MALDI target functionalization with deposited thin films of lanthanum stearate – An efficient tool for in situ enrichment of human globin adducts of chlorinated organic compounds

“Lab-on-a-plate” methodology encapsulates a number of different approaches aimed to shorten extensive sample processing for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis. Lately, we have proposed two approaches to the enrichment of chlorine-containing adducts of human globin (HHb) in a “lab-on-a-plate” format based on different techniques for the sorbent application to MALDI target spots: (i) droplet-free electrospraying of metal oxide nanoparticles and (ii) deposition of lanthanum stearate thin films (FLa). The latter approach has turned out to be more time- and cost-effective and, therefore, seems to be more promising. In this work, we assessed the quantitative characteristics (sensitivity, selectivity) of the “thin-film” procedure in order to estimate its analytical potential. The FLa-modified MALDI target was used for the on-spot enrichment of HHb adducts from the tryptic digests of the protein incubated with two model mono- and dichlorine-containing alkylating agents. The sensitivity of the technique is in the range of hundreds of fmol. Furthermore, the FLa-based procedure shows high selectivity (maximum molar ratio of modified/unmodified form of LLGNVLVC 112 VLAHHFGK is 1:500). As a case study, on-plate extraction of HHb adducts, formed due to the interaction of the protein with in vitro generated diclofenac metabolites, was performed on FLa-functionalized spots. This resulted in specific extraction of the HHb adducts with two diclofenac oxidation products from the tryptic digest of modified HHb. The developed approach appears to be effective for in situ enrichment of chlorine-containing adducts of HHb.