Determination Of Taurine By Coulometric Titration

Taurine is a sulfonic non-protein amino acid,and it has many physiological effects.Therefor,it gets a wide application in food,clinical medicine,cosmetic and so on.Though many effective analytical methods have been applied to determine the content of taurine,all of these methods have their own limitation,and don't have the characteristics of fast,simple,high degree of automation and satisfactory accuracy.The coulometric titration method was first proposed for the analysis of the content of taurine.The routine coulometric titration and the ethanol-aqueous system coulometric titration were successively developed.At the same time,the dissociation constant of taurine in aqueous solution and ethanol-aqueous solution were studied.Firstly,the dissociation constant of taurine in aqueous solution and ethanol-aqueous solution in different proportion were studied.The pH value of taurine solution was determined by potentiometric titration method,and then the dissociation constant of taurine was calculated based on the Br?nsted-Lowry acid-base theory.In aqueous solution,the first dissociation constant was 1.20,and the second dissociation constant was 8.86,which is closed to the literature value,thus indicated the validation of the method.The dissociation constant of taurine in different ratio of ethanol-aqueous solution was also determined.In 50%ethanol-aqueous solution,the pK_a1 of taurine was determined to be 1.96,pK_a2 was8.55,the effect of ethanol for dissociation of taurine was discussed in detail.It also provides a theoretical basis for the accurate determination of taurine in ethanol-aqueous system by coulometric titration.Because taurine is a weak acid,direct titration would lead to a poor precision.The formaldehyde was used in the routine coulometric titration to release the H⁺of taurine,then the H⁺reacted with the OH^-generated by cathode electrode until the titration end-point.The content of taurine could be obtained by Faraday's law.Hydrochloric acid standard solution was selected as the object to study the basic electrolytic conditions,such as species and concentration of sustainable electrolyte,constant current strength and so on.The pH of end-point,the addition amount of formaldehyde and the react time of formaldehyde and taurine were also studied to decide the optimum.The results showed that the determinations of 3 taurine samples by coulometric titration were agreed well with the potentiometric titration,which is recommended by the Chinese Pharmacopoeia.The relative standard deviations were less than 0.38%,and the recoveries of the method were between 99.42%¹00.4%,which indicated high precision and accuracy.The whole process could be completed automatically in 10 minutes.This method was quick,convenient,highly automatic,and had satisfactory precision and accuracy.In order to overcome a series of problems brought by formaldehyde,and taking the experimenter and environment into consideration,the ethanol-aqueous system coulometric titration was proposed.Based on the above basic electrolytic conditions,the species and amount of organic solvent,pretreatment of glass electrodes,and the pH of end-point were studied to decide the optimum.The stability experiment,interference experiment and the current efficiency verification experiment were developed to prove the robustness of this method.The recoveries of the method were between 99.21%⁹9.67%,the relative standard deviations were less than 0.56%.The results of 3 taurine samples were agreed well with potentiometric titration and HPLC,and precision of the method was better.