Chromatography Forum

It was discussed in another thread some time ago about the use of a precolumn before the injector to clean up the baseline in gradients (due to accumulation of hydrophobic impurities on the column head during equilibration).

I would like to try this, however I realise that I need to connect the precolumn only on channel A (weak mobile phase). If I connect it just before the injector - the impurities will elute from the precolumn during the gradient anyhow.

I am using an Agilent 1100 with binary high pressure pump, and I am not sure of exactly where to install it. Another option is maybe to use a very high adsorbing material before the injector - such as Hypercarb? Any opinions on this matter?

thanks!

It seems to be much simpler to clean up the solvents before pumping them (if you can´t obtain clean solvents).

Hi, Mattias

The best spot would be just before the mixing tee, but I'm not sure how accessible that is in the 1100.

Hans is right, of course. The best "cure" is prevention.

You could place the precolumn just about anywhere, but before the degasser might be the easiest. However, there may be some backpressure (i.e., flow resistance) from the pre-column, and this could affect how your solvent mixing works, especially if you have a quat pump.

Another way to purify the water is to pass it through a large membrane disk (e.g., C18 Empore Disks from 3M). You can buy them in a size that would fit a mobile phase filtration system. They are designed to extract of flow rates near 200 mL/min, and this would get you a quick removal of hydrophobic impurities.

Thanks for your comments! This application would be run in a different part of the world - and I am not so sure that I can do such much about the water quality.

Filtration of the water through discs could work fine - but my experience with mobile phase filtrations is that you add more junk than you remove.

I do not know how fancy you want to be, but you can build an auto-regenerative system by using additional switching valves, small C18 columns or pre-columns before the injector and maybe an additional pump. But I guess if in that "part of the world" they can not use HPLC grade water, probably they won't be able to invest into a system I described above.

Another solution would be to use the HPLC system itself and a C18 column to clean their mobile phase A (if you think that filtrations by using disks will add more impurities).

Finally, the use of Hypercarb will not provide any benefit over conventional C18 columns for this job...

One is inclined to wonder why discs should be any more susceptible than columns regarding introduction of dirt.
Also, I never even considered using a cleaning column in-line, because I didn´t want to bother with monitoring breakthrough.

I think the concern about disks is more enviornmental. Many labs may have a generally poor air quality (by HPLC solvent grade standards), and the process of using large size glassware, filtering, and transferring may indeed introduce some new problems.

I would like to believe that it would be better to do it, rather than not, but I can understand why some labs are reluctant.