Electrochemical behaviour of some naturally occurring hydroxy derivatives of 9,10-anthraquinone in chloroform at mercury and glassy carbon electrodes: application of AC polarography to the analysis of rhubarb roots

Electrochemical behaviour of some naturally occurring hydroxy derivatives of 9,10-anthraquinone such as chrysophanic acid (Ch), rhein (Rh) and emodin (Em) at mercury and glassy carbon electrodes using two different supporting electrolytes in chloroform is described. In the presence of piperidinium perchlorate (0.75M) + piperidine (0.25M) as a suitable acid supporting electrolyte, the reduction of Ch and Rh was a reversible two-electron process without complicating chemical reactions or adsorption phenomena, but the reduction process of these compounds in the presence of tetrabutylammonium perchlorate (TBAP) 0.5M + 5% acetic acid (AcOH) in chloroform was quasi-reversible. In both supporting electrolytes the overall reduction process of Em was irreversible. In the AC polarography and DP voltammetry at a GC electrode, the detection limit for Ch, Rh and Em was acceptably low and the relative standard deviation for the determination of 5 x 10(-6)M level, never exceeded 2%. AC polarography has been used for the determination of Ch and Em in a local rhubarb sample after extraction into chloroform and separation by column chromatography.