EPA-TSC/NERL: 515.1: Chlorinated Acids in Water by GC/ECD
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Official Method Name
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Determination of Chlorinated Acids in Water by Gas Chromatography with an Electron Capture Detector |
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Current Revision
| Revision 4.1, 1995 |
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Media
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WATER |
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Instrumentation
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Gas Chromatography with Electron Capture Detection |
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Method Subcategory
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Organic |
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Method Source
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Citation
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Brief Method Summary
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A measured volume of sample of approximately 1 L is adjusted to pH 12 with 6 N sodium hydroxide and shaken for one hour to hydrolyze derivatives. Extraneous organic material is removed by a solvent wash. The sample is acidified, and the chlorinated acids are extracted with ethyl ether by shaking in a separatory funnel or mechanical tumbling in a bottle. The acids are converted to their methyl esters using diazomethane as the derivatizing agent or alternatively trimethylsilyldiazomethane (TMSD). Excess derivatizing reagent is removed, and the esters are determined by capillary column/GC using an electron capture detector (ECD). Note: Method 515.1 calls for a solvent wash step after hydrolysis and prior to acidification and derivatization. Dacthal, the parent di-ester, does not hydrolyze, and is extracted in the wash step, leaving the mono- and di-acid metabolites to be measured. |
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Scope and Application
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This is a gas chromatographic (GC) method applicable to the determination of certain chlorinated acids in ground water and finished drinking water. This method is also applicable to the determination of salts and esters of analyte acids. This method should be used by or under the supervision of analysts experienced in the use of GC and in the interpretation of gas chromatograms. |
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Applicable Concentration Range
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Ranges differ for each analyte depending on matrix and instrumentation. |
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Interferences
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(1) Contaminants in solvents, reagents, glassware and other sample processing apparatus that lead to discrete artifacts or elevated baselines in gas chromatograms. (2) Acid forms of the analytes are strong organic acids which react readily with alkaline substances and can be lost during sample preparation. (3) Organic acids and phenols, especially chlorinated compounds. (4) Interferences by phthalate esters can pose a major problem in pesticide analysis when using the ECD. These compounds generally appear in the chromatogram as large peaks. (5) Matrix interferences may be caused by contaminants that are coextracted from the sample. (6) Rinsing apparatus with MTBE between analyses can minimize contamination from sample carryover. (7) Use the same solvent for each analysis to reduce the interferences from variable solvents. |
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Quality Control Requirements
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Laboratory Duplicate (LD), Field Duplicate (FD), Laboratory Reagent Blank (LRB), Field Reagent Blank (FRB), Laboratory Performance Check Solution (LPC), Laboratory Fortified Blank (LFB), Laboratory Fortified Matrix (LFM), Quality Control Sample (QCS), Performance Evaluation Sample (PE), Surrogate Analyte, Internal Standard |
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Sample Handling
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Grab samples must be collected in glass containers which must not be prerinsed with sample prior to collection. Prior to collection, add 1 mL of 10 mg/L mercuric chloride to the bottle to produce a concentration of 10 mg/L. If residual chlorine is present, also add 80 mg/L of sodium thiosulfate prior to collection. After collection, shake sample containing preservative(s) vigorously for one minute. Keep samples iced or refrigerated at 4oC and away from light until extraction. |
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Maximum Holding Time
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Analytes present in samples (prior to extraction) are stable for 14 days when properly stored. However, analyte stability may be affected by sample matrix. Extracts should be stored at 4oC and away from light. Most extracted analytes are sta |
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Relative Cost
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$201 to $400 |
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Sample Preparation Methods
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