|Perchlorate has been used in solid rocket
propellants. It has now found it's way into drinking water
supplies, and foods such as lettuce and milk. C&EN featured an
article in August 2003 on perchlorate contamination n the Colorado
California has an action limit of 4 ug/L as an unregulated chemical requiring monitoring in ground water. On March 11, 2004 OEHHA announced a PHG of 6 ug/L.
The Environmental Working Group and Texas Tech University have reported finding perchlorate in lettuce and milk.
Perchlorate has become an important environmental contaminant. A by-product of the explosive industry, it has been detected in groundwater in numerous locales. Currently EPA is especially interested in monitoring perchlorate in drinking water supplies.
We passed the first perchlorate PT study conducted in the spring of 2000 and are currently accredited by CA ELAP for perchlorate by EPA Method 314.0.
EPA 314 can be subject to matrix interferences, especially in the presence of high amounts of other anions. Contamination in foods which were irrigated with perchlorate-tainted water has become important, as reports have surfaced of contaminated lettuce and milk (presumably from cows fed alfalfa containing perchlorate). IC has difficulty with this type of complex matrix. Also pCBSA has been noted as an interference near the retention time for perchlorate by EPA 314.
We have developed an IC-MS/MS method to determine perchlorate. Due to the extreme specificity of MS/MS, matrix problems can be greatly reduced, and false positives essentially eliminated. Also, very low detection limits can be achieved due to the reduction in chemical noise. We can routinely detect sub-parts per billion levels in water.
Use of this method will allow us to greatly improve our perchlorate analytical capabilities. IC-MS/MS can be used to confirm IC results, to analyze for lower levels important in site assessment and remediation, and to detect low levels in foods and other complex matrices where EPA 314 simply cannot meet desired detection limits. Lettuce, spinach, and onions have been analyzed with detection limits of ~ 1 ng/g.
CA DTSC has approved WCAS for projects which require IC-MS/MS confirmation of perchlorate.
The chromatogram below demonstrates detection of 0.1 ug/L perchlorate under chromatographic conditions similar to EPA 314, however using MS/MS in the negative ion mode as the detector. In this case the molecular ion for ClO4-, 99 amu, is focused through the first quadrupole, loses a single oxygen in the reaction cell, and the daughter ion ClO3- 83 amu is focused through the second quadrupole, and onto the detector. This type of detection makes this analysis more sensitive and very specific. For a quotation...
water and wastewater
produce (lettuce, zucchini, celery, green beans, and dates)
milk and dairy products
soy milk and other baby foods
EPA has now published methods like this for perchlorate. They distinguish an LC-MS/MS method, EPA Method 331, from an IC-MS/MS method, EPA Method 332, based upon the use of a suppressor. Our method complies with the latter.
For more information click on LC-MS/MS.
IC-MS/MS of Perchlorate
9240 Santa Fe Springs
Formerly West Coast Analytical Service (WCAS) and Bodycote Testing Group