Insecticides and herbicides in soils 75
in amounts down to 0.0001–0.05 1–50 µg kg
−1 . The methods are applicable to those
urea and carbamate herbicides that can be hydrolysed to yield an aromatic amine. A
solution of the herbicide is first spotted on to a silica gel G plate together with herbicide standards (5–10 µg) and developed with chloroform or hexane-acetone (5:1). The
plate containing the separated herbicide or the free amines is sprayed with 1-fluoro1,4-dinitrobenzene (4% in acetone) and heated at 190
◦ C for 40 minutes to produce
the 2,4-dinitrophenyl derivative of the herbicide amine moiety. Acetone extracts of
the areas of interest are subjected to gas chromatography on a column of 1% of
XE-60 and 0.1% of Epikote 1001 on Chromosorb G (AW-DCMS) (60–80 mesh)
at 215
◦ C.
Westlake et al [89] determined m-S-butylphenyl methyl-(phenylthio) carbamate
(RE 11775) in soil by a gas chromatographic procedure. The sample is extracted
with dichloromethane, chloroform or acetonitrile, followed by clean-up, if necessary,
on a column of Florisil, silica gel or alumina. The purified residue is submitted to
gas chromatography on either a stainless steel column (90 cm × 6 mm) packed with
5% OV-225 on Gas-Chrom Q (60–80 mesh) and operated at 242
◦ C with nitrogen
as carrier gas and a flame photometric detector operated in the S mode, or on a
glass column (90 cm × 6 mm o.d.) with identical packing and operated at 195
◦ C with
hydrogen as carrier gas (100 ml min
−1 ) and an electrolytic conductivity nitrogen detector. Recoveries of added RE 11775 from soil samples were about 100%. Down to
0.1 mg kg
−1 could be determined in soil.
Reeves and Woodham et al [90] have described a gas chromatographic method
for determination of Methomyl in soil. The residues were extracted from soil with
dichloromethane, and the extracts were purified on a column of Florisil. The purified and concentrated extracts were then analysed by gas chromatography on a glass
column (180 cm × 5 mm) packed with 10% DC-200 on Chromosorb WHP (80–100
mesh) and operated at 140
◦ C, with nitrogen as carrier gas (80 ml min
−1 ) and a 394 nm
S-interface filter. The limits of detection were 0.05 mg kg
−1 for soil; the recovery
was 90.8.
Soils treated with Carbamyl and Carbofuran have been analysed by gas chromatography following conversion of N-methyl carbamates to their pentafluorobenzyl
derivatives [91].
Bromilow et al [92] has described a gas chromatographic procedure for the determination of down to 10 µg kg
−1 of Oxamyl (S-methyl N-N’-thiooxamimidate) without
interference by Oxamyl oxime (S-methyl N-N’-dimethyl N-hydroxythiooxamimidate)
in soils.
Oxamyl is extracted from the soil with dichloromethane or acetonedichloromethane and is separated from interfering coextractives by chromatography of
the trimethylphenyl ammonium hydroxide derivative of Oxamyl on a Florisil column.
The recovery of Oxamyl from soil samples was checked by adding known volumes
of standard solutions of Oxamyl to the sample before extraction Mean recoveries
of Oxamyl from the samples fortified over the range 0.02–0.4 mg kg
−1 varied from
87–96%. The recovery of Oxamyl was similar at all of the fortification levels tested,
except that there was more variation at the very low levels.
Several other sulphur-containing carbamate insecticides/nematicides and their
oxidation products give peaks when injected into the gas chromatograph with
trimethylphenyl-ammonium hydroxide, some of these peaks having retention times
in amounts down to 0.0001–0.05 1–50 µg kg
−1 . The methods are applicable to those
urea and carbamate herbicides that can be hydrolysed to yield an aromatic amine. A
solution of the herbicide is first spotted on to a silica gel G plate together with herbicide standards (5–10 µg) and developed with chloroform or hexane-acetone (5:1). The
plate containing the separated herbicide or the free amines is sprayed with 1-fluoro1,4-dinitrobenzene (4% in acetone) and heated at 190
◦ C for 40 minutes to produce
the 2,4-dinitrophenyl derivative of the herbicide amine moiety. Acetone extracts of
the areas of interest are subjected to gas chromatography on a column of 1% of
XE-60 and 0.1% of Epikote 1001 on Chromosorb G (AW-DCMS) (60–80 mesh)
at 215
◦ C.
Westlake et al [89] determined m-S-butylphenyl methyl-(phenylthio) carbamate
(RE 11775) in soil by a gas chromatographic procedure. The sample is extracted
with dichloromethane, chloroform or acetonitrile, followed by clean-up, if necessary,
on a column of Florisil, silica gel or alumina. The purified residue is submitted to
gas chromatography on either a stainless steel column (90 cm × 6 mm) packed with
5% OV-225 on Gas-Chrom Q (60–80 mesh) and operated at 242
◦ C with nitrogen
as carrier gas and a flame photometric detector operated in the S mode, or on a
glass column (90 cm × 6 mm o.d.) with identical packing and operated at 195
◦ C with
hydrogen as carrier gas (100 ml min
−1 ) and an electrolytic conductivity nitrogen detector. Recoveries of added RE 11775 from soil samples were about 100%. Down to
0.1 mg kg
−1 could be determined in soil.
Reeves and Woodham et al [90] have described a gas chromatographic method
for determination of Methomyl in soil. The residues were extracted from soil with
dichloromethane, and the extracts were purified on a column of Florisil. The purified and concentrated extracts were then analysed by gas chromatography on a glass
column (180 cm × 5 mm) packed with 10% DC-200 on Chromosorb WHP (80–100
mesh) and operated at 140
◦ C, with nitrogen as carrier gas (80 ml min
−1 ) and a 394 nm
S-interface filter. The limits of detection were 0.05 mg kg
−1 for soil; the recovery
was 90.8.
Soils treated with Carbamyl and Carbofuran have been analysed by gas chromatography following conversion of N-methyl carbamates to their pentafluorobenzyl
derivatives [91].
Bromilow et al [92] has described a gas chromatographic procedure for the determination of down to 10 µg kg
−1 of Oxamyl (S-methyl N-N’-thiooxamimidate) without
interference by Oxamyl oxime (S-methyl N-N’-dimethyl N-hydroxythiooxamimidate)
in soils.
Oxamyl is extracted from the soil with dichloromethane or acetonedichloromethane and is separated from interfering coextractives by chromatography of
the trimethylphenyl ammonium hydroxide derivative of Oxamyl on a Florisil column.
The recovery of Oxamyl from soil samples was checked by adding known volumes
of standard solutions of Oxamyl to the sample before extraction Mean recoveries
of Oxamyl from the samples fortified over the range 0.02–0.4 mg kg
−1 varied from
87–96%. The recovery of Oxamyl was similar at all of the fortification levels tested,
except that there was more variation at the very low levels.
Several other sulphur-containing carbamate insecticides/nematicides and their
oxidation products give peaks when injected into the gas chromatograph with
trimethylphenyl-ammonium hydroxide, some of these peaks having retention times