Fenoprop

9.9.1 Natural waters 9.9.1.1 Gas chromatography

Devine et al. [385] adjust the water sample (1L) to pH2 with hydrochloric acid and extract it with benzene (100, 50 and 50mL). The extract is dried over sodium sulphate, concentrated to 0.1mL and methylated by the addition of diazomethane in ethyl ether (1mL). After 10min, the volume is reduced to about 0.1mL, acetone is added and an aliquot is analysed by gas chromatography on one of three columns: (1) 5% SE-30 on 60-80 mesh Chromosorb W at 175°C, (2) 2% QF-1 on 90-100 mesh Anakron ABS at 175°C or (3) 20% Carbowax 20M on 60-80 mesh Chromosorb W at 220°C. In each instance nitrogen is the carrier gas and detection is by electron capture. The minimum detectable amount of pesticide in water was 2 parts per 109 for MCPA (4-chloro-2-methyl-phenoxyacetic acid) and 0.010.05 parts per 109 for 2,4-D (2,4-dichloro-phenoxyacetic acid) and its esters, 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), Dicamba, Trifluralin (2-methoxy-3,6-dichlorobenzoic acid), and Fenoprop. Recoveries were 5060% for MCPA and Dicamba and 80-95% for the other compounds.

Croll [33] has given details of the use of back-flushing with electron-capture gas chromatography for the determination of phenoxyacetic acid type herbicides in water. Attention is paid to equalization of column resistance under operating and back-flushing conditions; base-line drift is thereby minimized. The system has been successfully used (with a variety of stationary phases, temperature ranging from 25 to 225°C and nitrogen flow rates from 25 to 200mL min-1.

Colas et al. [386] have described methods for the separation and determination of down to about 1ppm of phenoxyalkanoic herbicides. Those present as salts or esters are hydrolysed by heating the water sample (1L) under reflux with sodium hydroxide for about 1h and the free acids are then extracted at pH2 with chloroform or dichloromethane (recoveries usually about 70%). After evaporation of the solution to dryness, the residual free acids are dissolved in acetone and treated with diazomethane and the methyl esters are analysed on a temperature-programmed column (1.5m x 6mm) containing 5% silicone D0W710 on Chromosorb W AW (45-60 mesh). Helium is used as carrier gas. For some separations other stationary phases are used. Typical results are presented for MCPA, MCPP and 2,4-D. Possible interference from phenols, chlorinated biphenyls and surfactants is discussed.

Larose and Chau [387] state that owing to the similar retention times of several common phenoxyacetic acid type herbicides, the alkyl esters are subject to incorrect identification if several herbicides are present. Also, the sensitivity obtainable by means of electron-capture detection of the alkyl esters by some herbicides, such as MCPA and MCPB is very poor and therefore the method is generally not suitable for the determination of these compounds in water. In addition, the methyl ester of MCPA has a very short retention time close to the solvent front and is prone to interference from sample coextractives, which usually appear in this region. In fact the MCPA methyl ester often cannot be detected even at higher levels because of overlapping with coextraction peaks when the same gas chromatographic parameters as for the determination of organochlorine pesticides are used. Hence other derivatives have been considered.

Carnac [388] studied a modified technique of dynamic distribution in liquid-liquid systems used for concentration of traces of organic substances in water. An organic solvent is placed on granules of copolymer of styrene and divinylbenzene. The technique has been used for determination of phenoxyalkanecarboxylic acids by gas-liquid chromatography with a flame ionization detector using chloroform as the solvent; the limit of detection is 5-10^g L-1.

Chau and Terry [389, 390] have discussed the disadvantages of the gas chromatography of methyl esters produced by reaction with diazomethane and have developed the reaction conditions for forming 2-chloroethyl and pentafluorobenzyl esters of phenoxyacetic acids.

Agemian and Chau [391] have reported a method for determining low levels of 4-chloro-2-methylphenoxyacetic acid and 4-(4-chloro-2-methylphenoxy)-butyric acid in waste waters by derivatization with pentafluorobenzyl bromide. The increased sensitivity of the pentafluorobenzyl esters of these two herbicides over the 2-chloroethyl and methyl esters as well as their longer retention times make pentafluorobenzyl bromide the preferred reagent.

These workers [391] used a gas-liquid chromatograph equipped with a nickel detector, a 6ft x 1/4in i.d. (1.8m x 6mm) coiled glass column and an automatic sampler connected to a computing integrator for data processing. The column used was 3.5% w/w OV-101 and 5.5% w/w OV-210 on 80-100 mesh Chromosorb W, acid washed and treated with dimethylchlorosilane. The operating conditions were as follows: injector temperature 220°C, column temperature 220°C, detector temperature 300°C, carrier gas argon-methane (9:1) at a flow rate of 60mL min-1. Agemian and Chau [391] found that the few organochlorine pesticides that are eluted in the same fraction as the pentafluorobenzyl derivatives of the phenoxyacetic acid herbicides do not interfere because they have distinct retention times. Organophosphorus pesticides do not interfere. Twenty-four of the most widely used phenols either are eluted with the PCBs and organochlorine pesticides or have distinct retention times from those of the pentafluorobenzyl esters of the two herbicides. The whole of the above procedure, at a level of 0.5^g L-1 MCPA in 1L of distilled water, gave an average recovery of 75-80% with a coefficient of variation between 9 and 15%.

