EPA Method 326


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EPA Method 326:
Inorganic Oxyhalide Disinfection By-products in Drinking Water by Ion Chromatography with Postcolumn Reagent for Trace Bromate Analysis. Official Name: Determination of Inorganic Oxyhalide Disinfection By-products in Drinking Water Using Ion Chromatography With the Addition of a Suppressor Acidified Postcolumn Reagent for Trace Bromate Analysis

Summary:
About a quarter of a milliliter of sample is introduced directly into an ion chromatograph equipped with a guard column and a suppressor device. The target anions are separated and measured using an analytical column and a conductivity detector. To facilitate low-level detection of bromate, the suppressed effluent from the conductivity detector is combined with an acidic solution of potassium iodide (KI) containing a catalytic amount of molybdenum (Mo) VI. The mixture is heated and the bromate reacts with iodide to form the tri-iodide ion which is measured by the UV/VIS detector.

Scope:
This methods determines inorganic oxyhalide disinfection by-product anions in reagent water, surface water, ground water, and finished drinking water. In addition, bromide can be determined in source or raw water (but not in finished drinking water).

Citation:
EPA Web site for Analytical Methods for Drinking Water

Interferences:
(A) Coelution: Direct chromatographic coelution, concentration dependent coelution, and ionic displacement effects (which can shift rentention times) can all cause interferences by coelution. It may be possible to overcome by adjusting chromatographic conditions (e.g., changing columns), diluting the sample, or using pretreatment cartridges. Care must be taken when using these steps to ensure that analyses are not adversely affected.(B) Contamination: Interferences may be caused by contaminants in the reagent water, reagents, glassware, and other sample processing apparatus that lead to discrete artifacts or elevated baselines.(C) Particulate: Samples containing particles > 0.45 um, and reagents containing particles > 0.20 um can damage chromatography columns and flow systems. Filtration should be use to prevent damage.(D) Carry over: Carry over peaks from one analysis to another may also cause interferences as false positives.(E) Chlorine dioxide: Sample matrices with residual chlorine dioxide will result in the formation of additional chlorite prior to analysis.(F) Chlorite: The presence of chlorite can interfere with the quantitation of low concentrations of bromate on the postcolunn UV/VIS absorbance detector.

QC Requirements:
Initial Demonstration of Capability must show acceptable Demonstration of Accuracy (IDA)and Precision (IDP) and the Detection Limit (DL) must be determined. Laboratory Reagent Blanks (LRB) and Laboratory Fortified Blanks (LFB) must be run with every analysis batch. Continuing Calibration Checks (CCC) must be run after every 10 samples and after the last sample. Relative Percent Difference (RPD) for field or laboratory fortified sample matrix duplicates must be within prescribed limits depending on analyte concentrations. A surrogate of dichloroacetate is added to all blanks, samples, and standards and its recovery must be 90 - 115%.

Maximum Holding Time:
28 days (chlorite 14 days)

Media:
WATER

Subcategory:
Inorganic

Concentration:
5 - 500 ug/L (5 - 100 ug/L for Bromate) -- Conductivity; 0.1-15.0 ug/L (Bromate) -- UV-vis

Sample Prep:
None

Precision:
Precision and accuracy values were determined by analyzing eight replicates of fortified reagent water (see Table 3 of the method), using the conditions specified in Table 1 of the method. Values for all analytes were determined using conductivity detection. Additional data are available in the method.

Detection:
Detection Limits determined by analyzing 8 replicate laboratory fortified blanks (LFB) at a concentration estimated to be near the Detection Limit over at least 3 days. The procedure is similar to that found in 40 CFR 136, Appendix B, with the addition of a multi-day analysis component.

Revision Number:
Revision 1.0, June 2002

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