Determination at low ppm levels of dithiocarbamate residues in foodstuff by vapour phase-liquid phase microextraction-infrared spectroscopy

A methodology based on the vapour phase (VP) generation of carbon disulphide from non-volatile dithiocarbamate compounds has been developed for determination of pesticide residues in foodstuff at low ppm levels. The method involves a selective reaction combined with liquid phase microextraction (LPME) and transmission infrared measurements. The use of a home made transmission cell improved the detection limits (LOD) compared to the use of attenuated total reflectance measurements by a factor of approximately 80. Using the most appropriate experimental conditions for the CS2 generation and LPME preconcentration, the precision of the methodology, expressed as the relative standard deviation (RSD), was of the order of 3.1% and the absolute LOD was 0.3 μg dithiocarbamate, which corresponds to 60–120 μg kg−1, for a sample mass ranging from 2.5 to 5 g. The usefulness of the methodology has been evidenced by the determination of mancozeb residues in strawberries, lettuce and corn samples at concentrations between 1 and 5 mg kg−1, where the VP-LPME IR provided results comparable with those obtained by a head space gas chromatography mass spectrometry reference procedure.