Using mixtures of solvents as a mobile phase

[Tequila]

Dear members of this forum,

I work with a HP 1100 and I used the multichanel solvents as a great way to work. Tha problem is the low solubility of phosphate in acetonitrile and in methyl alcohol. I woluld like until what concentration of phosphate in buffer is possible to work without precipitation.
Thanks in advance for your help,

Diego Delmonte

[DR]

I would guess that ~50mM PO4 would be soluble in 90-95% ACN. Go ahead and add that bit of water to get the PO4 in. Straight ACN causes pumping problems in many systems, so there's another reason (besides solubility of PO4) to have a little water in your B phase anyway.

[HW Mueller]

Also, it is fairly easy to check into precipitation by careful mixing of solutions in a test tube. Described before.

[Consumer Products Guy]

Tequila - like HW mentioned, always test a buffer mixture in advance for precipitation, and of course remember to filter. What's the story on pumping pure ACN? I've been doing that for 25 years on HP 1050 and 1100 quat pumps and haven't had any issues.

[Cliff Mitchell]

Peter Carr and Adam Schellinger recently published a paper on this subject in LCGC.

http://www.lcgcmag.com/lcgc/article/art ... p?id=97119

The paper should be available to all regardless of subscription status.

Cliff Mitchell

[HW Mueller]

Why don´t manufacturers change to membrane pumps?? Most of the problems with pumps, discussed recently, will be gone.
(Of course there will be new problems, some people will pump goo into their columns).

[tom jupille]

HW, why would you expect fewer problems with membrane pumps?

[HW Mueller]

There are no piston seals, and therefore no associated problems. You also have valves, in my case, with a cheap rugged industrial pump these have never caused any problems. They pump anything that flows with those things. The stainless steel membrane can crack if you pump air. Then you have a mess, but since the oil pump which moves the membrane goes back and forth only the oil stays pretty much in the pump. It has not happened in years, no maintenance other than adding oil in years. I am using a flow regulator to regulate/monitor flow. This device could stand some improvement. If I understand this correctly, then the membrane pumps offered by Agilent are regulating pumps, wonder how the valves behave....

[tom jupille]

Okay, but I'm sort of a "Darwinian" where instrumentation is concerned. When a technology that was formerly available drops from sight, I take that as evidence that the surviving technologies were (on the whole) better. The two membrane-pump systems that I remember were the old Micromeritics system (arguably killed by underfunding and/or poor marketing) and the HP 1090. The latter was certainly in production for a long time, and was a well-regarded instrument.

I'll agree with your point about seals, but I would guess that the catastrophic consequences of membrane failure were more of an issue than occasional seal changes. As far as I know, no one else has commercialized a membrane pump for HPLC.

[DR]

...What's the story on pumping pure ACN? I've been doing that for 25 years on HP 1050 and 1100 quat pumps and haven't had any issues.

Count yourself as lucky. Some pumps that use a ruby ball/sapphire seat check valve system have problems pumping straight ACN as the balls eventually tend to 'float' and not seal consistently, wreaking havoc on flow consistency. Generally, a switch to a ceramic ball & seat will cure this problem.

[HW Mueller]

Last time someone mentioned an Agilent membrane pump, here, I checked their site and found what seems to be a membrane pump, still marketed:
DR5 Solvent Delivery System (High Pressure Pump). What is it, it´s not completely clear to me.