Combining voltammetry with HPLC: application to electro-oxidation of glycerol.

The combination of cyclic voltammetry and "online" chromatographic techniques for product detection is limited by the typically long analysis times in chromatographic columns. Therefore, traditionally, product analysis is performed offline after long bulk electrolysis experiments. To overcome the limitation of the inherently different time scales of voltammetry and high-performance liquid chromatography (HPLC), we suggest here to adopt rapid online sample collection with a micrometer-sized sampling tip placed close to the working electrode, followed by offline analysis of the sample fractions in an HPLC system. To demonstrate this concept, we applied online fraction collection and offline HPLC analysis to the glycerol electro-oxidation on Au and Pt electrodes in alkaline media and show that we can successfully follow the concentration changes of glycerol and its reaction products in good correspondence with the current profile obtained simultaneously with voltammetry. Moreover, the method allows for a detailed discrimination of the different mechanisms of glycerol oxidation on both electrodes. Therefore, this simple approach enables the monitoring of soluble reaction products during voltammetry with an HPLC system and thereby allows for new insights into the mechanisms of complex multistep electrode reactions.