We use buffer for routine analysis. We do not have block purge frit (LC 1100 quarternary pump) problem whenwe are using TFA, TEA or ammonium acetate buffers (concentration up to 10 mM at 1 ml/min flow rate). However, we have problem with block purge frit (need to replace nearly every week!!) when we used 62:38 1mM Na2HPO4: CH3CN with pH 5.5 as their mobile phase. at 1 ml/min flow rate (without any gradient). We flush the LC system using 90:10 H2O:MeOH for 60 mi, followed by 50:50 H2O:MeOH for 60 min and followed by 100% MeOH for 30 min and stored the system in 100% MeOH. We will never stop the LC system stagnant with buffer solutions in the LC system. All solvents filtered with 0.45 um filter prior used. We use fresh buffers solutions every day.
For your info, the quaternary pump LC1100 do not have seal wash option. However, the buffer concentration use is very low, which is 1 mM.

Do you have any experience/suggestions which will help us to overcome this problem? Has anyone face similar problem with Agilent LC1100 Quad pump before, especially the phosphate buffer???

You may already do this (couldn't tell for sure by your post), but make the buffer mixture first, THEN FILTER.

I hope you realize that you are getting no buffering whatsoever using the "buffer" you describe.

Hi All,

I have used Shimadzu and Waters LC before, even with 20 mM phosphate buffer. Never have frit getting block!!. If there is problem with our buffer preparation, it will also happen in other LC brand!!!. That is why we would like to ask anyone facing this problem before???

You're likely getting polyphosphate formation catalyzed by acetonitrile. Can you switch to an acetate buffer or use less acetonitrile? While this problem normally occurs with much higher concentrations of phosphate (~20 mM, and quite pH dependent), this may be your problem. See http://www.chromatography.co.uk/TECHNIQS/hplc/valves.htm

You can work with much higher concentrations of phosphate in your mobile phase. I do not think that the problem is the buffer.

Checked the above net address, does anybody know what polyphosphate-like is??
I tend to agree with the last anon. There has been a bottle on my shelf for several years without a spec of precipitation, the label says:
60%buffer(phosphate, 25mM, pH 2.8) + 40%CH3CN.

Hi Mueller,

Are you using LC1100 Agilent pump?? We suspected that the PTFE purge frit is too eficient to trapped the impurities.Unfortunately, it become a problem instead. For your info, the clogged purge frit looks new but it created high pressure (over limit pressure) and we can only overcome by changing the frit. It sounds strange to me too, but it really happen!!

What are you filtering and what is the filter made out of? Many people mistakenly filter ACN or MeOH. In addition, they may also filter the prepared mobile phase that as the organic in it. There is no need to filter mobile phase with the organic added since the organic is filtered by the manufacturer.

Why is this important?

The filter can dissolve in ACN or MeOH. An example is cellulose acetate. I knew of a large testing lab that was plugging column after column. The reason: the cellulose acetate filter was dissolving in the mobile phase that they were filtering and plugged the column within 24 hr.

Filter the salt containing aqueous portion only. Change to an acetate buffer at 5 - 10 mM. Do not filter the organic or the mobile phase after addition of organic. That may be plugging things up.

There is no need to flush the system with MeOH. That's a waste of solvent. If you feel the urgent need to store your system, simply change the aqueous portion of your current mobile phase to 100% water instead of buffer.

My personal opinion is that you do not need to worry so much about short storage periods in buffer. Today's LC systems can handle this. Just my $0.02.

Steven:
We use membrane pumps or gas pressure vessels, no piston pumps in the lab. Thus, there are only plugging problems due to frits, no pump problems due to precipitates etc. One can usually see clogging of frits only if the culprit is colored, but discolored frits need not necessarily plug.

dm:
If one uses cellulose acetate filters one deserves trouble, how about regenerated cellulose, never had problems with those. These are especially made for HPLC mobile phases, the manufacturers tell one what is compatible.
On flushing with MeOH: We have samples where flushing is needed after each injection, so.....it all depends. But, column handling has been discussed extensively before.

Dr. Mueller:
Cellulose acetate is probably the most popular filter material on the market. Most people simply reach into a drawer in the lab, grab the first filter that fits the manifold that they use and filter their liquid. A good material to use is polypropylene. Another good material is Teflon, although this must be wetted prior to using.

Regarding flushing the system, I have never heard of an entire HPLC system needing to be completely flushed with methanol after every injection. That's madness. Autosamplers do have wash solutions and when manually injecting samples it is, of course, a great idea to flush the syringe and injector valve (in the inject position, of course) with MeOH. I disagree with flushing an entire system free of salts if it is only going to be unused for a few hours or overnight. I can tell you for sure that when these products are being developed at the HPLC manufacturer they are not being so rigorously flushed every day. In these places they are used every day, night and weekend without troubles.

It is a good practice but I think that sometimes it causes more problems than it avoids.

The thinking was going more to washing the column with MeOH, now MeOH certainly would not be the choice to get rid of buffer remains. Also, plugging can be due to other things than buffer precipitation.
Example from a project we are working on presently: In the clean-up of the synthesis products of C-14 nonylphenol, one injection causes a considerable increase in back pressure, as well as radioactivity built-up on the column and scintillation detector. If one doesn´t want to collect a "mess" at the second injection one has to wash the column and detector with MeOH, the detector with acid in addition. Nothing mad about this, just an absolute neccessity dictated by the problem at hand.

Sounds like a difficult project. Hopefully you are using a column that is large enough such that you can perform less injections.

I agree, plugging can occur for many reasons. Most were explained quite well at the beginning of this thread. I was offering a less likely, difficult-to-diagnose possibility.