Transcript DETECTION LIMITS, PQLs AND NJQLs Presented by Stu Nagourney NJDEP, OQA MDL DEFINITION  Defined at 40 CFR 136 Appendix D  The minimum concentration of.

DETECTION LIMITS, PQLs
AND NJQLs
Presented by
Stu Nagourney
NJDEP, OQA
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
OTHER DEFINITIONS
 IDL
 RL
 ML
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
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
WHY YOU CAN’T SET PERMIT
LEVELS @ 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
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!!!
PQLs to NJQLs
 The Department recognizes that the
current PQL data is based upon outdated technology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
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