Flow injection-FTIR determination of dithiocarbamate pesticides

A flow injection Fourier transform infrared spectrometric procedure has been developed for the determination the dithiocarbamate pesticides Ziram and Thiram in solid samples. All the operations involved, such as extraction, filtration and measurement, were integrated in the experimental set-up in order to avoid excessive manipulation of samples and standards. Ultrasonic assisted and mechanical extraction were evaluated for the solubilization of the analytes and, additionally, the effect of carrier flow rate, sample loop volume and the ratio between sample mass and volume of solvent employed were studied. Quantitative extractions with chloroform were obtained for both Ziram and Thiram, after 5 and 2 min, respectively, of mechanical shaking of sample slurries. Absorbance measurement, in the wavenumber range of 1600-1460 cm-1 for Ziram and 1400-1315 cm-1 for Thiram, was carried out, and the area values of the peaks obtained, as a function of time, were interpolated in external calibration lines prepared from standard solutions of Ziram and Thiram in chloroform. Analyses of commercial formulations and spiked soil samples incubated two weeks were in a good agreement with values found by other methodologies. Absolute detection limits of 400 micrograms for Ziram and 785 micrograms for Thiram and variation coefficients of 6.4% and 2.5% were obtained by use of the aforementioned methodology.