Column breakage

01 Polyimide coating fracture:

Polyimide coating protects frangible but resilient fused silica tubing.

Possible causes:

continuous heating or cooling of the column oven, vibration of the column oven fan, and pressure on the tubing caused by wrapping the column around the circular column holder, which eventually breaks at the weak point; the polyimide coating is scratched Or wear can present weak points such as column hooks and labels, metal edges of GC ovens, column cutters, and various items on the lab bench with sharp tips or edges.

02 The column breaks itself:

This situation is relatively rare. Generally speaking, larger diameter chromatographic columns are easy to be broken and handled, and 0.45-0.53mm inner diameter columns should be handled with more care than 0.18-0.32mm inner diameter columns to prevent breakage.

A broken column is not unusable. A broken column is very susceptible to damage if it is continuously exposed to high temperatures or run multiple temperature programs at high temperatures. Exposure of the second half of a fractured column to high-temperature oxygen can rapidly damage the stationary phase. The first half of the column remains intact due to the passage of carrier gas. If a broken column is not heated but only exposed to high temperature or oxygen for a short time, the second half of the column will not suffer any serious damage.

Thermal damage

When the temperature of the column exceeds the upper temperature limit of the column, it will accelerate the damage of the stationary phase and the surface of the pipeline. This can result in excessive column bleed, active peak tailing, and/or reduced column efficiency (resolution). Even if the column is thermally damaged, it can still be used. Remove the column from the detector. At the isothermal temperature limit of the column, it is heated for 8-16 hours. Cut 10-15cm from the end of the column that connects to the detector. Install and condition the column as normal. Columns often cannot be restored to their original performance, but can still be used. Column life is shortened after thermal damage.

It is important to note that thermal damage is greatly accelerated in the presence of oxygen. Excessive heating of a column with leaks or high levels of oxygen in the carrier gas can quickly and permanently damage the column.

Oxygen damage

Oxygen is the enemy of many capillary GC columns. At or near room temperature, the column will not be damaged, but the column will be severely damaged as the column temperature increases. Typically, for polar stationary phases, severe damage can occur at lower temperatures and oxygen concentrations. Oxygen damage only occurs with prolonged exposure to oxygen. Brief exposure to oxygen (such as injecting air or quickly removing the septum nut) is not a problem.

Leaks in the carrier gas path (eg, gas lines, fittings, injectors) are the source of oxygen exposure. The stationary phase is quickly damaged as the column heats up. This can result in excessive column bleed, active peak tailing, and/or reduced column efficiency (resolution). The symptoms are similar to thermal damage. Unfortunately the oxygen damage was found to have been severely damaged by the time the column was already damaged, and in less severe cases the column could still be used but with reduced performance. In severe cases, the column will be completely unusable.

Chemical damage

Relatively few compounds can damage the stationary phase. The introduction of nonvolatile compounds (eg, salts) into the column chromatography generally reduces its performance, but does not damage the stationary phase. Flushing the column with solvent usually removes carryover and restores column performance. The main compounds that should be avoided from entering the column are inorganic or mineral acids and bases.

Only perfluorinated acid has been reported as an organic compound that can damage stationary phases. These include: trifluoroacetic acid, pentafluoropropionic acid, and heptafluorobutyric acid. They require high concentrations (eg 1% or higher) to be destructive. Most problems occur during splitless or large bore direct injection, where a large amount of sample deposits on the front of the column.

Column is contaminated

Column contamination is a common problem in capillary GC. Often, a contaminated column is undamaged but can no longer be used. Generally speaking, there are two basic pollutants: non-volatile pollutants and semi-volatile pollutants. Non-volatile contaminants or residues will not be eluted and will accumulate in the column. Semi-volatile contaminants or residues will accumulate in the column but will eventually be eluted out.

Prolonged heating (often called column bakeout) is not recommended for handling contaminated columns. Because baking out the column may turn some contaminant residues into insoluble substances that cannot be removed from the column by solvent cleaning. If this happens, there is usually no way to restore the column. The column can sometimes be cut into two pieces, and the second half may still be usable. When baking out the column at the isothermal limit of the column, the time should not exceed 1–2 hours.

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