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 t echniques for the detection and measurement of vitamin C (L-ascorbic a cid) in a commercially available fruit drink via its two electron oxid ation at platinum electrodes. Glucose is found not to interfere with t he 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, fa. 240 Wcm(-2) average inte nsity) is used to 'burn' surface adsorbed passivating species off the electrode. Both methods cause agitation of the solution in the bulk ph ase 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 me dia where electroanalysis without simultaneous ultrasonic or laser sti mulation 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.