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Reasons for column performance degradation

Time:2018/09/25   Pageviews:0    Share:
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Column rupture

The polyimide coating of the fused silica capillary column breaks if it breaks a little, the polyimide coating protects the fragile fused silica capillary, the oven is continuously heated and cooled, the oven fan shakes, and the chromatogram When the column is wound on a circular column, the capillary will be stressed, and finally it will break at a small weak point. The scratches or wear formed by the polyimide coating will cause weakness, which will often be caused when the blade or the sheet touches the capillary. Scratches, column hooks and labels, metal edges in the oven, column cutters, and various similar things on the lab bench are sources of sharp edges or flakes.2ml snap chromatography vials

The column itself ruptures very little, and the column manufacturing industry pays attention to eliminating any columns with weak points, so as not to affect the perfection of the column, the large inner diameter column is more likely to rupture.

Thermal damage

Exceeding the upper temperature limit of the column will cause accelerated damage to the stationary phase of the column and the surface of the tube, which will cause excessive column loss, active component tailing, and reduced column efficiency. Therefore, it takes a long time to run above the temperature limit before the column is significantly damaged. When there is oxygen, it will greatly accelerate the thermal damage. In the case of leakage or overheating, the column will accelerate the damage and permanently damage the column.

Setting the GC's maximum column temperature at or above the high temperature limit is best to avoid thermal damage. This avoids accidental overheating of the column. If the column is subjected to heat loss, it will still have some The function. Remove the column from the detector, heat it at the constant temperature for 8-16 hours, cut off the column to the end of the detector by 10-375px, install the column as normal and age it. However, this column does not return to its original performance, but often it still has a certain function, and the life of the column will be shortened after thermal damage.2ml snap chromatography vials

Oxygen damage
The column will not be damaged at near room temperature, and the column will be severely damaged if the column temperature rises. Generally, for a polar stationary phase, the temperature and oxygen concentration at which severe damage occurs are low. Prolonged exposure to oxygen is problematic. There is no problem when exposed to oxygen for a short period of time, such as injecting air or removing the septum nut.

Where there is a leak in the carrier gas channel (such as a gas path, a joint, or an injector) is often the source of oxygen. When the column is heated, the stationary phase is quickly damaged, which prematurely causes excessive column loss, tailing of the active compound, and reduced column efficiency. In less severe cases, the column will also have some separation, but performance has dropped. In severe cases, this column is completely unusable.

Keeping the system out of contact with oxygen and avoiding leakage is the most effective way to avoid oxygen damage. Good maintenance of the GC system includes periodic leak detection of pipelines and pressure regulators, periodic replacement of septa, use of high purity carrier gas, and installation of oxygen. Capture and do not wait for the carrier gas cylinder to be empty before replacing it.2ml snap chromatography vials

Chemical damage

A relatively small number of compounds can damage the stationary phase, and the entry of non-volatile compounds (high molecular weight or high boiling point) into the column often degrades column performance but does not destroy the stationary phase. These deposited residues can be removed by washing the column with solvent to restore column performance.

The main compounds to avoid entering the column are inorganic or mineral bases and acids, including hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid. The base includes potassium hydroxide, sodium hydroxide, ammonium hydroxide. These acids and bases do not volatilize and accumulate at the front of the column. If it is left there, it will destroy the stationary phase, causing the column to lose a large amount prematurely, tailing the active compound, and reducing the efficiency of the column. Its signs are similar to heat loss and oxygen damage.

Since chemical losses occur at the front end of the column, processing or cutting the front end of the column by 0,5–1 m eliminates any chromatographic failures, and in the more severe cases, a segment of 5 m or longer can be cut off. If a guard column is used, the length of the column is reduced, but the guard column needs to be treated. Acid or alkali often destroys the deactivated surface of the fused silica tube, causing the peak shape of the active compound to deteriorate.

The column is contaminated2ml snap chromatography vials

There are two basic types of contaminants: non-volatile and semi-volatile, non-volatile or residue that cannot be eluted from the column, but accumulates in the column so that it becomes coated The column that stains the residue, thus affecting the distribution of the solute, ie the solute dissolves and evaporates out the normal distribution of the stationary phase, and the residue also interacts with the active compound, causing peak adsorption problems (even causing tailing or reduction) Peak area). Active solutes are those that contain hydroxyl or amino groups and some thiol groups and aldehydes, semi-volatile contaminants or residues that accumulate in the column and eventually elute. However, it takes several hours or several days to completely elute. Like non-volatile residues, they also cause peak shape deterioration and peak area reduction. In addition, they often cause many baseline problems (unstable, drifting). , noise, ghost peaks, etc.).

Source of pollutants2ml snap chromatography vials

There are many sources of pollutants, of which injection is the main source. Samples extracted from the worst substrate, biological fluids and tissues, soils, wastewater, etc., containing a large amount of semi-volatile and non-volatile substances, even with careful and thorough extraction methods, the sample will contain a small amount of these substances and brought to the injection In the sample. Several to hundreds of injections can cause accumulation of residue. Injection techniques such as on-column injection, splitless injection, and large-diameter columns directly feed large amounts of sample into the column. These injection methods often cause chromatography. Column contamination.

Maintenance measures

Minimizing semi-volatile and non-volatile sample residues is the best way to reduce contamination problems, but the presence of contaminants is often unknown. Strict and thorough purification of samples is the best way to prevent contamination problems. Using a guard column can reduce or delay the contamination of the column. If the column is contaminated, the best way is to wash it with solvent to remove contaminants. It is not recommended to use long-term heating to treat contaminated columns. 2ml snap chromatography vials

This is the end of the introduction of Reasons for column performance degradation. I hope it can help you.


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