Lab Technology Day May 3, 2018 Department of Environmental Quality The Proposed Now Required Method Detection Limit Procedure Department of Environmental Quality
2 Now Required! NC began requiring use of the new procedure effective April 1, 2018. Department of Environmental Quality 3 Exception! NC requires MDLs only if required
in the method itself.for now. A general requirement in a QC section outside the method does not apply ...for now. Example: SM 4020 B-2011 Department of Environmental Quality 4 Basic Overview Initial MDL Determination 1. Background Determination 2. Spike Level Determination
Ongoing MDL Verification Multiple Instruments MDL Department of Environmental Quality 5 Initial Vs. Ongoing Verification Initial Verification: When a new method is implemented or if a method was rarely used in the last 24 months. Also, when the laboratory does not have adequate data to perform the Ongoing Verification.
Ongoing Verification: Prepare and analyze at least two spikes and two method blanks quarterly. Update MDL calculations yearly (every 13 months). Department of Environmental Quality 6 Background Determination Procedure now requires an evaluation of background contamination through the analysis of method blanks.
Department of Environmental Quality 7 Determine MDLb for Method Blanks For Initial Determination Process a minimum of 7 method blanks through entire procedure If all blanks are non-detects, then MDLb does not apply Department of Environmental Quality
8 Method Blank MDLb (Initial Determination) If some (but not all) of the method blank give numerical results, set MDLb equal to the highest method blank result. If all of the method blanks are nondetects, then the MDLb is set to equal the MDLs. Department of Environmental Quality
9 Method Blank MDLb (Initial Determination) If all method blanks give numerical results, then calculate MDLb as: Mean of blanks + (Students t x Std Dev) However, if the mean is negative, then use zero for the mean. Department of Environmental Quality
10 Method Blank MDLb (Determination Summary) MDLb = MDLs if all blanks are ND
MDLb = Highest blank value if some, but not all, blanks are ND MDLb = (Std Dev x t-value) if all blanks are numerical and their mean is negative MDLb = Mean of blanks + (t-value x Std Dev) if
none of the above criteria are Department of Environmental Quality true 11 Spiked Blank MDLs (Initial Determination) Select spiking level Process a minimum of 7 spikes
Calculate results as specified in the analytical method Evaluate the spiking level Calculate the MDLs Department of Environmental Quality 12 Selecting the Spiking Level First, estimate the initial MDL using one or more of the following: The mean concentration of a set of method blanks plus 3 x the Standard Deviation.
The concentration value corresponding to an instrument signal-to-noise ratio in the range of 3 to 5. The concentration equivalent to 3x the Standard Deviation of replicate instrumental measurements of spiked blanks. Department of Environmental Quality 13 Selecting the Spiking Level Estimation of the initial MDL (continued): That region of the calibration where there is a significant
change in sensitivity (e.g., a break in the slope of the calibration). Instrumental limitations. Previously determined MDL. Department of Environmental Quality 14 Selecting the Spiking Level Spiking levels are typically set at 2 10 times the estimated MDL.
Note: Spike < 10 x MDL rule is gone. Spiking levels in excess of 10 times the estimated MDL may be required for analytes with very poor recovery. Department of Environmental Quality 15 Process a Minimum of 7 Spikes Spikes must go through all steps of the preparatory and analytical methods.
Must be prepared in 3 separate prep and analysis batches on 3 separate calendar dates. Prep and analysis may be on the same day, but that is not a requirement unless specified by the method. Department of Environmental Quality 16 Spiked Blank MDLS (Initial Determination)
Calculate Results as Specified in the Analytical Method Statistical outliers may not be excluded unless documented as gross failures. Calculate the MDLS MDLS = Students t x Std Dev Department of Environmental Quality 17 Determine Final MDL Determine MDLs = Students t x Std Dev
Determine MLDb = Mean of Blanks* + (Students t x Std Dev) HIGHER of the two is the new MDL Department of Environmental Quality 18 Initial MDL Determination 19
Ongoing Data Collection During any quarter in which samples are being analyzed prepare and analyze a minimum of two spikes on each instrument separate batches same spiking concentration as in the initial determination Department of Environmental Quality 20
Ongoing Data Collection If using multiple instruments, ensure that at least 7 spikes and 7 method blanks are completed each year. If only one instrument is in use, a minimum of 7 spikes are still required, but they may be drawn from the last 2 years of data collection. Department of Environmental Quality 21
Ongoing Spike Collection If any analytes are repeatedly not detected in the quarterly spike analyses, or do not meet the qualitative identification criteria of the method, then this is an indication that the spiking level is too low and should be adjusted upward. This would require a new initial MDL determination. Department of Environmental Quality 22
Ongoing Blank Collection Additional method blanks beyond what is routine are not needed. The method blank population should include all of the routine method blanks analyzed with each batch during the course of routine sample analysis. Department of Environmental Quality 23 Ongoing Verification
Laboratories also have the option to use only the last six months of method blank data or the fifty most recent method blanks, whichever criteria yields the greater number of method blanks. Department of Environmental Quality 24 Ongoing Verification At least once every 13 months, re-calculate the MDLS and MDLb from the ongoing spike and
method blank results. Include all data generated within the last 24 months, but only spikes with the same concentration as that used in the initial MDL determination. Department of Environmental Quality 25 Ongoing Verification Include the initial MDL spikes, if the data was generated within the last 24 months.
Exclude any data associated with failing calibrations or batches with failing QC that caused associated samples to be re-analyzed. Department of Environmental Quality 26 Ongoing Verification If the method has been altered in a way that can be reasonably expected to change its sensitivity, then use only data collected after the change.
Must still have at least 7 replicates in 3 separate batches on 3 separate days. If not, start over with initial MDL determination and start new ongoing data collection. Department of Environmental Quality 27 Ongoing MDL Verification 28
Spiking Level Verification At least once per year, re-evaluate the spiking level. If more than 5% of the spikes 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. Department of Environmental Quality 29 Multiple Instrument MDL
If a laboratory uses a single MDL value that represents multiple instruments, then all the instruments must be used in the determination of that MDL. Department of Environmental Quality 30 Multiple Instruments Procedure A minimum of two spikes and two method blanks prepared and analyzed on different calendar dates is required for each instrument.
Each analytical batch may contain one standard and one method blank analyzed together. However, they are not required to be analyzed in the same batch. Department of Environmental Quality 31 Multiple Instruments Procedure The same prepared spikes and blanks may be analyzed on multiple instruments so long as the
minimum requirement of 7 preparations in at least 3 separate batches from 3 separate dates is maintained. Department of Environmental Quality 32 Adding A New Instrument Analyze a minimum of two spikes and two method blanks on the new instrument. If both method blank results are below the existing
MDL, then the existing MDLb is validated. Combine the new spike results with the existing spike results and recalculate the MDLs as an ongoing MDL determination. Department of Environmental Quality 33 Adding A New Instrument Recalculated MDL is validated if: 1) It is within 0.5 to 2.0 times the existing MDL. 2) Fewer than 3% of the method blank results (for the
individual analyte) have numerical results above the existing MDL. If either of these two conditions is not met, then a new MDL must be determined. Department of Environmental Quality 34 Thank you! Department of Environmental Quality 35
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