Determination of α‐Lipoic acid on a Pyrolytic Graphite Electrode Modified with Cobalt Phthalocyanine

Abstract

In this work voltammetric techniques were explored for quantification of α‐Lipoic acid (ALA) using a pyrolytic graphite electrode modified with cobalt phthalocyanine. Cyclic voltammograms recorded in phosphate buffer solution containing 1×10−3 mol L−1 of ALA presented an oxidation peak located at +0.8 V vs. SCE. The modification of the electrode produced a 100 mV shift of the onset oxidation potential to less positive value and a substantial increase in the ALA oxidation current. Among the voltammetric techniques explored, differential pulse voltammetry showed the best performance for quantifications of the analyte in low concentrations. Limits of detection and quantification of ALA obtained corresponds to 3.4×10−9 mol L−1 and 1.2×10−8 mol L−1, respectively.

Easily Prepared Co3O4Doped Porous Carbon Material Decorated with Single‐wall Carbon Nanotubes Applied in Voltammetric Sensing of Antioxidant α‐lipoic Acid

“…As one can see from Figure 3 b, the electrochemical response at TPCo 3 O 4 &SWCNT@CPE was much better‐comparing electrodes made from commercial carbon powder itself or in a combination of SWCNT). The well‐defined anodic peak originated from the oxidation of α‐lipoic acid at new TPCo 3 O 4 CPE with or without SWCNT is evident from this figure, pointing out the possible catalytic effect of a certain amount of Co on lipoic oxidation, bearing in mind fact that cobalt phthalocyanine was used before for electrode modification [20].…”

“…The use of different electrode materials or modifiers can also cause different reaction mechanisms on the electrode surface. Although the reduction of α‐lipoic acid was recorded at a dropping mercury electrode and rotating disc electrode of mercury on gold [34], the irreversible oxidation of α‐lipoic acid at high anodic potentials was confirmed at the most of used electrodes (platinium and carbon based and a lot of modified electrodes [15–23]). Based on Tafel plot of CV recorded at scan rate of 25 mV/s (Figure 4b), with corresponding regression line E (V)=0.097 log I (A)+1.449 and Tafel slope of 97 mV (i. e.between 60 and 120 mV/dec), it was assumed that the electro‐oxidation occurs via an electrochemical–chemical (EC) mechanism, with the chemical determining step [35], similarly to previously reported results [17, 19].…”

“…LOD of the proposed method was better and once comparable in the most of reported articles where researchers have used electrodes from GC (5.75 μM and 1.8 μM), Pt (13.15 μM), fluorine‐doped tin oxide electrodes (3.68 μM), GCE modified with MWCNT (19 μM) and SnO 2 nanoparticles (0.13 μM)[15, 16, 17, 19, 21, 22], while the better LOD with a much smaller working range was reported at mercury electrode using adsorptive stripping anodic voltammetric technique (linear range of 0.050–0.90 μM and LOD of 0.012 μM [14]. It could be seen that only DPV and amperometric determinations at BDDE [18], more complicate pyrolytic graphite electrode modified with cobalt phthalocyanine [20] and more sensitive square‐wave anodic stripping voltammetry at screen‐printed graphene electrodes modified with manganese (IV) oxide [22] exceed validation method parameters obtained in this study. It is obvious that our electrode is comparable with the reported ones.…”

“…The electrochemical approach to LA quantification has significant advantages over other methods, not only in terms of simplicity, speed, and no‐expensive apparatus but primarily due to the elimination of limitations in real sample applications originating from the matrix. α‐Lipoic acid was determined at unmodified electrodes, mercury electrode [14], platinum electrode [15], glassy carbon [16, 17] boron‐doped diamond electrode [18], while for modification of LA sensitive electrodes were used: fluorine‐doped tin oxide [19], cobalt phthalocyanine at pyrolytic graphite [20], multi‐walled carbon nanotubes [21], SnO 2 nanoparticles and cetyltriphenylphosphonium bromide [22] and also manganese (IV) oxide on screen‐printed graphene electrodes [23].…”

Improvement of electrocatalytic effect in voltammetric sensors based on phthalocyanines

“…In classical works phthalocyanines are adsorbed directly to the electrode surface [24]. For instance, a graphite electrode modified with CoPc has been used to detect thiols and disulfides [24] or lipoic acid [25]. Carbon Paste Electrodes (CPEs) prepared by mixing graphite with a phthalocyanine and a mineral oil or an epoxy resin have been successfully used to detect phenols [26] amitrol [27] nitrites [28] or citric acid [29] among many others.…”