ABSTRACT
This paper describes a simple and reliable method for the sensitive and selective determination of the pesticides Glyphosate and Glufosinate and their main metabolites aminomethylphosphonic acid (AMPA) and 3-[hydroxy(methyl)phosphinoyl]propionic acid (MPPA) in surface water. The developed method is based on ion chromatography hyphenated to electrospray tandem mass spectrometry and does not require derivatization. A membrane suppressor, regenerated at pH 9, has been used in this work to strongly improve the peak shape of AMPA, which suffered from huge tailing due to the interaction of this compound with acidic membrane suppressors. With this modified suppressor the sensitivity for AMPA improved about 100 times. Moreover, addition of 40% methanol to the hydroxy eluent improved MS sensitivity for all compounds by 1.3-2.8 times. The separation is performed on a strong anion exchange column. Glyphosate and AMPA are detected in the negative ion ESI mode, whereas Glufosinate and MPPA show much better sensitivity in the positive ion ESI mode. Surface water samples were spiked with the labelled parent compounds. Sample preparation comprised a filtering step over coupled solid phase extraction Ba, Ag and Na cartridges to remove chloride and sulphate ions. The performance characteristics of the method were determined with real surface water samples. Samples containing 12.6 g L-1 chloride were also used in the validation process and showed no problem. Nitrate is not removed from the samples and may give ion-suppression for Glyphosate. Linearity of the method was established over at least three orders of magnitude in the measuring range 10-2000 ng L-1 for surface water. The reliability of the results was ensured by the application of the criteria from the Dutch Technical Agreement (NTA 8379) concerning "identification", "indication", and "absence" of substances. The limit of quantitation with regard to identification was 10 ng L-1 for all compounds and the limits of detection with regard to indication were 6.5-9.6 ng L-1. The recovery (94-104%) and reproducibility variance (5.5-6.2%) were excellent. The suitability of the developed method was demonstrated by the analysis of 172 surface water samples of low to moderate salinity from different parts of The Netherlands. AMPA was identified in 99% of the samples and always exceeded the maximum allowable concentration of 100 ng L-1. The maximal concentration found in surface water was 9900 ng L-1. Glyphosate was identified in 82% of the samples and in only 6% Glyphosate exceeded the maximum allowable concentration of 100 ng L-1. MPPA was identified in about 75% of the samples whereas Glufosinate was rarely detected and never exceeded the limit of quantitation.
