Multipoint immobilization of papain via its inert centre offers an attune pH extractor: selective separation of CH3Hg+ from inorganic mercurials in aqueous admixtures using extractor's cystine residues.

Without any pre-traetment, the selective separation of CH3Hg+ from Hg22+ and Hg2+, in aqueous admixtures is a long-pending issue; herein, is harnessed with solid-phase extraction using 'silica-gel immobilized papain', {Si(OSi)4 (H2O)x}n{OSi(CH3)2-O-C6H2(NN+)3(papain)}4.yH2O; where, x(0.3), n(1057) and y(2677) (determined instrumentally). The enriched diazo-groups couple the enzyme via multipoint mode, that occurs at the inert centre, the O‑carbon relative to tyrosine's phenolic-OH, wherein the hard-soft binding capacity of sulphur containing protein-groups involves in sorption restore the status quo. The enzyme remains bonded up to 90 cycles, with a performance 88% to the initial. The papain's cystine residues (302 μM.g-1) quantitatively extract the various Hg-species at pH 3.25 with a high breakthrough capacity [BTC μmol.g-1; Hg22+(287), Hg2+(297), CH3Hg+(268)] and were selectively stripped with thiourea (10 μg.mL-1) to attain a good preconcentration factor (PF: 17). The CH3Hg+ was selectively separated from two critical binary aqueous admixtures, CH3Hg+-Hg22+ and CH3Hg+-Hg2+, through isocratic stripping using thiourea (10 μg mL-1) as an elluent; wherein, the recovery for each Hg-species was quantitative (93 ± 2%). The material was stable at a heating flux of 343 K and endured mineral acids up to 4 mol.L-1; eventually, the extractor's sorption efficiency ζ⁎(thermal/chemical), the ratio, BTCtreated/BTCuntreated for CH3Hg+ was close to unity (0.92 ± 0.05), indicating the restoration of qualitative extraction quality. The sorption selectivity for CH3Hg+ was slightly compromised by the stress of real water (ground water: 86% and irrigation water: 70%) and biological samples (pineapple juice: 62% and cow urine: 67%).