Separation and determination of sugar alcohols in detergents using field desorption

The field desorption (FD) method is a soft ionization technique that can analyze nonvolatile, thermally labile compounds with minimizing fragmentation. While advantageous for analyzing viscous materials like detergents, FD traditionally lacks chromatographic separation, making it challenging to distinguish stereoisomers such as D-sorbitol and D-mannitol, which have identical molecular masses. Additionally, FD has historically been limited to qualitative analysis due to manual sampling variability and volatilization under high vacuum. This study demonstrates a novel approach to overcome these limitations. Researchers synthesized deuterated D-sorbitol and D-mannitol to serve as internal standards for quantitative analysis. Using a ruthenium on activated carbon (Ru/C) catalyst in D₂O, they achieved 98% deuterium content at 80 °C. These internal standards proved essential for achieving acceptable recovery rates (108-117%) in model detergents, particularly at higher concentrations. A significant breakthrough in this research is the first-ever demonstration of stereoisomer separation using the FD method alone. By reducing the emitter's rising current rate from 51.2 mA/min to 3.2 mA/min, the researchers were able to separate sorbitol and mannitol based on their different retention times. This separation is attributed to differences in the compounds' physicochemical properties, such as crystallinity and solubility, which influence their desorption energy from the emitter surface. Compared to electrospray ionization (ESI), which suffered from matrix effects and instability for sugar alcohol analysis, the FD method provided a more direct and reliable quantitative route. Although current FD instruments are not yet optimized for precise current control, this study establishes FD as a valuable tool for quality control in detergent production, offering both isomer separation and direct quantification without complex derivatization.