Quantitative Analysis of Cholesterol and Cholesterol Ester Mixtures Using Near-Infrared Fourier Transform Raman Spectroscopy

Near-infrared Fourier transform Raman spectroscopy is a rapid and nondestructive technique that can provide reliable qualitative in situ information about the chemistry of biological samples. We have combined this technique with partial least-squares (PLS) regression to perform a quantitative determination of free and esterified cholesterol in two synthetic sample series. In 66 ternary mixtures containing various proportions of cholesterol, cholesterol linoleate, and oleate, the standard errors of prediction were 1.27, 1.17, and 0.94%, respectively. For the second series of experiments concerning the sensitive problem of quantitative analysis of cholesterol palmitate and stearate mixtures, the standard error of prediction for 49 samples was 3.02%. It is also possible to extract quantitative information for a single component of the ternary mixtures independently. These results are of great importance when-as in the case of arterial samples-many chemical species are present. Comparison between Raman spectra of ternary mixtures and atherosclerotic rabbit aorta shows that many bands, assignable to free and esterified cholesterol, are easily observed in the aorta spectrum.