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© 2012 AOAC INTERNATIONAL

AOAC O

FFICIAL

M

ETHODS

OF

A

NALYSIS

(2012)

G

UIDELINES

FOR

S

TANDARD

M

ETHOD

P

ERFORMANCE

R

EQUIREMENTS

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.