Dwell volume with MS detector?

[sjmarin]

This might be a dumb question , but all the methods I know for measuring dwell volume involve a UV detector, running a gradient from 0-100% A to B with B having some UV active component like acetone. I have a mass spec. How can I measure dwell volume with a mass spec?

[tom jupille]

The easiest thing would be to borrow a UV detector for the morning and use that (all the dwell volume is pre-detector anyway).

If you really want to use the MS, you can adapt the UV procedure. Find a compound that that you can detect nicely and for which you have a broad linear range.

In your A reservoir, put a solution of that compound at a low level (just above the LLOQ). In the B reservoir put a solution of the same compound at a higher level (near the upper end of your linear range). Run a gradient from 0 - 100%B and monitor the signal. The computation is identical to that for the UV detector.