EPA-OGWDW/TSC: 314.1: Perchlorate in water using inline column IC
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Official Method Name
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Determination of perchlorate in drinking water using inline column concentration/matrix elimination ion chromatography with suppressed conductivity detection |
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Current Revision
| Rev. 1.0, May 2005 |
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Media
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WATER |
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Instrumentation
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Ion Chromatography |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Wagner, H.P., Pepich, B.V., Pohl, C., Later, D., Joyce, R., Srinivasan, K., DeBorba, B., Thomas, D., Woodruff, A., and Munch, D.J., 2005, Determination of perchlorate in drinking water using inline column concentration/matrix elimination ion chromatography with suppressed conductivity detection: U.S. Environmental Protection Agency Report 815-R-05-009, Revision 1.0, 38 p. |
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Brief Method Summary
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Water samples are collected in the field using a sterile filtration technique. The sample, without cleanup, is concentrated onto the concentrator/trap column, which is placed in the sample loop position and binds perchlorate more strongly than other matrix anions. The sample matrix anions are rinsed from the concentrator column with 1 mL of 10 mM NaOH. This weak rinse solution allows the concentrator to retain the perchlorate while eluting the majority of the matrix anions, which are directed to waste. The concentrator column is switched in-line and the perchlorate is eluted from the concentrator column with a 0.50 mM NaOH solution. Following elution from the concentrator, the perchlorate is refocused onto the front of the guard column. The eluent strength is then increased to 65 mM NaOH which elutes the perchlorate from the guard column and onto the analytical column where perchlorate is separated from other anions and remaining background interferences. The sample loading and matrix elimination steps must use the same eluent flow direction as the elution and analytical separation steps. Perchlorate is subsequently detected using suppressed conductivity and is quantified using an external standard technique. Confirmation of any perchlorate concentration reported at or above the MRL on the primary column is accomplished with a second analytical column that has a dissimilar separation mechanism. |
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Scope and Application
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This is a sample pre-concentration, matrix elimination ion chromatographic (IC) method using suppressed conductivity detection for the determination of perchlorate in raw and finished drinking waters. This method requires the use of a confirmation column to validate all perchlorate concentrations reported at or above the MRL on the primary column. Precision and accuracy data have been generated for perchlorate, with both the primary and confirmation columns, in reagent water, finished groundwater, surface water and a Laboratory Fortified Synthetic Sample Matrix (LFSSM). The single laboratory Lowest Concentration Minimum Reporting Level (LCMRL) has also been determined in reagent water. |
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Applicable Concentration Range
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Interferences
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Interferences can be divided into three different categories: (i) direct chromatographic co-elution, where an interfering analyte response is observed at very nearly the same retention time (RT) as the target analyte; (ii) concentration dependant co-elution, which is observed when the response of higher than typical concentrations of the neighboring peak overlaps into the retention window of the target analyte; and (iii) ionic character displacement, where retention times may significantly shift due to the influence of high ionic strength matrices (high mineral content or Total Dissolve Solids) overloading the exchange sites on the column and significantly shortening the target analyte's retention time. A direct chromatographic co-elution may be solved by changing columns, eluent strength, modifying the eluent with organic solvents (if compatible with IC columns), changing the detection systems, or selective removal of the interference with pretreatment. Sample dilution will have little to no effect. The analyst must verify that these changes do not induce any negative affects on method performance by repeating and passing all the QC criteria. Sample dilution may resolve some of the difficulties if the interference is the result of either concentration dependant co-elution or ionic character displacement, but it must be clarified that sample dilution will alter your MRL by a proportion equivalent to that of the dilution. Therefore, careful consideration of DQOs should be given prior to performing such a dilution. |
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Quality Control Requirements
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Each laboratory using this method is required to operate a formal Quality Control (QC) program. The minimum requirements of this program consist of an initial demonstration of laboratory capability, and the analysis of laboratory reagent blanks, fortified blanks and samples as a continuing check on performance. The laboratory is required to maintain performance records that define the quality of the data thus generated. |
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Sample Handling
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Once representative samples are obtained (at the time of collection), they must be sterile filtered to remove any native microorganisms. Perchlorate is known to be susceptible to microbiological degradation by anaerobic bacteria. Samples are sterile filtered to remove microbes and stored with headspace to reduce the potential for degradation by any remaining anaerobic organisms. Remove a sterile syringe from its package and draw up approximately 25 mL of the bulk sample (fill the syringe). Remove a sterile syringe filter from its package without touching the exit Luer connection. Connect the filter to the syringe making sure that no water from the syringe drops on the exterior of the filter. Depress the syringe plunger gently and discard the first 3-5 mL. Open a sterile sample container without touching the interior. Using gentle pressure, pass the sample through the filter into the sample container. During this process do not let the syringe or filter make contact with the sample container. Following filtration, seal the sample container tightly, label and prepare the container for shipment. Syringes and filters are single use items and must be discarded after each sample. Field samples must be chilled during shipment and must not exceed 10oC during the first 48 hours after collection. Field samples should be confirmed to be at or below 10oC when they are received at the laboratory. Field samples stored in the lab must be held at or below 6oC until analysis, but should not be frozen. |
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Maximum Holding Time
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28 days |
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Relative Cost
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$201 to $400 |
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Sample Preparation Methods
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