NEMI Method Summary

Method Summary Information

Method Number: D6239 Media: WATER
Revision: Current edition approved August 10, 1998. Originally published as D6239-98.
Method Source: ASTM International
Subcategory: RADIOCHEMICAL Analytes in this method
Official Name: Standard Test Method for Uranium in Drinking Water by High-Resolution Alpha-Liquid-Scintillation Spectrometry
Descriptive Name Uranium in Drinking Water
Source Info: ASTM International
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Citation: ASTM Volume 11.02
 
Brief Method
Summary:
 This test method is based on solvent extraction technology to isolate and concentrate uranium in drinking water for counting via a high-resolution alpha-liquid-scintillation spectrometer.
To determine total uranium, as well as limited isotopic uranium (238U and 234U) by activity in drinking water, a 200 mL acidified water sample is first spiked with 232U as an isotopic tracer, boiled briefly to remove radon, and evaporated until less than 50 mL remain. The solution is then made approximately 0.01 M in diethylenetriaminepentaacetic acid (DTPA) and the pH is adjusted to between 2.5 and 3.0. The sample is transferred to a separatory funnel and equilibrated with 1.50 mL of an extractive scintillator containing a dialkyl phosphoric acid extracting agent. Under these conditions only uranium is quantitatively transferred to the organic phase while the extraction of undesired ions is masked by the presence of DTPA. Following phase separation, 1.00 mL of the organic phase is sparged with dry argon gas to remove oxygen, a chemical quench agent, and counted on a high-resolution alpha-liquid-scintillation spectrometer and multichannel analyzer (MCA).
Scope And
Application:
 This test method covers determining the total soluble uranium activity in drinking water in the range of 0.037 Bq/L (1 pCi/L) or greater by selective solvent extraction and high-resolution alpha-liquid-scintillation spectrometry. The energy resolution obtainable with this technique also allows estimation of the 238U to 234U activity ratio.
Applicable
Conc Range:
 > 0.037 Bq/L
Interferences: During the development work on this method, less than 1% of 241Am, 238Pu, 210Po, 226Ra, 222Rn, and 230Th present in the original sample were found to extract under the conditions described for the extraction of uranium by this procedure. Uranium extraction is quantitative at pH values from 1.0 to 5.0 but extraction of 230Th and 238Pu increased slightly at pH values below 2.5 and phase separation was slower and less complete at pH values above 3.5. DTPA concentration is not critical in the range of 0.001 M to 0.1 M as long as a stoichiometric excess relative to the concentration of interfering ions, especially ferric ion (Fe3+), is maintained. As much as 30 mg of Fe3+ did not interfere with the extraction of uranium when the DTPA concentration was 0.010 M, and as much as 250 mg of Fe3+ did not interfere when the DTPA concentration was increased to 0.10 M. As much as 2000 mg of calcium ion (Ca2+) did not present an interference in a 0.010 M DTPA solution. Sulfate ion (SO42-) did not interfere with the extraction of uranium at concentrations as high as 1 M, but hydrogen oxalate (HC2O4-) concentrations greater than 0.001 M and dihydrogen phosphate (H2PO4-) concentrations greater than 0.2 M resulted in decreased uranium recovery. These concentrations, however, are several orders of magnitude higher than the normal concentration of these ions in drinking water.
Beta- and gamma-emitting radionuclide interference is minimized (typically 99.95 % rejection of beta/gamma pulses) according to McDowell and McDowell (2) by the pulse-shape discrimination of the high-resolution alpha-liquid-scintillation spectrometer.
Quenching, often a problem with liquid scintillation counting, is significantly reduced by the use of extractive scintillator technology and will
QC Requirements: Whenever possible, the project leader, as part of the external quality control program, should submit quality control samples to the analyst along with routine samples in such a way that the analyst does not know which of the samples are the quality control samples. These quality control samples, which usually include duplicate and blank samples, should test sample collection and preparation as well as sample analysis whenever this is possible. In addition, analysts are expected to run internal quality control samples that will indicate to them whether the analytical procedures are in control. Both the external and internal quality control samples should be prepared in such a way as to duplicate the chemical matrix of the routine samples insofar as this is practical. The quality control samples that are routinely used consist of five basic types: blank samples, replicate samples, reference materials, control samples, and "spiked" samples.
Sample Handling:
Max Holding Time:
 
Relative Cost: Unknown
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