Influence of mobile phase changes on pump life

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

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I have a system running with two Shimadzu LC-40B XR pumps, one with LPGE.
After 6 months I had strong pulsations and the membrane in the pump started leaking (increase in volume of the rinsing solution). The leaking decreased the flow throught the column effecting the resolution etc.
The pulsation and flow problems were fixed by changing the valves and membrane... well sort off. I still see some strange falling in pressure every odd 30-60 mins in isocractic mode (gradient is even stranger). Still working on this - suggestions appreciated.

So that's the background. My main question is: can changes of mobile phases be harmful to the pump (seal, piston)?

All solvents are compatible with the materials used. As far as I know so should any combinations of compatible solvents should also be compatible - no reactions occur on mixing.
I need to change solvents quite often as the system is in a uni lab and we have various projects running each with different samples and methods. I try to limit the changes by grouping analysis. So that I change things once a week.

Thanks
If you use your system heavily at high flow rates the seals will wear out. I've got LC-30AD pumps which are a little older, but similar technology. On the system that is purely analytical (max 600uL/min), they go from one year to the next without difficulties. On the system that runs a mix of analytical and semi-prep (3.5mL/min) the pump seals need replacing after a matter of a few months. It's mostly the pump that handles the organic solvents that needs changing. I don't think changing solvents (provided they're compatible with the seals) is the problem (we change solvents all the time on the analytical system too) - it's the quantity of stuff we're pumping. If you look at the specs, those seals aren't rated to pump huge volumes. Pity they have a huge cost...
Thanks for the reply. Very interesting insight to the life of seals in your system.

I ran methods at:
a. 1 ml/min
b. 0.4 mL/min (close to pressure limit but very rarely - once a month)
c. 0.2 ml/min

6 months per seal change is rather absurd. Added to the fact, that we don't run 24/7.

Could you share the specification of the seals? I can't seem to find it. Much appreciated.
Are you changing an aqueous buffer with an organic mobile phase on the same pump?

If you have a buffer, then change to organic like Methanol, if you don't remove all the buffer it can fall out of solution when the methanol contacts it and cause salt crystals to form at the seal which will wear both the seal and piston.

If you do need to change from buffer to organic, then always flush with DI Water first, then flush with the Organic phase. This will prevent salt crystals from possibly forming and doing damage.
The past is there to guide us into the future, not to dwell in.
"6 months per seal change is rather absurd."

Not really. In fact, many SOPs use a PM replacement frequency of 6 month (or 9-12 months, as needed) for HPLC pump piston seals in many types of HPLC pumps. Piston Seal wear is dependent upon many things including training (not using good procedures may damage them), solvent compatibility, using proper flushing steps as Jim mentioned, on-time, average pressure values, temperature, storage conditions and so on. The correct way to determine what is "normal" for your system is first to make sure the system has been properly maintained (A PM performed and the system inspected and tested), then being used properly (this includes operator training), always running degassed solutions, with appropriate compatible liquids and being flushed out following good chromatography guidelines. Once those steps have been taken, you can begin to monitor wear by performing an inspection service every few months. This would include initially running properly designed Seal Leak Checks, using an SOP to establish the conditions as well as removal of the pump head(s) to examine the valves, seals and pistons (for excessive wear and also buffer deposits) and look for any wear deposits in any filters or lines.

There are some systems, due to design, which EAT seals up every few months (w.g. some SSI), even when everything is done perfectly. Other systems can go a year or more, with regular use and not need replacements. Seals are normal wear and tear parts so they need to be checked (and replaced) on a regular basis using established SOPs and procedures to insure the pump(s) are working as designed.
Note: You mentioned pressure instability issues. That can be caused by MANY things, but poor priming/flushing and especially inadequate degassing of the mobile phase are two of the most common reasons for that observation. Maybe the degasser is contaminated or broken? They should be professionally serviced every 3-5 years and if purchased from ebay or auction site, you can be sure they are broken!
There's an interesting paper from Applied Automation, Inc. in the Journal of Chromatographic Science from 1985 (https://academic.oup.com/chromsci/artic ... edFrom=PDF)

They discuss corrosion problems that occur with ACN and Methanol carriers.

