Agilent Technologies 7500 ICP-MS Operator's Manual page 446

Agilent 7500 ICP-MS ChemStation Operator's Manual
Performing a Quantitative Analysis
For standard addition:
• Y=aX+[blank]+bkg
• Y=aX+b+bkg. Normally, select this equation.
• Excluded
6 To weight the equation, make the following settings.
1) Select an equation from the Weighting Method drop-down list in the upper right
section of the Edit Calibration dialog box.
2) Double-click on the Weight field to turn on weighting.
Double-clicking the field will alternately toggle the setting between on and off.
Generally, weighting is turned on when a low concentration is quantitated using a
calibration curve with a wide dynamic range. When weighting is turned on, the
calibration curve is drawn with weighting applied to a lower standard deviation
(SD) level. The calibration curve is calculated based on the standard deviation SD at
each concentration level. In other words, the calibration curve is affected more by a
high-SD level. Generally, the SD of a high-concentration sample tends to be higher
than that of a low-concentration sample. Consequently, calibration without
weighting results in a smaller error on the high concentration side and a larger error
on the low concentration side.
Therefore, when a low concentration is quantitated using a calibration curve with a
wide dynamic range, set weighting to on and draw the calibration curve with a
heavier weighting applied to the low concentration side (low SD) than the high
concentration side (high SD). When the data used for individual levels contains a
different number of replicates, apply weighting to the level with a lower standard
deviation (SD) for the drawing of the calibration curve.
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