Electrochemical Discrimination of Dihydroxybenzene Isomer at Different Thiols Self-Assembled Monolayers on Gold and Simultaneous Determination of Catechol and Hydroquinone

The discrimination effect of dihydroxybenzene isomer including catechol (CAT), hydroquinone (HQ) and resorcinol (RE) on bare gold, and a series of thiols self-assembled monolayers (SAMs) including mercaptohexanol (MCH), 6-mercaptohexanoic acid (MHA), mercaptoethylamine (MEA), thiol-modified double-stranded DNA (ds-DNA), single-stranded DNA (ss-DNA) is first investigated by cyclic voltammetry ( CV ) and linear scan voltammetry ( LSV ). Results show that CAT, HQ and RE can not be electrochemically discriminated simultaneously by bare gold or thiols SAMs based on their oxidation or reduction peaks. Furthermore, RE has a big interference on the electrochemical response of CAT and HQ. At acidic solution (pH 4.4), in presence of RE, CAT and HQ can not be discriminated on bare gold, ds-DNA or ss-DNA SAMs. However, CAT and HQ can be discriminated well at MCH, MHA, and MEA SAMs on gold based on the difference of reduction peak potentials (Δ E pc ) as 219, 212 and 165 mV respectively. MCH SAMs is chosen to study simultaneous determination of CAT and HQ due to bigger Δ E pc and current response. We fix the potential at 0.7 V for 60 s to enrich the oxidation products of CAT and HQ, then investigated the relationships of reduction peak current ( i pc ) with the concentrations of CAT and HQ. The i pc values are linear with the concentrations of CAT and HQ in the range of 7.0 × 10 −6 ∼1.04 × 10 −3 M. The limit of detection (LOD) is calculated to be 5.9 × 10 −7 M for CAT and 8.3 × 10 −7 M for HQ (S/N = 3). The MCH SAMs on gold is applied to the simultaneous determination of CAT and HQ in lake water sample and satisfactory result is obtained.