Getting Started with Hard Modeling Factor Analysis

This is a tutorial for PEAXACT software for quantitative spectroscopy from S-PACT. Its main objective is to get you familiar with one of the spectra analysis methods: Hard Modeling Factor Analysis (HMFA). The tutorial addresses to PEAXACT users and persons interested in PEAXACT.

In this tutorial you learn how to:

1. Create a representative sample
2. Create a Hard Model for the representative sample
3. Use the model to analyse a series of spectra from a reactive process

If you have PEAXACT installed on your computer you may try this tutorial right away. If you don't have PEAXACT yet, get a free trial now.

The big picture

HMFA can be used if you have a series of samples with varying but unknown composition, e.g. from a reaction process, and you would like to estimate qualitative concentration profiles of the involved chemical species. You don't even have to know what those species are. HMFA uses a Hard Model (a peak representation of a representative mixture spectrum) to analyse variations among the samples. As a result it delivers estimates of the pure component spectra and concentration profiles.

HMFA is one of the less complex analysis methods because it requires nothing more than the data you would like to analyse.

Preparations

You can find data of this tutorial in %ProgramFiles%\S-PACT\PEAXACT 5\Data\MidIR - Reaction. The directory will be referred to as DATA in the following.

• Start PEAXACT.
• Choose File > New Session > Mid-IR from the menu which opens a new modelling session with default settings for mid-infrared data.

Create a Representative Sample

A representative sample is one that contains all peaks of all components present in the mixture. It could be a measured sample, but often one cannot find such a sample. Then it has to be computed from available samples. PEAXACT will do so by calculating a mean spectrum from the most different spectra within a selected sample set.

• Choose Data > Load Table... from the menu, browse to DATA\Analysis and select DataTableReaction.xls to load 29 mid-infrared spectra of a reaction involving 3 components.
• Select all samples in the Samples Panel.
• Choose Data > Create Representative Sample from the menu.
• In the dialog, enter 3 for the number of samples to be considered for calculating the representative sample. Optionlally, change the path and filename for saving the representative sample. Click OK to continue. The representative sample will be added to the Samples Panel.
• Normally you would now have to perform a sanity check and verify that the calculated representative spectrum really contains all relevant peaks. In this case the sample looks fine.

Create a Hard Model for the Representative Sample

• Right-click on the representative sample in the Samples Panel.
• Choose New Hard Model for Active Sample from the context menu. A new model is added to the Model Tree Panel.
• Choose Edit Model > Hard Model > Add & Autofit Peaks from the menu.
• In the dialog, enter 30 and continue. Wait until all 30 peaks have been fitted.
• Optionally save the model (File > Save Model).

Perform Hard Modeling Factor Analysis

• Select all but the representative sample in the Samples Panel.
• Choose Analysis > HMFA > Component Analysis from the menu.
• In the dialog, enter the number of pure components you want to get identified. Enter 3 (remember: it is a reaction involving 3 components). Also, you could select the kind of closure constraint for concentrations. Choose Normalization which forces the sum of all component concentrations to be one.
• Click OK to start the analysis.
• HMFA results are displayed in a Report Window from where you can choose between different graphical and tabular reports, including plots of the identified componenet spectra and concentration profiles. Click the Export button if you want to save results to a file.
• Click Create Hard Model to add a new model to the Model Tree Panel containing a Hard Model of the 3 identified components. E.g. you can further use this model for calibration.

This concludes our quick tutorial on HMFA. Check out our other tutorials on the PEAXACT Quick Start page.