Preference on inlet solvent filter/frit

[Assembler]

There seems to be two general types of inlet mobile phase bottle filters:

Glass Frit:

Pros: What Agilent uses and what we currently use
Cons: More expensive (~$43)

Stainless Steel:

Pros: Less expensive (~$21?)
Cons: Never used these on our systems (Agilent 1100)--will they work?

Our lab would like to buy about 22 of these filters, and we don't know for certain which ones we should buy. Also, I haven't taken into consideration tubing sizes, so I don't know if that's a factor.
Thanks for looking.

[mbicking]

My advice would be to not use them at all! (That should generate some interesting replies!) After seeing them plug and fail many times, always with different symptoms, I have stopped using them in my lab.

If you must use them, then you must change the aqueous filter regularly - at least every two weeks. You can soak the glass filters in organic solvent, but do not sonicate them. The stainless steel filters can be cleaned in dilute nitric acid and used again. However, they have a very large holdup volume, and be very careful when you change solvents, as the volume inside the filter can contaminate the new solution.

[Assembler]

My advice would be to not use them at all! (That should generate some interesting replies!) After seeing them plug and fail many times, always with different symptoms, I have stopped using them in my lab.

Isn't it better for the filter to plug up rather than some particulate matter (e.g. salt) get into the HPLC and mess up HPLC components? I don't think we've ever had a problem with plugged up inlet mobile phase frits.

[mbicking]

If you put good quality solvents into the mobile phase bottle, then there should be nothing to get into the system. Every time you prepare a solution with a dissolved solid, you must filter the solution to remove particulates. If you use HPLC grade solvents, they are already filtered. If the bottle is clean and you keep the cap on, there isn't much chance of contamination.

The filters don't really do much after that.

[Assembler]

Every time you prepare a solution with a dissolved solid, you must filter the solution to remove particulates.

Aaaand that's why we at this cheap lab need inlet solvent filters. We don't do this step even though we should. We are too cheap to buy more filtering apparatuses.

Regardless of what our lab does, you, sir, make a good argument for not using filters. However, why then would the filter plug up? Poor filter/frit design?

[juddc]

I have to respectfully disagree with Dr. Bicking.

I've used the stainless units for years without any of the difficulty that Dr. Bicking describes. I have seen them clog upon occasion and the primary symptom of that clogging is what dkreller observed in another thread. I don't tend to sonicate them, I simply replace them every 6 months or so. Also, a rinse with neat methanol every few days on your aqueous filter / line will keep it clear of biological growth, elinimating the need for replacement every two weeks.

A question for Dr. Bicking: If there's nothing in your MP and it's sufficiently clean to run minus filter stones, then why were your filter stones clogging? Something must have gotten in there.

With that said, I don't consider the filter stones to be anything more than insurance against gross particulates getting into the system (dust, etc). They're absolutely not a substitute for filtering your mobile phase and I would never recommend tham as such. For your own sanity, filter your MP through a membrane with a pore at least 10X smaller than your column's particle size and you won't go wrong.

[mbicking]

We should clarify some things here.

My experience with the SS units is good, and I have indeed never had them plug. However, since most of what I do is method development, and I am always switching solvents around, cross-contamination becomes an issue. Switching out units is possible, but just one more thing to slow down progrees. That said, if I were going to use any filter it would be the SS ones. However, be aware that the pore size is not very small - 1 - 2 um in most cases, if not larger.

I also visit many different labs, and in general the non-regulated labs tend to forget about the filters. (I've seen some things that would make a microbiologist cry!) In those cases, they are going to have problems eventually, or continuously, depending on their practices.

Finally, the glass filters have a pore size of about 10 um. That will take care of the rocks and boulders that fall from the ceiling, and just about nothing else. They also have a lower surface area, hence less capacity, and are a perfect growth medium for bugs; seen it many times. You are better off not using anything, IMO.

But if you are always using the same solutions, then the filters would be less of a problem, but they do need to be changed at some interval. But I bet you could take them out and not notice a difference, ... unless you are the lab that is too lazy/cheap to filter the solutions. In that case, good luck.

[Assembler]

Thank you for sharing your experiences and advice, Gentlemen. I'm going to try and change the practices of this lab with respect to pre-use mobile phase filtering.

[mbicking]

If you encounter any resistance, just remember the mechanic in that old commercial, "You can pay me now, or you can pay me later!"

[HPLCCONSULT]

I have a problem with this statement: "If the bottle is clean and you keep the cap on, there isn't much chance of contamination."

In the real world the solvent bottles often have debris on the outside near the neck (you may or may not be able to see it). When you pour solvents into your mobile phase reservoirs it is always possible to introduce some particulate matter into them. Additionally, I think it is very possible that some of the high grade solvents are not filtered down to the level we would ideally like them to be. So using a solvent filter of 5 or 10 micron porosity makes sense as "first source" guard. Some pumps, such as the HP/Agilent model 1050, 1100 and 1200-series also incorporate a porous Teflon filter in the pump inlet (Prime Purge Valve) as an additional precaution and we regularily see these clogged up with all kinds of "stuff" at major Pharma client's labs. So those extra filters are doing their job too. Why run without any filters ? If you take care of them they should last for many, many years. If you do clog one (and do not want to attempt to clean it), then I am sure everyone will agree that replacing a ~ $30 part to keep a $50K instrument running should not be an issue.

