Biphasic sonoelectroanalysis: Simultaneous extraction from, and determination of vanillin in food flavoring

Biphasic sonoelectroanalysis is employed in the detection of vanillin (4-hy droxy-3-methoxybenzaldehyde). Ethyl acetoacetate is characterized as an ele ctrochemical and sonoelectrochemical solvent and it is shown that quantitat ive electrochemical measurements can be made in this solvent of relatively low dielectric constant. The electrochemical oxidation of vanillin in this medium is shown to give oxidative linear sweep voltammetric signals sensiti ve to microadditions. In addition, the near reversible kinetics of vanillin in ethyl acetoacetate facilitate sensitive square-wave voltammetry. Electr ode passivation leads to typically diminishing peak heights for the same co ncentration of vanillin, but by employing ultrasound between each scan, pea k heights are maintained by quantitative depassivation of the electrode sur face. Microadditions of 0.05 mM vanillin to ethyl acetoacetate yield a line ar calibration plot with r = 0.9987 and a detection limit of 0.016 mM. The determination of vanillin in natural vanilla essence is then achieved by th e exploitation of biphasic sonoelectrovoltammetry in aqueous ethanolic vani lla pod extract and ethyl acetoacetate. In contrast with silent voltammetry , ultrasound facilitates emulsification and extraction of vanillin in the e xtract permitting an analytical square-wave voltammetric signal to be obtai ned. Microadditions to two separate samples of vanilla essence facilitate q uantification of vanillin in the extract. Close agreement with a blind anal ysis of the samples using HPLC-UV is observed with a limit of detection in the biphasic medium of 0.020 mM. Biphasic sonoelectroanalysis removes the n eed for sample degradation or a separation step, which would lengthen and c omplicate the analytical protocol. It can therefore be concluded that bipha sic sonoelectroanalysis demonstrates an attractive alternative to currently accepted techniques.