As we have seen in our first paper on the subject, Backflush is an essential element of light gas chromatographic analysis.

CHEMLYS explains how to adjust the backflush in micro GC.

The Backflush allows the protection of the analysis column with a guard precolumn.

With Micro GC Fusion, it's very simple. Just set the parameter « backflush time » In seconds.

The pre-column and the analysis column are in series.

Backflush time is the time from which the Backflush pneumatic valve activates after the sample gas injection. This action separates the precolumn and the analysis column. The precolumn is back-baked and the compounds that have had time to pass through the analysis column will be separated and detected.

We start an air analysis (oxygen and nitrogen) with a relatively short backflush time, in our example 5s.

Then we will increase the time of Backflush by 1s in 1s until we see the appearance of the compounds of interest.

With a backflow time of 5s, no signal is detected. All compounds were backflushed. Backflush was too short.

Then we move to a 6s setting, the compounds appear. Now you have to make sure that the backflush lets all the oxygen and nitrogen pass.

This increases the time to 7 seconds. It is found that the area of compounds is identical. This means 6s was the right setting.

On the molecular sieve column, if the backflush time is set to oxygen and nitrogen, this setting will also be suitable for carbon monoxide (CO) analysis.

If methane is to be analysed on this column, the same procedure should be followed by focusing on the appearance and disappearance of the methane peak.

In conclusion, adjusting its backflow with MicroGC Fusion is simple and very fast. It must be done step by step but the analyses being very fast it does not take much time.

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