AWWA WQTC59000

Detection of N-nitrosodimethylamine (NDMA) and other nitrosamines in water supplies is of concern because many nitrosamines are classified as probable human carcinogens. A number of analytical methods exist for detecting nitrosamines in water but they are supported by GC/MS electron ionization (EI) methods, which are not selective and can produce potentially non-distinctive fragmentation patterns. Positive chemical ionization (PCI) using ammonia reagent gas is selective for amine and nitrosamine groups, which provides increased selectivity compared to EI. Development of a selective, sensitive and affordable bench-top analytical method for nitrosamines, at relevant drinking water concentrations (low ng/L range) was the primary objective of this project. In order to evaluate our method, N-nitrosamine-free water was spiked with a mixture of eight N-nitrosamines as well as isotopically labeled standards. Samples were passed through a combination of solid phase extraction materials (Ambersorb® 572 and LiChrolut®EN). The analytes of interest were eluted with dichloromethane and concentrated under a stream of nitrogen. Concentrated extracts were injected into an Agilent GC (6890) coupled with an MSD (5973) (single quadrupole) system operating in PCI-NH3 mode. Nitrosamines were detected using selected-ion-monitoring and quantified using an isotope dilution method. Using this approach, the method detection limit for NDMA was 1 ng/L (S/N). To further validate this method, real drinking water samples were collected from three different water treatment plants and/or distribution systems, extracted and analyzed for nitrosamines. The highest concentration of NDMA detected was from a distribution system sample (180 +/- 10 ng/L). Several sample concentrations were independently confirmed by another laboratory using GC/HRMS, with good agreement between the two sets of results. This method could be used as an important tool for investigating low molecular weight, polar compounds in water. Includes 13 references, tables, figures, appendix.