DEVELOPMENT OF THE WRc METHODS FOR CHLORTOLURON, ISOPROTURON, LINURON, METHAM SODIUM AND METHYL ISOTHIOCYANATE, AND CHLORMEQUAT (CG 9896 SLD) Final report to the Department of the Environment
Report No DWI0325

Sept 1988

SUMMARY

Analytical methods for a range of agricultural chemicals of environmental concern have been examined with the intention of producing outline methods with limits of detection of better than 0.1 µg/1. For each chemical the analytical technique chosen was high performance liquid chromatography (HPLC).

For the first group of chemicals, the herbicides chlorotoluron, isoproturon and limuron it was shown that limits of detection of 0.01 µg/1 are possible by extracting 1 litre of water using octadecylsilane (ODS) cartridges and with acetonitrile as eluting solvent in HPLC. However severe interference, was encountered when extracting river water, and for the successful determination of these substances a means of overcoming the interference is required.

For chlormequat, liquid chromatography of the coloured complex formed with hexamtrodiphenylamine (HNDPA) after extraction of the chemical from 1 litre of water gave a limit of detection of 0.002 µg/l much better than that required. An alternative, PHLC with reversed phase ion pair separation, gave only a poor limit of detection.

Work on metham sodium included the investigation of the options of determining methan sodium directly or of determining it in terms of its degradation product methyl isothiocyanate. It was concluded that direct determination was more viable since no method could be found for the rapid conversion to methyl isothiocyanate. Different HPLC columns and eluting solvents were tested and an outline method is presented involving the preconcentration of metham sodium on octadecylsilane followed by HPLC using a micellar mobile phase.

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