EPA Method 515.2

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EPA Method 515.2:
Determination of Chlorinated Acids in Water using Liquid-Solid Extraction and Gas Chromatography with an Electron Capture Detector - Revision 1.1.

Summary:
A 250-mL sample is adjusted to a basic pH with sodium hydroxide 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 a resin based extraction disk. The acids are converted to their methyl esters using diazomethane or alternatively, trimethylsilyldiazomethane (TMSD). Excess derivatizing reagent is removed, and the concentrations of acids are measured by detecting the derivative esters using a capillary column gas chromatography (GC) system equipped with an electron capture detector (ECD).Note: Method 515.2 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.

Scope:
This method determines certain chlorinated acids in ground water and finished drinking water.

Citation:
Methods for the Determination of Organic Compounds in Drinking Water - Supplement III (EPA/600/R-95-131)

Interferences:
(A) Glassware contamination: Thoroughly clean glassware, including baking or solvent rinse.(B) Reagent contamination: Use high purity reagents. NOTE: When purifying solvents by distillation stabilizers and preservatives are removed, making them potentially more dangerous and decreasing shelf-life.(C) Neutralization/Adsorption: Acid-rinse glassware and acidify sodium sulfate reagent to prevent loss of organic acids.(D) Organics: Organic acids, phenols, phthalate esters, and chlorinated compounds that can interfere and can be partially removed using alkaline hydrolysis and extraction.(E) Phthalate ester interference: Avoid the use of plastics and use pure reagents to avoid contamination by these ubiquitous compounds.(F) Contamination from sample carryover: Rinsing apparatus with MTBE between analyses can minimize contamination.(G) Extracted interferences: Interference from extracted non-target compounds, with retention times similar to target compounds, can be reduced by using confirmation analysis.(H) TMSD: The TMSD derivatizing agent can obscure the signal from 2,4-dichloro-phenylacetic acid surrogate. Using diazo-methane or a different surrogate overcomes this interference.(I) Variable solvents: Use the same solvent for each analysis.

QC Requirements:
Initial demonstration of laboratory capability, followed by determination of surrogate compound recoveries in each sample and blank, monitoring internal standard peak area or height in each sample and blank, analysis of laboratory reagent blanks (LRBs), laboratory fortified matrices, laboratory fortified blanks (LFBs), and QC samples. A MDL for each analyte must also be determined.

Maximum Holding Time:
All analytes but 5-hydrocy-dicamba are stable in water for 14 days, though stability should be checked.Extracts can be stored for 14 days.

Media:
WATER

Subcategory:
Organic

Concentration:
Ranges differ for each analyte depending on matrix and interferences.

Precision:
Precision and accuracy values calculated using seven replicate analyses of fortified reagent water samples. Additional data are available in the method. NOTE: Dacthal monoacid and diacid metabolites are included in the scope of the method, but only Dacthal diacid metabolite was used in the validation studies.

Detection:
MDLs were determined using the standard deviation of replicate analyses of an analyte-fortified reagent water sample multiplied by the t-value for (# of samples - 1) degrees of freedom at the 99% confidence level. Detailed instructions for how MDLs are determined are found at 40 CFR part 136, Appendix B.

Revision Number:
Revision 1.1, 1995