Monitoring of pesticides in agricultural water and soil samples from Andalusia by liquid chromatography coupled to mass spectrometry

This work describes the development of an analytical method for determining 32 pesticides, widely used in agricultural areas from the south of Spain, by liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization (ESI) in positive mode. The chromatographic and the MS parameters of the studied compounds were optimized in order to improve selectivity and sensitivity. The separation was carried out in a C18 column using as mobile phase methanol (MeOH) with 0.01% acetic acid (A) and 0.01% acetic acid (B) with a flow of 0.2 mL/min in gradient mode. The molecular ion was selected for the quantification in selective ion monitoring (SIM) mode. A solid-phase extraction (SPE) method with HLB Oasis cartridges was applied to allow preconcentration of the target analytes from water samples. However, extraction of the compounds from soil samples was carried out by sonication using liquid-solid extraction with methanol/water. In addition, a clean-up step by SPE using also HLB Oasis cartridges was necessary for soils. The proposed analytical methodology was validated in the target environmental matrices by the analysis of spiked blank matrix samples. Detection limits (LOD) varied between 10 and 50 ng/L for water and 0.5-2.5 μg/kg for soils, while quantification limits (LOQ) ranged from 25 to 50 ng/L for water and 1.5 to 5.0 μg/kg for soils. Good recoveries (60-110%) and precision values (<15%) were obtained for all compounds in the target matrices. This methodology has been successfully applied to the analysis of incurred water and soil samples from agricultural areas of Andalusia (south Spain). The results revealed the presence of some pesticides at several concentration levels both in the soil and water samples. Carbendazim, simazine and diuron were the pesticides most frequently detected in water samples, while only the herbicides simazine, diuron and terbutylazine were found in soil samples.