Result Types in the OMNISEC software
The OMNISEC system and software are excellent at collecting, calculating, and offering an abundance of characterization data for your macromolecular samples. One of the (good) challenges that creates is choosing how to best present that data in a way that is meaningful to you and your colleagues. In previous posts I’ve discussed tips for generating figures and creating reports. This time, I’m going to focus on one aspect of the calculated data: the different Result Types available.
What and where are the Result Types?
The Result Types are the parameter values calculated based on your sample’s detector responses, as indicated by your limits and baselines. They include molecular weight, concentration, intrinsic viscosity, hydrodynamic radius, molecular weight distribution, and radius of gyration.
If after reading those you think, “I’ve seen those terms grouped together somewhere before,” that’s because you have! Each Result Type has a toggle button located on the main tool bar in a section just to the right of the detector channel section, as shown below.
You might be more familiar with reviewing these parameters in reports as average values for your samples, such as Mn, Mw, IVw, etc. But those average values are determined from the collection of calculated molecular weight, intrinsic viscosity, etc. values from each data slice. The ability to plot the calculated Result Type at each data slice allows you to observe these parameters over the distribution of your sample.
There are three main ways in which you can view these Result Types: the Derived Data, Overlay Data, and Distribution Plot windows. I’ll explore each of these in the next three sections.
Derived Data
The Derived Data window highlights the baseline subtracted detector responses between the limits of integration. This is the portion of your chromatogram used to calculate results, and if you select one of the Result Types in the main tool bar, you can superimpose the calculated result at each data slice. In the image shown above, the molecular weight, intrinsic viscosity, hydrodynamic radius (Rh), and radius of gyration (Rg) are plotted over the refractive index (RI), low angle light scattering, and viscometer detector responses.
Since the example above is a linear polymer, it is expected that each of those parameters would descend as the sample fractions eluted. And that’s exactly what the data shows!
In the Derived Data view and the others that follow, the Result Types are displayed as solid lines where there is sufficient detector response in all required detectors to calculate the result. The dotted lines represent the portions of sample where there is insufficient detector response in at least one required detector and thus the data is extrapolated. These solid and dotted lines correspond with the colorful shading within the limits in the Raw Data view, explained in a previous post.
Overlay Data
The Overlay Data view is perfect for comparing multiple analyses, whether they’re different samples or multiple injections of the same sample. Along with a single detector response, you have the ability to overlay one of the Result Types with the chromatograms. The selected result will appear color-coded with the chromatogram.
In the image above the refractive index chromatograms of a polystyrene sample (red) and polymethylmethacrylate (PMMA) (purple) sample are overlaid, along with the calculated intrinsic viscosity. I chose to display intrinsic viscosity because the overlaid results clearly show that at a given molecular size (vertical data slice), the intrinsic viscosity of PMMA is lower than that of polystyrene. This type of data presentation can offer insights or confirm differences in molecular weight, shape, or structure between different samples.
Distribution Plot
The distribution plot is designed to present your calculated results against an x-axis of either retention time molecular weight. A common use of the distribution plot is to display intrinsic viscosity as a function of molecular weight, both on log scales. This is a Mark-Houwink plot, and is a valuable tool for observing differences in molecular structure from sample to sample, including branching. Tip: the Distribution Plot can be used in overlay mode to compare multiple samples. The Mark-Houwink plots of the same polystyrene and PMMA samples from the Overlay Data section are presented in the image below.
In addition to using the toggle buttons on the main toolbar to choose which of the Result Types to display, the Distribution Plot has several other options that can be accessed through the drop-down menu just above the plot, as shown in the image below. This is where you can switch from a linear to log x-axis, retention volume or molecular weight x-axis, single or multiple y-axes per channel, and more. Another Mark-Houwink plot tip: use Single y-axis per channel to ensure the data are presented on the same scale, allowing fair comparisons.
Final thoughts
I hope the information in this post helps the next time you want to dive deep into an interesting data set. The OMNISEC software allows you to view your calculated data and present it in ways that complement the numerical data of the reports. If you have any questions, please don’t hesitate to contact us or email me directly at kyle.williams@malvernpanalytical.com.
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