Trace determination of nitrosamines in finished drinking water by direct-inject LC-MS/MS

Advanced Topics in Organic Chemistry
Oral Presentation

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Disinfection byproducts, such as N-nitrosodimethylamine (NDMA) and other nitrosamines, have historically been problematic contaminants which occur during the drinking water treatment process. These nitrosamines are classified as probable human carcinogens and are nearly ubiquitous in drinking water treatment plants. As such, many regulatory agencies have established limits for these compounds, and there has been considerable effort in developing methodology for the trace determination of nitrosamines in drinking water. Current methodology typically relies on some form of sample preparation/concentration followed by GC-MS analysis. For example, EPA method 521 describes the determination of six nitrosamines in finished drinking water with offline solid phase extraction using activated charcoal and a large concentration factor to reach a reporting limit of 2 ng/L.

The work presented here describes a direct-inject LC-MS/MS approach which eliminates the tedious and slow off-line sample preparation steps, allowing for the rapid analysis of drinking water while meeting the detection limits and quality control requirements of EPA method 521. The two keys to this application are sensitivity and matrix elimination since electrospray ionization is quite susceptible to ion suppression. By leveraging the extreme sensitivity of modern commercial mass spectrometers, the low detection limits required by EPA method 521 are attainable without the need for large concentration factors or very large injection volumes. The small, polar nitrosamines typically have very little retention on conventional reversed-phase media; however, by carefully controlling the conditions of the chromatographic separation, they can be efficiently separated from the ionic matrix component typical of finished drinking water. This results in a robust and sensitive technique capable of determining N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosomorpholine (Nmor), N-nitrosopyrrolidine (Npyr), N-nitrosopiperidine (Npip), and N-nitrosodi-n-butylamine (NDBA) at 2 ng/L in finished drinking water.