Towards the rational design of N-(1,3-dimethylbutyl)-N′-phenyl-1,4-benzenediamine (6PPD) electrochemical sensor†

Abstract

N-(1,3-Dimethylbutyl)-N′-phenyl-1,4-benzenediamine (6PPD) is a common additive in tires. 6PPD protects rubber from oxidative damage by ozone. Leaching of 6PPD in the environment leads to the formation of harmful byproducts such as 6PPD quinone. In this work we provide the fundamental basis for the detection of 6PPD by electrochemical techniques. We use cyclic voltammetry to study the adsorption of 6PPD on glassy carbon. We show that adsorbed 6PPD can be reversibly oxidized and reduced without disturbing the adsorption process. This result enables repeated electrochemical titrations. We determine, in neutral condition at 22 °C, an adsorption constant of K_ads = 1.2 ± 0.5 μM⁻¹ and kinetics of adsorption k_ads∈[0.74–5.60] × 10⁴ L mol⁻¹ s⁻¹. Based on this knowledge we demonstrate the lowest concentration of 6PPD ever detected electrochemically, 10 nM. We also identify current challenges for electrochemical sensing of 6PPD. Multiple layers are formed at concentrations above 4.6 μM and the slow kinetics of adsorption requires long (hour) measurement time to reach maximum sensitivity.