What are the reasons for rt variation
The time taken for a particular compound to travel through the column to the detector is known as its “Retention time”. This time is measured from the time at which the sample is injected to the point at which the display shows a maximum peak height for that compound.
Different compounds have different retention times. For a particular compound, the retention time will vary depending on:
- the pressure used (because that affects the flow rate of the solvent)
- the nature of the stationary phase (not only what material it is made of, but also particle size)
- the exact composition of the solvent
- the temperature of the column
The retention time depends on many factors: analysis conditions, type of column, column dimension, degradation of column, existence of active points such as contamination.
It means that Analytical experimental conditions have to be carefully controlled, if you are using retention times as a way of identifying compounds.
Does Rt vary between runs or within one run?
RT may vary between runs. Chances of varying RT within run are less. The obvious / probable reasons of varying RT are already discussed in my previous answer.