Welcome Back! You and your lab have been through a lot these last few months and now it’s time to get your LC back up and running. After it has been down for a few months, it likely needs a little TLC before it’s performing optimally again. Just like a car that sits around for a long time without being used needs its fluids, filters, and tires checked and maintained, an LC has similar needs.
Let’s walk through the system and get you back up and running. Before starting anything, you should consider performing preventative maintenance (PM) according to your manufacturer’s specifications. Another excellent resource that can help is “Routine LC Maintenance: Simple Steps to Preventing Unexpected Downtime.” After any PM or other maintenance that you decide to do is completed, you can move on to getting the rest of the system ready.
If there are old solvents sitting on the solvent rack, dispose of them all in the proper waste streams and replace them with fresh solvents. This includes solvents for seal washes and needle washes etc. ALL solvents should be replaced. At this point you should also replace your column with a union and divert your flow stream directly to waste, making sure the detector is disconnected from the flow path. You should also note right now whether any buffer was in the system. If so, you’ll need to flush all pumps and lines containing buffer with water to prevent any salt precipitation in the system. Your pumps will need to be primed and purged according to the LC manufacturer’s specifications. After this, start the pumps with low flow rates (0.2-0.4 mL/min) and purge any buffer from the lines with water for 10-20 minutes. Also, be sure to rotate any valves in the system that might contain buffer.
Next, flush a strong organic solvent, like isopropyl alcohol, through the system by priming and purging the pumps. Flushing the system for 10-20 minutes at 0.2-0.4 mL per minute should adequately flush the system. Finally, you can load your desired mobile phase solvents onto your LC, though you should not incorporate buffers yet. After all of these steps are completed, all buffers and organic contaminants should be flushed from your LC.
Now you are ready to reconnect the detector into the flow path. Follow the same order of solvent flushing as above. Start with aqueous and transition to organic. With your entire system now flushed, you can begin running diagnostics.
At this point, installing an LC column will help you to identify any problems that might exist as many can show up when there is back pressure on the system. Observing not only your baseline, but also your back pressure can help you determine if anything needs to be fixed or replaced.
Erratic baselines can indicate the presence of air bubbles. To fix this, further purging of your pumps or entire system can fix this problem. If you see systematic fluctuations in pressure profile or detector, this can be more indicative of a pump problem. The culprit is likely a faulty check valve or a worn pump seal that requires cleaning or replacement. For all these PM tasks or repairs, make sure to follow your LC system manufacturer’s guidelines. Many standard parts are available on our website.
If everything checks out, then a diagnostic/system suitability tests with a column in place and an appropriate system suitability mix should be performed to see how well the instrument is performing. Comparing the current results with previous tests can also be useful to make sure your instrument is performing optimally.
Good luck on getting your systems back up and running and if you have any questions, we are always here and happy to help.
Other Useful Resources: