Page 125 - Applied Pharmacognosy

Types of Chemical markers

Column bleeding

• column bleeding is thermal degradation of the stationary phase
• To ensure an acceptable lifetime of the column, the column should not be

heated above certain temperature.

• The absorbent may decomposes or boil out and deposit in the detector. This

would destroy the column and the detector at the same time.

• Every column has a tag attached that states its composition and operation

temperatures.

• Despite proper care, most columns have a very limited lifetime since the

stationary phase gradually degrades upon heating