UV-absorber added to water (for gradient baselines)

[Rob Burgess]

Hi All,
I have just read something interesting from the DryLab chromatography reference guide about how to handle baseline drift. It mentions adding a UV-absorber to the water to increase its absorbance and make it equal that of the organic.

This is a new approach to me. Does anyone practice this out there? We often get problems with our gradient baselines drifting and I was wondering if this truly is a way to counteract some of these problems. There is a mention of using salts and hydrophillic compounds. Anything specific in particular?

[DR]

Anything you can do to get the RI of your A & B phases to match will minimize the gradient baseline effect.

I have never bothered with it.

[tom jupille]

Rob, the two references to the technique cited in Snyder and Kirkland's Practical HPLC Method Development book date back to 1982-83. The book states that "The matching . . . can be done conveniently by trial and error.", but then the authors are primarily theoreticians. I don't think I've ever met anyone who does this in "real life", and I can suggest two reasons:
- data systems generally handle a reasonable amount of linear drift quite gracefully
- by the time you get down to a sensitivity where the typical amount of drift is likely to be a problem, its magniture is usually far eclipsed by garbage peaks on the gradient (usually coming from CRUD in the A solvent).

As far as candidate additives go, a neutral salt like sodium nitrate would probably be a good choice for "UV absorbing and unretained". The catch is it that doesn't take much to provide the requisite few mAU.