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6.4.1 At least once per year, re-evaluate the spiking level. If more than 5% of the spiked samples do not return positive numerical results that meet all method qualitative identification criteria, then the spiking level must be increased and the initial MDL re-determined following the procedure in Section 6.1. 6.4.2 At least once every 13 months, re-calculate MDLS and MDLb using the equations in Section 6.2. Include data generated within the last 24 months, but only data from the same spiking level. A spreadsheet that collates each spiking level can be helpful for comparison. Documented instances of gross failures (e.g., instrument malfunctions, mislabeled samples, cracked vials) may be excluded from calculations. The rationale for removal of specific outliers shall be documented and maintained on file with the results of the MDL determination. If the laboratory believes the sensitivity of the method has changed significantly, then the data set used for calculations may be limited to the most recently collected data, while maintaining compliance with the requirement for at least seven replicates in three separate batches on three separate days (see Section 6.2.3). 6.4.3 Include the initial MDL spiked samples if they were analyzed within the last 24 months. 6.4.4 Only use data associated with acceptable calibrations and batch QC. 6.4.5 For MDLb calculations, include method blanks for all routine batches, with the exception of batches that are rejected and the associated samples reanalyzed. If the method has been altered in a way that can be reasonably expected to change its sensitivity, then only use data collected after the change. 6.4.6 Ideally, use all method blank results from the last 24 months for the MDLb calculation. The laboratory has the option to use only the last 6 months of method blank data or the 50 most recent method blanks, whichever criteria yields the greater number of method blanks. 6.4.7 The new calculated MDL is equal to the greater of the MDLS or MDLb. 6.4.8 If the new calculated MDL is within 0.5 to 2.0 times the existing MDL and fewer than 3% of the method blank results (for the individual analyte) have numerical results above the existing MDL, then the existing MDL may remain unchanged. If the new calculated MDL is not within 0.5 to 2.0 times the existing MDL or more than 3% of the method blank results (for the individual analyte) have numerical results above the existing MDL, then the new calculated MDL shall be used going forward. NOTE: The range of 0.5 to 2.0 approximates the 95th percentile confidence interval for the initial MDL determination with 6 degrees of freedom and is used to determine if the two values are statistically similar. 6.5) Determination of Initial MDL for a Specific Matrix 6.5.1 This section describes the determination of an MDL in a specific matrix other than a general quality systems matrix described in Section 5.3.1. 6.5.2 Analyze the sample matrix to determine the native (background) concentration of the analyte(s) of interest. 6.5.3 If the response for the native concentration is at a signal-to-noise ratio of N 5-20, determine the matrix-specific MDL according to Section 6.2, but without spiking additional analyte. Calculate MDLb according to Section 6.2.12, using method blanks, not the sample matrix. 6.5.4 If the response for the native concentration is at a signal-to-noise ratio is less than 5, then the analyte(s) should be spiked into the sample matrix to obtain a concentration that will give results with a signal-to-noise ratio of approximately 10-20. 6.5.5 If the analyte(s) of interest have signal-to-noise ratio(s) greater than —20, then the resulting MDL is likely to be biased high ' 6.6) Determination of the Limit of Quantitation (LOQ) 6.6.1 The LOQ shall be at or above the lowest corresponding calibration standard concentration, with the exception of methods using a single-point calibration, and must be greater than the MDL. 6.6.2 Each selected LOQ shall be verified through analysis of initial verification samples. An initial verification sample consists of spikes prepared and analyzed at concentrations at or below the selected LOQ. 6.6.3 All sample processing and analysis steps performed for routine sample analysis shall be included in the LOQ verification testing. 6.6.4 The LOQ shall have a signal-to-noise ratio of 6 or greater, twice the minimum for the MDL.