Analysis of nitrosamines by capillary electrospray‐high‐field asymmetric waveform ion mobility spectrometry‐MS with programmed compensation voltage

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Abstract
Emerging disinfection by‐products (DBPs) in drinking water are an important public health concern. Certain DBPs, such as nitrosamines, are probable carcinogens, and exposure to halogenated DBPs may lead to birth defects. It is difficult to obtain complete separation of nitrosamines by chromatographic techniques. Thus we explored high‐field asymmetric waveform ion mobility spectrometry (FAIMS) as an alternative separation technique for the characterization of individual DBPs in a complex matrix. We first used ESI‐FAIMS‐MS to separate four nitrosamines: N‐nitrosodi‐n‐butylamine (NDBA), N‐nitrosodi‐n‐propylamine (NDPA), N‐nitrosopiperidine (NPip), and N‐nitrosodiethylamine (NDEA) in the compensation voltage (CV) spectra. The optimal CVs with a fixed dispersion voltage of –4000 V were found to be –1.2 V (NDBA), 2.7 V (NDPA), 7.5 V (NPip) and 10.1 V (NDEA). In addition, FAIMS‐MS effectively reduced the chemical noise and dramatically improved the LODs by as much as tenfold compared to the conventional ESI‐MS technique. To further improve sensitivity, an on‐line CE system was used in combination with FAIMS‐MS to take advantage of the higher ionization efficiency. The calibration curves for the four nitrosamines were linear over a range of 5 ng/mL to 1000 ng/mL with an r2 value of 0.9929 to 0.9992. To increase sample throughput, a multiple‐injection strategy was developed, in which the CV values were preprogrammed so that the FAIMS device allowed different nitrosamines to pass through at selected time windows. The potential application of the proposed method was demonstrated for the analysis of drinking water samples spiked with nitrosamines.