The others – 6 helpful data channels in the OMNISEC software
If you’ve ever worked with GPC/SEC data, then you know that the system conditions can have a significant impact on your samples’ chromatography. Things like temperature, flow rate, and system pressure can all affect your data. Wouldn’t it be convenient to be able to monitor these parameters in real time? And review them after the fact at each saved data point?
With the OMNISEC software, you can! In this post I’ll describe where to access these other data channels and highlight some benefits these data bring to your analyses.
Why did you call them “the others”?
The name I gave these parameters in the title of this post was taken from the label of the toggle button in the Channels section of the main tool bar in which they are located: Other. This button is situated on the right side of the Channels section, and when you click the bottom half of the icon a menu appears which allows you to select which parameters you would like to display.
As you can see in the image above, there are three main types of data available: temperatures (of various system components), and the flow rate and pressure of the pump.
Temperatures
Each of the temperatures you can set for the OMNISEC system are available under the Other channel: Autosampler, Detector Oven, Column Oven, and MALS temperatures.
If you observe an unusual shift in your detector baselines, checking the temperature is a good way to determine if the temperature was stable during the analysis. You can see very minor variations in the column temperature in the image above, but nothing more than a fraction of a degree. Plots like this confirm consistent temperatures throughout the entire system.
Pump flow rate
Like stable temperatures, a consistent flow rate is critical to obtain quality GPC/SEC data. And the visual representation of the flow rate should be consistent because it will mirror what you enter in the Instrument Controls. What’s nice about this is it allows you to observe changes to the detector signals when the flow rate is changed, as shown below.
This example shows a system starting at a flow rate of 0 mL/min at time 0, then immediately increasing to 0.5 mL/min. After a few mL, the flow rate is increased to 1.0 mL/min, whereupon the refractive index detector’s response increases, then drops, and eventually stabilizes. After 10 mL, you can see how the refractive index response continues to change with adjustments to the flow rate, which is expected.
Pump pressure
We’ve saved the best for last! This one is my favorite, mainly because the pump pressure measurement can be affected by the sample or changes to the system. This feature is especially useful if you are experiencing over-pressurization alarms. When that happens to me, I open the sequence that was running when the issue occurred, open the last data file, and activate the pump pressure channel. It allows me to determine exactly when in the run the pressure limit was exceeded, and sometimes, like in the image below, I can learn why.
Looking closely at the example above, the initial pump pressure was about 228 PSI and steady. Then, just after 13 mL once the sample began to elute, the pump pressure started climbing. The pump pressure eventually reached about 920 PSI where it plateaued. Since the pump pressure occurred simultaneously with sample elution, that tells me the sample concentration and intrinsic viscosity combination is too high. In this example I was lucky – the system didn’t over-pressurize – but I knew I had to change something about my analyses otherwise I would over-pressurize the system within a few more injections.
Since the pump pressure occurred simultaneously with sample elution, that tells me the sample concentration and intrinsic viscosity combination is too high. The easiest thing to do from here is to dilute the sample by reducing the injection volume. If that doesn’t work, than preparing a more dilute sample solution would be next. I would also check on the post-column filter, and unless the pressure quickly returned to its previous level of 228 PSI, I would replace the frits and membrane.
Being able to monitor the pump pressure allows you to observe the pressure of viscous samples even without a viscometer detector, and also helps ensure you remain well below the maximum pump pressure threshold.
Final thoughts
In conclusion, I hope this post increases your understanding of these helpful data channels I have dubbed the Others. While they’re not the most exciting data being collected, the temperatures, flow rate, and pressure of your analyses can offer valuable information, especially when troubleshooting or working through an unusual result. 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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