Agemian and Chau [392] using the above method compared the penta-fluorobenzyl bromide reagent for forming esters and the boron trichlor-ide-2-chloroethanol and dicyclohexylcarbondiimide-2-chloroethanol reagents for forming 2-chloroethyl esters of phenoxyacetic acid type herbicides, coupled with a complete solvent extraction system to obtain multiresidue methods for determining these compounds in natural waters at sub-microgram per litre levels.

The nine herbicides studied by these workers were Dicamba, MCPA, MCPB, 2,4-DB, Picloram (4-amino-3,5,6-trichloropicolinic acid), 2,4-D, 2,4,5-T, Silvex and 2,4-DP.

Lopez-Avila et al. [393] used isotope dilution gas chromatography-mass spectrometry to determine Dicamba and 2,4-D in natural waters, at the low microgram per litre level. Stable labelled isotopes are spiked into the sample before extraction and the ratio of unlabelled isotope was used to quantitate the unlabelled compounds. Average recoveries exceeded 84% and the relative standard deviation was better than 19%.

Triclophon (3,5,6-trichloro-2-pyridyloxyacetic acid) has been determined [394] in river waters in amounts down to 5ng L-1 by an acid-catalyst esterification reaction of the herbicide with boron trifluoride-trifluoroethanol. Triclophon was first extracted from acidified river waters with diethyl ether and the resulting concentrate esterified under nitrogen at 80°C for 1h. The trifluoroethyl ester product was cleaned up by silica gel column chromatography and determined by gas chromatography with electron-capture detection. Recoveries from actual river waters were 90-93% with coefficients of variation of less than 4%. With only slight modifications at the clean-up stage, the proposed method was useful for the simultaneous determination of MCPA, 2,4-D and 2.4.5-T.

9.9.1.2 Thin-layer chromatography

Bogacka and Taylor [395] determined 2,4-D and MCPA herbicides in water using thin-layer chromatography. In this method a 1L sample of filtered water is treated with 50g of sodium chloride and 5mL of hydrochloric acid and the herbicides are extracted into ethyl ether (200, 100 and 100mL). The extract is dried with anhydrous sodium sulphate, concentrated to a few millilitres and passed through a column (180mm x 15mm) of silica acid with 90% methanol-acetic acid (9:1) as stationary phase and the herbicides are eluted with 150mL of light petroleum saturated with the methanol-acetic acid mixture. The first 30mL of eluate is rejected. The remaining eluate is evaporated to dryness, and the residue is dissolved in ether and concentrated to about 0.1mL before thin-layer chromatography on silica gel G-Keiselgel G (2:3) (activated for 30min at 120°C) with light petroleum-acetic acid- liquid paraffin (10:1:2) as solvent. The developed plates are air dried, sprayed with 5% silver nitrate solution and dried, then sprayed with 2M potassium hydroxide-formaldehyde (1:1), dried at 130-135°C for 30min, sprayed with nitric acid, and observed in UV illumination. For the determination the spots are compared with standards. Evaluation by the method of standard addition gave recoveries of 95.1% and 88.8% respectively with standard deviations of 14.2% and 14.3% for 2,4-D and MCPA respectively.

These workers [396] also examined thin-layer chromatography of 2,4-DP (Dichlorprop) and MCPP (mixture of Mecoprop and 2-(2-chloro-4-methylphenoxy)propionic acid). In this method the ethyl ether extract of the sample is purified on a column of silicic acid and the herbicides are separated by thin-layer chromatography on silica gel- Kieselgel (2:3) with light petroleum-acetic acid-kerosene (10:1:2) as solvent. The sensitivity is 3^g of either compound per litre, the average recoveries of Dichlorprop and MCPP are 85.7% and 87.4%, respectively, and the corresponding standard deviations were 13.9% and 15.5%.

Meinard [397] described a new chromogenic reagent for the detection of phenoxyacetic acid herbicides on thin-layer plates. The separated phenoxyacetic acids are detected (as violet spots on white background) by spraying the plate with a solution of chromotropic acid ((4g) in water (40g) and sulphuric acid (56g)) then heating at 160°C. The limits of detection for 2,4-D, 2,4,5-T and MCPA range from 0.05 to 0.2^g by spraying with silver nitrate reagent followed by exposure to UV radiation.

9.9.1.3 Paper electrophoresis

Purkayastha [398] examined the applicability of paper electrophoresis to nine ionizable chlorinated phenoxyacetic acid type herbicides including

2,4-D, 2,4,5-T, MCPA, Fenoprop, Dicamba, Trifluralin (2-methoxy-3,6-dichlorobenzic acid), and Picloram (4-amino-3,5,6-trichloropicolinic acid). Solutions were applied to paper moistened with pyridine-acetic acid buffer solution, pH3.7, 4.4, or 6.5, and a voltage of 2-4kV was applied. After 30min the paper was air-dried, sprayed with ammoniacal silver nitrate solution, and exposed to UV radiation. Experimental variation that increased the mobility of the spots included the applied voltage from 2 to 4kV (potential gradients of 50-100V cm-1), and adding a foreign electrolyte (e.g. potassium nitrate) to the buffer. Addition of methanol to the buffer resulted in decreased mobility as well as a variation in the relative mobilities of the compounds.

