This is part 5 of a tour through PEAXACT - Software for Quantitative Spectroscopy from S-PACT. It introduces the centerpiece of PEAXACT - the Spectral Hard Model - and the Component Fitting Analysis.
Spectral Hard Model
The previous part mentioned the three major elements of a model: Pretreatment Model, Spectral Model, and Calibration Model. A Hard Model is another type of spectral model which calculates component weights by fitting peak curves to the spectrum. Hard Models have many interesting advantages over other models, e.g. they can deal with overlapping and shifting peaks.
Hard Models are composed of peak curves (aka peak models). Peak models are grouped together to form component models. The task is to create a model which represents the mixture you want to analyze.
With PEAXACT you can automatically fit peak models to a spectrum or use the Plot Panel to interactively add and edit them. Peak models are shown as cyan lines.
Peak fitting is an easy way to deconvolve overlapping signals. By first fitting peaks to a mixture spectrum and then grouping and assigning peaks to components, you have one of several ways to create the Hard Model of the mixture. The resulting component models are displayed as blue lines. The Hard Model - the sum of all peak and component models - is shown as red line.
Spectral Hard Models can be created for any real-life mixture, whether it has just a few peaks or several components with lots of peaks.
Component Fitting Analysis
If you have measured several mixture spectra, you wouldn't want to build separate Hard Models for each individual mixture composition, but just one model to fit them all. A good Hard Model only needs a few known spectra to create it, e.g. for finding the initial peak models, and then can be used to analyze many unknown samples.
A Component Fitting Analysis automatically fits the Hard Model to mixture spectra and as a result delivers component weights. Component weights correspond to the contribution of each component to a mixture. Component weights can be interpreted as component areas, correctly taking overlapping and shifting peaks into account. This makes component weights very suitable for monitoring concentration changes.
More Hard Modeling
In its early days, PEAXACT was a software for a specific method called Indirect Hard Modeling. Today, it is the leading brand for all kinds of spectral Hard Modeling methods. If you want to learn more about spectral Hard Modeling, have a look at the following articles:
- S-PACT web page: Introduction to Hard Modeling
- Blog article: How does IHM work?
- Blog article: How does HMFA work?
- Scientific paper: Fully automated indirect hard modeling of mixture spectra