How to calculate Amount/Concentration: Calibration Curve Fit Types - Tip278

OBJECTIVE or GOAL

Calculate Amount/Concentration (Calibration Curve fit types) and review Cubic Spline Fit. 

ENVIRONMENT

• Empower
• Empower Tip of the Week #278

PROCEDURE

Cubic Spline Fit: To generate a Cubic Spline Calibration Curve, Empower performs a cubic polynomial fit between every two amounts (or levels), matching the slope and second derivative at every point boundary. The Cubic Spline Fit adjusts the shape of the calibration curve on a point-by-point basis. This fit is used with detectors that do not have a linear response, such as an Evaporative Light Scattering Detector (ELSD).

STEP 1
Because the Cubic Spline Calibration Curve is fit thru every point, the correlation coefficient = 1 and the standard error = 0. No curve coefficients are calculated or stored when this fit type is used (Figure 1).

STEP 2
Each Cubic Spline segment of the Calibration Curve is represented by the equation seen in Figure 2. Empower uses an iterative method to solve for x when given a y value. 

 

ADDITIONAL INFORMATION

This can be done with either the Pro or QuickStart interface.