Office
of
Water
AOAC­
Maria6/
01.
ppt
EPA's
Efforts
on
Detection
and
Quantitation
Maria
Gomez­
Taylor
Analytical
Methods
Staff
U.
S.
EPA
Office
of
Water
AOAC­
Maria6/
01.
ppt
Sampling
and
Analysis
Methods
for
Low
Level
Metals
Maria
Gomez­
Taylor
Analytical
Methods
Staff
U.
S.
EPA
Office
of
Water
AOAC­
Maria6/
01.
ppt
Why?

 
Lawsuit
challenging
concepts
used
for
development
of
detection
and
quantitation
in
EPA
Method
1631,
among
other
issues
 
Settlement
Agreement
between
EPA
and
Petitioners/

Intervener
 
Petitioners:
Alliance
of
Automobile
Manufacturers,
Inc.,

Chemical
Manufacturers
Association
(
CMA),
Utility
Water
Act
Group
(
UWAG)

 
Intervener:
American
Forest
&
Paper
Association
 
The
specific
method
detection
limit
(
ML)
of
0.2
ng/
L
and
minimum
level
of
quantitation
(
ML)
of
0.5
ng/
L
in
EPA
Method
1631
were
not
addressed
in
the
Settlement
Agreement
and
remain
as
promulgated
Office
of
Water
AOAC­
Maria6/
01.
ppt
40
CFR
part
136,
Appendix
B
MDL
Procedures
 
Based
on
procedures
described
in
"
Trace
analysis
for
wastewaters,"
Glaser
et
al,
Environ
Sci
Technol,
15:
1426
(
1981)

 
Codified
by
EPA
(
49
FR
43234,
Oct.
26,
1984)

 
Provides
99%
confidence
of
detection
 
Provides
matrix
independent
procedure
 
Includes
procedures
to
compensate
for
background/
interferences
Office
of
Water
AOAC­
Maria6/
01.
ppt
Current
Use
of
EPA's
MDL
Procedure
 
Used
as
a
benchmark
of
performance
 
Required
for
startup
tests
 
Referenced
in
many
rules
and
permits
 
Currently
established
precedent
Office
of
Water
AOAC­
Maria6/
01.
ppt
40
CFR
part
136,
Appendix
B
MDL
Procedures
 
Step­
by­
step
procedures
for
calculating
an
MDL
(
1)
Select
appropriate
low
concentrations
(
2)
Analyze
7
replicates
spiked
at
the
low
concentrations
(
3)
Calculate
an
MDL
based
on
the
results
of
the
7
replicates
(
4)
Perform
iterative
determination
of
the
MDL
if
required
Office
of
Water
AOAC­
Maria6/
01.
ppt
Calculating
the
MDL
 
The
MDL
is
calculated
using
the
following
formula
MDL
=
Student's
t
x
SD
of
replicate
measurement
Office
of
Water
AOAC­
Maria6/
01.
ppt
Calculating
the
ML
 
The
ML
is
EPA's
minimum
level
of
quantitation
 
Calculated
as
3.18
x
MDL
rounded
to
the
nearest
multiple
of
1,

2,
5,
10,
etc.

 
Approximately
equal
to
10
Sigma
 
Equivalent
to
ACS
LOQ
 
In
practice,
equals
lowest
calibration
point
 
10
Sigma
allows
for
analytical
variability
 
Has
withstood
numerous
court
challenges
 
Iteration
at
multiple
laboratories
ensures
reliability
Office
of
Water
AOAC­
Maria6/
01.
ppt
Improvements
Being
Considered
 
Change
to
the
MDL
definition
to
conform
with
the
procedure
 
From:
The
MDL
is
the
minimum
concentration
of
a
substance
that
can
be
measured
and
reported
with
99%
confidence
that
the
analyte
concentration
is
greater
than
zero
 
To:
The
MDL
is
the
measured
concentration
at
which
there
is
99%
confidence
that
a
given
analyte
is
present
in
a
given
matrix
 
Eliminate
blank­
subtraction
 
Blank
subtraction
will
not
alter
the
standard
deviation
and,

therefore,
will
not
alter
the
MDL
 
Disallow
a
zero
or
negative
response
as
a
result
 
Require
the
laboratory
to
repeat
the
MDL
procedure
at
a
spike
level
2­
5
times
higher
Office
of
Water
AOAC­
Maria6/
01.
ppt
Improvements
Being
Considered
(
continued)

 
Add
rounding
rules
 
3
significant
figures
for
results
 
2
significant
figures
for
the
MDL
 
Evaluate
other
detection/
quantitation
concepts
against
EPA's
selection
criteria
