Keep your GPC/SEC system in shape over the holidays
The holiday season is upon us! And with it, hopefully, a bit of time off to spend with friends and family. That means you’re less likely to be in the lab to check on your GPC/SEC system. That’s ok! In this post, I’ll discuss ways to keep your GPC/SEC system in shape so that it’s ready to go once you return.
The information below will help you keep your system idle through a short hiatus (< 3 months) or properly store it during a longer break (> 3 months). The procedures for aqueous or organic systems are the same, however, you must take care to prevent bacterial growth in aqueous systems. This means that an aqueous storage solution needs a preservative, such as methanol or sodium azide.
Short term – less than 3 months
For breaks of this length, you can keep the system running at an idle flow rate of 0.1 mL/min. The flow of the storage solution helps flush particulates and maintains positive pressure on the columns and other system components. Follow the steps below to keep the system idle until your return.
Firstly, you’ll want to ensure you have a salt-free storage solution that is stable and does not grow bacteria. A vacuum-filtered 10% methanol in water solution works well for aqueous systems. For instruments typically in organic conditions, the plain solvent (e.g. pure DMF or THF) will work.
Secondly, consider your column set. If your columns are compatible with the storage solution you choose then you can leave them in place. If you’re going to be leaving your system for more than three months, I suggest removing your columns once they are in a suitable storage solution.
Thirdly, gently flush your storage solution through the system. I recommend a slow flow rate such as 0.1-0.2 mL/min. Setting this up to occur overnight works well and ensures that your system, even with a column set, will be flushed with the storage solution.
Fourthly, after your system is in the storage solution, you’ll need to purge the lines containing static mobile phase. This includes purging detectors (RI & viscometer channels, if present) and priming the autosampler injection line. While using a slow flow rate, ensure you’ve set the purge time to at least 5 minutes to allow enough storage solution to flush the lines. For a demonstration on how to switch the mobile phase, please see the video below.
At this point, set the system temperatures to ambient and leave the system running at 0.1 mL/min. Refill the reservoir and empty the waste container as necessary; 0.1 mL/min = 144 mL a day. Or place the waste line in the reservoir to recycle the storage solution mobile phase.
Long term – 3 months or more
To prepare a system for long-term storage, follow the steps described in the previous section. With the system at ambient temperature, you may turn the flow off and power the system down. For extended breaks, I recommend removing the tubing lines from the mobile phase and waste bottles. Store or dispose the mobile phase solution and waste appropriately and secure the tubing lines to the top of the unit. By keeping the inlet and waste lines elevated, you will minimize the chances of the storage solution dripping out.
Now is also a good time to remove the column set. Be sure to replace the column set with a union to keep the flow path closed.
Start up
Once the holidays are over (bummer!) and you’re ready to use your GPC/SEC instrument again, the start-up procedure is roughly the shut-down procedure in reverse.
Firstly, get the system running at 0.1 mL/min in a mobile phase of the storage solution. If you had removed your column set, now is a good time to reinstall it. Anytime I add a column set to a system I like to connect the inlet and let the outlet flush to waste. After 25-30 mL of mobile phase have passed through, roughly two column volumes, then I connect the outlet to the rest of the system.
Secondly, put your working mobile phase back on the instrument. Flush the system with the mobile phase, including purging the detectors and priming the autosampler. Now the temperatures can be set to working levels and the flow rate increased incrementally. Once you reach your regular flow rate it may be helpful to do one last set of detector purges. That way you can zero the RI detector and ensure its signal is on scale. After that, you’ve successfully kept your GPC/SEC system in shape and should be all set!
Back seal wash pump
If you have an OMNISEC with one of these, don’t forget about it. The back seal wash pump should already be flushed with 10% methanol in water since that’s its recommended working solution. If you’re keeping your system idle for less than three months, then simply turn off the back seal wash pump by disconnecting the power cable from the unit. For longer storage, run the pump until the solution is drained and then turn it off.
For further information on the back seal wash pump, please refer to the OMNISEC System Basic Guide. The Basic Guide, along with the User Manual and Interactive Help, can be found on the software’s Start Page.
Final thoughts
In conclusion, I hope this helps you keep your GPC/SEC system in shape. Furthermore, 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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