Method Update Rule of 2015:
New Method Detection Limit
Determination
David Caldwell
OK DEQ
Laboratory
Accreditation Program
‘MDL’
Method Update Rule of 2015:
• Final Rule
• This action has been withdrawn from the Office
of the Federal Register.
• Final rule (signed December 15, 2016)
The final rule has been signed by the EPA
Administrator and is being prepared for
publication.
• Fact sheet
• Documents related to this rulemaking can be
found on EPA’s docket at regulations.gov. The
Docket Number is EPA-HQ-OW-2014–0797.
MDLs
• What are the uses
• When to use
• How to maintain the level of
sensitivity for compliance reporting of
permits
• How the Laboratory uses method to
determine the sensitivity for the
compliance testing
Why Talk about MDLs?
REPORTS
• B
BELOW
• P
PRACTICAL
• Q
QUANTITATION
• L
LIMITS
MDLs some uses of Data
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National Primary Drinking Water
Regulations
40 CFR Part 141
Reviews Existing Drinking Water Standards
every 6 years
–
Federal Register / Vol. 82 , No. 7 /
Wednesday, January 11, 2017 / Proposed
Rules
3. Analytical Feasibility
To determine if changes in analytical feasibility
could possibly support changes to PQLs, EPA
relied primarily on two alternate approaches to
develop an estimated quantitation limit (EQL):
–
an approach based on the minimum
reporting levels (MRLs)
–
an approach based on method
detection limits (MDLs).
• ODEQ
• Water Quality Standards
• 252:690 Appendix B
– Wastewater Permit Limits
Laboratory
• MDL and reporting limits
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Commercial
Municipal
Industrial
Governmental
What is a Method Detection Limit (MDLs)
A BRIEF DESCRIPTION OF WHAT IS A
METHOD DETECTION LEVEL
Principle Rule Changes
Old
New
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Estimation of Detection Limit
Evaluation of Laboratory Fortified
Blank
MDL=𝑋+𝑡(𝑛𝑛−1,1−∝=0.99)𝑆
Reporting
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Estimation of Detection Limit
Evaluation of Blanks
Evaluation of Laboratory Fortified
Blank
𝑀DL=𝑋+𝑡(𝑛𝑛−1,1−∝=0.99)𝑆
Testing must be across all instruments
used for that method
Only use data associated with
acceptable calibrations and batch QC.
Quarterly Verification
Annual Recalculation
Reporting
𝑀DL=𝑋+𝑡(𝑛𝑛−1,1−∝=0.99)𝑆
MDL- Method Detection Limit
X- Standard Deviation of Laboratory Standards
𝑡 – Student T test with degree of freedom
Method Detection Limit Calculation
PQL Reporting
PQL Reporting
MDLs are used to identify
the minimum concentration
of analyte that can be
distinguished from a nondetect result.
Method Detection Limits
Method Detection Level (MDL) for appropriate
analytes or method parameters is determined
before analyzing samples and is repeated at
least annually.
Method Detection Limit
Laboratory’s Use
• Reflect current operating conditions
• Incorporate entire analytical
process
• Include data from low-level spikes
and (Proposed) method blanks
analyzed over multiple days
• Include (proposed) criteria for
evaluating false positives in blanks
Method Detection Limit
Estimation of level to test
• The mean plus three times the standard deviation of a
set of method blanks,
or
• The concentration value that corresponds to an
instrument signal/noise in the range of 3 to 5,
or
• Three times the standard deviation of spiked blanks,
or
• That region of the standard curve where there is a
significant change in sensitivity,
or
• Instrumental limitations,
or
• Previously determined MDL.
Current MDL Calculations
MDL = S * t of spike results
Reported MDL
➢ Determine the mean and variance of the standards
➢ Calculate the mean
➢ Calculate the standard Deviation
➢ > 10 % RSD
➢ Statistical: Student t Test value with degree of freedom
➢ Look up Student t Test value for the number of
sample analysis – one for the degrees of freedom
➢ Quantitation Limit will be 3.3 X MDL
(Practical Quantitation Limit)
Proposed Method of Calculation
• Run series of seven (7) blanks
• Run series of seven (7) spikes
• Compare the blanks vs. spike
– Greater of the variance is used
• MDL = S * t of spike results
• Reported MDL
• Quantitation Limit will be 3.3 X MDL
(Region 6 requirement)
• Analyze Quarterly MDL check standard
Examples
• Ammonia Testing
– Permit Limit of 0.2 mg/L
• (Practical Quantitation Limit)
– MDL listing from previous year of 0.05 mg/L
– Practical Quantitation Limit of 0.17 mg/L
Example # 1:
1.0 mg/L Estimate Standard
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1.0 mg/L
0.97 mg/L
0.94 mg/L
1.12 mg/L
0.98 mg/L
1.05 mg/L
1.10 mg /L
• Mean
1.0229 mg/L
• Deviation 0.0069 mg/L
Example # 1: Calculations
Deviation 0.0069 mg/L
• Student t Test for 6 degrees of freedom
3.14
• MDL = 0.0069 X 3.14
• MDL = 0.022 mg/L
• PQL = 0.073 mg/L
Example # 2:
0.1 mg/L Estimate Standard
• 0.092
• 0.086
• 0.120
• 0.079
• 0.066
• 0.111
• 0.090
• Mean
0.092 mg/L
• Deviation 0.0184 mg/L
Example # 2: Calculations
Deviation 0.0184 mg/L
• Student t Test for 6 degrees of freedom
3.14
• MDL = 0.0184 X 3.14
• MDL = 0.057 mg/L
• PQL = 0.188 mg/L
In Summary
Example 1
• MDL = 0.022 mg/L
Example 2
• MDL = 0.057 mg/L
• PQL = 0.073 mg/L
• PQL = 0.188 mg/L
Previous Year:
MDL listing from previous year of 0.05 mg/L
Practical Quantitation Limit of 0.17 mg/L
Example Proposed Procedure
Blanks
• 0.055
• 0.023
• -0.011
• 0.082
• 0.009
• 0.022
• 0.099
• Mean
0.040 mg/L
• Deviation 0.040 mg/L
0.1 mg/L Estimate Standard
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0.092
0.086
0.120
0.079
0.066
0.111
0.090
Mean
0.092 mg/L
Deviation 0.0184 mg/L
Example Proposed Procedure
• Deviation 0.0401 mg/L
• Student t Test for 6 degrees of freedom
3.14
• MDL = 0.0401 X 3.14
• MDL = 0.126 mg/L
• PQL = 0.415 mg/L
verify MDL is within 0.5 to 2.0 times the existing MDL, and fewer than 3%
Ammonia Summary
Existing Procedure
• MDL = 0.057 mg/L
Proposed Procedure
• MDL = 0.126 mg/L
• PQL = 0.188 mg/L
• PQL = 0.415 mg/L
Laboratory Report
– Reporting Limit of 0.2 mg/L
• (Practical Quantitation Limit)
– MDL listing from previous year of 0.05 mg/L
– Practical Quantitation Limit of 0.17 mg/L
Conclusion
Questions
[email protected]
405-702-1000
David Caldwell