Gas‐liquid chromatographic determination of NDMA in dimethylamine and in laboratory prepared herbicidal dimethylamine formulations

Abstract

AbstractA method is described for the analysis of trace levels of N‐nitroso‐dimethylamine (NDMA) in anhydrous and in 60% (w/w) aqueous dimethylamine (DMA). Anhydrous DMA was converted to 60% (w/w) aqueous DMA, which was diluted with absolute ethanol and analyzed by a gas‐liquid chromatograph coupled to a thermal energy analyzer (g.l.c./t.e.a.) for the presence of NDMA. Experiments showed that NDMA was not generated in the g.l.c. injection port during analysis. The NDMA contents in seven samples of aqueous DMA and four samples of anhydrous DMA ranged from 55.0 μg −1 of 60% (wlw) aqueous sample to non‐detectable levels. The minimum detectable amount was 40 pg, which corresponds to 0.1 μg g−1. Anhydrous DMA was found to contain the lowest level of NDMA. 2, 4‐Dichlorophenoxyacetic acid (2, 4‐D), 4‐chloro‐2‐methylphenoxyacetic acid (MPCA) and 3, 6‐dichloro‐ 2‐methoxybenzoic acid (dicamba) were formulated with 60% (w/w) aqueous DMA into the corresponding DMA salts. The resulting herbicides were analyzed for NDMA, the levels of which were compared with the initial levels present in the 60% (w/w) aqueous DMA. Heating and stirring during formulation were found to be the main factors causing increased levels of NDMA.