I've recently been studying similar phenomena and I can say with confidence that switching back and forth between these two organic solvents can exacerbate the corrosion of stainless steel over just seeing one solvent for extended periods of time. Will this kind of corrosion on the steel pump cause the results you're seeing? I don't know... but it's something to at least consider.
The pressure instability issues that the original poster described are probably not a degasser/air-bubble issue, and probably do relate to failed seals. Shimadzu use a diaphragm on the back of the pump plunger to act as a seal wash pump, drawing wash solvent into the space behind the plunger seal as the plunger moves backwards. This is quite a neat design, but it moves quite a bit of solvent, so they use a recycling wash solvent. The original poster noted that the wash solvent reservoir is gradually filling up (rather than disappearing through evaporation) which is absolutely a diagnostic feature of a leaky piston seal on a Shimadzu system. Once you have leaky seals, you also get irregular pressure, particularly as I think this pump continues the Nexera's design of parallel rather than series pump heads. If the seal in one has partially failed, the pressure will drop dramatically every time that side is doing the pumping. (Incidentally, this can be an issue with priming, as it's quite possible to have a Nexera pump that's bubble-free and working fine on one side, but not the other, so when you purge, it looks OK, but you're only purging half a pump...)
I'm sorry, original poster, I can't find the specifications I once had on how much volume those seals are supposed to pump before they fail. But if you're using your system really heavily, even at analytical flows 0.6mL/min plus, I wouldn't be at all surprised if the seals fail in under a year. You may not be doing anything wrong. The trouble is, they are quite expensive. The other problem is that replacing them is a gamble: if you replace the pistons at the same time, it's even more expensive, but if the pistons are in any way scratched, they will trash a new set of seals very, very rapidly... so it's a matter of having a look at the pistons and hoping you can judge whether they're damaged.
Don't be too disheartened; you may need to replace seals, but if these new pumps are similar to the Nexeras, they're actually pretty decent pumps, and not hard to service. We have to change seals in ours a bit more than we'd like, but they give us good, reproducible gradients and cover a wide range of flow-rate.
KarolLbn wrote:
Thanks for the reply. Very interesting insight to the life of seals in your system.

I ran methods at:
a. 1 ml/min
b. 0.4 mL/min (close to pressure limit but very rarely - once a month)
c. 0.2 ml/min

6 months per seal change is rather absurd. Added to the fact, that we don't run 24/7.

Could you share the specification of the seals? I can't seem to find it. Much appreciated.


Another thing to consider is that if you let a pump sit for long periods of time unused, the seals can stick to the piston, which causes increased wear on startup, especially if there is some residual buffer salts in the pump. I used to keep the reagent bottles full and run the pump at 0.05ml/min as a standby method. Barely any flow but it kept the pump seals and pistons lubricated with the solvents and I seemed to get longer life from them, especially on my Glyphosate instrument which could sit for two weeks before more samples arrived. With high buffer mobile phases having a seal wash option if available helps also.
The past is there to guide us into the future, not to dwell in.
I found the source of the expected life-time of seals in Nexera pumps: the Shimadzu status-check feature (in my case in LCMSsolution) gives read-backs of usage and the suggested point for replacement. On the pumps, the suggested point for replacement is 90L pumped by each head.
Since the heads work in parallel rather than series, I'm guessing this means you get 180,000mL total as the expected seal life-time, which is 3000 hours at 1mL/min (a 24/7 year is about 8760 hours). This means basically if you're in a high-throughput lab running 1mL/min methods you will probably need to replace the seals more than once a year. If you start to use these pumps in semi-prep mode at 4-5mL/min you will be replacing them even more often.
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