In Empower, instead of forcing through zero, can a zero point be added to a calibration curve? - WKB83587

ENVIRONMENT

• Empower
• Calibration curve

ANSWER

No.

It is not possible to enter a 0,0 point. You cannot add any points that are not measured.

This practice would be non-compliant; it would artificially weight the curve toward the origin. Only points that have been measured can form a calibration curve.

The only option is to force the curve fit through zero. However, this should only be used if the intercept is shown through method validation not to be statistically different than zero.

From EM 200-1-1. Title: Environmental Quality – Validation of Analytical Chemistry Laboratories

A calibration curve (whether linear or nonlinear) must not be forced through the origin unless it is demonstrated (e.g., during method development) that the intercept (i.e., y[x = 0]) is not statistically different from zero (e.g., by performing a t-test for the y-intercept or comparing it to the MDL.).

Arbitrarily forcing a calibration curve through the origin may adversely impact low-level quantitative results. Similarly, when calibration curves are generated using regression analysis, the curves must not be artificially weighted toward the origin by including the point (0,0) one or more times.

ADDITIONAL INFORMATION

Calibration Curves, Part I: To b or Not to b? | LCGC - Page 3