The recovery rate of a matrix spike sample is below the quality control acceptance criteria identified in the analytical method (13% - 111%). Is the corresponding field sample valid? What steps should be taken?
The corresponding field sample is valid. Some source water matrices may make it difficult to meet the matrix spike (MS) acceptance criteria. However, MS sample results will not be used to adjust Cryptosporidium recoveries at any individual source water, and no resampling will be necessary for MS samples that do not meet Method 1622/1623 recovery guidelines. The water system?s corresponding field sample will be accepted for calculation of the initial Crypto bin concentration.There may be steps that the lab can take in analyzing the samples that will improve recovery. The lab should contact the EPA Cryptosporidium Laboratory QA program at email@example.com to discuss the result and provide a description of the problem and their opinion regarding whether the water matrix was problematic in the analysis.
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