Since the retention of ionizable compounds is very sensitive to the mobile phase pH, it is necessary to control the pH of the mobile phase by the addition of a buffer. A buffer maintains the pH when a small amount of acid or base is added.

Have a look to the following homepage: http://www.hplc.eu/Downloads/ACE_Guide_BufferSelection.pdf

Regards

Formic acid is a better ion-pairing agent than TFA, if you are using MS in line with HPLC. 0.1 % TFA works great for HPLC elutions. best wishes.

Hi Zahia,

most stationary HPLC phases based on silica particles are much more stable during longer time periods when the mobile phase is slightly acidic. As Biswapriya described , 0.1 % TFA is best for HPLC only - if you want to do ESI, you need to add formic acid to get a sufficient amount of ions to the detector.

I attached a link where they describe the function of TFA in HPLC analysis.

http://www.piercenet.com/product/trifluoroacetic-acid-tfa

Thank you very much Jaques, Biswapriya and Marcus for the answers

Hi Zahia,

by accident I found a nice link, which is even better then the one I send you 2 days ago. btw: You can always uprate our contributions if you like them ;-)

http://www.sepscience.com/Techniques/LC/Articles/274-/HPLC-Solutions-64-Why-Acid

Thank you Marcus

Best regards

Zahia

I don't known how good is the modern LC column stationary phase end capping of the silca silanol group. Normal pka of the silanol is around 4, pH below 4 will prevent the hydroxy group from extesive ionization. Polar ion groups in hydrophobic C8,C18 column is not desired.