Speciation of copper by using a new fullerene derivative as a mixed-mode sorbent

Abstract

A new fullerene derivative was synthesized by photochemical reaction of C₆₀ fullerene and rubeanic acid in a toluene–ethanol medium. The synthetic procedure was optimized by UV–visible spectroscopy, using the spectrum for C₆₀ fullerene as reference; C₆₀–rubeanic acid derivative, a novel adduct of C₆₀ fullerene, exhibits an increased absorption band between 425 and 500 nm corresponding to the maximum absorption of rubeanic acid. The dark brown solid obtained was characterized by elemental analysis, and XRD and solid state ¹³C CP–MAS NMR spectroscopies. The band observed at 61.8 ppm is typical of sp³ atoms in the modified fullerene that forms by addition of amines to double bonds in fullerene, which bond covalently to the rubeanic acid group to form a monoadduct. The C₆₀–rubeanic acid derivative can thus be used as a mixed-mode sorbent material for the speciation of cationic and neutral species. The adsorptive potential of the new derivative as a model for the preconcentration of copper traces on the pendant group of rubeanic acid, and neutral copper complexes (e.g. the pesticide copper oxinate) on the fullerene core has for the first time been assessed in this work. Both species are initially retained by the derivative and subsequently discriminated by sequential elution with various reagents. The proposed automatic method can accurately resolve mixtures of both types of copper species in ratios from 1 : 17 to 17 : 1 with relative errors less than 7%.