APPLICATION OF NORMAL AND 2ND-ORDER DERIVATIVE SPECTROSCOPY IN IDENTIFYING ORGANIC-ACIDS AND SUGAR ACIDS IN LIQUID-CHROMATOGRAPHY WITH ONLINE PHOTODIODE-ARRAY DETECTION

The UV-spectra of 16 compounds including organic acids and sugar acids were recorded at pH 2.5 using photodiode array detection in three dif ferent chromatographic systems: an ion exchange column with phosphate buffer as eluent (I), a C-8 reversed-phase column with sulphuric acid as eluent (II) and a C-8 reversed-phase column with hydrochloric acid as eluent (III). Differences in the normal spectra in each of the syst ems were evaluated by calculating match factors between the spectra. N ormal spectra and the second-order derivative spectra gave match facto r ranges of 603 - 1000 and 0.1 - 999, respectively. The similarity bet ween the normal spectra was very good and excellent between chromatogr aphic systems I and II. On the other hand, the similarity between the second-order derivatives of the spectra was not as good. Thus the norm al W-spectra can be used, together with the retention times, for relia ble identification despite of the spectral similarity of some acids. M olecular connectivity indices up to the sixth order were correlated wi th the retention parameters. The correlation was only moderate in all the systems.