How does NMR spectroscopy benefit from Indirect Hard Modeling (IHM)?

This article answers a frequent question about the Indirect Hard Modeling (IHM) method for quantitative spectra analysis, implemented in the PEAXACT software from S-PACT. It shows how nuclear magnetic resonance (NMR) spectroscopy - especially mid-resolution NMR - benefits from the IHM approach.

Related IHM Resources

IHM for NMR

Hard Modeling is mainly beneficial for mid-resolution NMR instruments that are making their way into real-time process analysis. In contrast to high-resolution instruments these spectra often suffer from overlapping signals and more pronounced relative shifts.

In this situation, the definition of an integration range is no longer feasible - the signal cannot be captured by a reasonable integration range. This is where the spectral Hard Model comes into the game…

First, define a set of peaks for each component (either with the help of a pure spectrum or a mixture spectrum in which the peaks can unambiguously assigned to components):

Second, merge the pure components into a mixture model. From this moment on, the individual peaks are just a means to the end of representing the shape of each component; the more relevant quantity now is the partial intensity which each component contributes to the mixture, that is the concentration.

Third, define how flexible the model must be in order to correctly respond to possible shape changes of peaks in a measured mixture spectrum. Shifting peaks will need more flexibility than others, multiplets should only shift as a whole. This step is facilitated if you already have mixture spectra at hand. Also, you only need to do this once. Peaks of the Hard Model are automatically fitted to new mixture spectra, i.e. you don't have to process each spectrum from the scratch.

Fourth and finally, if your model is well set and flexibility is validated, you may apply it in an unsupervised manner to an instrument connected to your process. You come up with a real-time output of concentrations – what makes your benchtop NMR a proper Process Analyzer!

Comparison to Peak Deconvolution

The well-informed NMR analyst may immediately recognize the close relationship to global peak deconvolution techniques. Indeed, Indirect Hard Modeling can be considered a more advanced form of peak fitting which we call "component fitting". Because of the linking of peaks the fitting problem has much less degrees of freedom which results in a physically more reasonable fit... a very relevant benefit for the NMR community with its strong physical background.

Try it Yourself

If you are interested in evaluating Indirect Hard Modeling (IHM) for your NMR spectra, try it out for free now.

 

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