Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p6
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 6/9)
Character Range: 729882–732754

Matrix spikes below). The laboratory should use statistically derived quality control limits from ongoing LCS percent recovery data, for all target analytes, and report such QC limits with the sample data.

    3.3.5         Matrix spikes
A matrix is the component or substrate (e.g. water, soil) that contains the analyte of interest. A matrix spike is an aliquot of sample spiked with a known concentration of target analyte. A matrix spike documents the effect (bias) of matrix on method performance.

Matrix spikes should be added to the analysis portion before extraction or digestion and, in most cases, added at a concentration as close as practicable to the corresponding regulatory level (e.g. the relevant HIL or EIL). If the analyte concentration is less than half the regulatory level, the spike concentration may be as low as half the analyte concentration but not less than the LOR.

To avoid differences in matrix effects between sample and spiked sample, the matrix spikes should be added to the same nominal mass of soil sample as that which was analysed for the unspiked sample.

There should be one matrix spike per soil type per process batch.

If the percent recovery of the matrix spike is below the expected analytical method performance, the laboratory should investigate the likely cause and, where a suitable amount of soil mass remains, re-extract and analyse another spiked soil. It may be necessary to use other internal calibration methods (for example, isotope dilution, a modification of the analytical method or alternative analytical methods) to accurately measure the analyte concentration in the extract.

If, after investigation, the matrix spike percent recovery is still below method QC limits then this failed recovery should be reported to the client with an explanation to show the limitations of the method for that particular matrix. An acceptable LCS result may indicate that it is the matrix, not the method, that may be the issue but it is not acceptable to assign poor recovery to matrix effects, without a reasonable investigation.

    3.3.6         Surrogate spikes (where appropriate)
Surrogate spikes are known additions to each sample, blank, matrix spike or reference sample, of compounds that are similar to the analytes of interest in terms of:
    * extraction efficiency
    * recovery through clean-up procedures
    * response to chromatography or other determination
    * instrumental detector response
but which:
    * are not expected to be found in real samples
    * will not interfere with quantification of any analyte of interest
    * may be separately and independently quantified by virtue of, e.g. chromatographic separation or production of different mass ions in a GC/MS system.
Surrogates provide a means of checking that no gross errors have occurred at any stage of the procedure and which may