which or where would be the first filter after solvents?

[coquim]

I´m looking and cleaning some filters and check valves and could see that there is no filter before the primary inlet check valve. The filter suction in the bottle is actually the first one, but after these the solvents pass trough the solenoid valve and reach the primary inlet check valve, only passing trough the suction filter in the bottle ( someone know the efficiency of these filters?????)
So, i think there must be some filter before the solenoid valve or before the check valves.
I really wanna know what you think about...

Best regards!

[tom jupille]

The standard is just what you describe: a "sinker frit" filter on the end of the inlet line in the solvent reservoir. The porosity is usually something like 5 or 10 micron. These are not a substitute for using filtered mobile phase, but are a last line of defense against particulate contamination.

My 0.063 pesos' worth is that adding additional (or finer) filters is not generally a good idea because they add flow resistance (especially once they start to clog) and can cause more cavitation/loss of prime problems than they cure.

[Dan]

Tom,

Things that you said in your post reminded me that people (myself included) often take those sinker frits in the solvent resevoir for granted, forgetting that they are even there.

The sinker frits can become clogged or contaminated. This is especially true when using ion pair reagents in the moble phase (the longer the alkyl chain, the more prone to contamination of the frit). The frits need to cleaned or replaced periodically.

It may seem obvious, but my experience has been that those frits are often overlooked.

Thanks for the reminder.

Been there, done that!
Regards,
Dan

[HW Mueller]

One can be in for some bad surprises if one ignores these "sinker frits". For example, some "last drop" varieties have been drawing in air when parts of them emerged above the mobile phase level.

[coquim]

Thanks for your answer guys! i appreciate!

i´ve never thought before about dead volume and the increase pressure if i add a filter on the line, but its sound very logic...
so the recipe is: to filter and sonicate solvents everyday before using (i wash sinker filters once a week at least, and clean solvents reservoir at the time i must add more solvent, in case of water i clean it everyday because i know water can produce "microfilm", and also know MeCN produce a kind of sticky substance in 4 or more days, isn´t it?

bye and thanks again!

[HW Mueller]

We discussed this many times: Really pure water does not support life, so unless you contaminate it (dust, some other carbon containing materials) it does not form microbe films, etc. I have stored water for about a year in tightly closed bottles at about 4°C without any UV deterioration.
I can´t think of any reactions taking place with ACN under most HPLC conditions. Also, I have stored unopened high grade ACN bottles for years at ~4° without noticeable change.

[Bruce Hamilton]

I suspect the sticking effect of pure acetonitrile on some pump check valves ( eg ruby/sapphire ) may have been what he was alluding to, rather than degradation of the solvent.

My comment would be that, if you are suitably filtering the solvents, or using HPLC grades without filtering ( as appears more common these days for many solvents and volatile buffers ), there should be no need for cleaning of the sinker filters any more frequently than about once every 2 - 3 months.

If you have to clean the mobile phase filters more frequently than that, you should review your mobile phase preparation, as you are likely to have downstream problems in your HPLC as well at some stage. Even time you clean filters, there is the opportunity for different muck to contaminate the filters.

I would suggest that filters be cleaned ( backflush with warm solvents, with ultrasonication - if permitted by the manufacturer, as some glass sinters may start to disintergrate, creating a more serious, less obvious, problem ) with both warm water and solvent, even if only usually exposed to one of them, using misible transition solvents, if required.

The easiest test is to remove the filter from the line and liquid, and let gravity drain it. Compare the time to that of a new filter with the same solvent, usually a few tens of seconds for water, and a few seconds for acetonitrile and methanol.

Please keep having fun,

Bruce Hamilton