It has been my personal experience that you should NOT be having issues with clogged solvent frits. If you are, then you should evaluate your solvent choices and procedures for filling the bottles. In twenty plus years of HPLC analysis I have only seen one of my own filters ever partially clog up and it was in an aqueous environment where it is more likely (my fault as the solution had started to grow things after two days).

[Bruce Hamilton]

Gosh Merlin, no blood spilt yet, boring....

Anyway my view...
Like Merlin, I change solvent compositions frequently - lots of short runs. I use the Agilent glass mobile phase inlet frits - for several reasons:-
1. They provide a good barrier when changing solvents - little chance of drops of liquid running out of the solvent line when removing or adding to solvent bottles.
2. I've stopped filtering most buffers made from HPLC ( or better ) reagents - eliminating potential contamination from the filter system.
3. They allow me to use the full contents of the solvent reservoir, as even if part of the sinter is uncovered, the capillary action will prevent air sucking.
4. Even though my reservoir bottles are sealed with only 2 small capillary ( 40mm x 0.010" ID FEP ) vent lines to ambient, visible particles can appear from several sources ( including the sinter ) over time, especially when frequently switching solvents.
5. They are very easy to clean, warm solvents, including water, are very effective for me.
6. They last decades.

The filter in the pump is post-mixing on my system, which is obviously there to catch pump debris and for the times when I inadvertently try to dissolve insoluble inorganic buffers into high acetonitrile gradients.

Yes, the sinters do mean that I have to be more rigorous in flushing lines, however they conveniently fit into 50 ml PP conical centrifuges tubes which also conveniently sit within 250ml-10L Duran bottle openings, so it's easy to flush sinters, lines, and, most importantly, autosamplers, without messing up more glassware.

I've also extensively used the SS filters ( usually 7 um pore size ), and the Upchurch all-polymer type, all without too much trauma - although I worry about the large metal sinter surface and some active mobile phases with the metal systems, and solvents on the polymeric one..

As column particle size deceases, the avoidance of particles probably becomes more of an issue, and having less exposure/transfers is going to become more important, and sinters will probably become smaller, perhaps more like inline filters.

Please keep having fun,

Bruce Hamilton

[lmh]

We've always used inlet filters, and never had a blockage, but we've had one inlet-filter related disaster (see below).

mbicking, we do indeed work in a building where rocks fall off the ceiling. Ceiling tiles are a catastrophe in a lab, particularly when they fall apart like ours do. Add to this a dusty air-con system, and a fume extraction system that sucks the entire floor's rubbish under the crack under the door, and we have a big problem. On the other hand, we filter all aqueous buffers, and prepare fresh daily (OK, OK, sometimes 2 days go by, but never more). We also have no windows, which helps to control algal growth, and keeps the down-trodden workforce appropriately gloomy.

I'd favour inlet filters, particularly in our environment. My only proviso relates to a disaster we had with a Waters Alliance module that was used for ion exchange and reverse phase, alternately. We followed Waters' advice rigorously on flushing between solvent-changes, but nevertheless had a problem with salty buffers lingering in the inlet filter, and precipitating when we moved it to pure acetonitrile. Two runs further into the sequence, the check valves were getting blocked. Our solution was to reserve two bottles exclusively for salty buffers, and two for organic solvents, but we did also toy with the idea of keeping some inlet filters exclusively for each application.

I have a soft-spot for the sintered glass filters from Agilent; when I first inherited an instrument, it had been used with the same bottled water for months, and the inlet filter was a nice green colour. The normal white background helps to make problems visible!

[HW Mueller]

There can be another problem with inlet frits. For instance, a VALCO version has a Teflon(R) housing which is connected to a 1/8" tube by pressing the tube into the teflon housing. Since this is a "last drop" device it can easily happen that this housing-tube connection is above the mobile phase level, so that it could and did draw in air. On this one, as on some others, the frit is also just pressed into the housing, probably with some spaces that allow elephants to go through. Thus I use these inlet frits only if I think I need some psychological padding.
Incidentally, dkreller just started another chain describing the classical inlet frit problem.
Imh, you got algae colonies without seeing/noticing anything in the UV detector?
Oh yes, some have mentioned another problem: carryover. We have blown out solvents, with N2, on frits of the type in the second picture above. Stop and go N2 flows show stop and go liquid foaming . . . . not that easy to get stuff out.
We put in a wire screen ahead of the injection port, this has needed cleaning just less than once a year (when pressure rises without column in line). The membrane pump used here, or especially the pressure vessels used instead of a pump, are not very sensitive to the low amounts of solids that we have apperantly encountered in our mobile phases.

[lmh]

Thanks for the tip about blowing out with nitrogen. I'll remember that one.

I haven't a clue what the algal colonies were doing to UV detection. As soon as I saw the state of the inlet filters and the bottle, I got rid of the bottle, changed the filters, flushed the system copiously, and I haven't seen so much as a single algal cell peering back at me out of a bottle since then. Algae are fine things, but they belong in the big wide world, not in my solvent bottles.

[Chris0000]

Not to forget:

The biggest advantage of the Filter:
The tip of the inlet-line will stay at the ground of the bottle