Standard Methods: 7110 C: Gross Alpha Radioactivity by Coprecipitation

Summary
Analytes
Revisions
Data and Sites

Official Method Name

7110 C. Coprecipitation Method for Gross Alpha Radioactivity in Drinking Water

Current Revision

Standard Methods 18th, 19th, 20th ed.

Media

WATER

Instrumentation

Alpha Scintillation

Method Subcategory

Radiochemical

Method Source

Standard Methods

Citation

Standard Methods Online - Standard Methods for the Examination of Water and Wastewater

Brief Method Summary

All alpha-emitting radionuclides of interest (mainly radium, uranium, and thorium isotopes) are coprecipitated with barium sulfate and iron hydroxide as carriers, thereby separating alpha-emitting radionuclides from other sample dissolved solids. The combined precipitates are filtered and counted for alpha activity. Relatively large samples can be analyzed so that sensitivity is improved and counting time is minimized.

Scope and Application

For drinking water samples with high dissolved solids content, e.g., 500 mg/L or higher, Method 7110 B is severely limited because of the small sample size possible and the very long counting times necessary to meet required sensitivity (3 pCi/L). This coprecipitation procedure (7110 C) eliminates the problem of high dissolved solids and gives increased sensitivity.

Applicable Concentration Range

Interferences

Soluble ions that coprecipitate and add to the mixed barium sulfate and iron hydroxide precipitate weights result in counting efficiencies that are biased low. Iron hydroxide precipitates collected on membrane filters without a holding agent flake when dried and are easily lost from the filter. Add 5 mg paper pulp fiber to the sample to help secure the iron hydroxide to the filter. Preferably use glass fiber filters because the surface glass fibers help to secure the precipitate.

Quality Control Requirements

See Section 7020 Quality Assurance/Quality Control.

Sample Handling

Plastic or glass containers. Preserve samples with concentrated HCl or HNO₃ to pH <2. If HCl is used to acidify samples to be analyzed for gross beta activities, convert the acid salts to nitrate salts before transfer or samples to planchets.

Maximum Holding Time

1 year

Relative Cost

Greater than $400

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Alpha radiation(12587-46-1) Alpha particles Alpha radiation Gross alpha Gross alpha particle activity Radioactivity, alpha Total alpha radioactivity	N/A	102% Bias (ML)	N/A

Precision Descriptor Notes:	In collaborative test with 18 laboratories participating, gross alpha activities for four different samples were calculated with four different alpha-emitting radionuclide standard counting efficiencies. Thorium-230, a pure alpha-emitter, appeared to be the best standard for gross alpha counting efficiency. A comparison of the 18 laboratory grand average results (calculated with the thorium-230 counting efficiency) and known gross alpha particle concentrations showed accuracy indexes of 91.9, 99.4, 122, and 94.5%, respectively, for an average accuracy index of 102%. The t-test for bias showed a significant positive bias for Sample C but no significant bias for the other three samples.
Detection Level Note:

Precision Descriptor Notes:

In collaborative test with 18 laboratories participating, gross alpha activities for four different samples were calculated with four different alpha-emitting radionuclide standard counting efficiencies. Thorium-230, a pure alpha-emitter, appeared to be the best standard for gross alpha counting efficiency. A comparison of the 18 laboratory grand average results (calculated with the thorium-230 counting efficiency) and known gross alpha particle concentrations showed accuracy indexes of 91.9, 99.4, 122, and 94.5%, respectively, for an average accuracy index of 102%. The t-test for bias showed a significant positive bias for Sample C but no significant bias for the other three samples.

Detection Level Note:

Revision	PDF/Link
Standard Methods 18th, 19th, 20th ed.
Standard Methods 19th edtion (1995)
Standard Methods 18th edtion (1992)
Standard Methods Online

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Standard Methods: 7110 C: Gross Alpha Radioactivity by Coprecipitation

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