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3.4.13 Quality control samples

The use of the types of quality control (QC) samples (see Table 3.32) described below should be standard practice.

Quality control samples Description
Blanks * Materials that do not (or should not) contain the chemical or radionuclide being analysed for. Ideally, the blank should be of a similar material (‘matrix’) to the samples being tested. A variety of blanks may be used, to determine the potential for contamination of the samples at various stages of the sample collection and analysis procedure.
* Field/method blank (typically applicable to water sampling). A radionuclide/chemical free sample that is taken to the field and then processed, transported and analysed in the same manner as the actual samples.
* Analytical blank. A radionuclide/chemical free material used in analytical testing laboratory to evaluate background contamination and cross-contamination.

Duplicate samples Samples taken either to assess reproducibility of the field sampling procedure (‘field duplicate’) or to enable inter- or intra-laboratory comparison (‘split samples’). Note: it is very difficult to collect duplicate soil samples as contaminant concentrations may vary over very small distances. However, duplicate samples of waters should yield the same result.

Standard samples Samples that contain known concentrations of the chemical or radionuclide being analysed for. These samples may be used by the analytical testing laboratory as a check on analytical results or may be submitted with the batch of samples for analysis. Typically, only standard solutions would be submitted in the latter case, because of the difficulty of preparing homogenous soil samples.

External quality control samples Samples of material spiked with a level of radioactivity known only to an external laboratory. These are tested alongside the field samples, to provide reassurance that the analyses are correct.

Table 3.32 Quality control samples