AWWA WQTC55175

Recently, 1,4-dioxane, which the US Environmental Protection Agency (USEPA) classifies as a B2 probable human carcinogen, has been detected in specific ground and surface waters. The findings of 1,4-dioxane in water systems prompted the need for extensive monitoring of the compound in drinking water. But the currently available methods have high detection limits of 10 to 50 ug/L. The high reportable detection limits are the results of poor extraction efficiency and the volatile nature of the compound. Orange County Water District (OCWD) Laboratory of Fountain Valley, California, has examined extraction and analysis techniques to establish a more sensitive and reliable method to analyze for 1,4-dioxane to less than 1 ug/L in drinking water samples. The OCWD Laboratory has developed a very reliable method to determine sub part per trillion levels of N-nitrosodimethylamine (NDMA) by gas chromatography/mass spectrometry (GC/MS) using positive chemical ionization with methanol or acetonitrile. Since 1,4-dioxane and NDMA have similar properties in that they are both very water soluble, volatile and polar, 1,4-dioxane was successfully included in the existing method for NDMA. To accommodate 1,4-dioxane into the existing analytical method for NDMA, 1,4- dioxane-d8 and NDMA-d6 were both used as internal standards. The pH of a 1L sample was adjusted between 4 and 11 and extracted three times with 60 ml of methylene chloride. The extract was evaporated to 1 ml using nitrogen gas at 35 degrees celsius in a water bath. The retention times of 1,4-dioxane and NDMA were 11.43 and 11.86 minutes with 60 m capillary column, respectively. The retention time differences of 0.43 minutes was far enough to change chemical ionization settings from 1,4-dioxane to NDMA, which multiple settings are necessary to perform simultaneous determination of these compounds without decreasing instrument sensitivity. The modified extraction and instrument techniques generated method detection limits, as the basis of a 1 L sample size, that range from 0.1 to 0.2 ug/L for 1,4-dioxane and 0.2 to 0.3 ng/L for NDMA. For the positive chemical ionization, methanol or acetonitrile have several advantages over ammonia gas with respect to safety and system maintenance. Also the modified liquid-liquid extraction technique using a separatory funnel could save 80% of the extraction time compared to the continuous liquid-liquid extraction technique. The results of recent work on the analysis of 1,4-dioxane and NDMA from groundwater, surface water and reclaimed water samples are included. This study clearly demonstrated the GC/MS using chemical ionization with methanol was very sensitive, reliable and cost effective for the simultaneous analysis of 1,4-dioxane and NDMA from aqueous samples. Includes 12 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

01/01/2001

Number of Pages:

18

File Size:

1 file , 420 KB