Combined Determination of 1,4-Dioxane and Nitrosamine Contaminants in Drinking Water Using SPE and CSR-LVSI GC-MS

Global concern over the carcinogenic potential of 1,4-dioxane and several nitrosamines has resulted in increased interest in the development of more efficient testing methods for these contaminants in drinking waters. In the U.S., the current methodologies recommended for the analysis of 1,4-dioxane and nitrosamines in drinking waters are Environmental Protection Agency (EPA) Methods 522 and 521, respectively. EPA Method 522 is a relatively simple gas chromatography–mass spectrometry (GC-MS) method using electron ionization (EI), while Method 521 requires positive chemical ionization (PCI) using liquid methanol or acetonitrile reagent gas, along with tandem mass spectrometry (GC-MS/MS). The method described here uses the same coconut charcoal sorbent solid phase extraction (SPE) cartridges and dichloromethane eluent recommended in EPA Methods 522 and 521 to concentrate 0.50 L water samples to 10 mL extracts. However, both the extraction and instrumental analysis portions of EPA Methods 522 and 521 have been combined by analyzing a single quantitatively collected SPE tube extract for both 1,4-dioxane and nitrosamines during a single chromatographic run. The benefits of the current combination method include fewer samples to collect, ship, and extract; a reduction in solvent use; and higher sample throughput. Because the final SPE extract cannot be concentrated via evaporation due to volatile compound loss, we employed concurrent solvent recondensation–large volume splitless injection (CSR-LVSI), which uses a standard splitless injector to deliver 50 μL injections of extract to a pre-column connected to a typical GC column for separation followed by EI MS analysis. When combined with selected ion monitoring (SIM), this large volume injection allows for practical quantitation limits (PQLs) as low as 10 ng/L for 1,4-dioxane and 0.5–2.0 ng/L for the nitrosamines. Introduction 1,4-Dioxane is a highly water-soluble synthetic organic solvent used to stabilize chlorinated solvents; 1,1,1-trichloroethane (TCA), for example, may contain up to 8% 1,4-dioxane. Improper disposal of chlorinated solvents can lead to the accumulation of 1,4-dioxane in ground and surface waters used as drinking water sources [1]. Global concern over the carcinogenic potential of 1,4-dioxane, along with its identification as a Group 2B compound by the World Health Organization’s (WHO) International Agency for Research on Cancer (IARC), has led to increased regulatory interest in this compound. For example, as a part of Unregulated Contaminant Monitoring Rule 3 (UCMR3), the U.S. EPA is requiring that all municipalities serving drinking water to more than 10,000 people monitor 1,4-dioxane levels for 12 consecutive months between 2013 and 2015. The mandated method for 1,4-dioxane analysis is EPA Method 522, which was developed for part-per-trillion (ppt) analysis of drinking waters using solid phase extraction (SPE) cartridges and gas chromatography–mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. The 1x10-6 cancer risk assessment level for 1,4-dioxane is 0.35 μg/L and, as a result, the proposed minimum reporting level (MRL) for 1,4-dioxane as part of UCMR3 is 70 ng/L (70 ppt) [2].