narrow-bore chromatography peak broadening

[k.vd.wetering@nki.nl]

Hi,

I am currently trying to miniaturize an excisting LC/MS method. I previously used a column with an ID of 2 mm, but am now changing to a column with an ID of 1mm. I do however get serious peak broadening on the 1mm column. Peaks are up to twice as broad as on the 2 mm ID column. Both columns are Luna C18(2), 150 mm in length and have a particle size of 3 µ.
Things that I have tried to solve this problem include:
reduce the post column volume by 75%
remove the guard column
reduce the amount injected with 75%

Unfortunately, this all did not help in reducing the peak broadening.
It might be important to add that I am running a gradient, so I expect that pre column dead volume is less imprtant (although I expect this also to be relatively small).

Any suggestions are well appreciated.

best,
Koen

[Uwe Neue]

You can test your system for suitability in pretty much the same way as one can test a UV-based system: remove the column, inject a standard, and measure the peak width. If the peak width approaches what you are getting with the column, you have a problem.

This experiment does not tell you where the problem is. Considering your description, it could very well be the tubing of the MS before the evaporation step.

[Hfranz]

You might consider the following:
What is the ID of the tubing?
Do you have potential gaps such as a connecting union?
Have you used the correct ferrules to establish the connection?
Are you sure you have connected the tubing(s) with zero void volume?
I can recommend using new Viper connections. Connections with these are dead volume free by design. More: http://www.dionex.com/en-us/Dionex_HPLC ... 70654.html