Because glycerol which is known commercially as glycerin is polar and interacts with column thus causing tailing.

Do an internet search of HPLC methods for Glycerol (HILIC probably).  But you will have to use a 'refractive index detector (RID)' for high % concentrations or isocratic methods.  Alternatively you will have to use an 'ELSD or evaporative light scattering detector' for low ppb concentrations or gradient methods.  Pure glycerol does not have a 'very good' UV spectrum.

We need more information to answer your question. What are your analytes? Without knowing what you're looking for we really can't help you.

Have you seen Resteks GC literature? A method outline is here:-

http://www.restek.com/Technical-Resources/Technical-Library/Foods-Flavors-Fragrances/fff_FFAN2127-UNV

thanks all  for your information