Identifying ozone-reactive precursors of N-nitrosodimethylamine (NDMA), a probable carcinogenic disinfection byproduct, is crucial for minimizing its presence in treated drinking water. However, detecting trace-level NDMA precursors in complex environmental water matrices remains challenging, particularly when using mass spectrometry (MS). This study presents a solid-phase extraction (SPE) method utilizing mixed-mode cation-exchange (MCX) cartridges to isolate NDMA precursors from environmental waters, facilitating their identification via MS. Samples are adjusted to pH 7, loaded onto preconditioned MCX cartridges, and eluted with Milli-Q water (2% formic acid) to remove potential interferences and enhance retention. The retained precursors are then desorbed using alkaline methanol (MeOH) (MeOH + 5% aqueous ammonia). The method is especially suitable for non-volatile N,N-dimethylhydrazine (DMH)-like precursors, as volatile DMH-like compounds such as 1,1,2-trimethylhydrazine (TMH) showed poor recovery (36%). When applied to three environmental water samples, including two sewage effluents and one sewage-impacted river water, the method showed high mean recoveries (>80%) with relative standard deviation (RSDs) typically <8% for various NDMA precursors.

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