Chromatography Forum

Hi all,

I need to buffer a urine sample at pH7 for a glucuronide hydrolysis step. What would you suggest in terms of buffers that would be compatible with ESI-LCMS? pKa of Formic and Acetic acid are both a bit too low. It's a dilute and shoot or straight protein precipitation method, no SPE or further sample clean-up. I've heard of bicarbonate buffers being used, would these be stable at high temperatures (50deg) in a water bath?

Thanks for your assistance!

Ammonium Formate adjusted to pH 7 with Ammonium Hydroxide.

Ammonium formate has virtually no buffering capacity at pH7. Ammonium bicarbonate may be OK but any acid in the sample will produce CO2 and reduce the buffer concentration. Actually I would not mind using a non-volatile buffer for your sample preparation: it is not as if you would use it for your mobile phases and the amount loaded on the column will be very limited. You could even divert the LC flow to the waste before your analyte elute to make sure the buffer doesn't enter the mass spec.