Proficiency testing for contaminated soil analysis

Precision within a laboratory can be tightly controlled by the operation of internal quality control schemes. This can be achieved by undertaking replicated analysis of samples and/or possibly by analysing replicate samples. The analysis of certified reference materials offers a means whereby bias can be estimated. Another means of estimating a laboratory s performance is via participation in inter-laboratory proficiency-testing schemes. Originally, external quality control or inter-laboratory proficiency-testing schemes had been made available to assist laboratories to identify those areas where remedial action was considered necessary, in order to improve the quality of data 

One of the major disadvantages of using a consensus mean value instead of the true value is that it can never be stated with absolute certainty whether a result which appears to be outside the range of acceptability is in fact closer to the true value than the consensus mean. However unlikely, it may be that a majority of laboratories have generated poor results and a small number of laboratories have generated good results but it is the minority of laboratories that are assessed as poor performers. This situation could be avoided if certified reference materials were distributed. However, there are few reference materials that closely match or resemble all relevant matrices and determinands of interest, including concentration levels. 

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