EPA-NERL: 509: Ethylene thiourea in water using GC with a N-P detector
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Official Method Name
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Determination of ethylene thiourea (ETU) in water using gas chromatography with a nitrogen-phosphorus detector |
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Current Revision
| Rev. 1.1, 1995 |
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Media
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WATER |
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Instrumentation
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Gas Chromatography with Nitrogen - Phosphorus 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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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. |
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Brief Method Summary
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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). |
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Scope and Application
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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). |
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Applicable Concentration Range
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Concentration range is dependent on the instrument calibration range. |
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Interferences
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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. |
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Quality Control Requirements
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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. |
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Sample Handling
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Grab samples must be collected in 60-mL glass containers fitted with Teflon-lined screw caps. Conventional sampling practices should be followed; however, the bottle must not be pre-rinsed with sample before collection. The samples must be iced or refrigerated at 4oC and protected from light from the time of collection until extraction. Samples should be extracted as soon as possible after collection to avoid possible degradation of ETU. All samples must be extracted within 14 days of collection. Extracts must be stored under refrigeration and protected from light. Extracts must be analyzed within 28 days of extraction. ETU may chemically degrade in some samples even when the sample is refrigerated. When this method was developed, mercuric chloride was used to ensure against biological degradation. No suitable preservation reagent has been found other than mercuric chloride. However, the use of mercuric chloride is not recommended due to its toxicity and potential harm to the environment. Biological degradation may occur only rarely in samples with limited biological activity such as finished drinking waters. |
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Maximum Holding Time
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Sample extraction must occur within 14 days of collection; extracts must be analyzed within 28 days of extraction. |
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Relative Cost
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$201 to $400 |
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Sample Preparation Methods
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