Cobalt Stearate Structures as a Metal Affinity Sorbent for Sample Preparation in Laser Desorption/Ionization Mass Spectrometry

A new metal-affinity sorbent based on cobalt (II) stearate monolayers has been developed, characterized and applied in a lab-on-target format. Cobalt (II) stearate monolayers were obtained using the classical Langmuir method on the surface of an aqueous subphase in a special bath. Then, the monolayer was collapsed in two directions. The parameters characterizing the obtained structure as a sorbent have been determined: specific gravity (0.022 ± 0.003 mg/m²), specific surface area (22 ± 2 m²/g), isoelectric point value (3.7 pH units), humidity (63 ± 2%), structural unit ([Co(C₁₇H₃₅COO)₂]H⁺), and chemical stability (stable in standard aqueous eluents and polar organic solvents used in metal affinity chromatography). It is shown that collapsed monolayers of cobalt (II) stearate (FCo) meet the requirements for metal-affinity sorbents. In spin columns (packet chromatography method), sorption of diclofenac was carried out and specific interaction of the monolayer with chlorine-containing compounds was demonstrated. A method for functionalization of a target for matrix-assisted desorption/ionization mass spectrometry (MALDI-MS) is proposed, during which the sorbent is formed directly on the target surface, preserving the structure and metal-affinity properties. The method is characterized by its cost-effectiveness, simplicity, and reproducibility, and the formed sorbent is characterized by a high level of adhesion to the substrate and remains on the surface throughout the entire experiment. The target surface was formed, and the conditions for conducting metal-affinity chromatography on a functionalized surface in the “lab-on-target” format were determined. It was shown that the adduct of globin with a chlorine-containing compound can be determined at 0.5% protein modification, and collapsed monolayers of cobalt (II) stearate formed on the target surface for MALDI-MS provide a high level of sensitivity, specificity, and selectivity of analysis in the “lab-on-target” format. An integrated approach has been developed for determining chlorine-containing protein adducts in this format using a new metal-affinity sorbent based on cobalt stearate (II) monolayers.