Gradient PQ

[stepluke]

Mark, be careful that Caffeine does not contaminate your degasser.

I recall this experiment being tried at a major HPLC manufacturer that I used to work. The result was contamination of the semi-permeable teflon tubing inside the degasser with Caffeine - which was found to be leaching out for quite some time afterward.

[Mark Tracy]

Interesting. These same degassers then should be easily contaminated by ion-pair reagents or amines that are common mobile phase additives. I do know that early degassers (HP-1050 for example) were quite susceptible to contamination, but modern designs use different polymers and are much less likely to become contaminated. I have also seen cases (again older designs) of acetone migrating across channels of a degasser.

[John]

I had the idea of running water through channel A and the running the chromophoric reagent in methanol or acetonitrile as channel B. This would be more accurately simulate a real system. But maybe the response would be non-linear since the tracer could have different chromophoric properties when dissolved in different solvent mixtures.

[DR]

The chromophore wouldn't change, but the steps would reflect the sum of that which was intended to absorb + the RI artifact inherent in the solvent switch, so I wouldn't recommend it.