Hi everyone,

I'm working with five anlaytes of bile acids in LC/MS
cholic acid - 408.57 g/mol,
lithocholic acid 376.57 g/mol,
Deoxycholic acid 392.26 g/mol,
hyodeoxycholic acid - 392.26 g/mol and
Chenodeoxycholic acid - 392.26 g/mol

I tried looking at the fragments by direct infusion with 5 ppm conc. I didnt see any fragments that are consistent everytime. Even the articles that I have surfed didnt give much details about the fragments. Im wondering is there any way to get the fragments by APCI-MS. I got [M-H]- for all acids and other than that I didnt get any other fragments.

Now, I have moved forward to separate these bile acids and I have got another problem that deoxycholic acid and chenodeoxycholic acid are not separating because of the same transition. Im using 0.2 mM ammonium acetate in water and 80:20 of acetonitrile and methanol. Could you please anyone help regarding the APCI-MS fragments of bile acids and the separation of these mentioned acids.

I'm using Zorbax Eclipse XDB-C8 column, Does the flow rate or pressure will affect the retention time? Because everytime my pressure is fluctuating (+ _ 300).

Thank you very much in advance,
Sree