Method
detection
limits:
application
to
organic
environmental
chemistry
data
Terry
L.
Wade,
Jose
L.
Sericano,
Yaorong
Qian,

Gary
Wolff,
Guy
Denoux.

Texas
A&
M
University
Geochemical
and
Environmental
Research
Group
°
Understanding
the
sources,
fate
and
effects
of
contaminants
requires
their
detection
at
trace
concentrations
(
e.
g.
pg/
g)
in
difficult
matrices.

°
Determining
analytes
at
trace
concentrations
requires
great
care
and
increases
cost.

°
Blank
concentrations,
matrix
type,
isolation
techniques,
and
instrumental
method
effect
detection.

°
Interpretation
of
trace
concentrations
remains
controversial.
Introduction
°
Questionable
Detection.

°
Limit
of
Detection
(
LOD).

°
Less
Certain
Quantitation.

°
Limit
of
Quantitation
(
LOQ).

°
Quantification
.

ACS
Guidance
Regions
°
The
LOD
is
defined
as
"
the
lowest
concentration
that
can
be
determined
to
be
different
from
a
blank"
(
Keith
et.
al.,
1983).

°
LOD
=
Blank
Concentration
+
3
SD
e.
g.
LOD
=
0.33
+
3(
0.10)
=
0.63
ACS
LOD
°
The
EPA
method
detection
limit
(
MDL)
is
defined
as
"
the
minimum
concentration
of
a
substance
that
can
be
measured
and
reported
with
99%
confidence
that
the
analyte
concentration
is
greater
than
zero
and
is
determined
from
analysis
of
a
sample
in
a
given
matrix
containing
the
analyte"
(
EPA.,
1984).

°
MDL
=
SD
of
7
replicates
X
3.14
(
Student
t
value
for
99%
confidence
interval).
EPA
MDL
°
Deuterated
PAHs
added
as
an
internal
standards.

°
Dried
samples
extracted
with
methylene
chloride.

°
Extracts
concentrated
and
exchanged
into
hexane.

°
Isolated
and
purification
by
silica/
alumina
column
and
size
exclusion
chromatography.

°
Analysis
by
gas
chromatography
/
mass
selective
detector
selected
ion
mode
(
GC/
MSD/
SIM)
.

PAH
Method
PAH
lowest
calibration,
LOD
and
MDL
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1
3
5
7
9
11
13
15
1
7
19
2
1
23
25
PAHs
Concentration
(

ng/

g)
MDL
LOD
Calib
PAH
lowest
calibration,
LOD
and
MDL
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1
3
5
7
9
11
13
15
17
19
21
23
25
PAHs
Concentration
(

ng/

g)
LOQ
Calib
PAH
LOD
Versus
MDL
0.00
0.20
0.40
0.60
0.80
1.00
0.00
0.20
0.40
0.60
0.80
1.00
MDL
LOD
LOD
>
MDL
LOD
<
MDL
PAH
Blank
Versus
LOD
y
=
1.865x
+
0.054
R2
=
0.89
0.00
0.20
0.40
0.60
0.80
1.00
0.00
0.10
0.20
0.30
0.40
Blank
LOD
PAH
Blank
Versus
MDL
y
=
0.17x
+
0.06
R2
=
0.17
0.00
0.10
0.20
0.30
0.40
0.00
0.20
0.40
0.60
0.80
1.00
MDL
Blank
°
ACS
LODs
and
EPA
MDLs
provide
similar
results.

°
The
LOD
approach
is
simpler
and
less
costly.

°
Both
the
LOD
and
MDL
were
less
than
the
lowest
calibration
standard
for
this
study.

°
Use
of
an
Instrument
Detection
Limits
(
IDL)
or
low
level
spiked
blank
should
be
investigated.

°
Interpretation
of
trace
concentrations
will
remain
problematic
in
spite
of
the
detection
approach.

Conclusion
