Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 2/9)
Character Range: 719212–722137

may be obtained through inter-laboratory comparisons.

This guideline recommends certain extraction procedures or, in some cases, complete methods—each laboratory should fully validate each method used (from extraction through to the determinative step) following the principles for quality assurance and method validation described in this Section and other relevant references (US EPA SW-846, APHA 2005-1040B method validation, NATA Technical Note 23, NATA Technical Note 17).

Validation should be performed on the range of soil types most likely to be analysed, or on the most complex soil type likely to be analysed (e.g. clay instead of sand).
All validation steps pertaining to the method should be recorded and retained while the method is being used.

Method performance should be based on extraction of a CRM and/or spiked samples (NATA Technical note 17) or compared with a more rigorous method.

The minimum validation data required are:
    * Accuracy Precision
    * Limit of detection (LOD)and limit of reporting (LOR)
    * Linearity (range over which accurate quantification is expected)
    * Uncertainty of measurement (MU).

    3.2.1         Accuracy
Accuracy is a measure of the closeness of the analytical result to the 'true' value (NATA Technical note 17). When low analyte concentrations are present the results of a reference method may differ by as much as ±30 % of:
    * the expected value of a certified reference material (CRM) of similar matrix; or
    * the value obtained by another currently-accepted and separately validated quantitative method for the sample matrix.
This is a particular issue when analyte concentrations are less than 10 times the minimum detectable concentration. Apparent lower recoveries than those specified for the method will occasionally be obtained for CRMs which have been assessed by more rigorous methods involving matrix dissolution. The specific analyte cited in the CRM certificate should match that being determined under this Schedule. For example, if the certified reference values are obtained using aqua regia digest, only the aqua regia method should be applied for comparison with this CRM. Otherwise, an alternative CRM should be used.

3.2.1.1         Percent recovery
This is the most realistic and useful component of the daily quality control performance (APHA 2005), and describes the capability of the method to recover a known amount of analyte added to a sample (in the form of either a laboratory control sample (LCS), matrix spike or surrogate compound spike).

The sample is spiked with a known quantity of the analyte, such that the total of the suspected natural concentration of the analyte plus the spike is within the working range of the method. For compliance monitoring, the spike level should be at or near the regulatory limit, or in the range of 15 times the background concentration.

If the background concentration is not