Voltammetric determination of flufenamic acid and adsorption studies with biochar in the absence / presence of cetyltrimethylammonium bromide.

In this article, a novel method for the determination of Flufenamic acid (FFA, pharmaceutical pollutant) is presented based on voltammetric oxidation at a carbon paste electrode (CPE) in-situ modified with cetyltrimethylammonium bromide (CTAB). The experimentally proved "erosion effect" of this surfactant enhanced the sensitivity of detection in the SWASV mode allowing us to quantify the analyte down to the low nanomolar level (with a LOD of 5.5 × 10 mol L FFA). The respective (electro)analytical procedure has been shown to be applicable in monitoring the residua of FFA in model aqueous solutions simulating polluted and then purified industrial wastewater. Furthermore, the process of removal of FFA via adsorption onto selected carbonaceous materials was studied in detail, when two conventional active carbon adsorbents were compared with biochar (BC) - a cheaper alternative. It has been found that although the latter as such does not attain the adsorption capacities of both active carbons, in-situ modification of BC with CTAB enhances its adsorption capacity up to 40% (from 125 mg g to ca. 175 mg g), as well as fastens the adsorption process (3x); both under conditions of testing. When considering the final procedure for removal of residual pollutant from model water samples with BC and the method of choice for quantification of the corresponding change(s) of FFA before and after purification, the principal role of CTAB has been revealed and defined. Namely, the functioning of CTAB had, in fact, double benefit: (i) enhancement of adsorptive capabilities of the BC adsorbent and (ii) improved sensitivity of the voltammetric detection with in-situ modified CPE.