Dear all,
I've been trying to identify an unknown impurity in my sample via LC-MS. The problem is, instead of yielding one particular mass in abundance, i have multiple mass peaks for that single unknown impurity. But when i injected the sample in a HPLC system, a single peak is detected for that impurity. How do I interpret my data? I'd like an explanation on how certain compounds could yield multiple peaks in an LC-MS analysis. How do i further confirm the molecular weight of said impurity without altering the LC method drastically?
Regards,
Theresa
A couple of things come to mind.
1. You may indeed have multiple compounds co-eluting in your HPLC method. So the peak you see in your method is not pure but rather a mixture of multiple compounds. You could check it by changing the HPLC method in multiple ways and seeing if the peak starts splitting or if another peak appears. This may however take multiple atempts and changes. Even if you do not see any change in peak numbers it is still not a guarantee that the peak is pure.
2. Your compound fragments in source. What you would see in that case is your molecular peak and its fragments. If the fragmentation is strong you may not even see the molecular peak. This can be resolved or improved with an appropriate tune method for your MS ion source. The amount of fragmentation may differ from source to source as well.
3. In addition to the molecular peak you see adducts, such as (M+Na)+, (M+K)+, (2M+H)+, (M+H+Na)2+ in positive ionization mode. These peaks can be identified with some quick math. The amount of these peaks can depend on the cleanlines of your system, the quality of the reagents used, etc. You can reduce the amount of these peaks by cleaning your system and using MS quality reagents and solvents. However, these aducts can help in identifying the mass of your compound.
some times HPLC method and column is not suitable for LCMS. i.e., Most probably the buffer agents that you are using for HPLC is not supporting LCMS analysis. So you have select buffer agents and column that are support for bothHPLC and LCMS.
- Badges
- Science topic