9.9.1.4 High-performance liquid chromatography

Arjmand et al. [399] determined Dicamba using solid-phase extraction and ion-pair high-performance liquid chromatography. The detection limit was 1.6^g L-1.

9.9.1.5 Miscellaneous

Marshall [400] used two methods for the infrared analysis of Dicamb-MCPA and Dicamba-2,4-D formulations. The 'indirect' method involved precipitation of the herbicides with hydrochloric acid and extraction with chloroform. The chloroform extract was evaporated to dryness, the residue was dissolved in acetone and the herbicides were determined by measuring infrared extinctions at the relevant wave-lengths. The 'direct' method involved dissolving the sample in acetone and measuring infrared extinctions. Although both methods gave good precision, the 'indirect' method was the more accurate.

Bogacka [401] used 4-aminophenazone as a reagent for the spectrophotometric determination of phenoxyacetic acid herbicides (2,4-D, Dichlorprop, MCPA) in water. The herbicides are extracted from an acidified 1L sample of water with ethyl ether. The extract is evaporated and the residue is eluted for 1h with 10g of pyridine hydrochloride at 207-210°C for 2,4-D, or at 225-230°C for Dichlorprop or MCPA. The resulting phenol derivative is steam distilled into aqueous ammonia (1M) extracted with light petroleum (after acidification of the distillate) and re-extracted into 0.05M aqueous ammonia for coupling with 4-aminophenazone in the presence of potassium ferricyanide. The extinction of this solution is measured at 515, 505 or 515nm, for 2,4-D, Dichlorprop or MCPA respectively. The respective sensitivities are 20, 20 and 80^g L-1 of water and the corresponding standard deviations of the recovery are 4.0%, 8.5% and 3.5%, The method is not suitable for the determination of mixed herbicides.

Liquid—liquid extraction

Suffet [402] has evaluated liquid-liquid extraction techniques for separating phenoxyacetic acid herbicides from river water. He used the p-value (defined as the fraction of the total solute that distributes itself in the non-polar phase of an equivolume solvent pair) concept in the development of equations, based on liquid-liquid extraction theory, relating the number of extractions and the water-to solvent ratios for the maximum recovery of the herbicide. Calculations show that a pesticide with a p-value of 0.90 or greater in an aqueous system can be 95% extracted from the aqueous phase by up to five extractions with a total volume of solvent up to 500mL. He confirmed his equations by measurements with 2,4-D. By the application of this concept to the simultaneous quantitative extraction of phenoxyacetic acid herbicides from water, Suffet [403] showed that the best solvents for 2,4-D and 2,4,5-T and their butyl and isopropyl esters are ethyl ether or ethyl acetate (2,4-D and esters) and benzene (2,4,5-T and esters). Thus a 90% recovery of 2,4-D from 1L of an aqueous solution is obtained by a two-stage serial extraction with 200 and 50mL of ethyl acetate under p-value conditions. Turbid samples should be filtered before extraction.

The most commonly used solvents for extracting phenoxyalkanoic acids have been ethyl ether [404-407] and chloroform, although benzene has also been used [400, 408]. Benzene is highly toxic, and has a high boiling point and relatively low dielectric constant compared with the above solvents. This solvent gave consistently low extraction efficiencies for 2,4-D and Dicamba. This supports Suffet's [403] p-value for 2,4-D of 0.195 for benzene compared with 0.996 and 0.990 for ethyl acetate and ethyl ether, respectively. Chloroform is also unsuitable because it is more toxic and has a lower dielectric constant than the other three solvents and its vapours cause anomalous responses when it is used near a gas chromatograph with an electron-capture detector.

Derivatization—gas chromatography

Chemical derivatization of phenoxyalkanoic acid herbicides has been used as a means for forming less polar and more volatile compounds for the gas-liquid chromatographic analysis. Alkyl esters [409-416] have been used extensively for this purpose. Examples of earlier work utilizing diazomethane for the formation of methylesters of phenoxyalkanoic acid herbicides are discussed by Devine et al. [385] and Colas et al. [386].

The conditions for the preparation of nitration, bromination and silylation using ^O-Ws-trimethylsilylacetamide and 2-chloroethylation derivatives, and 1-bromomethyl-2,3,4,5,6-pentafluorobenzene derivatives of 2,4-D and other herbicidal acids prior to gas chromatographic analysis, have been studied [389, 417].

9.9.2 Waste waters

9.9.2.1 Gas chromatography

Hill et al. [418] developed a multiresidue gas chromatographic method for the analysis of chlorophenoxy herbicides in waste waters and waste water sludges. The method, however, can only determine the acid form of chlorophenoxy herbicides. It was applicable to six herbicides, including 4-chorophenoxyacetic acid, 4-chloro-2-methylphenoxyacetic acid, 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-TP (2,4,5-trichlorophen-oxypropionic acid). The limit of detection of the chlorophenoxy herbicide was 5.0^g L-1 in an 11mL sewage sample for all the herbicides, except 2,4-dichlorophenoxybutyric acid.

