In-Tip Lanthanum Oxide Monolith for the Enrichment of Phosphorylated Biomolecules

Polymeric monoliths fabricated in tips with embedded materials of choice are important in separation science. Polymeric backbone however interferes in the enrichment and thus affects efficiency. This work focuses on the in-tip fabrication of lanthanum oxide porous monolith and its application in the enrichment of phosphorylated peptides and lipids. Polycondensation reaction uses an aqueous solution of LaCl₃·7H₂O with N-methyl formamide as porogen and propylene oxide as initiator. The aging time of monolith and temperature condition for the reaction are optimized to attain porous monolithic tip. A comparison of (i) solid phase batch extraction using La₂O₃, (ii) La₂O₃ embedded in poly(glycidyl methacrylate (GMA)/divinylbenzene (DVB)) tip, and (iii) pure La₂O₃ monolithic tip shows improved enrichment efficiency in the case of pure La₂O₃ monolithic tip. The monolithic tip achieves selectivity of 1:4500 as compared to solid phase extraction (SPE)(1:3500) and limit of detection down to 0.25 fmol. The in-tip La₂O₃ monolith strategy has better batch to batch reproducibility, reduced time of enrichment, and ease of operation in comparison to solid phase batch extraction. The developed strategy enriches phospho- content from biological samples like phosvitin and lipovitellin from egg yolk and phospholipids/phosphopeptides from human serum. The enriched phospho- moieties are analyzed by matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) except the phospholipids where laser desorption ionization (LDI)-MS is employed.