Rapid gas chromatographic method using nitrogen-phosphorus detection for N-nitrosodimethylamine in 2,4-D and MCPA herbicide formulations.

A simple and rapid analytical method has been developed for the determination of N-nitrosodimethylamine (NDMA) in amine salts of phenoxy herbicide formulations of 2,4-D and MCPA, plus mixtures of these with mecoprop and dicamba amine salts. Sample preparation consists of direct extraction using pre-packed disposable extraction tubes eluted with dichloromethane followed by cleanup on a disposable silica gel mini-column using ethyl acetate as eluting solvent. Samples are injected on-column for gas chromatography with a Megabore fused silica column; the NDMA is measured by a thermionic specific detector (TSD) that is selective for nitrogen-phosphorus (NP). A detection limit of 0.1 microgram/mL was easily attainable without any concentration step because the solvent volume is minimal. TSD and thermal energy analyzer (TEA) results have been compared and confirmed by gas chromatography/mass spectrometry. Recovery studies were performed as well as a reproducibility study on one of the 2,4-D formulations.