Phenoxy Acid and Other Acidic Pesticides: Single Class, Multiresidue Analysis of
Authors: Heberer Thomas 
Published: September 2006

Owing to their widespread use in agriculture and urban weed control and because of their high mobility in the subsoil, polar pesticides such as phenoxy acids and other acidic pesticides have been especially considered as a potential source of groundwater contamination. In Europe, pesticide residues tolerances in drinking water were set by the European Union Commission to 100 ng L−1for an individual compound and 500 ng L−1for the sum of pesticide residues. These maximum tolerances constitute a real challenge to analysts working in the field of pesticide residue monitoring. In the following article, analytical methods for the multiresidue analysis of phenoxy acids and other acidic pesticides in environmental samples at trace level concentrations are presented. Analytical methods using capillary gas chromatography (GC), high‐performance liquid chromatography (HPLC), capillary zone electrophoresis (CZE) and automated multiple development thin‐layer chromatography (AMDTLC) are described. GC methods are most often used in routine analysis of acidic pesticides owing to their unrivaled advantages in separation power. GC methods can be used in multiresidue analysis of up to more than 50 analytes at trace level concentrations. Owing to their high polarity and low volatility, acidic pesticides are not directly amenable to GC analysis, thus suitable derivatization methods are required. The applicability and drawbacks of several derivatization methods are described in detail. GC can be used with various detection methods such as electron capture detection (ECD), nitrogen–phosphorus detection (NPD), atomic emission detection (AED) or mass spectrometry (MS). GC/MS (gas chromatography/mass spectrometry) or GC/MS/MS (tandem mass spectrometry) detection provides the highest possible level of confidence independent of the complexity of the environmental matrix from water or even soil samples. The highest selectivity and sensitivity is achieved in selected ion monitoring (SIM) or in selected reaction monitoring (SRM) mode. Progress in coupling of HPLC to MS has improved the possibilities of identification and confirmation of analytes at trace level concentrations using HPLC methods and new promising analytical approaches such as HPLC coupled to atmospheric pressure ionization (API) MS/MS will gain much importance in the future. Enantioselective separation of different chiral isomers of phenoxy acid pesticides can be achieved applying CZE or by applying GC or HPLC with special chiral phases.

In water analysis, conventional liquid–liquid extraction (LLE) has mostly been replaced by solid‐phase extraction (SPE) methods to extract and enrich the analytes from the samples. Two standard operating procedures (SOPs) are presented as examples for the analysis of phenoxy acids and other acidic pesticides in environmental samples (water and soil). Detection limits down to the low nanogram per liter level or down to the low microgram per kilogram level can be achieved for water samples or soil samples, respectively. Several examples for the environmental analysis of actual samples show the performance and sensitivity of today's trace level multiresidue analysis.