Question

In gas chromatography, what problem results if the temperature is set too low for the detector? A. The compounds may move too quickly making them difficult to detect. B. The compounds will move too slowly resulting in broad peaks that are not easily detected. C. The compounds may condense in the detector and gum it up. D.The compounds may reverse their order of retention times making their identification difficult.

Answer 1

In gas chromatography we pass our sample mixture through a column and based on the interaction of samples and column we do seperate the components from the mixture.

When one molecule has strong interaction with the column then it will come later to the detector having more retention time. Here if we increase the temperature then molecules can be easily removed from the column and allmolecule will come at a same time to the detector which will make the analysis difficult. Similar situation when we decrease the temperature to a very low value then the compounds will move too slowly inside the column which will give us a broad peak and obviously it will be difficult to analyse.
The reason of broadness of peak at low temperature: At low temp the thermal energy of the system is less so the kinetic energy of the compounds are also less. If the kinetic energy of a compound can overcome the attractive force between the compound and column then only it will come out of the column. If the temp. is too low then it will come out of the column very slow, which indicates that the total amount of that compound will take a lot of time to come out of the column. As in Gas Chromatography we do get a spectrum of Intensity vs. retention time, the retention time will be much higher at low temperature as compared to that of high temperature. It simply indicates the reason of the broadness of signal.