This method is for the determination of gross alpha and gross beta particle activities in drinking water. The method is a screening technique for monitoring drinking water supplies for alpha and beta particle activities according to the limits set forth under the Safe Drinking Water Act. The method is applicable to the measurement of alpha emitters having energies above 3.9 megaelectronvolts (MeV) and beta emitters having maximum energies above 0.1 MeV.
An aliquot of a preserved drinking water sample is evaporated to a small volume and transferred quantitatively to a tared 2-inch stainless steel counting planchet. The sample residue is dried to constant weight, reweighed to determine dry residue weight, then counted for alpha and/or beta radioactivity. Counting efficiencies for both alpha and beta particle activities are selected according to the amount of sample solids from counting efficiency vs sample solids standard curves.
The radioactivity of the sample is not separated from the solids of the sample so the solids concentration can be a limiting factor in the sensitivity of the method. For drinking water samples with extremely high solids content (>500 ppm), Method 900.1 is recommended.
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| Hold Times, Preservatives, Preps, Collection, Analytical & Documentation | |
|---|---|
| Holding Time: | 5 days from sample collection to analysis if unpreserved and held in the original container for a minimum of 16 hours before analysis or transfer of the sample. None specified for preserved samples. |
| Preservatives: | Add 1N nitric acid to the sample to bring it to pH 2 (15mL 1N HNO3 per L of sample). |
| Required Preps: | 250mL Glass or plastic bottle with Teflon-lined lid |
| Collection Method: | Grab sampling |
| Analytical Methodology: | Gas-flow proportional counting system, or Scintillation detector system and Stainless steel counting planchets |
| Documentation: | 
900.0
|
| Analyte | Formula | CAS Number | Detection Limit | |
|---|---|---|---|---|
| Alpha Particles | 5 |
pCi/L | ||
| Beta Particles | 5 |
pCi/L | ||
* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.