Developments in chromato-polarography
Developments in chromato-polarography and the results obtained from its application to the analysis of mixtures of organic compounds are presented. The possibility of determining traces of organic impurities in organic substances by this technique is evaluated. The polarographic method is today one of the most important instrumental methods and has found wide application in analytical chemistry both of inorganic salts and also of organic compounds. When mixtures of different inorganic or organic compounds are present in the solution under test and have to be quantitatively evaluated, the problem is sometimes very difficult and complicated to solve, especially when there are present several ions or substances having similar electrochemical properties, i.e. the same or nearly the same half-wave reduction or oxidation potentials. When inorganic ions with the same or similar half-wave potentials are present, the problem can be quite easily solved by introducing complexing agents, which shift correspondingly the half-wave potentials of analysed substances, forming complexes of different stability. This procedure is usually not applicable in the case of mixtures of similar organic compounds, because they usually do not form analogous complexes having different electrochemical properties. This basic difficulty of polarography is especially important when homologues or isomers are present in the mixture, because such substances usually show identical or similar half-wave potentials. To solve the problem of quantitative separation and analysis of such mixtures it was necessary first to perform a preliminary separation of species and then perform polarographic analysis of these species. The way we have chosen was chromatographic separation using a 'liquid chromatogram' method combined with continuous polarographic detection of species eluted from the chromatographic column. Chromato-polarography is a method which combines the high sensitivity and other excellent properties of the dropping mercury electrode as detector —-such as the linear relationship between the diffusion current and the concentration of reducible substances—-with the high resolving power of the mixtures on the chromatographic column1. When the chromatographic column is filled with an adsorbent (e.g. alumina or an ion-exchange resin) characterized by a non-linear adsorption