Open tubular capillary liquid chromatography question

[jiayi0901jia]

hello.
I have a question for this topic. Now I have different size reversed capillary column with dimensions of 15, 50, 75 um ID, ~60 cm and theoretically 1-2 nm coating on the wall. I'm trying to optimize running condition. But I keep getting tailing and broad peaks. I tried flow rate range 0.01 to 0.001 mL/min and injection volume 300, 60 nl, and smaller injection volume by using split injection using T dead connection. I'm trying toluene, naphthalene, phenol for now.
Anyone has any idea on how to optimize it?

[M Farooq]

hello.
I have a question for this topic. Now I have different size reversed capillary column with dimensions of 15, 50, 75 um ID, ~60 cm and theoretically 1-2 nm coating on the wall. I'm trying to optimize running condition. But I keep getting tailing and broad peaks. I tried flow rate range 0.01 to 0.001 mL/min and injection volume 300, 60 nl, and smaller injection volume by using split injection using T dead connection. I'm trying toluene, naphthalene, phenol for now.
Anyone has any idea on how to optimize it?

Dionex has done some excellent work on determining the cause of poor peak shapes in capillary columns. They determined that cuts on the ends of a capillary have to be perfect in a microscopic sense in order to achieve acceptable peak shapes. In order to see the extra column effects, pick one unmodified capillary of the same length and the diameter, which should have no retention of your test analyte. If that peak is broad and tailed, chances are that your extra-column effects are significant. If the peak shape is good with an unmodified capillary, test your modified capillary and see if broadening is caused by the stationary phase chemistry. Try lowering the concentration of your analytes as much as possible?

See some classical papers by J.J. Kirkland... Sampling and Extra-Column Effects in High-Performance Liquid Chromatography; Influence of Peak Skew on Plate Count Calculations J Chromatogr Sci (1977) 15 (8): 303-316

[jiayi0901jia]

Thank you so much for the reply, which is very helpful. I tried bare fused silica column without extra column between injector and column, which gives 60 nL injection volume. The blank column also has a tailing somehow. any idea on how this happened?

[M Farooq]

Thank you so much for the reply, which is very helpful. I tried bare fused silica column without extra column between injector and column, which gives 60 nL injection volume. The blank column also has a tailing somehow. any idea on how this happened?

You will always see tailing to some extent because of extra-column effects. Gaussian peaks usually exist in the textbooks. I cannot recall the author of the book chapter, it is considered a classic work in extra-column effects. Perhaps it is in Advances in Chromatography Series (70s or 80s when science was done for science's sake). He shows how different peak shapes originate outside the column.

In the meanwhile see: J Chromatogr A. 2003, 1016(2), 129-41: Extracolumn band broadening in capillary liquid chromatography.