9.10 Miscellaneous herbicides

9.10.1 Natural waters

Dichlorbenil (2,6-dichlorobenzonitrile)

The persistence of this herbicide in a farm pond has been studied [419]. Dicamba (2-methoxy-3, 6-dichlorobenzoic acid)

This herbicide is discussed in methods for its codetermination with phenoxyacetic acid herbicides. Norris and Montgomery [420] have described a procedure for the determination of traces of Dicamba and 2,4-D in streams after forest spraying. Dicamba and its metabolites (3,6-dichlorosalicylic acid and 5-hydroxydicamba) were determined gas chromatographically. For analysis a 500mL aliquot of stream water was acidified to pH1 with hydrochloric acid and extracted with three 150mL portions of diethyl ether. Ether extracts were concentrated to 20mL and methylated with diazomethane in ether. The ether extracts were then concentrated to 1mL and injected into a gas chromatograph equipped with a microcoulometric detector. The 1.8m x 6.25mm glass column was packed with 60-80 mesh Gas-Chrom Q coated with 6% OV-1. The retention time of Dicamba was 2.6min. Methylation converts 3,6-dichlorosalicylic acid metabolite to Dicamba and the 5-hydroxy-dicamba metabolite which has a retention time of 6.6min.

Picloram (4-amino-3,5,6-trichloropicolinic acid)

Abbott et al. [421] described a pyrolysis unit for the determination of Picloram and other herbicides in water. The determination is effected by electron-capture-gas chromatography following thermal decarboxylation of the herbicide. Hall et al. [422] reported further on this method. The decarboxylation products are analysed on a column (5mm i.d.) the first 6in (15cm) of which is packed with Vycor chips (2-4mm), the next 3.5ft (107cm) with 3% of SE-30 on Chromosorb W (60-80 mesh) and then 2ft (60cm) with 10% of DC-200 on Gas Chrom Q (60-80 mesh). The pyrolysis tube, which is packed with Vycor chips, is maintained at 385°C. The column is operated at 165°C with nitrogen as carrier gas (110mL min-1). The method when applied to ethyl ether extracts of water and soil gives recoveries of 93 ± 4 and 90 ± 5% respectively. Dennis et al. [423] have reported on the accumulation and persistence of Picloram in surface waters and bottom deposits.

Pyrazon (5-amino-4-chloro-2-phenyl-3-pyridizone)

This pre- and post-emergent herbicide has been determined in water by spectrophotometric, thin-layer chromatographic methods [424-427] and by high-performance liquid chromatography [428]. The highperformance liquid chromatographic method is described below as it illustrates very well the applicability of this technique to trace organics and analysis in water.

Pyrazon was isolated from water samples (500mL) by rotary evaporation to dryness in vacuo, extraction of the solid residue with methanol (2 x 25mL) and further evaporation of the methanol extract (to approx. 2mL). Final concentration (to 0.5mL) was achieved by removal under a stream of nitrogen.

The equipment used consisted of two Model 6000A solvent delivery systems and a Model 660 gradient former (Waters Associates) and a Model CE212 variable wavelength UV monitor (Cecil Instruments) operated at 270nm. Syringe injections were made through a stop-flow septumless injection port. The column (15cm x 7mm i.d.) was packed in an upward manner with Spherisorb-ODS by a slurry procedure using acetone as slurry medium. A linear gradient was established from two solvent mixtures consisting of (a) 10% methanol in 1% acetic acid in water and (b) 80% methanol in 0.1% acetic acid in water. The initial concentration was 35% (b) in (a) and the final concentration was 100% (b) with the gradient terminated after 20min. The flow rate was maintained at 2.0mL min-1 throughout the analysis.

-1.1 -0.9 -0.7 -0,5 -0.3 Potential ot D.M.E. versus S.C.E ( V }

-1.1 -0.9 -0.7 -0,5 -0.3 Potential ot D.M.E. versus S.C.E ( V }

Fig. 9.17 Current—potential graphs for Glyphosate nitrosamine after anionexchange treatment and nitrosation of various amounts of Glyphosate added to 1L of tap water. A, 0 (reagent blank); B, 35; C, 70; D, 140; E, 210Dg added. (Reprinted with permission from Bronstad et al. [255]. Copyright (1976) Royal Society of Chemistry.)

Crathorne and Watts [428] determined the recovery efficiencies of Pyrazon from water by analysing samples of river water spiked at levels of 10, 50, 100 and 200^g L-1.

Glyphosate (N-phosphonomethylglycine)

This herbicide is manufactured by Monsanto, and marketed under the name Round-up. Brastad et al. [255] have described a polarographic method for determining Glyphosate residues in natural waters based on the polarography of N-nitroso derivative.

The Glyphosate nitrosamine has a single well-defined, differential pulse wave with a peak potential of -0.78V. Figure 9.17 shows a typical polarogram for single samples of tap water carried through the entire procedure after fortification at various levels. A Glyphosate concentration of 70^g L-1 gives a distinct Glyphosate nitrosamine wave.

