One-pot synthesis of an amphoteric polydopamine-silica sorbent for solid-phase extraction of pharmaceuticals from water and urine.

Abstract

A polydopamine-silica (PDA-SiO2) hybrid sorbent was fabricated via a one-pot, base-catalyzed sol-gel condensation and oxidative polymerization strategy, employing dodecyltrimethylammonium bromide (DTAB) as a cationic surface texture-directing agent. Following thorough sequential washing to ensure complete DTAB removal, the final sorbent - comprising an APTES-grafted silica core (providing protonatable amine binding sites) enveloped by a conformal polydopamine shell (5-10 nm, offering π-π stacking, cation-π, and hydrogen bonding interaction pathways)-was systematically evaluated for the simultaneous preconcentration of acidic (naproxen, mefenamic acid) and basic (amitriptyline, tamoxifen) pharmaceuticals from tap water and simulated biological matrices. Material characterization by SEM, TEM, FT-IR, XPS, BET, and zeta potential confirmed a non-porous, solid-core architecture with an amphoteric surface charge profile (pHpzc = 5.98), which is substantially higher than that of unmodified silica (pHpzc ≈ 2-3), confirming successful APTES and PDA functionalization. Under optimized conditions (pH 7.0, 5.0% (w/v) NaCl, 10.0 mL sample volume), simultaneous quantitative retention of all four analytes was achieved. A pH-responsive sequential elution protocol - 0.1% formic acid in methanol for basic drugs, followed by 2% NH4OH in methanol for acidic drugs - delivered class-selective desorption with recoveries of 89-98% across both tap water and synthetic urine matrices. The method exhibited excellent linearity over 1.0-500 µg L-1 (R2 ≥ 0.9982), limits of detection of 0.1-0.3 µg L-1, and a theoretical enrichment factor of 20 (10.0 mL → 0.5 mL), with experimentally confirmed values of 18.2-19.6 across all analytes, and maintained quantitative performance (recovery >91%) over five of six consecutive extraction-regeneration cycles, with a marginal decline to 86-88% observed only in the sixth cycle. Validated in spiked tap water (92-98 %, RSD < 5%) and synthetic urine (89-97 %, RSD < 5 %), the method demonstrated robust anti-matrix interference capability.

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