were subjected to gas chromatography,
on the 0.5% Carbowax 20M – 5% SE-30 column closely similar to that of the
methoxime derivative of Oxamyl. To check for possible interference in the analysis for Oxamyl from some of these other pesticides, 50 µg amounts each of the
Aldicarb [2-methyl-2-(methylthio) propionaldehyde O-(methylcarbamoyl) oxime] and
Thiofanox [3,3-dimethyl-1-(methylthio)-2-2 butanone O-(methylcarbamoyl) oxime],
and their sulphoxide and sulphone metabolites, were taken separately through the
procedure. No detectable peaks were observed, indicating that these potentially interfering compounds are not eluted in the Oxamyl-containing fraction taken from the
Florisil column.
Leppert et al [93] have described a procedure for the determination of
Carbosulphan and Carbofuran (2,3-dihydro 2,2-dimethylbenzofuran-7-y1-methyl carbamate) utilising gas chromatography with a nitrogen specific detector. Extraction was
carried out using hexan-2-propanol or a methanol buffer.
Bilikova and Kuthan et al [94] developed a gas chromatographic method for
the determination of submicrogram concentrations of Carbofuran (2,3-dihydro-2,
2-dimethylbenzofuran-7-y1-methyl carbamate) in soils. Soil samples are mixed with
methanol-water (80:20) and water samples are extracted with chloroform, After separation of the chloroform and weak alkaline hydrolysis, derivatisation is performed
with 1-fluoro-2,4-dinitrobenzene. The ester produced is isolated from the benzene and
cleaned up with acetone. The acetone extract is used to determine Carbofuran by gas
chromatography with a nitrogen-specific detector.
Methomyl (S-methyl(-N methyl carbamoxy thioacetimidate or (methylthio) acetyl
oxime) has been determined in chloroform extracts of soil in amounts down to
1 µg kg
−1 by gas chromatography-mass spectrometry [95].
High performance liquid chromatography
Several workers [96–99] have applied this technique to the determination of Aldicarl
and its metabolites [98] N-methylcarbamates [96] and Benfuracarb and Carbofuran
in soils.
Extraction from the soil by methylene chloride followed by clean-up on silica gel
is commonly used in these procedures.
Miscellaneous
Singhal et al [100, 101] have described a titrimetric method for the determination of
low levels of Oxamyl residues in soils. Their investigations revealed that after hydrolysis Oxamyl gave a brown precipitate with carbon disulphide and an alkaline solution of
copper (II) sulphate. This depicted below, reaction suggested a procedure for the determination of Oxamyl by titration with ethylene diamine tetracetic acid of the copper
remaining unreacted to the 1-(2 pyridylazo)-2-naphthol end-point indicator).
Cohen and Wheals et al [88] determined hydrolysable carbamate and substituted urea herbicides in soil in amounts down to 0.001–0.05 ppm. In this method,
a solution of the herbicide-containing extract of the soil is spotted onto a silica gel G
plate and developed with hexane: acetone (5:1). The plate is sprayed with 1-fluoro1,4-dinitrobenzene in acetone and heated to 190
◦ C to produce the 2,4-dinitrophenyl
derivative of the herbicide amine moiety. Acetone extract in the areas of interest on
the plate were subjected to gas chromatography,