4-(chloromethylsulphenyl)bromobenzene

Shiraishi and Otsuki [429] identified and determined 4-(chloromethyl-sulphenyl)bromobenzene herbicide in lake water using a combination of gas chromatography and mass spectrometry.

Paraquat (1,1'-dimethyl-4,4-bipyridium chloride and Diquat (1,1 '-ethylene-2,2-bipyridylium bromide)

Calderbank and Youens [430] and Pope and Benner [431] have described a spectrophotometric method for the detemination of Paraquat in water in amounts down to 0.1ppm. Paraquat, Trifluralin and Diphenamid have also been determined gas chromatographically in water [432, 433].

Soderquist and Crosby [432] added to the water sample (100mL), sulphuric acid (3mL) and platinum dioxide (25mg) and hydrogen was bubbled through for 1h, whereby Paraquat is converted into 1,1'-dimethyl-4,4'-bipiperidyl. This is extracted with dichloromethane (3 x 50mL) in the presence of 11mL of 50% sodium hydroxide solution and the combined extract is treated with 0.01N hydrochloric acid (4mL) and evaporated in a rotary evaporator at 50-55°C. The aqueous residue is transferred with 1mL of 0.01N hydrochloric acid to a 15mL screw-cap tube and shaken with 50% sodium hydroxide solution (0.5mL) and carbon disulphide (1mL). Aliquots of the carbon disulphide phase (1-10^l) are injected on to a glass column (66ft x 0.125in (20m x 3mm)) packed with 10% Triton X-100 and 1% potassium hydroxide on AW-DCMS Chromosorb G (70-80 mesh), and operated at 150°C with nitrogen as the carrier gas (30-40mL min-1) and flame ionization detection. The calibration graph is rectilinear for up to 1ppm of Paraquat. The limit of detection is 0.1ppm but recovery is only 36-43%, although reproducible.

To determine Paraquat in agricultural run-off water Payne [434] separated the sediment from the sample (2L) by adding calcium chloride to aid flocculation, leaving the mixture overnight in a refrigerator for the sediment to settle. A 1L aliquot of the filtrate is extracted with dichloromethane. The dichloromethane extracts are concentrated by evaporation and the Trifluralin and Diphenamid are determined by direct injection, without further purification on to a glass column 6ft x 0.25in o.d. (1.8m x 6mm)) packed with 10% DC 200 on Gas Chrom Q and operated at 220°C with helium as carrier gas (100mL min-1) and a Coulson electrolytic-conductivity detector (N mode). Paraquat is determined in the filtrate by a modification of a conventional colorimetric method. Recoveries of the three substances were between 82 and 95% from water.

Cannard and Criddle [433] have described a rapid pyrolysis-gas chromatography method for the simultaneous determination of Paraquat and Diquat in pond and river waters in amounts down to 0.001ppm. These workers emphasize the precautions necessary to avoid errors due to adsorption of the herbicides on to glassware.

Although other reactions occur that give smaller fragments, it will be apparent that the pyrolysis of both compounds produces few products with relative molecular masses comparable to those of the free bases, a feature which renders the method particularly suitable for both quantitative and qualitative analysis. However, for best results the procedure must be strictly adhered to.

The detection limits for the method applied to river waters are governed by two main factors: the size of sample that can conveniently be introduced into the pyrolysis tube and the ability of the column to resolve the bipyridyl peaks from those due to other pyrolysis products.

The most complex pattern obtained shows that no interference with Paraquat will occur, and that only slight interference with Diquat is likely. However a small Diquat pyrolysis peak can interfere to a slight extent with the 4,4'-bipyridyl peak derived from Paraquat but the value for Paraquat may be simply corrected when appropriate, as the size of the interfering peak is proportional to the size of the 2,2'-bipyridyl peak derived from Diquat.

Coha [435] used the ring oven technique to estimate traces of Paraquat and Diquat in water. Morfamquat and Diquat have been determined by reduction at the dropping mercury electrode [436].

Zen et al. [485] used square-wave polarography at a perfluorinated ionomer-clay-modified electrode (MCME) to determine down to 0.5ppb of Paraquat in natural waters. The clay that showed the best performance for the fabrication of the electrode is nontronite (Swa-1, ferruginous smectite). The elctrochemical behaviour of Paraquat showed that the cathodic peak at -0.70V versus Ag/AgCl permits adequate quantification of the analyte. Linear calibration curves are obtained over the 0-80ppb range, with a detection limit of 0.5ppb in pH8 phosphate buffer solution for 4min preconcentration time.

Thiabendazole

Capitan et al. [437] determined down to 0.1mg L-1 Thiabendazole residues in natural waters using solid-phase spectrofluorometry. Other fluorescent insecticides or herbicides did not interfere in this procedure.

9.10.2 Sea water

Thiabendazole

The solid-phase spectrofluorometric procedure [437] discussed in Section 9.10.1 has been applied to the determination of thiabendazole in sea water.

9.10.3 Potable waters

Glyphosate

The polarographic method [255] described in Section 9.10.1 has been applied to the determination of Glyphosate in potable waters.

