Application of column switching liquid chromatography to the determination of polar herbicides in diferent environmental matrices.: MCPA as a case study

The development of analytical methodology based on column-switching liquid chromatography (LC-LC) for the trace level determination of herbicides is discussed in this paper. Especial attention is given to the performance of different LC-LC configurations in order to improve method selectivity, using both diode array and tandem mass :spectrometry as detection systems. The determination of MCPA and metabolites in different environmental samples (water, soil and plants) is used as a model example. For the analysis of water and soil samples a short C-18 column (30 mm) was coupled to a larger similar column (1.20 mm) leading to satisfactory results, with average recoveries between 97 and 110%, for ground and surface water, and between 70 and 109% for soil. However, the higher level of coextracted interferences in the vegetal samples made necessary the use of two columns with different retention mechanisms. The potential of two RAM columns used as C-2 and coupled to a short C-18 column as C-l was investigated. The results were satisfactory for MCPA and its metabolite 4-chloro-2-methylphenol since they could be determined with recoveries between 91 and 110%, and 72-81%, respectively. Limits of detection were around 0.1 and 0.5 mug L-1 for ground and surface water, respec tively; between 0.02 and 0.05 mg kg(-1) for soil; and 0.05 mg kg(-1) for olive plants. The use of MS-MS as detection system allows the direct analysis of water and soil extracts, only requiring a prior dilution for the determination of the metabolite 4-chlorophenol in soil. However, in more complex matrices, as olive leaves, LC-LC coupling can be a useful tool as it allows the multiresidue determination of the three compounds investigated at very low concentration levels (limits of detection between 0.06 and 0.005 mg kg(-1)), with recoveries ranging from 96 to 104% and coefficients of variation below 3%.