Determination of the herbicide 4-chloro-2-methylphenoxyacetic acid and its main metabolite, 4-chloro-2-methylphenol in water and soil by liquid chromatography-electrospray tandem mass spectrometry.

A rapid and sensitive LC-electrospray tandem mass spectrometry method has been developed for the quantitation of 4-chloro-2-methylphenoxyacetic acid (MCPA) and 4-chloro-2-methylphenol in both water and soil samples. Soil samples were extracted in alkaline media and cleaned-up by solid-phase extraction with C18 cartridges before LC-MS analysis. The selectivity and sensitivity offered by the triple quadrupole allowed the direct injection of the water samples rendering a sample throughput of around 100 samples per day, without any sample pretreatment, rendering for MCPA a limit of detection of 40 ng/l. In order to increase the method sensitivity, mainly for metabolite, a previous solid-phase extraction step was also performed. The method was validated by means of recovery experiments using fortified water and soil samples, obtaining satisfactory recoveries for both compounds in water and for MCPA in soil. The validated procedures can be used for the specific monitoring of residues of MCPA and its main metabolite in environmental samples, as ground and surface waters and soils, providing more selectivity and sensitivity than the current UV-based methodology. Besides, sample manipulation is greatly reduced in comparison to other GC-MS based methods which require a previous derivatization.