Determination of organochlorine pesticides in ground water samples using solid-phase microextraction by gas chromatography-electron capture detection.

A direct immersion solid-phase microextraction coupled with gas chromatography-electron capture detection (SPME-GC-ECD) method was optimized and validated for the quantitative determination of 18 organochlorine pesticides in ground water. Ionic strength, stirring speed, adsorption and desorption time and pH were some of the parameters investigated in order to select the optimum conditions for SPME with a 50/30 DVB/CAR/PDMS fiber coating. The SPME-GC/ECD method showed good linear response below 10 ng L(-1) with R(2) values in the range of 0.9950-0.9997. The repeatability of the measurements were lower than 10%. Values of relative recoveries located within the acceptable range (80-120%). Limits of quantification (LOQ) from 4.5x10(-3) to 1.5 ng L(-1) were obtained. On average 8 organochlorines were found per sample, even so all the 18 organochlorines were quantified among them. Substances such as endrin ketone, gamma-BHC and beta-BHC were the pesticides determined in larger concentration (0.06-305 ng L(-1)), while methoxychlor and aldrin in smaller amounts (0.151-1.55 ng L(-1)). Measured levels of organochlorine pesticides were above the limits established by Brazilian regulations.