In this section, we discuss applications of the model in Table 14.2 to overlapped peaks in high-pressure liquid chromatography. The first example involves the incomplete separation of C60 and C70 buckminsterfuller-enes. The two-peak model (Table 14.2, k = 2) gave a good fit to the data (Figure 14.5). The peak area ratio of C60/C70 from nonlinear regression was 0.16. This sample was found to be 82.9% C60 and 17.1% C70 for a ratio of 0.21, in reasonable agreement with the above result, by a different HPLC method giving full baseline resolution of the peaks.
Figure 14.5 HPLC chromatogram of C60 and C70 buckminsterfullerenes on a reversed phase C18 column. Mobile phase was hexane at 0.8 mL/min. C60 82.9%; C70 17.1% ratio 4.85. (The authors thank Prof. J. D. Stuart, J. T. Doty, and J. Casavant, University of Connecticut, for providing the original chromatogram.)
In an analytical application of a multipeak model, be it that in Table 14.2, an exponentially modified Gaussian (eq. (14.2)), or any other model, care should be taken to calibrate the analysis properly. We recommend analyzing by nonlinear regression chromatograms of standard mixtures under the same conditions that give the overlapped separation of the sample. Calibration plots of area of component peak vs. concentration of standard can then be constructed for use in determinations with the real samples.
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