EPA-TSC/NERL: 331.0: Perchlorate in water by LC/EMI/MS
|
Official Method Name
|
Determination of perchlorate in water by liquid chromatography electrospray ionization mass spectrometry |
|---|---|
|
Current Revision
| Rev. 1.0, January 2005 |
|
Media
|
WATER |
|
Instrumentation
|
Liquid Chromatography-Mass Spectrometery (also High Performance LC-MS; HPLC-MS) |
|
Method Subcategory
|
Inorganic |
|
Method Source
|
|
|
Citation
|
Wendelken, S.C., Munch, D.J., Pepich, B.V., Later, D.W., and Pohl, C.A., 2005, Determination of perchlorate in drinking water by liquid chromatography electrospray ionization mass spectrometry: U.S. Environmental Protection Agency Report EPA/815/R-05/007, Revision 1.0, 34 p. |
|
Brief Method Summary
|
Water samples are collected in the field using a sterile filtration technique. Prior to analysis, isotopically enriched perchlorate (Cl18O4-) is added to the sample as an internal standard. The sample is injected without cleanup or concentration onto a chromatographic column (Dionex IonPak@ AS-21 or equivalent), which separates perchlorate from other anions and background interferences. Perchlorate is subsequently detected by negative electrospray ionization mass spectrometry. A remote controlled valve is used to divert early eluting cations and anions to waste. Prior to the elution of perchlorate, the valve is switched sending the chromatographic eluent to the mass spectrometer. This diversion helps prevent unnecessary fouling of the electrospray source. Perchlorate is quantified using the internal standard technique. |
|
Scope and Application
|
This method is used for the determination of perchlorate in raw and finished drinking waters. This method can be used to acquire data using either selected ion monitoring (LC/SIM) or multiple reaction monitoring (LC/MRM) detection.
The SIM and MRM mass spectrometry conditions described in this method were developed using a conventional LC system. |
|
Applicable Concentration Range
|
Method report does not expressly state range; however, it is noted that the calibration procedures for this method are designed to cover the full scanning range of the instrument. |
|
Interferences
|
All glassware must be meticulously washed and rinsed with reagent water. Disposable high-density polyethylene equipment may be used. If background contamination is a problem, detergents used in glassware cleaning should be investigated as perchlorate has been detected in some common laboratory detergents. Method interferences may be caused by contaminants in solvents, reagents, sample bottles and caps, and other sample processing hardware. All laboratory reagents and equipment must be routinely demonstrated to be free from interferences under the conditions of analysis. Subtracting blank values from sample results is not permitted. Matrix interferences may be caused by contaminants that are in the sample. The extent of matrix interferences will vary considerably from source to source. Samples high in organic carbon or dissolved solids may lead to elevated chromatographic baselines or interfering peaks. Hydrogen sulfate that is formed from the 34S isotope of sulfur is a common interference. Equipment used for sample collection and storage has the potential to introduce interferences. These interferences must be investigated during the Initial Demonstration of Capability (IDC) by preparing and analyzing a Laboratory Reagent Blank (LRB). This procedure should be repeated each time that a new equipment is used to ensure that background contamination does not interfere with the identification and quantitation of perchlorate. 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 Cl16O-4 and is initially confirmed during the analysis of the LRB during the IDC and is monitored in each Analysis Batch. |
|
Quality Control 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. |
|
Sample Handling
|
Once representative samples are obtained, they must be filtered to remove any native microorganisms. Perchlorate is known to be susceptible to microbiological degradation by anaerobic bacteria. Samples are filtered to remove microbes and stored with headspace to minimize the possibility that anaerobic conditions develop during storage. At a minimum, leave the top one third of the bottle empty to reduce the potential for degradation by any remaining anaerobic organisms. Samples must be chilled during shipment and must not exceed 10oC during the first 48 hours after collection. Samples should be confirmed to be at or below 10oC when they are received at the laboratory. Samples stored in the lab must be held at or below 6oC until analysis. Samples should not be frozen. |
|
Maximum Holding Time
|
28 days |
|
Relative Cost
|
$201 to $400 |
|
Sample Preparation Methods
|
