Using of photogenerated iodine for determination of 1,1-dimethylhydrazine in environmental objects

Abstract

A photochemical method for determination of 1,1-dimethylhydrazine H2NN(CH3)2 (unsymmetrical dimethylhydrazine (UDMH)) based on titration of the analyte with photogenerated iodine obtained by irradiation of an auxiliary solution containing potassium iodide and a mixture of sensitizers (EOSIN Y:auramine:fluorescein taken in a molar ratio 1:1:1) in an acetate medium (pH 6) has been developed. With increasing acidity, a decrease in the rate of photogeneration is observed which is most likely attributed to disproportionation of the resultant titrant. Since the titrant (iodine) content is controlled by the voltammetric method, the photochemical titration of UDMH is accompanied by a decrease in the current strength in the circuit of the amperometric setup and stabilization indicates the completeness of the reaction. Measurements of the photogeneration time necessary to compensate for the loss of titrant in the cell upon further irradiation of the solution in the presence of atmospheric oxygen provide quantitative assessing of the UDMH content in environmental objects. Since the analyte interacts with the titrant in a molar ratio 1:2, we suggest the possibility of UDMH oxidation to NDMA (N-nitrosodimethylamine). A photochemical method of UDMH determination in solution is thus developed with the detection and determination limits (0.49 and 1.62) μg/ml, respectively. Unfortunately, the sensitivity of the proposed methodology does not allow determination of a toxic chemical contaminant at the MPC level which necessitates preconcentration of the mobile forms of UDMH by steam distillation in a 40 % sodium hydroxide solution. The developed methodology matches the validation parameters by the indices of linearity, ranking, correctness and thus can be recommended for determination of the UDMH content in any analytical laboratory. The photochemical method was tested in the analysis of soil samples taken from background and contaminated territories as well as natural water. A slight excess of the UDMH content has been found in the soil taken from the former location of the military unit.