Consecutive titrations under non-equilibrium conditions. A new mode of automatic titration

摘要

A new mode of titration, 'the consecutive-monotonic mode', is based on measurements under non-equilibrium conditions, which permit the rapid completion of an individual titration. In spite of the non-equilibrium conditions, the consecutive titration is an absolute and accurate determination. This mode consists of a series of consecutive titrations performed in the same solution with monotonic addition of titrant. Each titration is discontinued at some time after the end point (the actual time is of no importance), a new portion of analyte is added to the cell and the titration is resumed. The end points of the titrations are usually delayed when equilibrium is slowly attained. The basic requirement is reproducibility in the delay, a condition fulfilled for many systems. About ten to twenty consecutive titrations can be performed in a single run with the same analyte from the same or different samples. The equivalence point is determined from the difference between two subsequent end points. In most cases, the duration of a single titration is 30-60 s and hundred titrations per hour are possible. Accuracy and precision obtained by this method are as good as for point-by-point titration. The fast titration rate permits performing redox titrations without removal of oxygen and acid/base titrations without removal of CO2. The amount of reagents and waste is considerably reduced. The instrumentation requirements are simple: a device for monotonic addition of titrant and a recording device. The consecutive-monotonic mode of titration overcomes problems like the slow response of the indicating electrode, of slow rate of the analyte/titrant reaction and of imperfect mass transport in the titrated solution in the vicinity of the end point. (C) 1997 Elsevier Science B.V.