Structures of cobalt stearate as a metal-affinity sorbent for sample preparation in laser desorption/ionization mass spectrometry

Abstract

The aim of this work was to develop, characterize and apply in a laboratory-on-plate format a new metal-affinity sorbent based on cobalt (II) stearate thin monolayers (films) — FCo. FCo were prepared by the classical Langmuir method and then collapsed. A bath with movable barriers was filled with an aqueous solution of CoCl2. A solution of stearic acid in hexane was dropwise applied to the surface of the aqueous subphase. The solution spread over the surface, forming a film (layer). After evaporation of hexane from the aqueous subphase, a monolayer of cobalt (II) stearate was formed on the surface, which was slowly compressed by movable barriers. The following parameters were determined for FCo prepared by the classical Langmuir method and then collapsed: specific mass (0.022 ± 0.003 mg/dm2), specific surface area (22.0 ± 2.1 m2/g), isoelectric point value (3.7 pH), moisture content (63 ± 2%), structures ([Co(C17H35COO)2]H+), chemical stability (stable in standard aqueous eluents and in polar organic solvents used in metal-affinity chromatography). Adsorption isotherm of the diclofenac from aqueous solution on FCo was investigated in spin columns (batch). The FCo structure can be obtained on the surface of a subphase drop deposited on a MALDI target plate. Thus the sorbent is formed directly on the surface, preserving the structure and metal-affinity properties. The technique is characterized by cost-effectiveness, simplicity and reproducibility. FCo formed on spot of MALDI target plate provide a high level of sensitivity, specificity and selectivity of the analysis, it is shown that HHb adducts with chlorine-containing alkylating agent can be determined at 0.5% protein modification. Thus, a comprehensive approach for the enrichment of chlorine-containing HHb adducts using a cobalt (II) stearate monolayers on MALDI target plate has been developed.