Selecting the Calibration Function
Weighting and Averaging Calibration Points

Weighting

With the default settings, Chromeleon weights calibration points of higher concentrations more strongly than lower concentrations, that is, the course of the calibration curve is oriented towards the calibration points of higher concentration. This makes sense as smaller concentrations also cause a stronger dispersion of the determined area values, which would distort the result beyond proportion.

To undo or even reverse this type of weighting, four additional weighting functions have been introduced:

1/Amount (X)

Nearly cancels out the weighting of higher amounts/signal values, i.e., low and high concentrations are weighted similarly.

 

 

1/Amount˛ (XX)

Causes over-proportional weighting of smaller amounts.

 

 

1/Response (Y)

Nearly cancels out the weighting of higher signal values. In this case, the Y-values (dependent signal values) of the Calibration Points are used as weight factors instead of the X-values (nominal amounts).

 

 

1/Response˛ (YY)

Causes over-proportional weighting of smaller signal values. In this case, the Y-values (dependent signal values) of the calibration points are used as weight factors instead of the X-values (nominal amounts).

 

Also, this weighting can be avoided by variation of the Number of Replicates. Smaller concentrations are injected more frequently than larger concentrations, more calibration points in the low concentration range support the calibration curve. Outliers are then less relevant.

 Tips:

The stronger weighting of higher concentrations is valid in all Calibration Functions, with the exception of Point-to-Point.

Outliers can be explicitly "disabled" by excluding a specific standard sample from the calculation. Exclude the sample on the Calibration tab page of the quantification method.

If you select Average all response values of each calibration level before Curve Fitting (A), two more weighting functions are available:

 

1/Rel.Std.Dev (S)

Each average value is reciprocally weighted with the related relative (and squared) standard deviation. This means that calibration levels with increased scattering are weighted less than calibration levels with less scattering.

 

 

1/Rel.Std.Dev.˛ (SS)

Causes over-proportional weighting of calibration levels with less scattering.

Averaging

To determine the calibration curve, all available Calibration Points are normally used. As dispersion is stronger for the lower calibration levels, many users verify the results by using a large number of calibration points. The calibration curve is thus determined by a larger number of points on the lower than on the higher level.

If all points of a Calibration Level are averaged before calculating the calibration curve, and the subsequent calibration is performed based on these average values only; the calibration curve is based on one point of each calibration level only.

When the Average all response values of each calibration level before Curve Fitting (A) option is selected, Chromeleon also uses the averaged values when calculating the 'Variance', Variance Coefficient', 'Standard Deviation', 'Relative Standard Deviation', 'Correlation Coefficient' and 'DOF-Adj. Coeff. of Determination' calibration variables.