refractive index detection

[olivia]

Is it correct that refractive index detectors should not be operated in gradient mode
Thanks Liv

[juddc]

Yes, that is correct. Also, you must pre-mix mobile phases. No gradient proportioning valves, even for isocratic mobile phases.

Other hints: Allow your MP run through your column to waste for at least an hour, or a few hours if using large GFC/GPC columns at your anticipated flow rate, then recirculate your MP. It will save MP and equilibrate the detector faster. Insulate the line from the column to the RI and if possible use a PEEK nut on the input to your RI. Also, keep the temperatures of your column and your cell close to one another if possible and don't run the columns cooler than the flow cell under any circumstances.

Best of luck!

[tom jupille]

juddc's suggestions were all good ones.

I'll give the smart-alec answer and say that the question is not whether RI should be used with a gradient but whether RI can be used with a gradient (the answer is "no"). The change in RI that results from changing the mobile phase composition by several percent is huge compared to the change caused by a few micrograms of analyte.