regarding derivitisation with TFA

[rrm1987]

mycophenolic acid response is low.So i analyzed with help of TFA(0.1%).But i could nt see any increase in the responses.Can any one suggest me what could be the reason? and when and where to use TFA?
conditions:
C18.5micron;
mp:ACN/0.1%TFA=60:40;
UV-254nm detection.

[mbreslav]

What is your detection mode? Acids are analyzed using negative ESI. In this case TFA is your enemy.

[James_Ball]

Did you notice a higher baseline when first adding the TFA?

We were doing analysis for Saccharin and to increase the retention time we added TFA but lost a little sensitivity because of a higher background absorbance on the UV.

[lmh]

With UV detection you have to keep two separate effects in mind:
(1) You can add TFA to improve your chromatography. You need the peak to separate from other things, and the degree of separation will depend on additives like TFA. TFA will also probably give narrower peaks, which will therefore also be taller, which improves their signal:noise ratio and improves detection, but the total peak area won't necessarily change.
(2) If you work on compounds that act like pH indicators, you need a pH at which your analyte absorbs, and if it changes its wavelength maximum with pH, you have to choose the right wavelength for the associated/disassociated state that it's in.