Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-IV Photometric titration of an acid

In Part I of this series, evaluation methods for potentiometric titrations of acids performed by stepwise addition of titrant were introduced. These methods are non-approximative and may therefore in principle be applied to titrations of acids of any strength. This paper demonstrates that photometric titrations performed by stepwise addition of titrant may also be evaluated by the proposed methods. The photometric method is compared with the potentiometric method of monitoring the course of a titration.     

Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-II Theory of titration of mixtures of acids, polyprotic acids, acids in mixture with weak bases, and ampholytes

A general method for evaluating titration data for mixtures of acids and for acids in mixture with weak bases is presented. Procedures are given that do not require absolute [H]-data, i.e., relative [H]-data may be used. In most cases a very rough calibration of the electrode system is enough. Further, for simple systems, very approximate values of the stability constants are sufficient. As examples, the titration of the following are treated in some detail: a mixture of two acids, a diprotic acid, an acid in presence of its conjugate base, and an ampholyte.     

An automated system for photometric titration by stepwise addition of equal volumes of titrant

A completely automatic system for photometric titrations is described. The system delivers measured volumes of sample, indicator solution and buffer solution, titrates and finally rinses the titration vessels. Titrations are performed by adding titrant stepwise in equal volumes to the sample, with measurement of absorbance after each addition. These results are used to calculate equivalence volumes. The system performs about 30 titrations per hour and has a loading capacity of 200 samples. It was tested by titrating calcium with EGTA in presence of calmagite as indicator.     

Acid-base titrations by stepwise additions of equal volumes of titrant with special reference to automatic titrations-I Theory, discussion of the gran functions, the hofstee method and two proposed methods for calculating equivalence volumes

The range of acid stability constants over which the Gran functions are applicable in evaluating acid-base titrations at normal concentrations is studied and found to be quite narrow. Alternatively, the titrations can be evaluated by using non-approximative methods based upon an equation that is derived without making the simplifying assumptions leading to the Gran functions. One such method, introduced by Hofstee, is discussed and the results of a study of the effects of a systematic error in the pH-determinations upon the determination of the equivalence volume are given. Two other non-approximative methods for evaluating acid-base titrations that are particularly suitable for use in automatic titrations of many similar samples are also described. These methods yield correct values of the equivalence volume regardless of a possible systematic error in the pH-values and are particularly useful for titrations of moderately strong and very weak acids (stability constants up to 10¹⁰–10¹¹ at 0.01M concentration) where the Gran functions cannot be used.