Paraquat and Diquat

In a method [438] for the preconcentration of Paraquat and Diquat from potable water the sample is passed through an ion-exchange column, followed by desorption, reduction with sodium dithionite and measurement of the reduced forms at 390nm for Paraquat and 379nm for Diquat.

Carpenter et al. [486] have described a method for the assay of two metabolites of the herbicides dimethyl tetrachloroterephthalate, monomethyl tetrachloroterephthalate and tetrachloroterephthalic acid via high-performance liquid chromatography with ion pairing. Samples are analysed via direct injection, without preparation, and analyte detection is accomplished with an ultraviolet photodiode array detector. The metabolites are extracted from positive samples with a petroleum ether-diethyl ether mixture, derivatized with N,O-bis-(trimethylsilyl)trifluoroacetamide, and confirmed by gas chromatography-mass spectrometry. The high-performance liquid chromatographic analysis of spiked drinking water samples yielded a recovery range of 92-106% with a mean recovery of 101% for tetrachloroterephthalic acid and a recovery range of 92-101% with a mean recovery of 96% for monomethyl tetrachloroterephthalate. The minimum detection limits for these two metabolites were 2.4 and 2.7^g L-1, respectively. In addition the gas chromatography-mass spectrometry analysis of spiked reagent water yielded mean recoveries of 91% for monomethyl tetra-chloroterephthalate and 86% for tetrachloroterephthalic acid. Twenty drinking water samples were split and analysed by the high-performance liquid chromatographic and the gas chromatographic-mass spectrometric methods and by US EPA method 515.1. Comparable results were obtained. The high-performance liquid chromatographic method, which is amenable to automation, typically allows for the analysis of up to 40 samples overnight.

9.10.4 Waste waters

Thiabendazole

The solid-phase spectrofluorometric method [437] described in Section 9.10.1 for the determination of Thiabendazole has been applied to waste waters.

9.11 Growth regulators

9.11.1 Natural waters

9.11.1.1 Gas chromatography

Dalapon (2,2-dichloropropionic acid)

Earlier gas chromatographic methods for determining this growth regulator include those of Getzendaner [439] and Frank and Demint [440].

The method of Getzendaner [439] is applicable to plant tissues and body fluid and doubtless to water samples. The sample was extracted with ethyl ether and the residue was analysed by gas chromatography on a glass column (4ft (1.2m) x 2mm) of 4% LAC-2R plus 0.5% of phosphoric acid on Gas Chrom S (60-80 mesh) at 100°C with nitrogen as carrier gas (85mL min-1) and electron capture detection. Recoveries of about 90% were obtained for 10ppm of the herbicide.

The Frank and Demint [440] method is directly applicable to water samples. After addition of solid sodium chloride (340g L-1) and aqueous hydrochloric acid (1:1) to bring the pH to 1, the sample was extracted with ethyl ether and the organic layer was then extracted with 0.1M sodium bicarbonate (saturated with sodium chloride and adjusted with sodium hydroxide to pH8). The aqueous solution adjusted to pH1 with hydrochloric acid was extracted with ether and after evaporation of the ether to a small volume, Dalapon was esterified at room temperature by addition of diazomethane (0.5% solution in ether) and then applied to a stainless steel column (5ft x 0.125in (1.5m x 3mm)) packed with

Chromosorb P (60-80 mesh) pretreated with hexamethyldisilazane and then coated with 10% FFAP. The column was operated at 140°C, with nitrogen carrier gas (30mL min-1) and electron-capture detection. The recovery of Dalapon ranged from 91 to 100%; the limit of detection was 0.1ng. Herbicides of the phenoxyacetic acid type did not interfere; trichloroacetic acid could be determined simultaneously with Dalapon.

In a more recently published method (Van der Poll and de Vos [441]) for the determination of Dalapon in natural water and plant tissues the herbicide is first esterified with 3-phenolpropanol-1 then determined by electron-capture-gas chromatography. As little as 0.001mg Dalapon per litre of water can be determined by this method. These workers used a gas chromatograph with two 63Ni electron-capture detectors. The detectors were operated in the pulse mode at 50V. Two columns, both glass, were used to determine the ester. Column A was packed with 3% OV-1 and 2.7% 0V-210 on Gas Chrom Q (80-100 mesh), column B with 1.8% OV-1 and 2.7% 0V-210 on Gas Chrom Q (80-100 mesh). The carrier gas was nitrogen, flow rate 70mL min-1 on both columns. The temperatures of the column oven, injectors and detectors were 160, 205 and 275°C respectively. Recoveries of between 94 and 103% were obtained. The response of the detector was linear up to nanogram amounts of the 3-phenylpropyl ester of Dalapon injected. As little as 0.001mg Dalapon per litre natural water can be determined by this method.

9.11.1.2 Capillary isotachophoresis

Stransky [442] investigated the possibility of determining the growth regulator Chloromequat, the quaternary cationic herbicides Diquat and Paraquat, and the triazine herbicides Atrazine, Simazine, Atraton, Prometryne, Demetryne and Methoprotryne in water extracts by capillary isotachophoresis. The more basic triazines could be determined directly using enforced isotachophoresis but very weak triazine bases had to be derivatized by nucleophilic substitution of chlorine by electron-donor or quaternary ammonium groups. Triazines could be quantitatively determined from a threshold value of about 15^g L-1.

