Blank Correction - Thermo Scientific Orion Versa Star Pro User Manual

Thermo Scientific

Blank Correction

Versa Star Pro meters with a pH/ISE module offer the option to use blank (non-linear)
correction for ISE measurements when a multi-point calibration is performed. The automatic
blank correction feature uses an algorithm to compensate for the non-linearity of an ion
selective electrode in low level standards and samples.
With the blank correction feature enabled, the meter decides whether blank correction is the
best measurement strategy by analyzing the electrode response during a multi-point calibration.
A separate blank does not have to be run. Graphically, blank correction is equivalent to drawing
a smooth curve through the lowest three points of the multi-point calibration and extrapolating to
zero concentration based on the assumption of Nernstian electrode behavior.
Multi-point calibrations at the lower limit of detection are desirable when the response of an ion
selective electrode is non-linear and cannot be characterized with a one or two point calibration.
This is usually seen as a low electrode slope. Generally, the electrode is behaving in a
Nernstian manner but the effect of a blank is being observed. See the figure below.
This blank may be a true reagent blank, traces of analate ion in the reagents or it may be the
"mud" value of the electrode. It could also be an interference in the reagents that becomes
apparent at low levels of analate ion, or it could be any combination of these effects. The
expanded version of the Nernst equation traditionally used for blank correction is as follows:
E = E + S * log (C + b)
0
In a multi-point calibration, a set of equations is generated and the relationship between them
evaluated. For example, the equations generated in a three point calibration would be:
E = E + S * log (C + b)
1 0 1
E = E + S * log (C + b)
2 0 2
E = E + S * log (C + b)
3 0 3
Appendix A
where b is the blank
Orion Versa Star Pro Meter User Manual
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Channel Specific Settings and Features
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