Ground water pesticides after sampling

An APCI-LC-MS method was developed and described for the quantitative determination of the anilide pesticides alachlor and metazachlor in ground water samples. After optimization of instrumental conditions detection limits of 0.001-0.005 pg L (50-300 pg injected) could be obtained. Recovery, precision and linearity data were reported [350]. The pesticide bentazone was one of the most frequently found compounds determined by APCI-LC-MS in shallow groundwater samples from twosandy and two clay catchment areas [351]. 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

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