Method 548.1

Determination of Endothall in Drinking Water by Ion Exchange Extraction, Acidic Methanol Methylation and Gas Chromatography/Mass Spectrometry

This method is for the determination of endothall in drinking water sources and finished drinking water.  A 100 mL sample is extracted using a liquid-solid extraction (LSE).  The analyte is eluted with 8 mL of acidic methanol.  After addition of a small volume of methylene chloride as a co-solvent, the dimethyl ester of endothall is formed within 30 minutes with modest heating (50°C).  After addition of salted reagent water, the ester is partitioned into 8-10 mL of methylene chloride. The extract volume is reduced and is analyzed by gas chromatography/mass scectrometry (GC/MS) or GC/FID (flame ionization detector) with a megabore capillary column.

Dissolved calcium, magnesium and sulfate are known potential interferences with the analysis.


(EPA: Office of Water)


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Method Data

Hold Times, Preservatives, Preps, Collection, Analytical & Documentation
Holding Time:   7 days from sample collection to extraction and a maximum of 14 days from extraction to analysis.
Preservatives:   Add 80 mg of sodium thiosulfate per liter of sample to the bottle prior to collection if residual chlorine is present. The samples must be iced or refrigerated at 4°C from the time of collection until extraction and analysis. Avoid excessive exposure to heat and light.
Required Preps:   250mL Amber glass bottle with Teflon-lined lid
Collection Method:   Grab sampling
Analytical Methodology:   GC/MS
Documentation:   548.1

Analyte List*

Analyte Formula CAS Number Detection Limit

* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.