Another selectivity enhancement method is derivatization. Examples of these are the many color reactions that are used in clinical analyses. Extra selectivity can be added if, instead of just single wavelength detection, the full spectrum of the absorbing product is measured. Spectral differences are enough to discriminate among closely related structural molecules, and mixtures can be analyzed using mathematical algorithms to fit the whole spectrum from weighted aggregates of the spectra for the components. This has been done very effectively in the direct measurement of the distribution of cholesterol over the three major lipoproteins in human serum in the single experiment.
Selectivity is enhanced even more by the combination of color derivatization and CD detection.
Shifting the CD activity from the UV to the visible spectral range greatly reduces the interferences from other compounds that are strong UV absorbers and are extracted along with the analyte of interest. This has proved to the most important factor in developing a convenient procedure for the accurate determination of enantiomeric purity in pharmaceutical drug formulations. The colr-inducing reagent is an optically active metal complex and the level of selectivity that is accomplished is unsurpassed. N. Purdie and K.A. Swallows, L.H. Murphy and R.B. Purdie, 1990. N. Purdie , 1991.