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6.2.4 Each of the replicate spikes is extracted or digested in the same manner as samples. Routine cleanup steps shall be included. If dilutions are routinely performed for entire batches of samples (e.g., soil batches run on older ICP/MS instruments), then the same routine dilution must be applied to the MDL spikes prior to analysis. Note: It is not acceptable to spike at a high concentration prior to extraction or digestion and then dilute down to the MDL spike concentration after preparation, unless that is part of the sample preparation procedure (e.g., Methanol extractions for Method 8260) 6.2.5 If there are multiple instruments that will be assigned the same MDL, then the spikes shall be distributed across all of the instruments. A minimum of 2 spiked samples and 2 method blanks shall be analyzed on different calendar days on each instrument. Each analytical batch may contain one spiked sample and one MB run together. 6.2.6 The same prepared extract may be analyzed on multiple instruments if the minimum requirement of 7 preparations in at least 3 separate batches analyzed on 3 separate calendar dates is maintained. 6.2.7 Statistical outlier tests should not be used to remove data for the initial MDL determination because the total number of observations is small and the purpose of the MDL procedure is to capture routine method variability. However, documented instances of gross failures (e.g., instrument malfunctions, mislabeled samples, cracked vials) may be excluded from the calculations, provided that at least 7 spikes and 7 method blanks are available and the reason for excluding data is properly documented. 6.2.8 Evaluate the spiking level: If any result for any individual analyte from the spiked samples does not meet the method qualitative identification criteria or does not provide a numerical result greater than zero, then re-prepare the spiked samples at a higher concentration. Note that qualitative identification alone does not ensure that quantitative results for the analyte can be obtained. 6.2.9 Make all computations as specified in the analytical method and express the final results in the method- specified reporting units. 6.2.10 Using the following equation, calculate the standard deviation of the replicate spike measurements and the standard deviation of the method blank measurements: �quatjon 1: S — rr�_r -r)` , where x=X—X X=individual measurement rr X= Mean Measured Concentration rT n=number of sample aliquots 6.2.11 Compute the MDL based on spikes (MDLs) as follows: Equation 2; MDLs =t x Ss,where t= Student's t-value appropriate for a slingle-tailed 99"' percentile t statistic and a standard deviation estimate with n-1 degrees of freedom(see Attachment I-) Ss = sample standard deviation of the replicate spiked sample analyses determined using Equation 1