Orange County Water District (OCWD) Laboratory has developed a cost-effective
and very sensitive detection method for NDMA and 1,4-dioxane using
GC/MS/MS/CI and GC/MS/MS/Purge-Trap, respectively. Since the demand of
these methods is very high to process over 2,000 samples each year. The lab
initiated the multi-residual analytical method to incorporate 1,4-dioxane with the
existing analytical method for nitrosamines. The solid phase extraction (SPE)
with 80 to 100 meshes of granular carbon uses 10 ml of methylene chloride for
extracting the interested analytes from the absorbent materials. The 10 ml extract
was concentrated to final volume of 1ml to be analyzed by GC/MS/MS with
positive chemical ionization with methanol reagent solution.
The developed analytical method generated the acceptable recovery and precision
for both nitrosamines and 1,4-dioxane for different matrix of aqueous samples
such as groundwater, surface water and reclaimed water. The reportable
detection limit of 1,4-dioxane was 0.05 parts per billion while the purge-trap
method was 1.0 part per billion.
Recently, 1,4-dioxane, which the US Environmental Protection Agency classifies as a B2 probable human
carcinogen, has been detected in the specific ground and surface waters. The
findings of 1,4-dioxane in the water systems prompted the need of extensive
monitoring of the compound in the 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 volatile nature of
the compound. Orange County Water District (OCWD) Laboratory 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.
OCWD Laboratory has been developed a very reliable method to determine sub
part per trillion levels of N-nitrosodimethylamine (NDMA) by GC/MS using
positive chemical ionization with methanol or acetonitrile. Since 1,4-dioxane and
nitrosamines have similar properties, very water soluble, volatile and polar, 1,4-
dioxane was successfully included in the existing method for nitrosamines. To
accommodate 1,4-dioxane into the existing analytical method, 1,4-dioxane-d8 and
NDPA-d14 were both used as internal standards. The pH of 500 mL 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 celsius
degrees 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, 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 for safety and system maintenance. Also, the
modified liquid-liquid extraction technique using separatory funnel could save
80% of 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, table.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 190 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 11/01/2007 |