9.12 Mixtures of pesticides and herbicides

9.12.1 Natural waters

9.12.1.1 Gas chromatography

Cohen and Wheals [443] used a gas chromatograph equipped with an electron-capture detector to determine 10 substituted urea and carbamate herbicides in river water, soil and plant materials in amounts down to 0.001-0.05ppm. 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^g) and developed with chloroform or hexane-acetone (5:1). The plate containing the separated herbicide or the free amines is sprayed with 1-fluoro-1,4-dinitrobenzene (4% in acetone) and heated at 190°C for 40min 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 (AE-DCMS) (60-80 mesh) at 215°C

Erney [73] had described a photochemistry technique using ultraviolet irradiation followed by gas chromatography to confirm the identity of organochlorine insecticides and some herbicides.

Kongovi and Grochowski [444] discussed the problems arising during the analysis of pesticides and herbicides by gas chromatography and electron-capture detection. During a routine run of pesticide standards (Lindane, Endrin and Methoxychlor) five peaks were obtained, and this led to a study of the Endrin molecule contaminants, and more specifically, to the decomposition of the Endrin molecule in relation to temperature (220-235°C) and nitrogen flow rate. Conclusions were eventually reached that the retention periods of compounds generally provide good criteria for identification, but that this was not always the case, particularly with esters of low-molecular-weight acids. Also the retention period alone does not serve as an absolute identifying criterion; other confirmation, e.g. mass spectroscopy, is required.

Lee et al. [445] developed a multiresidue method with a low detection limit for 10 commonly used acid herbicides in natural waters. These herbicides were Dicamba, MCPA, 2,4-DP, 2,3,6-TBA, 2,4-D, Silvex, 2,4,5-T, MCPB, 2,4,5-DB and Picloram. The method used solvent extraction and the formation of pentafluorobenzyl esters. The derivatives were quantified by capillary column gas chromatography with electron-capture detection. The detection limit was 0.05^g L-1. Recoveries of herbicides from spiked Ontario lake water (0.5-1.0^g L-1) were 73-108% except for Picloram recovery which was 59% at 0.1^g L-1.

Ishibashi and Suzuki [446] simultaneously determined Chlormethoxynil, Bifenox and Butachlor in river water by XAD-2 resin extraction and high-resolution electron-capture gas chromatography.

9.12.1.2 Gas chromatography-mass spectrometry

Yamato et al. [447, 448] have described a combination of gas chromatography with field desorption mass spectrometric analysis applied to Benzthiocarb (S-(4-chlorobenzyl-N,N-diethylthiolcarbamate),

Oxidiazon (2-t-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-2-1,3,4-oxadiazolin-5-one) and CNP (2,4,6-trichlorophenyl-4'-nitrophenylether) herbicides in water, and other environmental samples. They demonstrated the usefulness of this technique for screening unknown compounds in the natural environment.

9.12.1.3 Thin-layer chromatography

Abbott and Wagstaff [449] of the Laboratory of the Government Chemist UK have described a thin-layer chromatographic method for the detection of 12 acidic herbicides and 19 nitrogenous herbicides (carbamates, substituted ureas, and triazines).

Smith and Fitzpatrick [450] have also described a thin-layer method for the detection in water and soil of herbicide residues, including Atrazine, Barban, Diuron, Linuron, Monouron, Simazine, Trifluralin, Bromoxynil, Dalapon, Dicamba, MCPB, Mecoprop, Dicloram, 2,4-D, 2,4-DB, Dichlorprop, 2,4,5-T and 2,3,6-trichlorobenzoic acid.

Neutral and basic herbicides were extracted from water made alkaline with sodium hydroxide or from soil, with chloroform; extracts of soil were cleaned up on a basic alumina containing 15% of water. Acidic herbicides were extracted with ethyl ether from water acidified with hydrochloric acid or from an aqueous extract of soil prepared by treatment with 10% aqueous potassium chloride that was 0.05M in sodium hydroxide and filtration into 4M hydrochloric acid. The concentrated chloroform solution of neutral and basic herbicides was applied to a precoated silica gel plate containing a fluorescent indicator and a chromatogram was developed two-dimensionally with hexane- acetone (10:3) followed after drying by chloroform-nitromethane (1:1). The spots were detected in UV radiation. Atrazine, Barban, Diuron, Linuron, Monouron, Simazine and Trifluralin were successfully separated and were located as purple spots on a green fluorescent background. The ether extracts were dried over sodium sulphate, concentrated, and applied to a similar plate, which was developed two-dimensionally with chloroform-anhydrous acetic acid (19:1) followed after by drying by benzene-hexane-anhydrous acetic acid (5:10:2). The spots were detected by spraying with bromocresol green. Bromoxynil and (as the acids) Dalapon, Dicamba, MCPA, MCPB, Mecoprop, Dicloram, 2,4-D, 2,4-DB, Dichlorprop, 2,4,5-T and 2,3,6-trichlorobenzoic acid were seen as yellow spots on a blue background. The limits of detection were 1ppm in soil and 0.1ppm in natural water.

