The analytical accuracy that is associated with any particular lot of samples is measured through the analysis of laboratory control samples and matrix spike samples.
The laboratory control sample is a sample that has an interference free matrix, which is spiked with method target analytes.
The matrix spike sample is an actual environmental sample that is spiked with the method target analytes. The recovery of spiked analytes from laboratory control samples and matrix spike samples are used to determine laboratory performance and assess the suitability of a particular sample matrix for the analytical method involved.
Inherent interference, which can either artificially enhance or suppress the signal from an analyte, can be detected through the information, which is obtained by the calculated recoveries of a laboratory control sample. These samples, which are prepared and analyzed under the same conditions as matrix spike samples, provide assurance that the analytical method is in control when a poor matrix spike recovery is observed (which indicates matrix interference).
Precision of analytical work is routinely determined by the analysis of duplicate samples at a frequency of 10 or one per batch of samples, whichever quantity is greater. The Relative Percent Difference (RPD) between two results is calculated. The value of RPD falls within a known range for each analytical method that is employed.
For concentration of analytes that approach zero, the value of RPD can increase significantly, which does not mean a low precision in the analysis. To compensate for this limitation, a duplicate spike matrix is analyzed and the RPD is calculated to determine the precision.
AETL assumes that the analytical work performed on every sample received may be used in some type of future litigation. Therefore, all analytical data will be created to meet specific objectives as outlined in the statement of the particular project.
If sampling procedures do not provide representative samples, even the most rigid of analytical QC/QA programs cannot ensure that the results obtained are representative of the site. The AETL laboratory staff members responsible for the sampling process have many years of experience in obtaining representative samples from different matrices, and AETL’s quality assurance procedure for sampling ensures that the samples obtained are representative of the site.