AOAC Working Group Chair Orientation

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 98–102 97–103 95–105 80–110 80–110 80–110 60–115

10

10 –1 10 –2 10 –3 10 –4 10 –5 10 –6 10 –7 10 –8 10 –9

10%

1

1%

0.01

0.1%

0.001

100 ppm 90–107

0.0001 0.00001 0.000001 0.0000001 0.00000001

10 ppm

1 ppm

100 ppb 10 ppb

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.

© 2012 AOAC INTERNATIONAL