Direct Evaluation of Unsymmetrical Dimethylhydrazine with Wide Concentration Range in Wastewater by Ion Chromatography

Abstract

Current methods for measurement of unsymmetrical dimethylhydrazine (UDMH) in wastewater suffer from a small detection range and complex pretreatment. In this study, ion chromatography (IC) with conductivity detection was used to directly analyze UDMH in wastewater, without any derivatization pretreatment, and the measurement range was as wide as 0.5–1000 μg·mL⁻¹. The effects of column temperature and sample pH on the detection were investigated. Furthermore, the chromatography conditions were optimized by combining the effects of different combinations of nitric acid, 2,6-pyridinedicarboxylic acid (PDCA), and methanesulfonic acid (MSA) on the analysis of mixed samples of UDMH and alkali metal ions. The linearity of the detected peak height (H) and peak area (A) versus UDMH concentration was studied at low, medium, and high concentrations. A good linear relationship was observed in the range of 0.5–1000 μg·mL⁻¹, especially for A, the relative standard deviation (RSD) and correlation coefficient (R²) of which were 0.077–1.653% and 0.9998–1.0000, respectively. In addition, the method showed good sensitivity with a limit of detection (LOD) of 0.05 μg·mL⁻¹ and a limit of quantitation (LOQ) of 0.16 μg mL⁻¹. The precision and accuracy (expressed by recovery) were verified, where the RSD were less than 1.49% and 3.17%. Interference between hydrazines and alkali metal ions was discussed. Finally, actual UDMH samples were determined, confirming the applicability of the developed method for analyzing UDMH in wastewater during the degradation process.