Pulsed voltammetric/amperometric detection of polycyclic aromatic sulfur heterocycles (PASHs) at the gold disc electrode
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ORIGINAL PAPER
Pulsed voltammetric/amperometric detection of polycyclic aromatic sulfur heterocycles (PASHs) at the gold disc electrode for studies in petroleum asphalts Patrícia Schmidt 1,2 & Rayane Bueno Goularte 2,3 & Rejane Secretti Cargnin 1,2 & Paulo C. Do Nascimento 1,2 & Leandro Machado de Carvalho 1,2 Received: 7 May 2020 / Revised: 27 May 2020 / Accepted: 29 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This work describes the voltammetric and amperometric behavior of a high number of PASHs (sulfides, thiophenes, benzothiophenes, dibenzothiophenes, indenothiophenes, naphtothiophenes, thienothiophenes, phenanthrothiophenes, and acenaphtothiophenes) at gold disc electrodes aiming at their identification and determination in petroleum asphalts. The adsorption/redox processes expected for sulfur compounds at gold electrodes could be observed in all the studied PASHs in DMSO and hydromethanolic medium. Differential pulse (DP) voltammetry in non-aqueous solutions (0.1 mol L−1 NaClO4 in DMSO) was approached for determining non-volatile PASHs in asphalts submitted to different aging processes. It was found herein that the DP voltammetric monitoring of PASH oxidation at + 0.7 V (vs. Ag/AgCl/LiCl 3 mol L−1) for virgin/aged asphalts can be used for the comparative study of asphalts based on the consumption of PASHs. Additionally, pulsed amperometric detection (PAD) in hydroalcoholic solution (10 mmol L−1 acetate buffer in 65% methanol) coupled with a chromatographic separation was approached for determining volatile PASHs in asphalts submitted to thermal decomposition processes. A detection cycle of 2 s involving oxidative (0.4 s at + 0.4 V) and reductive (1.2 s at − 1.0 V) cleaning pulses after a detection pulse of − 0.8 V (0.4 s) applied successively to the gold electrode (vs. Pd/PdO) was found to be optimal for regenerating the gold surface during successive chromatographic runs of PASHs. Thus, reversed-phase liquid chromatography (LC)–coupled PAD was found useful to separate a complex mixture of PASHs. The optimized PAD and LC separation was further applied to investigate the presence of electroactive PASHs as volatile compounds in asphalt fumes generated at 260 °C. Keywords Polycyclic aromatic sulfur heterocycles (PASHs) . Gold disc electrode . Pulsed amperometric detection . Pulse voltammetry . Petroleum asphalts
Introduction For many years, polycyclic aromatic sulfur compounds have been neglected in environmental analysis, whereas its nonThis work is dedicated to the 65th birthday of Professor Fritz Scholz (Institute for Biochemistry, University of Greifswald) * Leandro Machado de Carvalho [email protected] 1
Department of Chemistry, Federal University of Santa Maria (UFSM), PO Box 5051, Santa Maria, RS 97105-970, Brazil
2
Graduate Program in Chemistry, Federal University of Santa Maria (UFSM), Santa Maria, RS, Brazil
3
Graduate Program in Chemistry, Federal University of Santa Catarina (UFSC), Florianópolis, SC, Brazil
sulfur analogs (PAHs) were further investig
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