cholesteryl carbonate ester : Mass spectrometry

[ta068]

I couldn't detect molecular ion peak of cholesteryl carbonate and cholesteryl ester by ESI and CI technique. Could anyone suggest me about others technique? or anyone can explain what happen when we detected molecular of carbonate/ester substances by ESI/CI technique.
Thank you for your suggestion
TA

[sassman]

Did you use positive or negative ESI? I think the carbonate might work better with negative mode. Is it ionizable? I cannot find a structure for this compound, but I'm guessing it is a weak acid. First try infusing (without LC) a 10mg/L solution of your sample into the MS and see if you get a peak that is close to the mass of your compound.