AWWA WQTC65989

Orange County Water District (OCWD) Laboratory has developed a cost-effectiveand very sensitive detection method for NDMA and 1,4-dioxane usingGC/MS/MS/CI and GC/MS/MS/Purge-Trap, respectively. Since the demand ofthese methods is very high to process over 2,000 samples each year. The labinitiated the multi-residual analytical method to incorporate 1,4-dioxane with theexisting analytical method for nitrosamines. The solid phase extraction (SPE)with 80 to 100 meshes of granular carbon uses 10 ml of methylene chloride forextracting the interested analytes from the absorbent materials. The 10 ml extractwas concentrated to final volume of 1ml to be analyzed by GC/MS/MS withpositive chemical ionization with methanol reagent solution.The developed analytical method generated the acceptable recovery and precisionfor both nitrosamines and 1,4-dioxane for different matrix of aqueous samplessuch as groundwater, surface water and reclaimed water. The reportabledetection limit of 1,4-dioxane was 0.05 parts per billion while the purge-trapmethod was 1.0 part per billion.Recently, 1,4-dioxane, which the US Environmental Protection Agency classifies as a B2 probable humancarcinogen, has been detected in the specific ground and surface waters. Thefindings of 1,4-dioxane in the water systems prompted the need of extensivemonitoring of the compound in the drinking water. But the currently availablemethods have high detection limits of 10 to 50 ug/L. The high reportabledetection limits are the results of poor extraction efficiency and volatile nature ofthe compound. Orange County Water District (OCWD) Laboratory has examinedextraction and analysis techniques to establish a more sensitive and reliable methodto analyze for 1,4-dioxane to less than 1 ug/L in drinking water samples.OCWD Laboratory has been developed a very reliable method to determine subpart per trillion levels of N-nitrosodimethylamine (NDMA) by GC/MS usingpositive chemical ionization with methanol or acetonitrile. Since 1,4-dioxane andnitrosamines have similar properties, very water soluble, volatile and polar, 1,4-dioxane was successfully included in the existing method for nitrosamines. Toaccommodate 1,4-dioxane into the existing analytical method, 1,4-dioxane-d8 andNDPA-d14 were both used as internal standards. The pH of 500 mL sample wasadjusted between 4 and 11 and extracted three times with 60 ml of methylenechloride. The extract was evaporated to 1 ml using nitrogen gas at 35 celsiusdegrees in a water bath. The retention times of 1,4-dioxane and NDMA were11.43 and 11.86 minutes with 60 m capillary column, respectively. The retentiontime differences of 0.43 minutes was far enough to change chemical ionizationsettings from 1,4-dioxane to NDMA, which multiple settings are necessary toperform simultaneous determination of these compounds without decreasinginstrument sensitivity. The modified extraction and instrument techniquesgenerated method detection limits, as the basis of a 1 L sample size, range from0.1 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 severaladvantages over ammonia gas for safety and system maintenance. Also, themodified liquid-liquid extraction technique using separatory funnel could save80% of extraction time compared to the continuous liquid-liquid extractiontechnique. The results of recent work on the analysis of 1,4-dioxane and NDMAfrom groundwater, surface water and reclaimed water samples are included. Thisstudy clearly demonstrated the GC/MS using chemical ionization with methanolwas very sensitive, reliable and cost effective for the simultaneous analysis of 1,4-dioxane and NDMA from aqueous samples. Includes 12 references, table.

Product Details

Edition:

Vol. - No.

Published:

11/01/2007

Number of Pages:

12

File Size:

1 file , 190 KB