Analysis of Dithiocarbamate Fungicides. Second-derivative UV-spectroscopic Determination of CS2, COS, and Thiram (TMTD)

The application of second-derivative UV-spectroscopy offers a highly sensitive and selective method for the determination of CS2 and COS, as acid hydrolysis products of dithiocarbamate und thiuram disulphide fungicides, using a methanolic amine absorption reagent (ethylenediamine, piperidine). With standard concentrations of 0.08-1.1 microgram CS2/ml and 0.3 to 2.0 micrograms COS/ml, respectively, calibration curves with good correlation coefficients (r > 0.999) were obtained. In comparison to the official method of the Deutsche Forschungsgemeinschaft (DFG method S15) the proposed alternative is at least 100 times more sensitive to CS2. Using the second derivative method it is possible not only to clearly differentiate between CS2 and COS but also to quantify both gases without resorting to tedious background corrections as compared to the direct photometric methods. Additionally, second derivative spectroscopy allows the direct determination of thiram in the concentration range 1-10 micrograms/ml after its extraction with chloroform. For example, thiram in water (10 micrograms/l) and in thiram/talc standards (10 mg/g) were determined with good precision (+/- 2.0%).