
DETECTION
DETECTION
LIMITS
Controlling
the
Addiction
Controlling
the
Addiction
With
Lab
QC
With
Lab
QC
Ken
Osborn
Ken
Osborn
East
Bay
MUD
East
Bay
MUD
Oakland,
CA
Oakland,
CA
Chair,
Standard
Methods
JTG
Data
Quality
Chair,
Standard
Methods
JTG
Data
Quality
What
we
do
°
Quality
Control
(
QC)
sample
2
­
5
times
MDL
routinely
analyzed
with
each
batch
of
samples.
No
special
scheduling
required.

°
Results
entered
into
LIMS
°
Long­
term
method
accuracy
evaluated
using
control
limits
How
we
use
it
°
On­
going
real­
time
measure
of
accuracy
°
On­
going
verification
of
non­
detects
°
Long­
term
measure
of
detection
capability
°
Daily
LIMS
QC
reports
generated
°
Reported
to
data
user
Why
do
it?

°
Value
to
data
user
and
laboratory
°
Provides
immediate
feedback
°
Includes
all
analytical
sources
of
error
°
Results
in
better
detection
limits
­
Large
data
set
reduces
uncertainty
­
Monitors
trace
level
capabilities
over
time
An
Example:

EPA
610
QC
Based
DLs
0.03
0.082
82
FLUORENE
27
0.03
0.089
89
FLUORANTHENE
27
0.02
0.068
78
DIBENZO(
A,
H)
ANTHRACENE
18
0.02
0.085
90
CHRYSENE
25
0.02
0.075
87
BENZO(
K)
FLUORANTHENE
21
0.03
0.067
82
BENZO(
GHI)
PERYLENE
18
0.03
0.090
90
BENZO(
B)
FLUORANTHENE
27
0.01
0.057
76
BENZO(
A)
ANTHRACENE
12
0.03
0.062
75
ACENAPHTHYLENE
16
0.05
0.064
76
ACENAPHTHENE
16
FNQS­
DL
(
ug/
L)

FNQS
(
ug/
L)

RECOVERY
(%)

ANALYTE
COUNT
(
N)
FNQS
=
False
Negative
Quality
Sample
A
Derivation

Recovery
=
100*
FNQS/
True

FNQS
=
(
True/
100)*
Recovery

S(
FNQS)
=
(
True/
100)*
S(
Recovery)


Lc
=
t*
S(
FNQS)


Lc=
t*(
True/
100)*
S(
Recovery)


True
=
100*
Ave(
FNQS)/
Ave(
Recovery)

Lc
=
t*
S(
Rec)*
Ave(
FNQS)/
Ave(
Rec)
