Question

4. The compounds in a mixture separated by GC can be identified by their retention times. If you Suructor nad not told you which peak in the GC chromatogram corresponded to which alker you didn't know the boiling points of the alkenes, how could you determine the identity or each peak by its retention time? Identities of the components in a mixture separated by GC can also be determined by the technique called "spiking". Suppose you had run a chromatogram of your product mixture of alkenes and then deliberately added a known sample of 2-methyl-1-butene to your product and reran the GC, how would the new chromatogram change? 6. What would be the effect of decreasing the carrier gas flow rate on the retention times and ability to resolve two closely spaced peaks? If you were to use a GC column half (1/2) the length of the one you actually used, how would the retention times of the alkenes be affected? How would the resolution (separation of the peaks) be affected?

Answer 1

4) Ans : By comparison of retention time of the reference substance with the test substance we can easily determined which peak corresponding to which alkene.

Under same condition ,same column ,flow rate , temperature cloumn flow the retention time of test and reference substance .

6) If flow rate of Carrier gas is decrease the retention time will increase ,also the resolution will increase as the interaction of samples with the stationary phase will more it will resolve mixture in better manner.

7) Ans : column length is proportional to number of therotical plate .

As number of therotical plate decree the retention time decrease .

If we use half length column then retention time will be reduced to half of original retention time.

The resolution of the mixture will be minimum if column length is reduced to half.

As sample interaction with stationary phase is less it will not resolve peaks in a proper way.

For question number 5) refer attached photo.

5) Ans - of a Sappose we had sun chromatogran mixture of celkenes. we will get chromale graph. chromatograph without spiling. Suppose, we have added a known amout of 2-methyl-J- butene. then run chromatogram again then- chromatograph with spicing 1 the pear area will increase of the peare which corresponds to 2-methyla 1-butone in above , peak area of B-compend is in neges hence we can identified that peau B is due to 2-methyl-lobytene.