A Comparison Between Pulsed Sonovoltammetry and Low Power Laser Activated Voltammetry for the Electroanalysis of Ascorbic Acid in a Commercial Fruit Drink

A comparison is made between two ‘dual activation’ electroanalytical techniques for the detection and measurement of vitamin C (L-ascorbic acid) in a commercially available fruit drink via its two electron oxidation at platinum electrodes. Glucose is found not to interfere with the analytical response. First in sonovoltammetry pulses of 25 Wcm−2 are applied and the current response characterized in the ‘pulse off’ period where a current plateau is attained. Second in laser activated voltammetry a 10 Hz pulsed laser (532 nm, ca. 240 Wcm−2 average intensity) is used to ‘burn’ surface adsorbed passivating species off the electrode. Both methods cause agitation of the solution in the bulk phase or at the electrode-solution interface and lead to regular renewal of the diffusion layer. The mass transport limited oxidation currents so obtained are found to scale with ascorbic acid concentration in media where electroanalysis without simultaneous ultrasonic or laser stimulation may be precluded due to electrode passivation. Application to the quantitative electroanalysis of ascorbic acid in the fruit drinks Ribena and ‘No added sugar’ Ribena is reported. The results obtained are in excellent agreement with those yielded by independent chemical and electrochemical methods.