lc-ms peak

[jiang295]

why peak in ms spectrum always fatter than those in uv spectrum. and peak in ms also has very long tail compared to uv.
flow path to uv and mass spect are very similar.

[kerri]

Well, that assumption would depend on the analyte and the MS instrument conditions. If you are talking about your own method, it is possible that the mass spec is just simply more sensitive than the UV and that's why the analyte tailing becomes apparent.

[H.Thomas]

Try cleaning your source - that often helps...

[sassman]

Assuming that you are using the same mobile phase, column, flow rate, etc. My guess would be that perhaps your source is not being flushed out quickly enough by the exhaust pump? What instrument and source type are you using?

[lmh]

if you are splitting the flow between the two detectors, check that the split is giving a sensible flow in both directions. Check also that you have no dead volumes in the MS side of the split.

[jiang295]

that is quite possible.
I am using waters ZQ, source is Z-spray.
exhaust pump is Edwards 30.

Assuming that you are using the same mobile phase, column, flow rate, etc. My guess would be that perhaps your source is not being flushed out quickly enough by the exhaust pump? What instrument and source type are you using?

[Uwe Neue]

Check the connection tubing between the UV and the MS. If the tubing has the diameter of a pipeline and its length is from Alaska to Texas, the peaks will become a bit wider and have tailing.

We try to set up our systems with minimal length of tubing between the UV and the MS. Also, the volume of the UV cell itself can be a factor.

[jiang295]

i checked them parallel rather than in series.

Check the connection tubing between the UV and the MS. If the tubing has the diameter of a pipeline and its length is from Alaska to Texas, the peaks will become a bit wider and have tailing.

We try to set up our systems with minimal length of tubing between the UV and the MS. Also, the volume of the UV cell itself can be a factor.

[Uwe Neue]

Then the combination of the connection tubing to the MS together with the split ratio might be the culprit. Shorter and smaller i.d. tubing to the MS might be useful.

[jiang295]

so you do not think that would be the problem of mass spect

Then the combination of the connection tubing to the MS together with the split ratio might be the culprit. Shorter and smaller i.d. tubing to the MS might be useful.

[Uwe Neue]

Most things that I can think of that would make wide peaks in the MS while the UV peaks are narrow do not create tailing. Since you say that the MS peak is not only wider but also more tailing, I am inclined to think that it is bandspreading in the tubing.

[jiang295]

could band broadening in the tubing cause tailing,
I heard that only excessive sample volume cause tailing.

Most things that I can think of that would make wide peaks in the MS while the UV peaks are narrow do not create tailing. Since you say that the MS peak is not only wider but also more tailing, I am inclined to think that it is bandspreading in the tubing.

[Uwe Neue]

You can try this all out by yourself, and confirm or dismiss my proposition that the tubing is the possible source of the problem. Disconnect the column and inject the same sample under the same mobile phase conditions and flow rate with the same setup, just without the column.

[lmh]

Uwe is quite possibly right, and it makes sense to have a quick look at his suggestions. Like I said (ages ago up there) check the split ratio. If you aren't using a purpose-built splitter but are just using a T-piece, it's quite possible nearly all your flow is going through the UV side of things, in which case even a small dead volume (e.g. wider-than-ideal tubing, or one poor fitting) can lead to significant changes in peak shape. In my very limited experience, dead volumes can lead to tailing as it sometimes takes longer to wash stuff out of an unwanted "appendix" than to get the first whoosh of material through.

[jiang295]

I think Uwe Neue is right. tubing might be culprit behide this.
however, you differ uwe neue in that you think it is dead volume rather than tubing itself cause tailing.
thanks for your guys help.

You can try this all out by yourself, and confirm or dismiss my proposition that the tubing is the possible source of the problem. Disconnect the column and inject the same sample under the same mobile phase conditions and flow rate with the same setup, just without the column.