Synthetic dyes that are used as color additives in foodstuffs are regulated by the Food and Drug Administration (FDA) under the Food, Drug, and Cosmetic Act (FD&C). The use of synthetic dyes not approved by the FDA, or the addition of dyes approved by the FDA above their maximum concentration limits in foodstuffs necessarily constitutes illegal food adulteration. Recently, rhodamine B (RhB), a bright-pink synthetic dye not approved for use in foodstuffs, has become an adulterant of interest due to its discovery in a large variety of food samples, and its identity as a potential carcinogen. Numerous chromatographic and spectroscopic methods have been developed for the analysis of RhB in food samples, as well as standard methods available for the analysis of synthetic dyes. However, due to the complexity of real food samples and the chemical diversity of synthetic dye concomitants, comprehensive chromatographic methods tend to be time consuming and expensive. Herein, we report a method for the determination of RhB in foodstuffs for the screening of real samples prior to subsequent full-blown chromatographic analysis, saving valuable time and resources. This screening method employs thin-layer chromatography (TLC) as a separation method, and, due to the strong yellow-orange fluorescence exhibited by RhB when excited with ultraviolet or green light, direct fluorescent measurement of RhB on the TLC plate using a fiber optic probe coupled to a commercial spectrofluorometer or to an instrumental set up for laser-induced fluorescence measurements. Qualitative analysis of RhB is based on its retardation factor, excitation and fluorescence spectra, and fluorescence lifetime. Quantitative measurements are made directly from the TLC plate to provide analytical figures of merit comparable to traditional fluorometric methods in liquid solution. The ability of the new method to determine RhB in food samples is then demonstrated with the analysis of chili powder.

Thesis Completion




Thesis Chair/Advisor

Campiglia, Andres


Bachelor of Science (B.S.)


College of Sciences





Access Status

Open Access

Release Date


Included in

Chemistry Commons