Chromatography Forum

Hey,

I am relatively new to LC-MS. I am working on an assay for paclitaxel using a Shimadzu QP8000. I have been using the APCI probe for analyses so far but I'm only getting a very weak response for the drug itself (there is a huge peak which I assume to be excipient related as I'm using a medical preparation atm). I have tried using 50:50 ACN and h20 with 0.1% formic acid, the same with 0.1% acetic acid, ammonium sulphate buffer (pH 5) with MeOH and ACN (50:10:40) and it remains weak.

Does anyone have any suggestions how I can increase ionisation for this molecule? Would a gradient elution help?

Cheers,

Merrin

Ammonium sulphate is not volatile and not appropriate to use with your LC-MS. Are the "excipient" and pclitaxel separated under the 50:50 H2O:ACN 0.1% formic acid? If not you probably have ion suppression problems. I would also clean the source as it might now be contaminated with salts which could limit your sensitivity...

Sorry I meant ammonium acetate.

Yes the peaks are separated. That's not a problem at all.

Thanks.

What is your LOQ?

I would suggest ESI over APCI, gradient elution using standard 0.1% formic acid in water / 0.1% formic acid in acetonitrile (or methanol).

Paclitaxel should be pretty easy to ionize and quantitate.