Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume 41, Number 7, August 2003, pp. 343-349
Multiresidue Determination of Acidic Pesticides in Water by
HPLC–DAD with Confirmation by GC–MS Using Conversion to the Methyl
Ester with Trimethylsilyldiazomethane
Thomas W. Moy and William C. Brumley
U.S. Environmental Protection Agency, Office of Research and Development, National
Exposure Research Laboratory, Environmental Sciences Division, P.O. Box 93478,
Las Vegas, NV 89193-3478
A multiresidue pesticide methodology is studied and results
for acidics are reported here, with base/neutral to follow. This work studies
a literature procedure as a possible general approach to many pesticides and
potentially other analytes that are considered to be liquid chromatographic
(LC) candidates, rather than gas chromatographic (GC) ones. The analysis of
the sewage effluent of a major southwestern U.S. city serves as an example
of the application of the methodology to a real sample. Recovery studies were
also conducted to validate the proposed extraction step. A gradient elution
program was followed for the high-performance LC (HPLC) leading to a general
approach for acidics. Confirmation of identity was by electron ionization–GC–mass
spectrometry (MS) after conversion of the acids to the methyl ester (or other
appropriate methylation) by means of trimethylsilyldiazomethane. The 3,4-dichlorophenoxyacetic
acid is used as an internal standard to monitor the reaction, and polychlorobiphenyl
#19 is used for the quantitation internal standard. Although others have reported
similar analyses of acids, conversion to the methyl ester is by means of diazomethane
itself, rather than by the more convenient and safe trimethylsilyldiazomethane.
Thus, the present paper supports the use of trimethylsilyldiazomethane with
all of these acids (trimethylsilyldiazomethane has been used in environmental
work with some phenoxyacetic acid herbicides) and further supports the usefulness
of this reagent as a potential replacement for diazomethane. The HPLC approach
here could also serve as the separation basis for an LC–MS solution for
confirmation of identity, as well as quantitation.
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