Virtual Internal Standard Correction - Agilent Technologies 7500 ICP-MS Operator's Manual

Agilent 7500 ICP-MS ChemStation Operator's Manual
Performing a Quantitative Analysis

Virtual Internal Standard correction

1 Definition of Virtual Internal Standard
The latest revision of ICP-MS ChemStation includes a function that allows the
internal standard correction factor that is applied to a given analyte to be calculated
from the actual signal change of one or more of the internal standards, based on the
relative mass of the internal standards and the analyte. This can improve the
accuracy of the internal standard correction factor applied, particularly when
available internal standards are widely separated in mass and when long-term drift
occurs which has a component that is mass dependent.
2 How to use
2-1. Background
The main reason for the use of internal standards in ICP-MS is to correct for
long-term drift, which results from changes to the characteristics of the interface
cones, especially small changes to the profile of the sample cone orifice, which can
occur after a prolonged period of analysing high dissolved solids samples. The fact
that this signal drift is sometimes different for different analyte masses means that
several internal standards may be useful to accurately correct for the signal drift. In
cases where the analytes are many mass units away from the nearest internal
standard, or a limited number of internal standards are available, the accuracy of the
correction can be improved by using interpolation of the drift correction factor
between the measured internal standard elements.
In addition to the accurate correction of mass dependent drift, interpolation of
internal standards can be used to correct for some aspects of matrix effects, since it
is said that the space charge is one of the biggest contributions to the matrix effect.
In this case we might expect to observe some mass dependency of the matrix effect,
similar to that observed due to drift caused by some heavy matrix introduction.
Virtual Internal Standard correction may also be used to correct for matrix effect,
where the main component of the matrix effect is mass dependent, in particularly
when available ISTDs are limited. Because this is just an optional function, you
should confirm that this option works well for your analysis.
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