Chromatography Forum

How much band broadening is contributed to the tubing between the outlet of the column and the detector. Is this the most common area for extra-column peak broadening?

Band broadening can actually happen within a column as a function of excessive tortuosity within the particles. One way to minimize this is to switch from a fully porous particle to either a monolithic stationary phase or to a core-shell stationary phase. Column diameter and particle diameter also play a role in determining the tortuosity portion of the equation.

Extracolumn effects are the (mostly) post-column opportunities for analyte diffusion in the mobile phase stream. Any variation in tubing diameter, bends that are too sharp and (especially) any junction where the tubing is not pressed fully into the fitting before tightening will cause the majority of extracolumn effects that result in band (peak) broadening. A short run of appropriately sized tubing with a minimum of sharp bends in it is ideal for use between column and detector.

thanks for the reply. is <0.007-in i.d tubing the norm for these connections?

yep or 0.010". I would suggest that unless you have very sharp peaks, you won't see much band broadening after the column as the volume of tubing is low so transit time is very short compared to typical peak widths. Maybe check the connections are good (no dead volume points) but band broadening mostly comes from problems upstream (mixing etc.) or in the column.

why do you think you are having a problem due to extra column volume effects?
which type of instrument are you using?
what is the column type?
what is the particle size, the column dimensions?

in a standard system with columns of down as 3mm ID these effects almost do not show.

The smaller the ID of the tubing, and the shorter you keep it , helps. Also be very careful when " swaging" screws and ferrules from and to the column. You do not need to add dead volume to the system.