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9. Refer to the gas chromatograph (below) of a mixture of Compound A (RT 1.11) and Compound B (RT-2.27), which was done on a general purpose column: START 51 1.10 227 RT AREA X000X TYPE ABHT AREAS 0.009 0.61 1.11 2.27 XX XX0X XX 55874 44.117 XXXX XX XX TOTAL AREAXX MUL FAC TOR-X Which compound has the highest retention time? b. Which compound is present in a larger amount assuming that their mass correction factors are equal? c. Which compound has the lower boiling point? d. What would happen to the retention times of compounds A and B if the column temperature were raised? a.

Answer 1

a. The GC plot shows the intensity of a peak against the time. Since compound A elutes faster, hence, compound A is retained less on the column and will therefore, have a lower retention time. Consequently, compound B has the highest retention time.

b. It is assumed that the peak widths are similar. Hence, it can be inferred from the plot that the peak for compound A has a greater height and hence, a higher area. The weight percent of a compound in GC is directly proportional to the area under the peak. Since compound A has a greater area, hence, compound A is present in larger amount.

c. The elution of a compound in GC depends on the boiling point of the compound. In GC, a mixture of compounds is passed through a heated column and the temperature of the column is increases in a pre-defined manner. When the carrier gas in the column attains the boiling point of the compound retained in the column, the compound is eluted with the carrier gas. The faster a compound elutes from the column, the lower is the boiling point of the compound. Since compound A is eluted fast, hence, compound A will have the lower boiling point.

d. If the column temperature is raised, the retention times of both compounds A and B are decreased or lowered than the given values. This is due to the fact that the carrier gas in the column attains the boiling points of the compounds faster (since they are at a higher initial temperature than the given figure) and hence, the compounds elute faster.