RI effect in UV detection

[thohry]

Hi all,

I've just read of the RI effect in gradient analysis (UV detector). So could anyone explain to me about the effect.

Thanks

[tom jupille]

In a nutshell, the flow cell in a UV detector is a long, skinny cylinder (typical woule be 1 mm diameter x 10 mm long = 8 microliters). Any light that passes through this flow cell that is not perfectly orthogonal to the axis will bend as it passes through the various interfaces ()air/quartz/solvent/quartz/air). How much it bends depends on the RI of the different materials. If the RI of the cell contents changes, then the amount of bending will shift, and some light that formerly got through the cell will be blocked (or some light which was blocked will get through -- either way the amount of light that gets through will change).

The magnitude of the effect depends on the details of the optical design of the detector (how well collimated is the light beam), but can be aggravated by poor maintenance (if the flow cell is out of alignment, proportionally more light will be "off axis".