Rapid characterization of organic UV filters and their photoproducts in sunscreens by thermal desorption electrospray ionization mass spectrometry for the photostability study
Dozens of organic components are utilized in personal care products as chemical ultraviolet (UV) filters with specific limits of concentration. However, some photo-unstable UV filters can degrade and produce toxic byproducts, so determining the photostability of UV filters has significant public health implications. To determine the photostability of UV filters in personal care products, samples are irradiated to induce the photodegradation of UV filters that is then monitored using spectroscopy or chromatography. Conventional chromatographic hyphenated mass spectrometric methods like GC-MS and LC-MS are highly regarded for their ability to identify photodegradation products. In comparison, thermal desorption electrospray ionization mass spectrometry (TD-ESI/MS) is an ambient mass spectrometry technique that is comparably more user-friendly and cost-effective for characterizing thermally stable compounds. We therefore developed a rapid and direct method to study the photostability of organic UV filters in sunscreens by exposing sunscreen products to artificial sunlight prior to TD-ESI/MS analysis. Several commonly used UV-filters in standard solutions and various sunscreen products (including lotions, lip balm, gels, sprays, etc.) were analyzed by this strategy. UV filter compounds and the photoproducts in highly complex and diverse sunscreen formulations can be directly tracked and identified without any sample pretreatment. For examples, the signals of ethylhexyl(dimethylamino) benzoate (OD-PABA), ethylhexyl methoxycinnamate (OMC), and diethylamino hydroxybenzoyl hexyl benzoate (DHHB) were decreased, and methylated derivatives and dealkylated fragments of OD-PABA, cyclodimers of OMC, and fragments of DHHB were generated. Since TD-ESI/MS can be used to directly and rapidly detect UV filter photoproducts in sunscreens, it is a highly viable strategy to evaluate the photostability of various formulations in the market.