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Appendix F, p. 9
Table A4. Expected precision (repeatability) as a function of
analyte concentration
a
Analyte, % Analyte ratio
Unit
RSD, %
100
1
100%
1.3
10
10
–1
10%
1.9
1
10
–2
1%
2.7
0.01
10
–3
0.1%
3.7
0.001
10
–4
100 ppm (mg/kg)
5.3
0.0001
10
–5
10 ppm (mg/kg)
7.3
0.00001
10
–6
1 ppm (mg/kg)
11
0.000001
10
–7
100 ppb (μg/kg)
15
0.0000001
10
–8
10 ppb (μg/kg)
21
0.00000001
10
–9
1 ppb (μg/kg)
30
a
Table excerpted from
AOAC Peer-Verified Methods Program, Manual on
Policies and Procedures
(1998) AOAC INTERNATIONAL, Gaithersburg,
MD.
The precision of a method is the closeness of agreement between
independent test results obtained under stipulated conditions. Precision
is usually expressed in terms of imprecision and computed as a relative
standard deviation of the test results. The imprecision of a method
increases as the concentration of the analyte decreases. This table
provides targets RSDs for a range of analyte concentrations.
Table A5. Expected recovery as a function of analyte
concentration
a
Analyte, % Analyte ratio
Unit
Mean recovery, %
100
1
100%
98–102
10
10
–1
10%
98–102
1
10
–2
1%
97–103
0.01
10
–3
0.1%
95–105
0.001
10
–4
100 ppm 90–107
0.0001
10
–5
10 ppm
80–110
0.00001
10
–6
1 ppm
80–110
0.000001
10
–7
100 ppb
80–110
0.0000001
10
–8
10 ppb
60–115
0.00000001
10
–9
1 ppb
40–120
a
Table excerpted from
AOAC Peer-Verified Methods Program, Manual on
Policies and Procedures
(1998) AOAC INTERNATIONAL, Gaithersburg,
MD.
Recovery is defined as the ratio of the observed mean test result to the
true value. The range of the acceptable mean recovery expands as the
concentration of the analyte decreases. This table provides target mean
recovery ranges for analyte concentrations from 100% to 1 ppb.
Table A6. Predicted relative standard deviation of
reproducibility (PRSD
R
)
a
Concentration (C)
Mass fraction (C)
PRSD
R
, %
100%
1.0
2
1%
0.01
4
0.01%
0.0001
8
1 ppm
0.000001
16
10 ppb
0.00000001
32
1 ppb
0.000000001
45
a
Table excerpted from
Definitions and Calculations of HorRat Values
from Intralaboratory Data
, HorRat for SLV.doc, 2004-01-18, AOAC
INTERNATIONAL, Gaithersburg, MD.
Predicted relative standard deviation = PRSD
R
. Reproducibility relative
standard deviation calculated from the Horwitz formula:
PRSD
R
= 2C
–0.15
, where C is expressed as a mass fraction
This table provides the calculated PRSD
R
for a range of concentrations.
See Annex D
for additional information.