Titration of strong and weak acids by sequential injection analysis technique

A sequential injection analysis (SIA) titration method has been developed f or acid-base titrations. Strong and weak acids in different concentration r anges have been titrated with a strong base. The method is based on sequent ial aspiration of an acidic sample zone and only one zone of the base into a carrier stream of distilled water. On their way to the detector, the samp le and the reagent zones are partially mixed due to the dispersion and ther eby the base is partially neutralised by the acid. The base zone contains t he indicator. An LED-spectrophotometer is used as detector. It senses the c olour of the unneutralised base and the signal is recorded as a typical SIA peak. The peak area of the unreacted base was found to be proportional to the logarithm of the acid concentration. Calibration curves with good linea rity were obtained for a strong acid in the concentration ranges of 10(-4)- 10(-2) and 0.1-3 M. Automatic sample dilution was implemented when sulphuri c acid at concentration of 6-13 M was titrated. For a weak acid, i.e. aceti c acid, a linear calibration curve was obtained in the range of 3 x 10(-4)- 8 x 10(-2) M. By changing the volumes of the injected sample and the reagen t, different acids as well as different concentration ranges of the acids c an be titrated without any other adjustments in the SIA manifold or the tit ration protocol. (C) 2000 Elsevier Science B.V. All rights reserved.