CSH and Heptafluorobutyric acid (HFBA)

Hi, 
I am running a LC-MS method to analyse a peptide in plasma (after SPE extraction). I am using as mobile phase:
0.1% HFBA in water
0.1% HFBA in ACN.
I can use a new column only for two batches (200 samples), why? Is there any problem with this mobile phase? Any particular recommendation?
Thanks a lot!
Best wishes, 
Kika