OMNISEC Virtual User Meeting 2022: Good Questions & Honest Answers
On 23 August we held an OMNISEC Virtual User Meeting. In addition to presentations and discussions led by myself and my colleague Dr. Ragy Ragheb, two current OMNISEC users also contributed. Professor Johnathan Brantley from the University of Tennessee, Knoxville and Dr. Hui Chong from E&J Gallo Winery were kind enough to share some of their work and how OMNISEC played a critical role. During the meeting there were many questions asked, and while we did our best to answer them at the end of the meeting, I thought I’d gather them in a post for all to view.
The following questions have been slightly edited for clarity.
How many columns can be used in OMNISEC for one sample analysis?
The number of columns used for one sample analysis depends on how many columns will fit in the system and the pressure generated by the columns. With OMNISEC, the largest number of columns I’ve used in a single set is five. However, I had to use a lower flow rate and a slightly elevated temp to minimize pressure.
What type of columns can be used in OMNISEC RESOLVE? Can you use HPLC columns, such as a silica C14 column? What are the column specifications?
The columns used in OMNISEC RESOLVE are GPC/SEC columns. HPLC columns are designed to interact with the samples, where GPC/SEC columns are designed to NOT interact with the sample. The separation in GPC/SEC is based on the sample’s size, and how well they diffuse in and out of the pores in the columns.
The column compartment in OMNISEC RESOLVE (shown below) can accommodate GPC/SEC columns with a length up to and beyond 300 mm, the typical analytical column length. Larger columns such as the Cytiva Superdex Increase columns will fit as well.
Does the UV-Vis PDA detector in OMNISEC REVEAL use all mentioned wavelengths at the same time for one sample, or do you select the wavelength for each sample?
The UV-Vis PDA detector records all wavelengths during a sample run. That way you’re able to look at multiple wavelengths and choose which ones are of interest afterward.
Are the detectors automatically activated?
If you don’t activate the laser of the light scattering detector or turn on the UV-Vis PDA bulbs before starting a sequence, the software will automatically turn them on prior to making the first injection. I like to turn them on during a baseline monitor to make sure things are working as expected.
Is there any degasser that can be offered and attached to OMNISEC to remove air bubbles before liquid entry or do we need to use a sonicator?
Yes! There is a degasser built into OMNISEC RESOLVE. When the mobile phase is pulled from the reservoir by the pump it first passes through a degasser. Unless you’re working with especially gassy sample solutions you shouldn’t need to degas the sample solutions prior to analysis.
What is the difference between the three Viscometer detectors: DP, DP robust and IP?
Each system with a viscometer detector will have DP and IP pressure transducers. DP = differential pressure; IP = inlet pressure. DP Robust indicates a new version of the DP transducer that has an adjusted range, hence the different baseline values.
Are there any time limitations for needle rinsing and purging?
Needle rinsing takes approximately 3-4 minutes. This is because the rinse process pulls enough mobile phase to completely fill the line from the reservoir to the needle. That way, even if your line is full of air, by the completion of a needle rinse it should be full of solvent and ready for an injection.
You have the option to set the purge time for the RI, DP, and IP detectors between 1-10 minutes. It’s a good idea to consider your current flow rate when purging. If you’re running at a slow flow rate, then purging for a longer duration might be helpful in completely flushing out the detector.
Why does the signal intensity vary by just changing injection volume while the concentration stays same?
When the injection volume changes the amount of mass introduced into the instrument changes. A 100 uL injection of 1 mg/mL sample provides the same amount of sample mass as a 50 uL injection of 2 mg/mL sample. So if the concentration is constant, as it would be when making multiple injections from the same sample vial, reducing the injection volume effectively dilutes the sample. The RI chromatograms of 80, 60, 40, and 20 uL injections of a sample are shown below.
How does the software validate sequences and data reporting?
There is an audit trail function available through the Optional Features mentioned by Ragy that can be used to confirm data integrity in accordance with 21 CFR specifications.
Biological sample extraction cannot get 100% clear soluble, how can we manage their analysis via OMNISEC?
In those cases I’d recommend using an established dn/dc value. Hopefully you can find a dn/dc value in the literature or through analyzing other more soluble samples. That way you can filter your sample and then let the OMNISEC software calculate the concentration of the sample for you.
I’m particularly curious about the limits between the 6000 and 2000 columns. Did your 6000-2000-1000 column series have any gap in the MW range?
No, because those T6000M columns are mixed bed columns, so they included resolution down to at least the range of the T2000 column. If the T6000M wasn’t a mixed bed column, and was a single-pore T6000 (without the M), then yes, there almost certainly would have been a gap.
What are minimum limitations of temperature and heating duration to be kept during preparation?
These limits will be sample dependent. Therefore, in general, I recommend being as gentle as possible, using as little heat as possible during sample preparation. Some samples will be more stable under warmer conditions than others.
What happens when Malvern Panalytical validates an OMNISEC at hardware level; i.e., IQ, OQ and PQ?
Malvern Panalytical service engineers can perform an IQ/OQ on OMNISEC. This involves ensuring the components, pump, injection mechanism, detectors, etc. are working properly. Please keep in mind that if you are using an OMNISEC REVEAL detector unit combined with a third party front end, only the Malvern Panalytical pieces of your system can be qualified. The third party components can be validated by the third party to give you a fully validated system.
Final thoughts
I hope this Q&A offers a bit of helpful insight for you and your OMNISEC. 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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