Calibration; Weighted Regression; Appendix B - Agilent Technologies 7500 ICP-MS Operator's Manual

Agilent 7500 ICP-MS ChemStation Operator's Manual
Appendix

Appendix B

This appendix includes descriptions and equations for Calibration, Quantitation,
SemiQuantitation and Averaging Repetition Files.

Calibration

Weighted Regression

When data with more than one repetition is used to create a calibration curve,
weighted regression can be selected. The count error for data collected in this
manner is represented as the standard deviation of the counts. Usually the count
error for higher concentrations is larger than that for lower concentrations. When
weighted regression is selected, lower concentrations are given more weight
because it is more desirable that the curve pass through points having lower error
than points having higher error.
The weight of each point is calculated as follows.
∑
−
2
=
−
2
w / ( S
S i
i i
i
where
S :
standard deviation of each point
i
n :
number of point
s
In case of 1/count, i changes to 1/count.
However, if a count0 level exists, weighting is not possible.
s
In case of 1/conc, i changes to 1/conc.
However, if 0 concentration exists in calibration levels, weighting is not possible.
Only linear regressions can be weighted.
/ ) n
A-13