Akira Motoyama

To provide safe and effective products to customers in the cosmetic industry, mass spectrometry (MS) is an indispensable analytical tool. In addition to its outstanding sensitivity and specificity, the method is applicable to a wide variety of compounds, which makes it irreplaceable for the development of cosmetics, which requires the analysis of complex systems. Because most cosmetic products are applied directly to the skin and function as they are designed, monitoring the molecular compositions of endogenous or exogenous compounds in or on the skin is crucial to ensure the safety and efficacy of a cosmetic product. Recent advancements in MS and ionization techniques, such as MS imaging and ambient ionization, now provide access to richer and deeper molecular information with less time and effort. This brief review discusses advanced ionization techniques that are currently used in the field of cosmetic science using two examples, namely, the use of desorption electrospray ionization and zero-volt paperspray ionization to detect trace molecules in or on human skin.

Three known iridoid glucosides (gentiournoside A, gentiournoside E and depressoside) were isolated from the flowers of Gentiana urnula Harry Sm. through activity-guided fractionations with a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. All three compounds exhibited excellent DPPH radical scavenging activities (IC₅₀: 10–20 μmol L⁻¹) comparable to that of ascorbic acid and Trolox. However, examination of the NMR data revealed that the reported chemical structure of depressoside, previously isolated from the leaves of G. depressa, needed correcting due to incorrect elucidation around C-7 of the iridane skeleton, and was corrected to 6-β-(2,3-dihydroxyphenyl)-d-glucosyl 7-O-(2,3-dihydroxybenzoyl)-loganate. Depressoside exhibited a much higher scavenging activity against superoxide radicals (IC₅₀: 45.5 μmol L⁻¹) than the other two extracted compounds (IC₅₀: more than 900 μmol L⁻¹) due to the crucial presence of a pyrogallyl unit.

Rationale: Zero volt paper spray ionization (zvPSI) is a newly developed sample introduction/ionization technique for mass spectrometry (MS), which combines favorable features of paper spray ionization (PSI) and solvent‐assisted inlet ionization (SAII). With a simple platform similar to PSI, zvPSI allows direct MS analysis of a broad type of samples (liquid, (semi‐)solid, and imprint) without applying voltage. Methods: In zvPSI‐MS, a rectangular paper slip was used as a sample loader, extraction medium, and droplet emitter to introduce sample extract into the inlet of a mass spectrometer. For (semi‐)solid and imprint samples, analyte(s) was directly extracted with solvent and instantaneously introduced into a mass spectrometer by aspiration. Solution samples were analyzed after being dried‐up or by dispensing directly onto paper. Ionization was achieved by SAII and ionized molecules were detected by an ion‐trap mass spectrometer. Results: The developed method allowed direct voltage‐free MS analysis of samples on filter paper substrate. Favorable features of PSI and SAII were successfully combined, such as fast data acquisition, flexible sample handlings, and direct extraction capability from solid samples (PSI), with no need for external high‐voltage, laser, or nebulizing gas to convert analytes into gas‐phase ions (SAII). Comparable to PSI and SAII, a wide variety of compounds such as amino acids, peptides, lipids and synthetic polymers were shown to be analyzed. Conclusions: The developed method (zvPSI‐MS) expanded the analytical utility of PSI and SAII to voltage‐free direct MS analysis of a broad type of samples (liquid, (semi‐)solid, and imprint). Copyright © 2015 John Wiley & Sons, Ltd.

An analytical method that enables direct and sensitive determination of endogenous melatonin (MLT) in human saliva was developed by means of column‐switching semi‐microcolumn liquid chromatography (i.d.: 1–2 mm)/mass spectrometry (LC/MS). The system allows direct injection analysis of a 400‐μL aliquot of saliva with minimal sample pretreatment (internal standard (IS) addition and vortex mixing) and a relatively short run‐time (10 min). The system consists of three columns to attain large volume injection and on‐line analyte enrichment. A pre‐column packed with a silica‐based mixed‐functional C8 (4.0 mm i.d. × 20 mm) was used for on‐line sample cleanup. MLT and an IS, the d7 isomer of MLT (d7‐MLT), were heart‐cut by valve switching and enriched at the top of the intermediate trapping column packed with a silica‐based C18 (4.0 mm i.d. × 10 mm). Subsequently, the analytes were backflushed into a semi‐micro C18 silica column (2.0 mm i.d. × 150 mm) for the final separation. MLT and IS were ascertained by positive electrospray ionization and selected ion monitoring (SIM). MLT was monitored based on its fragment ion at m/z 174.1 by in‐source collision‐induced dissociation (CID). The validation of this method revealed a detection limit of 2.5 pg mL ⁻¹ at a signal‐to‐noise (S/N) ratio of 5. The linearity of the method was established in the ranges 5–250 and 100–2500 pg mL ⁻¹ with a coefficient of determination of greater than 0.998. Accuracies, evaluated at five levels in the range 5–1000 pg mL ⁻¹ , were between 81 and 108% with a relative standard deviation (RSD) ranging from 1.3–20%. The method was successfully applied for the endogenous saliva MLT monitoring of two healthy subjects. Copyright © 2004 John Wiley & Sons, Ltd.