A solid-phase microextraction-gas chromatographic approach combined with triple quadrupole mass spectrometry for the assay of carbamate pesticides in water samples

A simple and sensitive method was developed for the quantification of five carbamate pesticides in water samples using solid phase microextraction (SPME) combined with gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS). The performance of five SPME fibers was tested in univariate mode whereas the other variables affecting the efficiency of SPME analysis were optimized by the multivariate approach of design of experiment (DoE) and, in particular, a central composite design (CCD) was applied. The optimum working conditions in terms of response values were achieved by performing analysis with polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber in immersion mode for 45 min at room temperature with addition of NaCl (10%). The multivariate chemometric approach was also used to explore the chromatographic behavior of the carbamates and to evaluate the importance of each variable investigated. An overall appraisement of results shows that the factor which gave a statistically significant effect on the response was only the injection temperature. Identification and quantification of carbamates was performed by using a gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS) system in multiple reaction monitoring (MRM) acquisition. Since the choice of internal standard represented a crucial step in the development of method to achieve good reproducibility and robustness for the entire analytical protocol, three compounds (2,3,5-trimethacarb, 4-bromo-3,5-dimethylphenyl-n-methylcarbarnate (BDMC) and carbaryl-d7) were evaluated as internal standards. Both precision and accuracy of the proposed protocol tested at concentration of 0.08, 5 and 3 mu g l(-1) offered values ranging from 70.8% and 115.7% (except for carbaryl at 3 mu g l(-1)) and from 1.0% and 9.0% for accuracy and precision, respectively. Moreover, LOD and LOQ values ranging from 0.04 to 1.7 ng l(-1) and from 0.64 to 2.9 ng l(-1). respectively, can be considered very satisfactory. (C) 2012 Elsevier B.V. All rights reserved.