Chromatography Forum

Hello,

I'm trying to develop an LC-MS/MS method for quantitative determination of alendronate in human urine. I'm thinking of using anion-exchange SPE for sample pre-treatment and an anion-exchange analytical column. I would appreciate any suggestions concerning the mobile phase, MS conditions or the sample pre-treatment protocol for the SPE as this is the first time i use anion-exchange chromatography. I also find rather strange the fact that most methods for alendronate employ fluorimetric detectors and extensive derivatization procedures instead of tandem ms. Is it because i might not get adequate sensitivity with the specific detector?

Thans, in advance

I don't have much experience with ion exchange, so all I can say is to make sure you can use volatile buffers with your column. I will address your other question:

I also find rather strange the fact that most methods for alendronate employ fluorimetric detectors and extensive derivatization procedures instead of tandem ms. Is it because i might not get adequate sensitivity with the specific detector?

With the few extremely polar compounds I have attempted to analyze (e.g. glyphosate, streptomycin), I have found that indeed the sensitivity is not as good (using LC-ESI-MS/MS) as with less polar molecules. The explanation (or hand-waving) I have heard for this behavior, is that extremely polar molecules do not concentrate near the surface of the droplet and thus fewer of them will desorb into the gas phase. I might expect that with HILIC, this explanation would not apply, but even when using HILIC, I have seen some poor sensitivity for extremely polar molecules.