78 Organic compounds in soils, sediments & sludges
urons can be hydrolysed to the corresponding substituted anilines; these compounds
are then determined by either gas chromatography directly [122] or as derivatives [123], or calorimetrically [124] after coupling with a suitable chromophore.
Methods based on hydrolysis lack specifically and involve lengthy procedures. These
disadvantages can be overcome by using liquid chromatography.
Miscellaneous urea herbicide(Chlorobromuron(3,4(bromo-3-chlorophenyl)-1methoxy-1-methylurea), Chlorotoluron (3(3 chlorotoluyl) dimethyl urea), Diuron
(N-(3,4 chlorophenyl) N,N dimethyl urea), Monolinuron (3(4,chlorophenyl-1methoxy- 1-methylurea), Linuron (3,(3,4 dichlorophenyl)-1-1-methoxy-1-methylurea)
Chloroxuron (3(3,4 dichlorophenyl-1-1 dimethylurea).
The above substituted urea herbicide residues have been determined using gasliquid chromatography by pyrolysis to the phenyl isocyanate in the injection heater
[118–125] with electron-capture detection. They have also been determined by highperformance liquid chromatography [126–128] and by gas chromatography using
a thermionic detector [129]. Lawrence and Laver et al [130] and Bûchert and
Lokke et al [131] have reported methods using gas chromatography determination
after alkylation. Bieser and Grolinmund et al [109] and Kahn et al [119] have
devised methods of measuring urea herbicides by gas chromatography without thermal
decomposition.
The gas chromatographic procedure described by Cohen and Wheals et al [88]
has been applied to the determination of various substituted urea herbicides in soil in
amounts down to 1–50 µg kg
−1 .
Caverley and Denney et al [132] applied gas chromatography to the determination of a range of substituted urea herbicides in soil. In this method acetone extraction
is followed by alkaline hydrolysis, steam distillation and concentration of anilines in
toluene, the last three steps being carried out in a single operation using a liquidliquid extractor. The anilines, after partition into hydrobromic acid, are brominated
and determined by gas chromatography with an electron-capture detector. The procedure is sufficiently sensitive for investigations into problems of crop damage and
can be applied to a wide variety of soil types. An additional deoxidisation step to
remove interference due to the presence of aniline metabolites is also described. The
limit of detection is 0.11 mg kg
−1 and recoveries at residual levels are generally better
than 80%.
Figure 3.4 shows the separation of 0.5 ng amounts of four derivatised herbicides.
A, Monolinuron; B, Fenuron: C, Linuron; and D, Chlorobromuron.
The inclusion of the deoxidisation step effectively removes the anilines without
degrading the parent herbicides. When this additional step was applied to soils from
fields treated with these herbicides, only small differences were found with the results
obtained when it was omitted. Large differences might be expected in situations that
favour reductive anaerobic conditions.
High performance liquid chromatography
Various workers have used this technique for the determination of urea-type herbicides
in soil [135–140] including Linuron and its metabolites [135] iso Proturon, Dichlorprop [137] Hexaflumuron [136], Diuron, Monuron, Chlorotoluron [134–138] and
Diuron [141].
urons can be hydrolysed to the corresponding substituted anilines; these compounds
are then determined by either gas chromatography directly [122] or as derivatives [123], or calorimetrically [124] after coupling with a suitable chromophore.
Methods based on hydrolysis lack specifically and involve lengthy procedures. These
disadvantages can be overcome by using liquid chromatography.
Miscellaneous urea herbicide(Chlorobromuron(3,4(bromo-3-chlorophenyl)-1methoxy-1-methylurea), Chlorotoluron (3(3 chlorotoluyl) dimethyl urea), Diuron
(N-(3,4 chlorophenyl) N,N dimethyl urea), Monolinuron (3(4,chlorophenyl-1methoxy- 1-methylurea), Linuron (3,(3,4 dichlorophenyl)-1-1-methoxy-1-methylurea)
Chloroxuron (3(3,4 dichlorophenyl-1-1 dimethylurea).
The above substituted urea herbicide residues have been determined using gasliquid chromatography by pyrolysis to the phenyl isocyanate in the injection heater
[118–125] with electron-capture detection. They have also been determined by highperformance liquid chromatography [126–128] and by gas chromatography using
a thermionic detector [129]. Lawrence and Laver et al [130] and Bûchert and
Lokke et al [131] have reported methods using gas chromatography determination
after alkylation. Bieser and Grolinmund et al [109] and Kahn et al [119] have
devised methods of measuring urea herbicides by gas chromatography without thermal
decomposition.
The gas chromatographic procedure described by Cohen and Wheals et al [88]
has been applied to the determination of various substituted urea herbicides in soil in
amounts down to 1–50 µg kg
−1 .
Caverley and Denney et al [132] applied gas chromatography to the determination of a range of substituted urea herbicides in soil. In this method acetone extraction
is followed by alkaline hydrolysis, steam distillation and concentration of anilines in
toluene, the last three steps being carried out in a single operation using a liquidliquid extractor. The anilines, after partition into hydrobromic acid, are brominated
and determined by gas chromatography with an electron-capture detector. The procedure is sufficiently sensitive for investigations into problems of crop damage and
can be applied to a wide variety of soil types. An additional deoxidisation step to
remove interference due to the presence of aniline metabolites is also described. The
limit of detection is 0.11 mg kg
−1 and recoveries at residual levels are generally better
than 80%.
Figure 3.4 shows the separation of 0.5 ng amounts of four derivatised herbicides.
A, Monolinuron; B, Fenuron: C, Linuron; and D, Chlorobromuron.
The inclusion of the deoxidisation step effectively removes the anilines without
degrading the parent herbicides. When this additional step was applied to soils from
fields treated with these herbicides, only small differences were found with the results
obtained when it was omitted. Large differences might be expected in situations that
favour reductive anaerobic conditions.
High performance liquid chromatography
Various workers have used this technique for the determination of urea-type herbicides
in soil [135–140] including Linuron and its metabolites [135] iso Proturon, Dichlorprop [137] Hexaflumuron [136], Diuron, Monuron, Chlorotoluron [134–138] and
Diuron [141].