Buffer problem at low UV

[project44]

Hi,
i want to use a buffer at pH range 3.5-4.5 but i don't want to absorb at 205nm! Unfortunately one of the compounds of interest absorbs at 205nm. I can't use formic or acetate buffers,so i would be grateful for any suggestion

[ebasarah]

same problem here....most good buffers such as phosphate, acetate, formate absorb more than 205 nm therefore the peak of interest will be greatly reduced.
try R.I detector instead...

[HW Mueller]

The signal to noise ratio will probably be reduced, not the signal if one is in a linear absorbtion situation, and if the mobile phase does not black out the light beam. Acetonitrile/phosphate may not be that bad, depending on the absorptivity of the analyte.

[tom jupille]

The catch to phosphate is that 3.5 - 4.5 is outside the buffer range.

Actually, you might try formate at a low concentration (maybe 5 - 10 mM). Because you would be close to the buffer pKa, you should (hopefully!) get reasonable pH control even with the low concentration, and your background absorbance might be low enough to live with. As Hans indicated, the problem is not going to be attenuation of your peak, but rather elevation of your baseline, with accompanying noise and limitation of the linear range.