Background Information on the

Proposed MDL RevisionThe following presentation was created by Richard Burrows who w

the members of The NELAC Institute (TNI) that took the lead on re

Method Detection Limit (MDL). It outlines the rationale for the pr

revision to the MDL and gives background information on the top

The MDL proposed by TNI went through several rounds of review 

diverse members and outside reviewers, including federal govern

agencies, state governments, municipalities, and commercial labo

all sizes.

The MDL proposed by TNI was then reviewed by the EPA work gro

composed of 14 different offices (including 8 of the 10 EPA region

work group made some minor changes to the MDL submitted by T

the version submitted by TNI and the MDL revision in the ProposeWater Act Methods Update Rule for the Analysis of Effluent are av

the Docket.The Revised MDL in the proposed rule does not address quantitat
Really – A revised MDL

procedure

Richard Burrows
Dawn of the MDL

 1984

USEPA the MDL procedure is promu

in 40 CFR, Part 136, Appendix B for 

the wastewater program and define

3.14 times the standard deviation o

low level spiked blanks.

The ML is also promulgated at this t
MDL Rising

 1999 USEPA published Method 1631B 

analysis of mercury using the old MDL appand modified ML definition, which provideopportunity for a legal challenge of the M

ML.

 2000 USEPA entered into a settlemen

agreement with the Alliance of Automobi

Manufactures, Chemical Manufacturer’sAssociation, Utility Water Act Group and A
What were the objection

 MDL procedure makes the assumption 

blank results are centered around zero

 If they are not, then the MDL will be an

underestimate and many false positives w

 MDL makes the assumption that short t

variance (7 replicates in one batch) is th

same as long term variance

 If it is not, then the MDL will be an undere

and many false positives will result
Secondary concerns

 Assumption of constant variance at diff

concentrations

 Assumption of normal distribution Lack of any guarantee of actual detecta Lack of use of LD in Currie’s classic LC / L

description of performance in the dete

quantitation range
The classic definition of “Detected”is fro

Lloyd Currie.

He called the value where you are almos

positive your detection is not backgro“Critical Level LC”.

What does detected mea

The MDL is equal to LC
Previous attempts to Upd

 Guidelines Establishing Test Procedures 

the Analysis of Pollutants; Procedures f

Detection and Quantitation

68 FR 11770March 12th 2003

 ACIL procedure (2003‐2005) Consensus procedure (2005‐2006) FACDQ Procedure (2005‐2007)
Reason #1 that we need 

 We need to make the Quantitation limi

meaningful

 Applies to MRL, LLOQ, or any quantitation 
0

123456789

1011

012345678

Reported Concentration

Replicate Number

9

Mean recove

90% recovery, 9% RSD

Spike #1 #2 #3 #4 #5 #6 #7 Mean 

10 9 8.3 9.8 9.3 8.1 8.6 10.0 9.0 

Spike True Valu

Calculated M

MDL = 2.29

Reported results

(without MDL)

ND ND ND ND ND ND 1
Reason #2 that we need 

 MDLs are needed in risk assessment

 Handling non‐detects

 Substitute a value such as 1⁄2 detection limit or

detection limit

 More sophisticated methods such as Maximu

Likelihood estimation and Regression on Ordestatistics

 These still benefit from a detection limit as low as 

If we do not have a detection limit, the Quantitation limit

will become the new Detection limit
What are our options?

 Replace the MDL

 DQFAC procedure ASTM IDE/WDE

 Stop reporting below the quantitation lim Leave the MDL alone

 Improve things for TNI labs at least, through

development of a standard by the EMMEC

 Modify the MDL

 Based on principles from the DQFAC and lear

from the Pilots

From NEMC 2012
Proposed MDL revision (201

2014)

 Has similarities to ACIL, Consensus and

FACDQ, but simplified and less differen

the current MDL

 One procedure rather than two, start with 

spikes and 7 blanks

 MDLS = tSs (Std Dev of spikes) MDLB = X + tSb (Std Dev of blanks)

 Use whichever is highest as the MDL

 Requires ongoing spikes
Proposed MDL revision

 Requires spreading the initial 7 replicates 

at least 3 batches

 Includes instructions for multiple instrume

with the same assigned MDL

 Requires that spike results meet qualitativ

criteria

 Requires ongoing (quarterly) spikes Recalculate (but do not redo) every year Includes instructions for determination of 

in a specific matrix
Run 7 spikes at or 

below desired 

LOQ (recommend 

1⁄2 LOQ)

Run 7 method 

blanks

Do 

results 

meet 

qual ID?

Calculate MDLs Calculate MDLb

Set higher of 

MDLs and MDLb 

as MDL

Set LOQ at spike 

level

Set LOQ at 3x 

MDL

Fix problem or 

raise spike level 

and repeat

No

Yes

Yes No

INITIAL DETERMINATION OF LOQ AND LOD

Is the spike level 

> 3X MDL?
Run 7 spikes at or 

below desired 

LOQ (recommend 

1⁄2 LOQ)

Run 7 method 

blanks

Do 

results 

meet 

qual ID?

Calculate MDLs Calculate MDLb

Set higher of 

MDLs and MDLb 

as MDL

Set LOQ at spike 

level

Set LOQ at 3x 

MDL

Fix problem or 

raise spike level 

and repeat

No

Yes

Yes No

INITIAL DETERMINATION OF LOQ AND LOD

Is the spike level 

> 3X MDL?

INITIAL DETERMINATION OF LOQAND LOD 

... 

