Chromatography Forum

Hi All,

I have a question. for report generation, i notice that in calculated properties, real gas density, real relative density, real denisty (C1-C5) is displayed in kg'm-3 unit.

Do GC measure the density of gas?if yes, then how they work on it?
Thank you.

A GC will measure the peak height or peak area of the chromatographic peak that elutes from the column. The concentration of the peak is calculated by comparing the area or height of the unknown peak versus that of a known calibration standard that was analyzed under the same parameters.

The instrument doesn't actually measure the density or concentration, it measures the response it gives at the detector, then it must use a standard you have provided(injected just as a sample)to calculate the unknown value.

Think of it like this. If I give you a measuring stick with graduations on it but no units, and you measure a box that is 5 units wide. Then I give you a calibrated ruler and you measure the measuring stick and find the graduations are 10cm apart, then you can calculate that the box was 50cm wide. The GC works the same way comparing the response of the unknown to the response of a known standard and calculating a value for the unknown response.

As explained in the post above, it is not measured. It is calculated by finding the mole% of each compound. The report generator has access to a database that contains the density of each compound when it is 100%. If you had only two compounds and you find that you have 60% A and 40%B, then you take 60% of density A and 40% of density B and sum them together. There may then be adjustments for temperature and pressure.

Gasman