ASTM: D6239: Uranium in Drinking Water

Summary
Analytes
Revision
Data and Sites

Official Method Name

Standard Test Method for Uranium in Drinking Water by High-Resolution Alpha-Liquid-Scintillation Spectrometry

Current Revision

Current edition approved August 10, 1998. Originally published as D6239-98.

Media

WATER

Instrumentation

Alpha Scintillation

Method Subcategory

Radiochemical

Method Source

ASTM

Citation

Annual Book of ASTM Standards, Section 11, Water and Environmental Technology, Volume 11.02, Water (I)

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 Concentration 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 (SO₄^2-) did not interfere with the extraction of uranium at concentrations as high as 1 M, but hydrogen oxalate (HC₂O_4-) concentrations greater than 0.001 M and dihydrogen phosphate (H₂PO_4-) 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

Quality Control 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

Maximum Holding Time

Relative Cost

Unknown

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Uranium-238(7440-61-1) 238U 238U Element U U-238 Uranium Uranium (PM10) STP Uranium (TSP) Uranium 238 Uranium PM2.5 LC Uranium PM2.5 STP Uranium, natural Uranium-238	0.037 Bq/L	100% Rec (ML)	6.20			3.30 Bq/L

Precision Descriptor Notes:	The collaborative test conducted on this test method included seven laboratories, each with one operator. Three radioactivity levels, 0.3 Bq/L (8.0 pCi/L), 3.3 Bq/L (89.3 pCi/L) and 13.5 Bq/L (365.4 pCi/L), of natural uranium were tested with three replicates per level. Each level also contained 1.83 Bq/L (49.5 pCi/L) Ra-226 (and progeny) and 1.9 Bq/L (52 pCi/L) Th-230. These collaborative test data were obtained using tap water available at each laboratory site. For other matrices, these data may not apply.
Detection Level Note:	None.

Precision Descriptor Notes:

The collaborative test conducted on this test method included seven laboratories, each with one operator. Three radioactivity levels, 0.3 Bq/L (8.0 pCi/L), 3.3 Bq/L (89.3 pCi/L) and 13.5 Bq/L (365.4 pCi/L), of natural uranium were tested with three replicates per level. Each level also contained 1.83 Bq/L (49.5 pCi/L) Ra-226 (and progeny) and 1.9 Bq/L (52 pCi/L) Th-230. These collaborative test data were obtained using tap water available at each laboratory site. For other matrices, these data may not apply.

Detection Level Note:

None.

Revision	PDF/Link
Current edition approved August 10, 1998. Originally published as D6239-98.

The Water Quality Portal contains sample results from sites that use this method.

Download WQP data

Select data:

Sites only
Sample results only

File format:

Comma-separated
Tab-separated
MS Excel 2007+

Sites where this method was used

Loading Sites ...

ASTM: D6239: Uranium in Drinking Water

WHO WE ARE

LEGAL