Sunday, October 25, 2020
Aging of GC column, in short, refers to the process of restoring column efficiency by baking the column at high temperature and taking the unstable stationary phase, possible impurities and pollutants out of the column by carrier gas.
What are the conditions that require aging treatment of the column?
1. Newly purchased column: For new column, prior to its initial use, the aging treatment can remove the stationary liquid that bonded unstably in the column or residual solvent in the packed column to ensure the stability of the properties of the new column.
2. For columns that have been left unused for a long time and need to be started again, the aging of the column can remove pollutants, oxygen and water caused by column being placed for a long time. And restore the properties of the column.
3. Columns that have been used for a long time or that have been through complex matrices and mass sample analysis: in this case, high boiling point impurities and pollutants remaining in the column can be mainly removed by aging; On the other hand, long-term use of column under high temperature will cause the loss of stationary liquid, exposing part of the active site. Through aging treatment, using the characteristics of thermal expansion and cold shrinkage of stationary phase, the active site on the inner wall of the column can be covered again. And restore the properties of the column.
How to operate, and what details do we need to pay attention to during the aging process?
1. Selection of aging temperature
In general, the aging temperature can be controlled between the maximum analytical temperature of the method and the upper limit of the constant temperature of the column.
The aging temperature can also be set to 20-30℃ lower than the upper limit of the column constant temperature; Or 20-30℃ higher than the maximum analysis temperature of the method.
It is important to note that each GC column has a temperature limit to which it can tolerate, and it is necessary to read the column box or instructions carefully before aging. In the aging process, once the column temperature limit is exceeded, it will lead to the loss of stationary phase and shorten the lifetime. Therefore, aging temperature can be lower as far as possible under the premise of ensuring the removal of impurities and pollutants.
2. Aging time
The specific aging process is generally set as program heating (slowly heating up to the set aging temperature), such as: the initial temperature is 35℃, 2-5℃/min, heating up to the aging temperature, and keeping 0.5-2h. The specific aging time can be determined according to the effect of impurity removal.
3. Prevent oxygen into the column
Because at high temperatures, with the presence of oxygen, the stationary liquid is easily oxidized, the stable silane bond will break, causing serious column loss and column efficiency declination.
Therefore, in order to avoid oxygen entering the column, the following points should be noted:
● Connect the gas inlet of the column to the injection port of the instrument. Place the end of the column in alcohol and take carrier gas to observe whether there are continuous bubbles. If not, check the column for mid-section fracture, installation, and leakage of the system.
● Set the carrier gas flow rate to the normal working value, the injection port, column oven and detector (if connected to the detector) to 35℃ or turned off the instrument temperature control system. The carrier gas is available for 15-30 minutes at room temperature to replace the oxygen that may exist in the instrument system and the column.
● Ensure that the other joints of the instrument are properly installed and pass leaking test.
4. Avoid pollution
In general, in order to avoid contamination of the detector, it is not recommended to connect the detector during the aging process. The normal operation is to use a solid pressure ring to plug the lower end of the detector and close the temperature. If the detector is connected, for the FID detector, there is no need to ignite, and air and hydrogen need not be turned on; If it is an ECD detector, tailing blowing should be set to avoid excessive heat and temperature which transfer to the ECD, so as to ensure the safety of the radioactive source inside the detector. In addition, it is prohibited to use hydrogen to age the column, that is to avoid hydrogen leakage and accumulation in the column temperature chamber, which will cause explosion.
5. Relevant maintenance shall be carried out before aging
For columns that have been used for a long time or that have through analysis of complex matrices and multiple samples, aging is to remove some of the residual contaminants. These contaminants tend to be compounds with higher boiling points which accumulate at the head of the column, such as proteins, pigments, gels, etc. in the sample. In order to avoid the pollutants to continue to transfer to the column while they can not be completely removed from the column inside the column, before aging column should be cut, appropriately cut off part of the column. In addition, it is necessary to maintain the injector liner, quartz cotton and the injector spacer to avoid secondary contamination of the column in the aging process. In conclusion, aging of column is meaningful after removing the source of pollution.
