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reasonable approach; however, some regulators may not allow it. It is up to each laboratory to determine and comply with the interpretation of the relevant regulatory agencies or receive an approved variance. • As surrogate compounds are not analyzed to concentrations below the quantitation limit, a MDL is not required for surrogates, except for DoD/DoE QSM analyses. 5.3) Matrix 5.3.1 MDL spikes shall be prepared in a quality system matrix (e.g., reagent water, Ottawa Sand, or sodium sulfate) free of the analytes of interest and free of interfering substances. 5.3.2 When analyzing a non-routine sample matrix, the laboratory shall investigate test matrix materials for MDL studies that might best match the sample matrix. This should be discussed with client before proceeding. 5.3.1 Provisions for initial MDL studies in a non-routine specific matrix are described in Section 6.5. 5.4) Accompanying QC and Analysis 5.4.1 Each preparation batch of MDL spikes shall include a method blank. 5.4.2 The instruments used to conduct the MDL analyses must meet all tune and calibration requirements. 5.4.3 Each analyte must be qualitatively identifiable (e.g., appear in both columns for dual column methods, characteristic ions for GCMS mass spectra, etc.). 1. The same integration settings that are used for samples must be applied to MDL standards. 2. Manual integrations to force the baseline for detection are not allowed. 3. It is not acceptable to perform special manual integrations to produce lower detection limits. 4. The signal-to-noise ratio for quantitation and confirmation (qualifier ions or confirmation column results) should be 3 or greater. 5.4.4 For methods that require confirmation using two separation columns with the same type of detector, results from both columns shall be obtained and can then be pooled when calculating MDLs. When different detector technologies are used for confirmation, the data are calculated separately for each detector and the final MDL will be the higher of the two. IPPF 6) Procedure 6.1) Procedural Variations Procedural variations are allowed only if deemed necessary in the professional judgment of the supervisor to accommodate variation in sample matrix, radioactivity, chemistry, sample size, or other parameters. Any variation in procedure shall be completely documented using a Nonconformance Memo and approved by a supervisor and QA Manager. Any deviations from this procedure identified after the work has been completed must be documented as a nonconformance, with a cause and corrective action described. A Nonconformance Memo shall be used for this documentation. 6.2) Initial Determination of MDL 6.2.1 Estimate the initial MDL using one or more of the following • The mean concentration of a set of method blanks plus three (3) standard deviations, • The concentration equivalent to an instrument signal-to-noise ratio in the range of 3 to 5, • The concentration equivalent to three (3) times the standard deviation of replicate instrumental measurements of spiked blanks, • That region of the calibration where there is a significant change in sensitivity, i.e., a break in the slope of the calibration, or • Previously determined MDL. 6.2.2 Select a spiking level, typically 2 to 10 times the estimated MDL. Spiking levels in excess of ten (10) times the estimated MDL may be required for analytes with poor recovery. 6.2.3 Process a minimum of seven (7) spiked replicates and seven (7) method blanks through all steps of the method. The replicates and blanks used for the MDL study must be prepared in at least three (3) different batches on three (3) separate calendar dates and analyzed on three (3) separate calendar dates. Note: Existing data generated within the last 24 months may be used as long as there are at least three (3) batches oreoared and analvzed on 3 seoarate days.