Metrohm Vision Manual - Manual (Page 146)

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To save the adjusted equation, click on Regression/Save Adjusted Equation. If you do not want to
save the adjusted equation, simply exit the prediction program.
The spreadsheet can be displayed in Designer Mode by a double right click. Designer Mode allows
copying results or saving the spreadsheet in Excel format.
5.8 Pre- and Post-Processing
Pre- and post-processing allows users to setup a parametric calibration equation. Parametric
Calibration predicts results from NIR spectra and a number of parameters, different for each sample.
For example, a standard equation applied to a sample spectrum will calculate the concentration of
the component of interest. If the user is interested in the amount of the component, the result needs
to be multiplied by the mass of the analyzed sample. Parametric Equation will allow the operator to
enter the independently measured sample mass during Routine Analysis, and will do the
multiplication (post-processing) automatically.
It may be expected that the above example input data for calibration will consist of reference method
results in the form of the amount of the component in each calibration sample, and the
corresponding sample mass. Vision can calculate the concentration values in the step called pre-
processing (by dividing the amount by mass), and then proceed with calibration based on
concentration.
More that one parameter can be used for pre- and post-processing. For example, calculation of the
tablet adjusted potency involves tablet weight and thickness. The mathematical operation is not
limited to multiplication and division. Subtraction and addition can also be used.
One can easily notice that pre- and post-processing steps are exactly opposite. Pre- and post-
processing should be used in cases when a calibration cannot be developed directly, but the
reference values can be transformed to a form directly related to the NIR spectrum.
Procedure for developing pre- and post-processing equations:
(The following procedure lists steps for the above-described example of predicting amount of the
component in a sample by indirect measurement of concentration.)
1. The calibration development should start with collecting spectra of the calibration samples.
For each sample the amount of the component and sample weight should be known. These
should be entered into Vision as regular constituents.
After checking product constituent
values, they should be displayed as
shown on the right.
2. The next step (pre-processing), will create a new constituent by combining the values of the
AMOUNT and WEIGHT into concentration.