Determination of acetylene in liquid oxygen
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Let’s discuss what the principle of concentration is when determining acetylene in liquid oxygen using chromatography What is the principle behind parsing? Did all the analyzed samples enter the chromatography column? How can we ensure that all the samples we have analyzed go into the chromatography column?
What a great analysis method this is – using a regular FID chromatograph with a microhydrocarbon column enables good separation, not only of acetylene but also of other hydrocarbons such as methane, ethane, ethylene, propylene, propane, and so on.
We used this method a long time ago and have given up on it; there’s no need for it anymore. As for how many items to enter? The size of the quantitation tube determines the amount of sample to be injected; concentration and separation are simply used to distribute the components evenly within 100 ML, after which quantification is carried out via the quantitation tube for injection.
The principle involves utilizing the fact that the impurities being analyzed (such as acetylene) have a higher retention value, or greater adsorption capacity, on the adsorption concentration column compared to the main component (liquid oxygen). As the sample passes through the adsorption concentration column at low temperature, the main component passes through, while the impurities (such as acetylene) are adsorbed by the adsorbent in the column and remain there. When the concentration of the impurity being detected exceeds the level that can be detected by the detector, the temperature of the concentration column is increased, causing the impurities to desorb; these impurities are then sent to the detection system via the carrier gas. Of course, the analyzed impurity components, together with the backflow, ensure that all pass through the detection system.
It is said that acetylene in a 100 ml gas sample is concentrated inside a concentration tube; I don’t understand this
There’s nothing difficult to understand: typically, a 100 ML syringe is used for sampling, and the concentration column is external; liquid nitrogen is used to cool this column, allowing the 100 ml of sample to be concentrated within it. This process is repeated several times. After that, the sample syringe is removed, the concentration column is heated for a few minutes, and then the sample is injected. The concentrated sample is placed in a concentration column, then heated to achieve uniform distribution, followed by injection for analysis.
Water analysis cannot be done this way, because concentration will cause freezing. Headspace or direct injection can be used; direct injection usually cannot employ a packed column.