LC VIM selector valve rotor seal rusting??

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

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It has happened a couple of times recently. Pressures exceed limits and after cracking open the selector valve, it can be seen that the rotor seal has build-up that looks to be rust.

There has been no change in the type of samples we run, nor the mobile phases used...

Any help in trouble shooting this would be great.
OK, I give up. What is a "VIM selector valve" ? And what kind of mobile phases have you been using?

FWIW, I have run in to situations where parts that were *supposedly* 316 SS weren't, with corrosion being the first symptom.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Hey thanks for the reply! We have since remedied the situation, sadly it wasnt something that could be fixed, just a new part had to be ordered (700 bucks ouch). We could have gotten a "for parts VIM" from ebay that we could have salvaged the part from for 500 bucks but it wasnt worth the risk.

To answer your question, and to help others who may have this issue:

Starting off, we are performing LC-MS/MS on urine samples testing for clinical drugs.

The VIM, or valve interface module, is one of the stacks we have on our LC system. After mobile phase (in our case A and B consisting of 0.1% Formic acid in water and 0.1% FA in MeOH) is pumped to the injector valve that the autosampler injects into, the sample and mobile phase go to our selector valve which is located on the VIM. The selector valves purpose is to allow multiplexing, so we can run two columns with two different methods to the LC simultaneously ( or close to simultaneously, one channel is open while the other is equilibrating the sample in the loop on the injector valve ready to pump in when scanning for the other channel finishes). It does this by a rotor in the selector valve that turns to allow different pathways to flow to waste or the MS. We started seeing nasty buildup behind the face of the valve (between the face where the plumbing connects and the rotor itself). This gunk ended up being (I think) grease from the broken bearing in the rotor. After taking it apart and turning it by hand it was rough. We tried sonicating the part to clean it but it only got rougher so Im almost certain it was the bearing broken. The reason we had high pressures is because it was not switching between channels properly, like getting stuck between two positions, not allowing the mobile phase to flow properly. Sadly the part that we replaced could not be opened up and the bearing replaced so we had to order another one from the manufacturer, in this case, from ValveCo https://www.vici.com/.

Ill edit this and upload a photo of the VIM too for reference when i get the chance :)
The problem you describe sounds exactly like a maintenance / training issue (or absence of maintenance in this case). While you did not tell us the brand or model of valve used, most high pressure HPLC switching valves require regular inspections and replacement of internal wear parts. - "The regular valve inspections involve periodically taking the valve apart to check for condition, wear and damage. These are usually conducted anywhere from once every few months to annually (it depends on your findings and the types of samples and methods used). If wear is observed (i.e. worn surfaces, scratches, discoloration, contamination), then the required parts should be replaced. For most valves this would include the valve rotor and in some cases perhaps other parts too such as the stator and/or isolation discs (depends on the exact valve used). The parts inside the valve wear out. This is normal. If you do not perform regular valve inspections and maintenance, inject dirty samples, acids, bases or in some cases incompatible chemicals they will wear out or show damage much faster and need even more attention (possibly requiring replacement of the whole valve). This is why the inspections are so important. Inspecting the valve(s) early, rather than after damage is seen will give you an idea of their actual internal condition and in some cases allow you to predict when they will be due for replacement parts. This will prolong their lifetime and contribute to quality methods.

Any observed brown, yellow or rusts colors inside these SS valves usually are often an indication that the valve has been used long past its recommended maintenance interval. It was overdue for inspection and repair of worn parts. When this happens, the mobile phase starts to leak past the high pressure sealing surfaces into the backside of the valve where it does not belong. *Over-pressuring a valve can also result in this type of failure too. Often a leak is observed at this point, but if small enough, may not be noticed right away. When the valve is left in this damaged condition the fluid eventually gets into the sealed bearing and pushes out the grease (resulting in a valve that no longer turns properly or seals well), contaminates the flow path and often leaves residual material on the valve surfaces (corrosion and other materials). The preventative solution is to include the valve in any/all regular inspection and preventative HPLC maintenance procedures, just like you do with the rest of the modules. As long as you follow the manufacturer's use guidelines and maintain the valve in proper condition, you are not likely to have the issue ever again." -
    Note: The quoted information above has been copied/posted by me, with permission, from an earlier related post to others provided by HPLC valve expert, Bill Letter.
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