MS Analysis of Retinoids by Atmospheric Solids Atomization Probe

Because of poor ionization in many MS probe interfaces (e.g., ESI, APCI, PI, LDI, MALDI), retinoid analysis is often by HPLC with use of retention time and absorption characteristics alone. We undertook a study of the ionization of retinoid standards and those produced by a genetically-engineered yeast strain to determine the feasibility of analysis with an atmospheric solids atomization probe (ASAP). Mixtures of known retinoids and the yeast extract were analyzed by ASAP. The known retinoids were detected easily, with good sensitivity and resolution, through the [M+1]⁺ ion. Retinol 1 and retinyl acetate 4 were detected through comparison of the protonated ion [M+1]⁺ and the major product ions, [M-H₂0]⁺ and [M-CH₃CO₂H]⁺ ions, respectively. The engineered yeast extract, containing genes of the carotenoid/retinoid pathway, showed production of 1 and 2. In other MS techniques, 2 must be analyzed in negative mode; the ASAP allowed detection of all compounds in positive mode. ASAP requires minimal sample preparation, rapid sample introduction and analysis, and high mass accuracy, making it ideal for many studies with natural products.