Why do chromatographic columns age

Aging, there are two cases
One is that after the packed chromatographic column is connected to the instrument, pressure test and leakage test should be conducted first, and then the column should be washed with carrier gas at a constant temperature for several hours and then subjected to analysis. This is generally known as the aging process of the column. The purpose of aging is to drive away the residual solvent, low boiling point impurities and low molecular weight stationary liquid of stationary phase, so as to make the baseline of recorder straight, and make the stationary solution redistribute on the surface of support at aging temperature, so as to make the coating more uniform and firm. After aging for a period of time, the packed column is stable in both efficiency and performance, so it can be used.
Another situation is that after one day's sample preparation, the column will be aged or baked for fear of residue in the column.
Why aging?
In order to completely remove the residual solvent and some volatile substances in the filler, there will be high boiling point impurities in the column after using for a period of time. These residual pollutants and samples can easily lead to problems such as tailing of chromatographic peaks and impurity peaks; on the other hand, it can promote the stationary liquid evenly and firmly distributed on the surface of the support, and reduce the loss of the column And the background noise.
When the chromatographic column is used at high temperature for a long time, the stationary phase will be slowly lost, which results in the exposure of silica based active groups in the inner wall of the capillary column, and the exposed silica based adsorption samples will also cause the problems of chromatographic peak tailing, baseline fluctuation and noise rise.
In order to avoid these situations, we need to aging the gas which has been used for a long time. Aging can remove the residual pollutants in the column.
In addition, the stationary phase on the inner wall of the column can also be allowed to cover some active points after thermal expansion and cold contraction, so as to prolong the service life of the column.
What is the focus of aging?
There are various opinions about the aging of gas chromatography columns. For example, some people set up a slow heating program all night, others run high and low for several cycles, and some laboratories simply and roughly rise to high temperature to bake.
What can we do to achieve good results?
Aging temperature
The maximum aging temperature is usually recommended to be the intermediate value between the maximum set temperature of the method and the tolerance temperature of the column.
It should be noted that the higher the temperature is, the more serious the loss of stationary phase will be. Therefore, the aging temperature and aging time need to be accurately grasped.
It is not suggested that the higher the aging temperature of chromatographic column is, the lower the temperature is, the better it is on the premise that pollutants can be driven away.
Aging time
In the specific aging procedure, the temperature will be slowly raised to the aging temperature, such as 2-5 ℃ / min, and then the aging process will continue for 2 hours. The rate of programmed heating can be set according to your own experience or experimental requirements.
And the aging time of the column mainly depends on the measured samples. If the instrument is used regularly, it can be aged once a to two weeks, and the aging time is not too long. It can be directly raised to the aging temperature. About 0.5-1 hour is enough. If the column is used for a long time, and the column into the sample end has been black, then the system aging. Cut off the length of 0.5-1 m at the injection port end, and then rise to the aging temperature at the rate of 5 ℃ / min, keep it for 20-30 min, then cool down to the initial temperature, and then increase to the aging temperature at the rate of 5 ℃ / min. this cycle is repeated twice. Clean and regenerate when necessary.
The inside of the column can not be seen or touched, so whether it is aging is generally judged by the old time, which is summarized by many people who do chromatographic columns.
Avoid oxygen
The more important thing to avoid is to avoid the presence of oxygen, which is also the most common cause of aging failure.
Because oxygen at high temperature is a good hand at breaking chemical bonds, and once the stationary phases in the chromatographic column are oxidized, the bond bond link between them will be destroyed, and the stationary phase can no longer be stably "fixed" in the chromatographic column, resulting in a large number of column loss and column efficiency will be greatly reduced.
Avoid pollution
In addition, from the perspective of avoiding pollution, it is not necessary to connect the detector when the new column is aging.
If you don't use FID and air, you can turn on the detector.
The newly filled column can not be used immediately and needs aging treatment. There are two purposes of aging, one is to completely remove the residual solvent and some volatile impurities in the filler, the other is to promote the stationary liquid evenly and firmly distributed on the surface of monomer.
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