Electrochemical determination of α-lipoic acid in human serum at platinum electrode

• The oxidation of lipoic acid (LA) at Pt and GC electrodes was investigated.
• The influence of pH and NaCl was established.
• The linear response range is from 50 to 800 μM LA.
• The limit of detection is 4.07 μM LA.
• A voltammetric method for LA determination in human serum was developed.

The voltammetric determination of α-lipoic acid (LA) in human serum was performed at platinum (Pt) electrode in acetate buffer solution. The influence of chloride ions on the electrochemical oxidation of LA was also investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in buffered aqueous solutions at both Pt and glassy carbon (GCE) electrodes. Pt electrode showed a better electrocatalytic activity related to LA oxidation unlike GCE. The electrochemical oxidation of LA at Pt electrode is a pH-dependent irreversible process involving the transfer of one electron and one proton and also is NaCl-promoted near to neutral pH. The anodic peak current from 0.55 V increases linearly with LA concentrations ranging from 10 to 800 μM at pH 4.5, the limit of detection (LD, determined by using the 3s/b criterion, where s is the standard deviation of the blank signal and b is the slope of the calibration plot) being of 13.15 μM. The LA determination in human serum samples was performed by DPV at Pt electrode in acetate buffer solution with no interference from ascorbic acid (AA), dopamine (DA) and uric acid UA). The LA amount in human serum was determined to be 15 μM, with the coefficient of variation of 1.51%.