EPA Method 314.1


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EPA Method 314.1:
DETERMINATION OF PERCHLORATE IN DRINKING WATER USING INLINE COLUMN CONCENTRATION/MATRIX ELIMINATION ION CHROMATOGRAPHY WITH SUPPRESSED CONDUCTIVITY DETECTION

Summary:
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.

Scope:
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.

Citation:
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.

Interferences:
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.

QC Requirements:
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.

Maximum Holding Time:
28 days

Media:
WATER

Subcategory:
Inorganic

Precision:
Precision and accuracy were obtained from a single laboratory testing of the method for seven water samples representing reagent water, chlorinated surface water, chloraminated surface water, chlorinated groundwater, and laboratory fortified synthetic sample matrix samples. Samples were fortified with 100 and 1000 mg/L of perchlorate.The method report presents precision and accuracy data for samples analyzed using two different columns (AS16 and AS20). The analyte data presented in NEMI are for samples using the AS16 column.

Detection:
The detection limit was determined through the analysis of 7 replicate reagent water samples fortified to 0.10 ug/L perchlorate with the AS16 columns and 0.03 ug/L with the AS20 columns.

Revision Number:
Rev. 1.0, May 2005

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