CONSECUTIVE TITRATIONS UNDER NONEQUILIBRIUM CONDITIONS - A NEW MODE OF AUTOMATIC TITRATION

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-equilibriu m conditions, the consecutive titration is an absolute and accurate de termination. This mode consists of a series of consecutive titrations performed in the same solution with monotonic addition of titrant. Eac h titration is discontinued at some time after the end point (the actu al 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 a re usually delayed when equilibrium is slowly attained. The basic requ irement is reproducibility in the delay, a condition fulfilled for man y systems. About ten to twenty consecutive titrations can be performed in a single run with the same analyte from the same or different samp les. The equivalence point is determined from the difference between t wo subsequent end points. In most cases, the duration of a single titr ation is 30-60 s and hundred titrations per hour are possible. Accurac y and precision obtained by this method are as good as for point-by-po int titration. The fast titration rate permits performing redox titrat ions without removal of oxygen and acid/base titrations without remova l of CO2. The amount of reagents and waste is considerably reduced. Th e instrumentation requirements are simple: a device for monotonic addi tion of titrant and a recording device. The consecutive-monotonic mode of titration overcomes problems like the slow response of the indicat ing electrode, of slow rate of the analyte/titrant reaction and of imp erfect mass transport in the titrated solution in the vicinity of the end point. (C) 1997 Elsevier Science B.V.