In a further thin-layer chromatographic method for determining carbamate and urea herbicides in water at the parts per 109 level Frei et al. [451] extracted a 500mL sample with dichloromethane (2 x 50mL) and evaporated the combined extract to 1mL at room temperature in a rotary evaporator and then to dryness at 40°C. The residue was dissolved in acetone (1 or 2 drops) and 0.5mL of sodium hydroxide and heated to 80°C for 30-40min, cooled and shaken with 0.2mL of hexane. 10^L of the hexane layer is applied to a 0.25mm layer of silica gel G-CaSO, 0.2% dansyl chloride in acetone is applied to the sample spot, and t4he chromatogram developed by the ascending technique with benzene-triethylamine-acetone (75:24:1). The plate is sprayed with 20% triethanolamine in isopropyl alcohol or 20% liquid paraffin in toluene, then dried. The fluorescence of the spots of the dansyl derivatives of the aniline moieties is measured in situ. Results are reported for carbamate pesticides, e.g. Propham, Chloropropham and Barban, and the urea pesticides, Linuron, Diuron, Chlorbromuron and Fluometuron; detection limits are about 1ng. Two-dimensional chromatography was used to eliminate interference.

9.12.1.4 High-performance liquid chromatography

Miles and Moye [452] resolved several classes of pesticides by highperformance liquid chromatography and detected them by fluorescence after post-column UV photolysis with or without prior conversion to o-phthalaldehyde-2-mercaptoethanol derivatives. In the presence of o-phthalaldehyde-2-mercaptoethanol fluorescence labelling reagent, most carbamates, carbamoyloximes, carbamothioic acids and substituted ureas gave sensitive responses, whereas dithiocarbamates, phenylamides and phenylcarbamates gave varied responses. In the absence of o-phthalaldehyde-2-mercaptoethanol reagent, strong fluorescence was observed following photolysis of several substituted aromatic pesticides. Detection limits for Aldicarb sulphoxide, Aldicarb, Propoxur, Thiram and Neburon, representing several classes of pesticides were 2.5, 2.3, 3.3, 3.8 and 2.0g L-1 respectively. The relative fluorescence (compared to equimolar methylamine) of some 50 pesticides from 10 different classes, in three solvents, and in the presence of o-phthalaldehyde-2-mercaptoethanol were recorded. Fluorescence responses were significantly affected by the choice of solvent.

Marvin et al. [453] have described an automated high-performance liquid chromatographic system using solid phase extraction for the analysis of mixtures of pesticides in waters. Pesticides determined included Propoxur, Carbofuran, Propham, Captan, Chloropropham, Barban and Butyrate.

A multiresidue method for determining pesticides has been described [454] which uses a graphitized carbon black cartridge to remove pesticides from the water sample followed by liquid chromatographic analysis. Down to 0.003 to 0.07^g L-1 of 35 pesticides could be determined. Pesticides studied included Oxamyl, Methomyl, Phoxan, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2,4-DB and MCPB.

Di Corcia et al. [455] used graphitized carbon black cartridges to extract polar pesticides prior to high-performance liquid chromatography. The cartridge was back flushed with the eluent to extract the pesticides prior to chromatography of the extract. Down to ü.ül^g L-1 of 27 polar insecticides were determined including Dichlorvos, Methoate, Oxamyl, Methomyl.

9.12.1.5 High-performance liquid chromatography—mass spectrometry

Bellar and Budde [456] applied this technique to the determination of 52 pesticides. Cappiello et al. [457] determined acidic, basic and neutral pesticides employing a liquid chromatography-mass spectrometry particle beam interface.

Cresenzi et al. [458] determined 20 acidic pesticides including 2,4-dinitrophenoxynilacetic acid, Mecoprop and Bromoxynil in river water using a benchtop electrospray liquid chromatograph-mass spectrometer. A reversed-phase LCC column was employed. The mobile phase was 0.1M K HPO -0.2M18Bu NF. Levels of 2.5-200ng of each pesticide could be determined by this technique with a recovery of >85%.

9.12.1.6 Mass spectrometry

Schulten [459-461] have identified many pesticides and their metabolites using field desorption mass spectrometry. However, these workers did not apply this method to environmental samples.

Lin Hung and Vyksner [462] determined Terbutryn, Aldicarb sulphone, Propoxur and Carbofuran in environmental waters using an electrospray interface combined with an ion-trap mass spectrometer.

9.12.1.7 Miscellaneous

Johnson et al. [463] studied the solid-phase extraction of pesticides from water samples, e.g. Trifluralin, Simazine, Atrazine, Propazine, Diazinon, Parathion-methyl, Arochlor, Malathion, Parathion and Chlorpyrifos.

9.12.1.8 Preconcentration

Dedek et al. [464] preconcentrated hydrophilic pesticides such as Methamidophos on an organic polymeric sorbent Wofatit Y77. The pesticides were then desorbed with cold or hot methanol prior to analysis.

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