Retention times during capillary column

Many compounds are resolved completely from each other using capillary columns. These compounds can be quantified accurately when standards of sufficient purity are available. The calibration mixture must be analysed under the same instrumental conditions which are used for the sample. Differences in sensitivity of the detector for different components in the sample are accounted for by the response factors during automatic calculation. A peak must be identified correctly before it is quantified. Identification is based on the retention times of designated peaks in the calibration table (the reference peaks) and those of the peak of interest. 

Figure 4.8 illustrates both effects for a capillary column test mixture. At 90°C, dodecane is eluted last at around 11 min. As the temperature increases in 10° increments, all of the peaks retention times decrease, and the entire separation takes only 3.6 min at 120°C. The solutes retention times decrease by about half for every 15-20°C increase in colmnn temperature. However, the last two peaks merge at 100-110°C, and naphthalene becomes the last peak at 120°C. Thus, careful attention must be paid to unambiguous peak identification during a separation optimization that includes the column temperature. 

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