Run 7 spik.e.s at or 

below desired 

... LOQ (recommend 

%LOQ) 

R
Run 7 spikes at or 

below desired 

LOQ (recommend 

1⁄2 LOQ)

Run 7 method 

blanks

Do 

results 

meet 

qual ID?

Calculate MDLs Calculate MDLb

Set higher of 

MDLs and MDLb 

as MDL

Set LOQ at spike 

level

Set LOQ at 3x 

MDL

Fix problem or 

raise spike level 

and repeat

No

Yes

Yes No

INITIAL DETERMINATION OF LOQ AND LOD

Is the spike level 

> 3X MDL?

lil 

I 

0 

Fix probl

em or 

raise 

spike level 

and repeat 

Run 7 spik.es at or 

bel ow desired 

LOQ (recommend 

LOQ} 

Do 

results 

meet 

quaiiD? 

Yes 

I 
Run 7 spikes at or 

below desired 

LOQ (recommend 

1⁄2 LOQ)

Run 7 method 

blanks

Do 

results 

meet 

qual ID?

Calculate MDLs Calculate MDLb

Set higher of 

MDLs and MDLb 

as MDL

Set LOQ at spike 

level

Set LOQ at 3x 

MDL

Fix problem or 

raise spike level 

and repeat

No

Yes

Yes No

INITIAL DETERMINATION OF LOQ AND LOD

Is the spike level 

> 3X MDL?

0 

Yes 

Calculate MDLs 

Ca
Run 7 spikes at or 

below desired 

LOQ (recommend 

1⁄2 LOQ)

Run 7 method 

blanks

Do 

results 

meet 

qual ID?

Calculate MDLs Calculate MDLb

Set higher of 

MDLs and MDLb 

as MDL

Set LOQ at spike 

level

Set LOQ at 3x 

MDL

Fix problem or 

raise spike level 

and repeat

No

Yes

Yes No

INITIAL DETERMINATION OF LOQ AND LOD

Is the spike level 

> 3X MDL?
Run 7 spikes at or 

below desired 

LOQ (recommend 

1⁄2 LOQ)

Run 7 method 

blanks

Do 

results 

meet 

qual ID?

Calculate MDLs Calculate MDLb

Set higher of 

MDLs and MDLb 

as MDL

Set LOQ at spike 

level

Set LOQ at 3x 

MDL

Fix problem or 

raise spike level 

and repeat

No

Yes

Yes No

INITIAL DETERMINATION OF LOQ AND LOD

Is the spike level 

> 3X MDL?
Does the revised procedure ad

the problems and concerns?

 Blank distribution not centered around 

 This is the most important cause of failure 

current MDL procedure for methods such ICPMS, and most Wet Chemistry procedur

results in high false positive rates

 Situation is getting worse because instrum

sensitivity is increasing and detection limit

pushed lower.

 Fully addressed in the revised procedur
Lead in Particulate Matte

0

50

100150200250300350

1234567

Ultrasonic extraction Quartz filter blanks
Does the revised procedure ad

the problems and concerns?

 Short term variance (one batch) is not e

to long term variance

 Initial replicates spread across batches and

instruments

 Ongoing data collection quarterly
Does the revised procedure ad

the problems and concerns?

 Assumption of constant variance and n

distribution

 No way around this issue without collectio

very large amounts of data

 Verification steps check for and correct pr

due to very “non‐normal” data distributio
Does the revised procedure ad

the problems and concerns?

 Lack of guarantee of actual detectabilit

 Not reasonable to expect that spikes at th

will reliably return detectable results

 Spikes used to generate the MDL must be 

detectable results and may typically be us

the LOQ

If spikes at the MDL return detectable results, then those results can b

to calculate a lower MDL!
Does the revised procedure ad

the problems and concerns?

 Lack of use of LD in Currie’s classic LC / L

description of performance in the dete

quantitation range
Does the revised procedure ad

the problems and concerns?

 Lack of use of LD in Currie’s classic LC / L

description of performance in the dete

quantitation range

 Accurate determination of LD is very diffic Typically quite close to the LOQ Instead, ensure that the LOQ has all the

properties of LOD

 Returns results above the MDL
Compatibility with

Quantitation Limit conce

 Spikes used to verify LLOQ (SW‐846) or 

(Drinking Water) will usually be suitable calculating MDLs.
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Aluminum by 200.7 

5 

I 

I 

I 

99% = 11 .7 

MDL(b)= 13.7 

MDL
= 16.4 

I I 

1 Does 

not fit normal distribution, S-W p=.0031 

MDltbl 

99% MDL(s) 

LOQ 
Copper (ug/L) by 200.8

-0.05

-.025

0

.025

0.05

te

MDL(b)

99%

MDL(s)

0.41

02

4

68

1012141618202224

Number of Method Blank Results

MDL(b

99% MDL(s

Fits normal d
Mercury (ng/L) by 1631

-0.02

-.01

0

.01

0.02

MDL(s)

99%

.015

MDL(b)

N um ber of M ethod B lank R esults

Does not fit normal distribution, S-W p=.0

MDL(s) = .096

99% = .098MDL(b)= .146
TP (mg P/L) by 365.1

-0.0002

0

0.0002

MDL(s)

MDL(b)

 99%

02468

10121416

N um ber of M ethod B lank R esults

MDL(s) = .000821

MDL(b)= .00095799% = .001

Fits normal distribution, S-W p=.822
NH3 (mg N/L)

-0.0002

0

0.0002

.0013

MDL(s)

99%

MDL(b)

.00

02468

1012

N um ber of M ethod B lank R esults

MDL(s) = .001119

99% = .0014MDL(b)= .001422

Fits normal distribution, S-W p=.251
Questions?