Determination of ten carbamate pesticides in aquatic and sediment samples by liquid chromatography-ionspray and thermospray mass spectrometry

Abstract

Ten carbamate pesticides which exhibit large differences in polarity were determined simultaneously in various environmental samples, using both column liquid chromatography (LC)-thermospray (TSP) mass spectrometry (MS) and LC-ionspray (ISP) MS. For sample clean-up, column chromatography with three stationary phases, neutral aluminium oxide, Florisil and aminopropyl-bonded modified silica, were tested. The aminopropyl stationary phase showed the best results, with acetone-dichloromethane (25:75) as eluent; analyte recoveries were 76–100% for all compounds with a relative standard deviation of 2–8%. In the ISP mass spectra of eight of the ten carbamates, the sodium adduct ion, [M + Na] +, was the base peak, while the protonated molecule, [M + H] +, was the most abundant ion with carbendazim and aminocarb. An eluent flow-rate between 100 and 300 μl/min was found to be optimum, with optimized nebulizer and drying gas flow-rates of 350 and 15 l/h, respectively. A capillary voltage of 3.5 kV resulted in the largest total ion current. The optimum extraction voltage with regard to analyte detectability and confirmation purposes was between 15 and 35 V. The detection limits obtained with the LC-ISP-MS system were typically in the 10–60 pg range (10 μl of 10 μg/l standard solutions), which is 10–150-fold better than obtained with LC-TSP-MS (selected-ion monitoring mode used in both instances). Large-volume injections of tap water spiked with selected carbamates at a level of 0.1 μg/l illustrated the potential of LC-ISP-MS with respect to analyte detectability. Furthermore, carbofuran was identified at a concentration level of ca. 5 μg/l in water samples from the Ebro delta. LC-TSP-MS of oxamyl and methomyl in a sediment sample containing a high percentage of organic matter was adversely affected by the presence of co-extractives. This problem did not occur with LC-ISP-MS.