Cationic amine-bridged periodic mesoporous organosilica materials for off-line solid-phase extraction of phenoxy acid herbicides from water samples prior to their simultaneous enantiomeric determination by capillary electrophoresis

Abstract

Two novel materials based on periodic mesoporous organosilica (PMO) with cationic amine-bridged ligands, (styrylmethyl)bis(triethoxysilylpropyl)ammonium chloride (PMO-STPA) and bis(3-triethoxysilylpropyl)amine (PMO-TEPA), were synthesized in this work to obtain materials with reverse-phase/strong anionic exchange mixed-mode or strong anionic exchange retention mechanism, respectively. The resulting materials were comprehensively characterized and showed functionalization with cationic amine-bridged ligands, and values of surface areas characteristic of mesoporous materials (higher than 100m²/g). These materials were evaluated for the off-line solid-phase extraction (SPE) of a mixture of six phenoxy acid herbicides (fenoprop, mecoprop, dichlorprop, 2-(4-chlorophenoxy)propionic acid (4-CPPA), 2-(3-chlorophenoxy)propionic acid (3-CPPA), 2-phenoxypropionic acid (2-PPA)) from water samples previous to their analysis by CE with diode-array detection using a dual chiral selector system (20mM of heptakis(2,3,6-tri-O-methyl)-β-CD (TM-β-CD) and 7mM of (2-hydroxypropyl)-β-CD (HP-β-CD) dissolved in 50mM phosphate buffer, pH 7.0) which enabled the simultaneous enantiomeric separation of the six phenoxy acid herbicides in 11min. SPE parameters were optimized and recoveries obtained for PMO-STPA and PMO-TEPA sorbents were compared. Under the optimized conditions, it was demonstrated that using 100mg of PMO-STPA sorbent, a maximum preconcentration factor (PF) of 1500 was achieved with 750mL of standard solution, allowing recoveries between 75.5 and 112.2%, with good repeatability (RSD=1.9-8.7%, n=6). Analytical characteristics of the method were evaluated in terms of precision, linearity and accuracy with method quantitation limits (MQL) between 0.4 and 14.3μg/L. The developed method was applied to the analysis of river samples and effluents from wastewater treatment plants, with recoveries ranging from 78.3 to 107.5%.

Keywords: Capillary electrophoresis; Cationic amine-bridged ligands; Chiral phenoxy acid herbicides; Periodic mesoporous organosilica; Simultaneous enantioseparation; Solid-phase extraction.