Electrochemically Assisted Injection in Combination with Capillary Electrophoresis-Mass Spectrometry (EAI-CE-MS) - Mechanistic and Quantitative Studies of the Reduction of 4-Nitrotoluene at Various Carbon-Based Screen-Printed Electrodes

• Published in: Electroanalysis (New York, N.Y.) Vol. 25; no. 1; pp. 117 - 122
• Main Authors: Palatzky, Peter, Zöpfl, Alexander, Hirsch, Thomas, Matysik, Frank-Michael
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.01.2013; WILEY‐VCH Verlag
• Subjects: Carbon; Carbon fibers; Electrodes; Electrophoresis; Electrophoresis, Graphene, Mass spectrometry, Nitroaromatic compounds, Screen‐printed electrode, Voltammetry; Graphene; Mass spectrometry; Nitroaromatic compounds; Oxides; Reduction; Screen-printed electrode; Separation; Voltammetry
• ISSN: 1040-0397; 1521-4109
• DOI: 10.1002/elan.201200393

Electrochemically assisted injection (EAI) is a recently introduced injection concept for capillary electrophoresis (CE) enabling the separation of neutral analytes by means of electrochemical generation of charged species during the injection process. EAI‐CE is particularly attractive in combination with mass spectrometry (MS) leading to enhanced performance of MS detection. In this work, a fully automated EAI injection device was developed and applied to mechanistic and quantitative studies of the reduction of 4‐nitrotoluene (4‐NT). Three different carbon‐based screen‐printed electrodes (SPEs) were used including unmodified carbon, carbon nanofiber and reduced graphene oxide SPEs. Under acidic conditions the main products of 4‐NT reduction were 4‐hydroxylaminotoluene (4‐HAT) and 4‐aminotoluene (4‐AT). The EAI‐CE‐MS approach enabled the separation and selective determination of both compounds. On the basis of this methodical concept it was possible to study the formation of reduction products of 4‐NT in dependence on electrode potential and electrode material. In contrast to conventional electrochemical techniques like cyclic voltammetry EAI‐CE‐MS provides detailed information regarding changes of the product composition in dependence on various experimental conditions. Over the complete potential range studied the ratio of 4‐HAT/4‐AT was clearly different for the reduced graphene oxide SPE compared to the unmodified carbon and carbon fiber SPE. The construction of mass voltammograms added considerably to the information content of voltammetric experiments. Another aspect of this work was the reliable quantitative determination of 4‐NT by EAI‐CE‐MS using isotopically labeled 4‐NT as an internal standard. In this way the “classical” problem of changing response characteristics at solid electrodes could be eliminated based on the assumption that the target analyte and its isotopically labeled form behave in the same way. A corresponding protocol for quantitative EAI‐CE‐MS determinations of 4‐NT was elaborated and applied to standard solutions and spiked soil samples.