EPA Method 332

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EPA Method 332:
Perchlorate in drinking water by IC-ESI/MS. Official Name: Determination of perchlorate in drinking water by ion chromatography with suppressed conductivity and electrospray ionization mass spectrometry

This method describes the instrumentation and procedures necessary to identify and quantify low levels of perchlorate in drinking waters using IC-ESI/MS. Drinking water samples are collected using a sterile filtration technique. A small volume of sample is injected into an ion chromatograph. Using an anion exchange column, perchlorate is separated from constituent cations and anions in the sample using a potassium hydroxide mobile phase. Due to the use of a non-volatile mobile phase, the eluate from the column is passed through a conductivity suppressor to remove the potassium (K+) ions of the mobile phase and to remove the analyte counter cations prior to the eluate entering the mass spectrometer. An 18O-enriched 35Cl18O4- internal standard (m/z 107) is used for quantitation to improve accuracy and ruggedness of the method. Identification is made by verifying the relative retention time of the two predominant ClO4- ions with respect to the internal standard. Qualitative confirmation of perchlorate is made by confirming that the m/z 99/101 area count ratio is within a specified range. If these conditions are met, along with passing all other QC requirements, then the concentration obtained using the m/z 101 quantitation ion is reported.

This method is applicable to the identification and quantification of perchlorate in raw and finished drinking waters.

Hedrick, E., Behymer, T., Slingsby, R.,and Munch D., 2005, Determination of perchlorate in drinking water by ion chromatography with suppressed conductivity and electrospray ionization mass spectrometry: U.S. Environmental Protection Agency Report EPA/600/R-05/049, Revision 1.0, 48 p.

Method interferences may be caused by contaminants in sample processing solutions and hardware that lead to discrete artifacts and/or elevated baselines in the chromatograms. These items must be routinely demonstrated to be free from interferences under the conditions of the analysis by analyzing LRBs. The use of polyethylene plastic is recommended in place of glass when possible. If glassware is used, it should be washed with detergent and tap water and rinsed with reagent water since perchlorate can be found in common lab detergent.Subtracting blank values from sample results is not permitted. In anion chromatography, cations are not retained and pass through in the void volume. The anions are separated by charge, size, and polarizability. Perchlorate, a large polarizable molecule, elutes later than common inorganic anions. Separation of perchlorate from the matrix ions combined with the specificity of mass spectrometry has resulted in a method that minimizes interferences for drinking water matrices. However, there are known conditions or contaminants that, if present, could result in bias in the reporting of perchlorate.Every effort has been made to address known interferences and to inform the analyst regarding interpretation of chromatographic and mass spectrometric data to determine if an interferant is present. The failure of mandatory QC requirements should alert the analyst to the possibility of an interferant.Lastly, it must be demonstrated that solutions containing a working level of the internal standard do not contain unlabeled perchlorate at concentrations greater than 1/3 of the MRL. The percent of 18O enrichment of the internal standard may vary between manufacturers. Poor isotopic enrichment of the internal standard may lead to sample contamination by Cl16O4- and is initially confirmed during the analysis of the LRB during the IDC and is monitored in each Analysis Batch.

QC Requirements:
Quality control requirements include conducting an initial demonstration of capability, and the on-going analysis of laboratory reagent blanks, fortified blanks, fortified sample matrices and internal standards, and conducting continual calibration checks and quarterly instrument performance checks.

Maximum Holding Time:
28 days



Method report does not expressly state range; however, it is noted that the concentration range is subject to the calibration range and models used for the sample analysis.

The precision and accuracy data presented are based on the detection of perchlorate in reagent water.

The detection limit is dependent on sample matrix, fortification concentration, and instrument performance; it is based on the analysis of at least seven replicate laboratory fortified blank samples.

Revision Number:
Rev. 1.0, March 2005