Presentation is loading. Please wait.

Presentation is loading. Please wait.


Similar presentations

Presentation on theme: "DETECTION LIMITS, PQLs AND NJQLs Presented by Stu Nagourney NJDEP, OQA."— Presentation transcript:

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

2 MDL DEFINITION 4 Defined at 40 CFR 136 Appendix D 4 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


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

5 MDL ISSUES TO CONSIDER 4 Many regulatory standards near detection limit 4 Lab credibility often associated with detection limits 4 Maze of tests and matrices make it difficult to find a universally applicable technique Calculating detection limits can be expensive

6 WHY YOU CANT SET PERMIT THE MDL 4 MDLs vary by day, lab., analyst & method 4 Precision at low levels are usually poor 4 Good for false-positives; false negatives may be reported 50% of the time 4 Inherent uncertainties make enforcing permit MDL values impossible

7 MDLs to PQLs 4 PQL: Practical Quantitation Limit 4 PQL = Average (Median) MDL x 5 4 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 4 The Department recognizes that the current PQL data is based upon out- dated technology 4 OQA already requires certified labs. to collect MDL data by method and media 4 What we need is current, representative data and a way to manage it

9 NJQLs & NJDEP 4 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) 4 NJQLs to be generated by analyte, matrix, method –DW –WP –SHW 4 DEP programs will have a choice in selecting an NJQL for their individual needs

Download ppt "DETECTION LIMITS, PQLs AND NJQLs Presented by Stu Nagourney NJDEP, OQA."

Similar presentations

Ads by Google