Abstract
A sensitive and highly selective methodology for the determination of a wide range of pesticides, based on the simultaneous element-specific determination of phosphorus, sulfur, chloride, bromine and iodine by gas chromatography hyphenated with octopole reaction cell-inductively coupled plasma mass spectrometry (GC-CC-ICP-MS) is described. The chromatographic system was optimised for separation efficiency and short run times and was coupled via a commercially available interface with an octopole reaction cell ICP-MS system which is equipped with an on-axis collision cell. Instrumental settings were optimised with respect to high sensitivity for the target nuclides 31P, 32S, 35Cl, 79Br and 127I and minimized background levels especially for the ions most affected by interferences, such as 31P+, 32S+. Helium and nitrogen were tested as additional plasma gases for possible sensitivity enhancement of the element-specific detection resulting from improved ionisation processes inside the plasma. Due to the multi-element capability of the instrumental setup and the good accuracy of the retention times that were achieved, identification of the detected pesticides can be carried out using their retention times, the element compositions and element ratios present in each chromatographic peak. For the different pesticides detection limits down to the ppt level or the low ppb level were obtained. The average RSDs of the retention times and the peak areas were better than 0.8% and 8%, respectively. The analytical methodology developed has been applied to the screening of different fruit extracts for pesticides. Peaks were identified by comparison of the retention times obtained and by their elemental composition. Quantitative results have been obtained both by external calibration and by using a compound independent calibration.
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