Peak shape is a complex problem which is affected by several factors, and will depend upon
the type of column, capillary or packed,
the temperature of the oven,
the chemical nature of the analyte,
and
the mechanism of separation involved, gas-liquid or gas solid.
At high concentrations close to or exceeding capacity overload an analyte can be made to 'beard' or to 'tail' using a gas liquid partition mechanism on a packed column by just changing the temperature. A lower temperature gives a bearded peak, a higher temperature gives a tailing peak.
[beard has a RT later than the center of the peak base and a tail has a RT earlier than the center of the peak base]
I still remember the technical reports of this phenomenon from Varian issued in the 1970s. I can't remember the technical guru's name but he was a reputable and noteworthy chromatographer, back in the day !
With porous gas solid mechanism packings as an overload condition is approached the limit of the support to elute an analyte causes the analyte concentration to loose symmetry as the smaller pores are full of analyte ( a maximum concentration elutes with a vertical slope and the excess amount is held up (a tailing peak) as the excess analyte waits for the 'road to clear'. There is a traffic jam so to speak.
Then there are issues of absorption which in small concentrations will delay the peak RT as the maximum concentration (the tip of the peak) is delayed in its elution. But given enough analyte to overcome the active sites the RT of the peak will come earlier but the absorbed portion of the analyte will delay its elution producing a tailing peak.
Capillary fused silica columns can also produce these effects but it is more common and more pronounced on packed columns.
I hope this is helpful.
Rodney George
consultant USA
