WORK PLANS - Laserfiche WebLink

Home Browse Search

• If none of the method blanks give numerical results for an individual analyte, the MDLb does not apply. All numerical results, including negative results and results below the current MDL, shall be included in the calculation. The only results that are not included are non-detects, such as when a peak is not present in chromatographic analysis. • If some, but not all, of the method blanks for an individual analyte give numerical results, set the MDLb to the highest MB result. If more than 100 method blanks are available, set the MDLb to the level that is no less than the 99th percentile of the method blank results. For"n" method blanks where n > 100, sort the method blanks in rank order. The (n * 0.99) ranked method blank result (round to the nearest whole number) is the MDLb. For example, to find MDLb from a set of 164 method blanks where the highest ranked method blank results are as follows: Rank: 160 161 162 163 164 Result: 1.5 1.7 1.9 5.0 10. Then 164 x 0.99 = 162.36, which rounds to the 162"d method blank result. Therefore, MDLb = 1.9 for n = 164 • Alternatively, you may use spreadsheet algorithms to calculate the 99th percentile to interpolate between the ranks more precisely. NOTE: It is important that there are a sufficient number of blanks with numerical results, nominally 20 or more, for this technique to be reliable. If there are fewer than 20 numerical results out of the 100 or more blanks in the set, then more blank data should be collected. • If all of the method blanks for an individual analyte give numerical results, then the MDLb can be as follows: Equation 3: MDL =X+ixS,, where f=Student's t-value appropriate for a single-tailed 99"1 percentile t statistic and a standard deviation estimate with n-1 degrees of freedom (see Attachment 1) Sb = sample standard deviation of the replicate method blank sample analyses determined using Equation 1 X= Mean Measured Concentration (use zero if the mean is negative) Alternatively, if all method blanks for an individual analyte give numerical results and there are more than 100 results available, then the MDLb may be set to the concentration that is greater than or equal to the 99th percentile of the method blank results (as in Sec. 6.2.12.b). This could be considered a more reliable estimate of the MDLb when the blank data are not normally distributed. • Select the greater of MDLS or MDLb as the initial MDL. V *_1r"UgW 6.3) Ongoing Data Collection 6.3.1 During any quarter in which samples are being analyzed, prepare and analyze a minimum of two (2) spiked samples on each instrument, in separate batches, using the same spiking concentration used in Section 6.2. If any analyses fail to produce positive results or do not meet qualitative identification criteria, then repeat the analysis of spikes one time. Repeated failure to produce usable results is an indication that the spiking level is not high enough and should be adjusted upward. In this case, the lab should consider repeating the initial MDL study. Note: It is not necessary to analyze more than one (1) method blank per batch for the quarterly analyses because the annual MDLb determination will be done using a population of method blanks from routine analytical batches during the year. 6.3.2 Ensure that at least seven (7) spiked samples and seven (7) method blanks are completed for the annual verification (Section 6.4). If only one instrument is in use, a minimum of seven (7) spikes are still required, but they may be drawn from the last 24 months of data collection 6.4) Ongoing Annual MDL Re-Evaluation