DETECTION LIMITS, PQLs AND NJQLs Presented by Stu Nagourney NJDEP, OQA MDL DEFINITION Defined at 40 CFR 136 Appendix D The minimum concentration of.
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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current PQL data is based upon outdated technology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