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DETECTION LIMITS, PQLs AND NJQLs

DETECTION LIMITS, PQLs AND NJQLs. Presented by Stu Nagourney NJDEP, OQA. MDL DEFINITION. Defined at 40 CFR 136 Appendix D

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DETECTION LIMITS, PQLs AND NJQLs

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  1. DETECTION LIMITS, PQLs AND NJQLs Presented by Stu Nagourney NJDEP, OQA

  2. MDL DEFINITION • Defined at 40 CFR 136 Appendix D • The minimum concentration of a substance that can be measured and reported with 99-percent confidence that the analyte concentration is greater than zero and is determined from the analysis of a sample in a given matrix containing the sample

  3. OTHER DEFINITIONS • IDL • RL • ML

  4. MDL CALCULATION • Seven (7) replicates at ~ [5 times] the background noise: should be at or near the low calibration standard • Multiply by (z) distribution factor • 3.14 time the S.D. = MDL • The MDL is more dependent upon precision than accuracy • Labs. must demonstrate that they can see a signal at the MDL

  5. MDL ISSUES TO CONSIDER • Many regulatory standards near detection limit • Lab credibility often associated with detection limits • Maze of tests and matrices make it difficult to find a universally applicable technique • Calculating detection limits can be expensive

  6. WHY YOU CAN’T SET PERMITLEVELS @ THE MDL • MDLs vary by day, lab., analyst & method • Precision at low levels are usually poor • Good for false-positives; false negatives may be reported 50% of the time • Inherent uncertainties make enforcing permit levels @ MDL values impossible

  7. MDLs to PQLs • PQL: Practical Quantitation Limit • PQL = Average (Median) MDL x 5 • Sources of MDL data • Interlaboratory low-level studies • Applying statistics to low-level cal. data • Method data where available • Most data is now 5-12 years old!!!

  8. PQLs to NJQLs • The Department recognizes that the current PQL data is based upon out-dated technology • OQA already requires certified labs. to collect MDL data by method and media • What we need is current, representative data and a way to manage it

  9. NJQLs & NJDEP • OQA is contracting for the development of a database to collect MDL data from NJ certified labs. and then generate NJQLs (avg. MDL x 5) • NJQLs to be generated by analyte, matrix, method • DW • WP • SHW • DEP programs will have a choice in selecting an NJQL for their individual needs

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