Linearity
•
The linearity of a method is its ability to provide measurement results that
are directly proportional to the concentration of the analyte , or are directly
proportional after mathematical transformation.
• The linearity is usually documented as the
ordinary least squares OLS
curve, or simply as linear regression curve,
of the measured responses peak area or height as a function of increasing analyte concentrations
• Peak area
shall be preferred compared to peak heights
for making the calibration curve
• The linearity of
the detector can be obtained by diluting of the analyte stock solution,
whilst the linearity of the analytical method
can be determined by making a series of concentration of the analyte from
independent preparations weighing, spiking
G. Indrayanto, Suciati, M. Yuwono 2010, in Encyclopedia Chromatography 3
rd
Edition,Taylor Francis, pp.2336-2339
• Analytical Methods Committee, Analyst 1988, 113: 1469-1471.
• W. Horwitz, Referee 1995, December, 2.
• J. van Loco; M. Elskens; C. Croux; H. Beernaert. Accred. Qual.
Assur 2002, 7: 281-285
‘Correlation coefficient r can not be used alone for proving the linearity
r close to 1 is not a reliable indicator of linearity
Assur 2002, 7: 281-285
• G. Indrayanto; M. Yuwono, in:J. Cazes ed, Encyclopedia of
Chromatography Supp., Marcel Dekker, Inc, New York, NY 10016, 2003.
• P.Araujo, J.Chromatogr.B. 2009 877, 2224-2234
• etc.
Evaluation of linearitycalibration curve
•
Relative process standard deviation Vxo- Funk’s et al. 1992 5 ; “sdv” CATS from CAMAG 5
• M
andel’ test should be OK
• Residual test
should be OK
• ANOVA-linearity testing
should be OK, p 0.01
• RSD of the Plot of response factor Vs. concentration
RSD 2.5 – 5 et al
. Xp must be less than the lowest concentration of
• Xp value- Funk’s et al
. Xp must be less than the lowest concentration of
the calibration curve
•
Y intercept 2
• “
r” value can not be used alone, even “r” is close to one
• Fisher Ratio according to Araujo 2009
• G value, Quality Coefficient According to D Beer et al., 2007
• Homogeneity of the linear-curve
Funk et al, 1992
Why did USP 3940 still use ‘R” ??
