Perchlorate is widely used as the oxidizer component in solid propellant for rockets, munitions, and fireworks. The risk of perchlorate contamination and its adverse health effects have raised concerns for soil, ground water, and drinking water.
Perchlorate in high doses can disrupt thyroid function and hormone production, and therefore negatively affect growth and development of fetuses, children, and normal metabolism in adults. Children who have been treated with perchlorate for their overactive thyroids are often found to have neurological and behavioral problems.
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California started to regulate perchlorate in drinking water in Oct. 2007, setting the Maximum Contaminant Level (MCL) at 6µg/L. In 2015, the state also established the Public Health Goal (PHG) for perchlorate at 1 µg/L, superseding the PHG of 6µg/L established in 2004. Massachusetts has even lower level at 2µg/L. More than 10 other states have similar health-based goals or advisory levels for perchlorate in drinking water.
The US EPA placed perchlorate in the first Contaminant Candidate List (CCL1) in 1998 and determined that perchlorate meets the Safe Drinking Water Act’s criteria for regulation as a contaminant in Feb. 2011. However, the regulatory standards for perchlorate have not yet been determined.
Multiple analytical methods have been developed for perchlorate analysis. Here we compared the different EPA methods:
|U.S. EPA Methods||Major features||Matrix||MDL*||Other comment|
|314.0||Suppressed conductivity; allows an alternate comparable suppressor||Low Ionic strength only||0.53 ppb||Need sample preparation for high ionic matrix samples|
|314.1||Preconcentration/matrix elimination, then suppressed conductivity||Low and high ionic strength||0.03 ppb||No sample preparation needed|
|314.2||2D-IC using 4 mm primary column and 2mm secondary column||same as Method 314.1||0.012 to 0.028ppb||No sample preparation needed|
|331||LC-MS/MS method that does not require chemical suppression; do secondary fragmentation and measure mass transitions||same as Method 314.1||0.019 ppb||Higher sensitivity and specificity compared to EPA Methods 314.0 and 314.1, but it is also more costly|
|332||LC-MS method requiring chemical suppression||same as Method 314.1||0.02 ppb||same as Method 331|
* MDL= Method Detection Limit
There are multiple sample preparation methods for chromatography, including accelerated solvent extraction/pressurized fluid extraction, supercritical fluid extraction, automated Soxhlet extraction and microwave extraction. Since perchlorate is highly soluble in water, vortexing, centrifugation, and filtration are often needed to extract perchlorate. However, automated accelerated solvent extraction can also be used to extract perchlorate from soil to reduce labor and save time.
Once the samples are prepared, they are analyzed as water samples using IC, IC-MS, LC-MS, or LC-MS/MS methods.