EPA Method 509

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EPA Method 509:
Determination of Ethylene Thiourea (ETU) in Water using Gas Chromatography with a Nirogen-Phosphorus Detector.

Summary:
The ionic strength and pH of a measured 50-mL aliquot of sample are adjusted by addition of ammonium chloride and potassium fluoride. The sample is poured onto a column of kieselguhr diatomaceous earth. ETU is eluted from the column with 400 mL of methylene chloride. A free radical scavenger is then added in excess to the eluate. The methylene chloride eluant is concentrated to a volume of 5 mL after solvent exchange with ethyl acetate. Gas chromatographic conditions are described which permit the separation and measurement of ETU with a nitrogen-phosphorus detector (NPD).

Scope:
This method utilizes gas chromatography (GC) to determine ethylene thiourea (ETU) in water. When a tentative identification of ETU is made using the recommended primary GC column (Sect. 6.7.1), it must be confirmed by at least one additional qualitative technique. This technique may be the use of the confirmation GC column (Sect. 6.7.2) with the nitrogen- phosphorus detector or analysis using a gas chromatograph/mass spectrometer (GCIMS).

Citation:
Munch, J.W., ed., 1995, Determination of ethylene thiourea (ETU) in water using gas chromatography with a nitrogen-phosphorus detector, in Methods for the determination of organic compounds in drinking water: U.S. Environmental Protection Agency Report EPA/600/R-95/131, Revision 1.1, p. 253-273.

Interferences:
Method interferences from contaminants in solvents, reagents, glassware and other sample processing apparatus may cause discrete artifacts or elevated baselines in gas chromatograms. All reagents and apparatus must be routinely demonstrated to be free from interferences under the conditions of the analysis by running laboratory reagent blanks.Interfering contamination may occur when a sample containing a low concentration of ETU is analyzed immediately following a sample containing a relatively high concentration of ETU. Thorough between-sample rinsing of the sample syringe and associated equipment with ethyl acetate can minimize sample cross contamination. After analysis of a sample containing high concentrations of ETU, one or more injections of ethyl acetate should be made to ensure that accurate values are obtained for the next sample.Matrix interferences may be caused by contaminants that are coextracted from the sample. The extent of matrix interferences may vary considerably from source to source, depending upon the sample. Tentative identifications must be confirmed using the confirmation column and the conditions discussed in the method report.Studies have shown that persistent ETU decomposition is circumstantially linked to free radical mechanism. Addition of a free radical scavenger is necessary to prohibit any free radical reactions.It is important that samples and working standards be contained in the same solvent. The solvent for working standards must be the same as the final solvent used in sample preparation. If this is not the case, chromatographic comparability of standards to sample may be affected.

QC Requirements:
Each laboratory using this method is required to operate a formal quality control program. At a minimum, this program should consist of an initial demonstration of laboratory capability; measurement of the surrogate compound in each sample; and analysis of laboratory reagent blanks, laboratory fortified blanks, laboratory fortified matrix samples, and quality control check standards.

Maximum Holding Time:
Sample extraction must occur within 14 days of collection; extracts must be analyzed within 28 days of extraction.

Media:
WATER

Subcategory:
Organic

Concentration:
Concentration range is dependent on the instrument calibration range.

Precision:
Precision and accuracy was determined through the single-laboratory analysis of 7 samples of fortified reagent water.

Detection:
MDLs were determined through the analysis of 7 replicate analyses of a fortified reagent water sample.

Revision Number:
Rev. 1.1, 1995