Bile acids are made in the liver by the cytochrome P450-mediated oxidation of

cholesterol. LC-high-resolution/accurate mass MS method is used for the analysis of bile acids  such as cholic acid, chenodeoxycholic acid, taurocholic acid, deoxycholic acid, lithocholic acid and ursodeoxycholic acid) was developed and successfully validated. They are conjugated with taurine or the amino acid glycine, or with a

sulfate or a glucuronide, and are then stored in the gallbladder, which concentrates

the salts by removing the water. Bile acids serve other functions, including

eliminating cholesterol from the body, driving the flow of bile to eliminate

catabolites from the liver, emulsifying lipids and fat-soluble vitamins in the

intestine to form micelles that can be transported via the lacteal system, and aiding

in the reduction of the bacteria flora found in the small intestine and biliary tract.

Conjugated bile acids are more efficient at emulsifying fats because, at intestinal

pH, they are more ionized than unconjugated bile acids. Cholesterymaine, NSPs,12-α hydroxlyase , Taurine level, cyclodextrin, 7-α hydroxycholesterol, 3-α

hydroxysteroid dehydrogenase  level are best biomarkers.

Thank you Ravi

the MS/MS spectra of this kind of compounds are usually less structural informative. however, the CID spectra obtained under positive mode will be very informative.

attachment is the cid spectra of oleanonic acid for your reference

Thank you Dr. Xiao

Dear Mohammad

I have not tested any MS for bile acid, so I can just tell some speculations according to my experience.

To my experience, the spectrometer is a important factor. It might be difficult to find diagnostic fragment from high energy CID spectra of this kind of compounds. The high energy CID spectra of all these compounds will be observed to be similar.

In the experiment of low energy resonance CID (for example, with an ion trap), the –OH at C-3 is very liable to be cleaved under positive mode. The protonated molecular ion may be not observed under positive mode. The other two –OH are also unstable. So the extensive RDA reaction might give a common fragment or neutral loss for all bile acids (see attachment).

In addition, the signals obtain under positive mode will be much weaker than that of the negative mode, so it is not suitable for quantitative analyses.

Dr. Afzal, We are also attempting to do the same on a QTRAP3200, and are having difficulty getting several of the compounds to ionize. For instance LCA, CDCA, and UDCA. Some of them seem to be detected better in positive mode, but the intensity is so weak it may not be useful for biological samples later after establishing standards. I'm not sure if this lined up with some of the problems you were having so thought I would contribute...