Chromatography Forum

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

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.

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