DETERMINATION OF N-NITROSODIMETHYLAMINE AT PART-PER-TRILLION LEVELS IN DRINKING WATERS AND CONTAMINATED GROUNDWATERS

The carcinogen N-nitrosodimethylamine (NDMA) may be quantitated routinely at ultratrace (ng/L) levels in drinking water or contaminated groundwater, The aqueous sample is passed through a preconditioned Empore C-18 filter disk to remove neutral nonpolar species and then extracted continuously overnight with highest purity dichloromethane. The latter is then concentrated to 1 mL, and a large aliquot (up to 200 mu L) is loaded onto a dual-stage carbon sorbent trap, after which the solvent is removed with ultrapure helium, The concentrated residues are then injected orate a gas chromatographic column using a short-path thermal desorber. NDMA is selectively detected using a chemiluminescent nitrogen detector (CLND) operated in its nitrosamine-selective mode. The reporting limit for this procedure, evaluated using two independent statistically unbiased protocols, is 2 ng of NDMA/L, A related procedure, employing an automatic sampler instead of the short-path thermal desorber, provides convenient analysis of heavily contaminated samples and exhibits a reporting limit (same protocols cited previously) of 110 ng of NDMA/L. When the two methods are used together in a ''two-tiered'' protocol, NDMA concentrations spanning 4 orders of magnitude (ng/L to mu g/L levels) may be measured routinely. The low-level procedure employing only the short-path thermal desorber was applied successfully to three sources of drinking water, where NDMA concentrations ranged between 2 and 10 ng of NDMA/L, The two-tiered protocol was applied to a series of contaminated groundwaters whose NDMA concentrations ranged between approximately 10-7000 ng of NDMA/L. The results agreed with those obtained from an independent collaborating laboratory, which used a different analytical procedure.