I've some problem with pumping pure acetonitrile with my pump (Hitachi-LaChrom).
I have not seen this problem on other pumps (HP1050/1090, Waters).

I have changed the control valves - no results.

Has anybody some idea what is going on there ?

Thanks.

Do you see the same problem with other solvents? Or see the same problem with more viscous solvents (i.e. IPA)? Is the problem high pressure and the pump shuts off? I've seen this problem and have changed both inlet and in-line filters, but not sure if your problem is that simple.

We have 3 Hitachi Systems - no problems with 100% acetonitrile. What is the problem you're referring to ?

My problem is that the HPLC starts work as usual with normal pressure, but after a few minutes pressure falls down to zero and ACN does not pass through the column.
There is not problem with high pressure. No problems with other solvents. If added 5% water to ACN - the problem disappears (isocratic pumping).
Do you have any idea about it?
Thanks.

It sounds to me as though you might have a leak - check all possible sites for leaks. I would also check the valve system. Is ACN solvent B ? perhaps you could put the A, C or D tube in there and retest. Also, if you disconnect the line from the pump to the injector and check to see if the solvent flow is constant (use a 10mL measuring cylinder and time it over 2-5 mins) with 100% ACN.

Like I said, we run systems with 100% ACN, 24/7 and dont see any problems.

Let me know the results. Hope this helps.

I've tried all Mike's suggestions :
- I tried to pump pure ACN through four channels (25% each) - no problems with pressure.
- No leaks detected in the system.
- I tried to pump ACN through A,B,C and D (100% each time) - also no problems!!!
- I checked the flow with 100% ACN - it is constant at every channel.
Now I think the problem was an air bubble that did not retain.
So, now the problem is solved...

Thank you very much.

Boris, Teva-Abic Veterinary Division.

If there was a problem with a bubble, I would recomend to take a preventing steps by degassing mobile pahse daily or installing an online mebrane degasser, to avoid the problrm from reoccuring.

And sometimes you can wash sink filters in sonicator.

As I started to use L-7100 Merck Hitachi pump several years ago, an serviceman pointed me, that all channels should be filled by solvent, even if I use only one channel. I use this pump mainly to GPC (one channel)and sometime i see air in coming to pump plastic tubes of non used channels. I observed sometimes unstable retention times too and there was helpfull flushing by 25% at 5ml/min several minutes all channels.
It looks Boris, that you solved problem in similiar vay, by fully filling tubes of non used channels. Maybe it is good idea to do such preventive procedure for this pump periodicaly?

Actually the observation by Jan is correct. All of the lines from the L-7100 proportioning valve connect into a small circular manifold attached to the suction valve (inlet check valve). It is good practice to have all of the lines in use, or alternately, remove the line not in use and replace it with a blocking screw. This works very well and saves the inconvenience of having solvent in all lines.