Chromatography Forum

Hello,

I need some suggestions regarding how to characterize unknow impurity@ m/z scan. I found an unknow impurity peak in stability sample @ Rt 9 min. I tried to run the sample with LC-DAD-Mass spec (API300), but I couldnt get the m/z scan of unknow impurity. Please let me know your suggestions.

Thanks,
Sri

As I understand it, you know there is an impurity, but can not get any MS signal for it?

There are several paths to explore:

1) if this is a degredation product, what kinds of reactions can happen to the starting material and what kinds of products can form? Oxidation? Hydrolysis (solvolysis)? Transesterification? What kinds of charges would the support? Was the ionization mode and pH selected appropriate to the type of ionization used?

2) What other method of detection might tell you somethign? Can you detect this with UV and get some idea of the nature of the chromaphore? Is the chromaphore pH or solvent sensitive?

3) Can you collect a fraction from the LC? While analytical LC is not great for prep LC purposes, if you can collect some of the material, you may have enough to try other anlaytical techniques. I like GC/MS, perhaps with derivitization. Or, perhaps the old colormetric spot tests? You are probably going to be workign under a microscope to see color in small drops.

Hi Don,

I guess it was hydrolytic degradation product, Ionization mode @ ESI negative mode, pH sensitive 8.0 so I choose ammonium carbomate buffer 10mM 65: 35 ACN. Wavelength 230nm. Problem is how to collect the fraction through analytical preparation ( we dont hav preparative LC).Please let me know ur suggestions/ideas. Main aim is to get the mass scan of the impurity.

Thanks,
Sri

For collectin the fraction, you need to be able to swith the column flow into a collection vessle at the correct time - to collect only the unknown. A three way valve, a stop-watch, and fingers to turn the valve will do it.

The reason I ask abou the degredation chemistry and sensitivity to pH etc. is to see if you can guess at the structure - and from guessing a tth structure come up with the better way to go after that specific compund, if you are able to indeed predict the correct product.