Electroanalytical studies of dyes

Acid and basic dyes and food colours have been determined by electroanalytical techniques, i.e., amperometric titration, potentiometry using ion selective electrodes developed here, and differential pulse polarography. Several procedures for the determination of the food colours Sunset Yellow FCF and Tartrazine in sparkling orangeade, Green S and Tartrazine in sparkling limeade, Amaranth and Green S in blackcurrant health drink, and Chocolate Brown HT, Green S and Tartrazine in sparkling dandelion & burdock have been developed by differential pulse polarography in Britton-Robinson buffer. Tetraphenylphosphonium chloride removes the large polarographic maximum obtained with Tartrazine at pH values greater than 4 and causes the peak potential of the colour to be shifted towards more negative potentials. The addition of tetramethylammonium chloride improves the polarographic baseline for the peaks of colours by suppressing polarographic maxima. The food colours in each drink could be simultaneously determined by the control of pH in addition to the use of tetraphenylphosphonium chloride. PVC and liquid state ion-selective electrodes have been developed for the determination of acid and basic dyes. The electrodes are based on basic dye 12-tungstosilicate, basic dye tetraphenylborate, tetraphenylphosphonium 12-tungstosilicate, quinoline phosphomolybdate and CI Basic Orange 30:1-Reineckate. PVC electrodes based on Crystal Violet tetraphenylborate and tetraphenylphosphonium 12-tungstosilicate have produced satisfactory results for the potentiometric titration of several acid dyes with Crystal Violet and basic dyes with sodium tetraphenylborate. The response of the electrodes was sufficiently fast that the electrodes could be used in connection with an automatic titrator. In general, the slope factor of these PVC electrodes was Nernstian, but it gradually decreased with time. Liquid state electrodes using a natural rubber membrane containing Crystal Violet 12-tungstosilicate or Crystal Violet tetraphenylborate as active material dissolved in o-dichlorobenzene have also been applied successfully to the potentiometric titration of dyes. The life of these electrodes is relatively long because of their easy regeneration. Amperometric titration employing differential pulse polarography showed a promising applicability for the determination of dyes. The end points for the titration curves of acid dyes with a standard Crystal Violet solution and basic dyes with a sodium tetraphenylborate solution were easily determined by a simple graphical method. The high solubility of the precipitate formed causes the curves to be rounded and also the end point to be reached late.