two compounds w/ same Rt..and optimization general advice?

[PeterPopoff]

Hello I was looking for advice on how to deal with this problem.


First I would like to describe WHY I think i'm having these problems and ask for general advice on how to gain the skills I need to not have these problems anymore...because thats part of why I think I don't know what to do. I'm a synthetic chemist by training, and lcms was previously just used to analyze reactions or product mixtures without caring about the QUALITY of the data. But now I am doing quant. work and it does matter very much If I am getting the best peakshape possible. knowing how to troubleshoot to get this quality data is my problem, so any resources you could suggest for gaining these skills is helpful.

I have oxymorphone and noroxycodone (and their deuterated counterparts) that elute at almost the same time. The peaks are not fully resolved and have some overlap.

Anyhow, the chromatography can't really be changed much because there are a million other compounds in this method and changing the chrom might throw alot of other stuff off and cause many problems at this point.

The problem in data analysis: The peaks are not being identified properly by the software. IE its not choosing what the peak for the correct compound and not integrating each peak seperatley as if it was a totally isolated peak on a chromatogram (like It would if I had nothing near it). I also had use specific product ions for each one, since if you choose to use other product ions for these compounds they will be very similar masses you are looking for. Should I try adding more product ions to the compounds to be used in their identification? Because as of right now...its identifying "both of them" as one compound for one of them....while for the other one it seems to identify just the one relevant peak.

I am using a shimadzu lcms with labsolutions software.

Can anyone provide recs on how to go about solving this problem so I can get on to the quantitation aspect?



also another question.

I have another drug in this method that I have tried optimizing and just cannot get good peak resolution. what do you suggest I do to fix this without changing the chromatography? This compound ionizes well and is very similar to other compounds that are working well. But when the method is run with LC and the whole 9 yards peak is too broad.


thanks

[Don_Hilton]

When you want to change the resolution or the peak width - you are looking to change the chromatography. Yes, when you change the chromatography, things move around - but sometimes you can move them all in directions that are to your advantage.

You might add a description of your system and pictures of your chromatograpy. It is possible that you are doing something with injection or the plumbing of your system that would make peaks broaden. So, column, flow, volumes, gradients, injection volume, solvents, and all that stuff might lead someone to point out a condition that is well away from optimal.

[PeterPopoff]

When I say break peaks, I don't mean that the peaks are dragging out. I mean that the shape is just not as neat as the others. Other compounds that looked like this were fixed simply by just optimizing the Q1 CE and Q3 energies...changing the peak from a disfigured or wide shape to a thin singlet peak. But I have ones where this doesn't seem to be working.


And as far as the two that are on top of eachother, the peak shape is fine, its just that they over lap a lot. There are other peaks within the method that are NOT fully resolved, but they identify and integrate seperately and just find (I assume this is on account of their different product ions used to identify them)