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From the author
As the author of PeakFit, I sought to create a tool for researchers to extract additional information from chromatographic, spectroscopic, and statistical peak data. From 1990 through 2002, through four releases, I maintained the product and sought to add new innovations in modeling and nonlinear fitting. In 2002, my company sold the product with a promise that it would see an even greater attention and that it would continue to evolve. Clearly that did not happen, and reserving certain rights, I endeavored to answer that lapse starting in 2015. I began with chromatography knowing its peaks were amongst the most challenging to effectively model. Five years of development later, PFChrom is finally ready.
As the R&D work continued, the objectives became much more stringent, and the aims for the product changed. I began with the intention of finding better core models in the two decades' time that had passed since I last created an update for PeakFit. In that aspect of things, I was unsuccessful. Instead, I worked with the only two theoretical models that ever managed to truly fit higher concentration chromatographic shapes, the Haarhoff-VanderLinde (HVL) diffusion model and the Wade-Thomas (NLC) kinetic model. I came to see these as the two principal models for chromatographic peaks because they represented the simplest of the two models born of well-crafted diffusion and kinetic theory.
Beginning with these, I discovered a common chromatographic distortion model which was applied to two different zero-distortion densities or 'ZDDs'. This meant it was now possible to create statistical generalizations of those densities, models which not only bridged these two principal theoretical models, fitting each effortlessly, but which opened the way for complete third and fourth moment modeling of chromatographic peaks. By treating the fitting problem as a statistical one, the HVL-NLC core theory has been expanded with a complete set of generalizations which manage any chromatographic shape, including the compression of gradient HPLC peaks, as well the dilation or overload of preparative shapes.
The other aspect of PFChrom v5 that is central to the near zero-error fitting in this new version is the acknowledgement that the real-world will not conform even to a beautiful statistical generalization of these theoretical models. It was also necessary to implement convolutions of instrument response functions or 'IRFs'. These are the different instrumental distortions which occur in real world instruments, flow systems, detectors, and where the additional mass transfer effects are not modeled by the statistical generalizations of the core models. Instead of fitting convolution integrals, PFChrom implements a much faster Fourier domain fitting. The new models in PFChrom weren't even in the realm of possibility those decades ago.
These ZDD and IRF innovations made it possible to take peak fits of real world data from thousands of ppm unaccounted variance to goodness of fits as low as 1 ppm unaccounted variance, with full significance in all fitted parameters. In the tutorials, you will see real-world HPLC gradient peaks fitted to even lower error. The v5 product is different from the older product you may know, or its technology as other software products copied it over the years. As a consequence of these innovations, you will have to start over in certain ways, much as I did, to get accustomed to entirely different approaches and methods for chromatographic peak modeling and analysis.
I have always believed scientists had a profound disdain for 'black box' algorithms. The documentation contains a large measure of information associated with the IRF and ZDD concepts you will need to understand in order to make maximum use of the new technology. There are more than ten tutorials, each of which illustrate aspects of chromatographic peak fitting which should significantly improve your analysis skills. If you take the time to explore these, you should be light years ahead of where we were in the prior state of this technology. The higher moments, which were always in a nebulous state of estimation, will now tell you a great deal about your chromatographic separations, columns, and instruments.
Much was added to the help system and to the tutorials to make this learning process as productive and fruitful as possible. The tutorials are intended to illustrate wholly new chromatographic technology, not simply how to navigate dialogs, menus, graphs, and reports. As you see the nuts and bolts of the software, you will also see a wholly new state of the science.
Unlike nearly all commercial software authored in recent times, PFChrom v5 is a single developer software product. As with the work of any single human being, there is the benefit of a coherence to the software design and function, but there is also the far greater likelihood of something slipping through. If I've missed anything, please report the failing. I will see to any issue as swiftly as I can.
PeakFit v1, first authored in 1990, was the first product of its kind. Three decades have passed since that original work. In that expanse of time, I have had the honor of working with Dr. James Wade, a skilled scientist and chromatographer who derived the NLC model in his thesis in the late 1980s. In the course of my work for PFChrom v5, I grew greatly in my respect for the innovative work of Haarhoff, VanderLinde, Thomas, and Wade. I built upon their work to create these generalized statistical models. Much of the best of the data I was furnished for the R&D of this new product was generously given to me by Jim Wade. His assistance in those earliest of times and in this recent work was invaluable.