An automatic digital thermometric titrator

Abstract

An apparatus is described for carrying out volumetric analysis wherein the cessation of heat change indicates the equivalence-point. Titrant is added a t constant rate to the titrand so that the voltage output of a thermistor temperature transducer varies linearly with time up to the equivalence-point. The voltage change is electronically differentiated to give a square wave of time period equal to the titre. A timing counter is automatically started at the origin of this square wave and stopped when it begins to decline. The titre is thus given in a digital form. The titrator will operate with titrations giving rates of temperature change greater than 0.01" C per second, and results are given for several different titrations.

Advanced undergraduate experiments in thermoanalytical chemistry

“…Thermometric titrimetry is dramatically more versatile than volumetric analysis and titrations are possible using this technique that give no discernible endpoint using a colorimetric indicator. Some thermometric titrimetry applications are the analytical determination of acids (11), bases (12), a mixture of Ca2+/Mg2+ using EDTA as titrant (id), Clũ sing Ag+ as titrant (14), a polybasic acid such as H3PO4 (12), a mixture of Hg22+/Hg2+ using C2042as titrant (15), Fe2+ using Ce4+ as titrant (16), Ag+ using CNas titrant (17). Titrations in molten salt solvents are also possible, for example the titration of Clwith Ag+ in molten LiNOa/ KNO3 eutectic at 431 K (18).…”

Apparatus for Automatic End Point Determination in Thermometric Titrations

“…RIESTLEY (1) has deqcribed an instrument for P the automatic deterbination of end points in routine thermometric titrations. This paper reports the details of an apparatus for the same purpose constructed using, for the most part, equipment already in svrvice in our laboratory.…”

“…The apparatus is capable of detecting end points for a fairly wide variety of titration curve (enthalpogram shapes and appears to be satisfactory for routine analyses, such as those involve d in control procedures. RIESTLEY (1) has deqcribed an instrument for P the automatic deterbination of end points in routine thermometric titrations. This paper reports the details of an apparatus for the same purpose constructed using, for the most part, equipment already in svrvice in our laboratory.…”

“…Similarly, a thirdderivative enthalpogram resembles a secondderivative potentiogram, in that the end point corresponds to the poiqt where the curve crosses the abscissa after an iniiial rise. The instrument described by Priestley (1) utilizes the first derivative of the potential across a thermistor to locate the end point, whereas the apparatus described in this report uses the third derivative of the imbalance potential of a Wheatstone bridge, one arm of which is a thermistor. Derivative thermometric titrations have been described by Zenchelsky and Segatto (4).…”