In the case of injecting a very concentrated substrate in a HPLC system, will we observe tailing or fronting?
I would say a fronting since the substrate that is not absorbed into the stationary phase will be eluted first.
What is your advice ?
If your concentrated injection overloads the column you will observe fronting. I would suggest reducing injection volume or sample concentration.
http://www.restek.com/techtips/What-Causes-Fronting-Peaks
Yes, abosolutely right as said by Serhan that column overloading causes peak fronting.
Dilute your sample.
gudluck
:)
When you mass-overload your column, peak distortion occurs when the non-linear region of the distribution isotherm is reached. This can be interpreted as fronting because the retention time at the peak maximum is shorter than a non-overloading peak. However, the shape of the peak looks like tailing.
You might also observe a flattened, spread-out top to your peak, so if you're using peak height to quantitate, be aware that it won't work well.
I agree with all of the above. A simple explanation is that when a column is overloaded, all the "active sites" on the bed are occupied so the solvent carries the "excess" compound down the column to an area of the column that has "open sites" causing fronting. I realize the explanation isn't entirely correct, but it helps people to understand what is happening and isn't too far from the truth.
Like Dr. Laura Shireman mentioned, the peak shape will be distorted. In extreme situations, more likely observed for flash chromatography than HPLC, the peak shape will often follow a gradient due to solubility in the mobile phase.
Column overload causes peak fronting while tailing is caused by active silanol groups
Active silanols do contribute to tailing. I've also seen both fronting and tailing caused by a solvent system being close to a compound's pKa.
Gaetan Glauser gave the more right answer, form my point of view. Of course it depends of the kind of isotherm the bind phenomena follows. I f it is similar to a lagnmurian one it will be that way, but the shape of the peak can be with a fronting if the isotherm is a more complex one. I advise to study
Schmidt-Traub, H. (2005). Preparative chromatography of fine chemicals and pharmaceutical agents (Weinheim ;;[Great Britain]: Wiley-VCH).
Guiochon, G. (2003). Modeling for preparative chromatography (Amsterdam ;;Boston: Academic Press).
Fronting. Tailing will happen when the analyte interacts strongly with stationary phase.
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