Ultraviolet resonance Raman spectroscopy as a robust spectroscopic tool for in situ sunscreen analysis

Current techniques being used for sunscreen analysis are incapable of direct determination of the active ingredients in sunscreen formulations. Therefore, the development of methodologies for rapid in situ analysis of sunscreens is desirable. This paper describes the application of ultraviolet resonance Raman spectroscopy (UVRRS) to the direct in situ analysis of sunscreen formulations. High-quality UV resonance Raman spectra were obtained for five sunscreen active ingredients (AIs), mixtures of the AIs and real sunscreen formulation samples. The spectra from the sunscreen formulations gave distinct spectral signatures indicative of the sunscreen AIs in each sample, with essentially no interference from the complex sunscreen matrix. Also, despite the fact that many of the AIs are fluorescent, no fluorescence interferences in the resonance Raman spectra were observed. Excitation wavelength-dependent studies throughout the 244-275 nm region demonstrate that the best discrimination of the AIs was achieved at an excitation wavelength of 244 nm. Thus, by tuning the excitation wavelength within the absorption bands of the AIs, complete identification of these analytes can be achieved in situ without any sample pretreatment or separation. The limit of detection found for a common AI in situ with this technique is 0.23% (w/w), the limit of quantitation is 0.78% (w/w), while the dynamic range is between 0.8% and 50% (w/w). The technique is fast, robust, lacks any major interference, and can be adapted for routine online quality control.