GB1426206A - Coulometric titrator - Google Patents

Abstract

1426206 Coulometric titration apparatus BRITISH PETROLEUM CO Ltd 8 May 1974 [21 May 1973] 24066/73 Heading G1N In a coulometric titration apparatus with electrolytic generation of titrant, the titration current comprises pulses containing a constant amount of electricity in addition to a uniform supplementary current and the supplementary current is a function of the impurity level in the apparatus prior to titration, when the apparatus is maintained in the end-point condition. One of the generating electrodes is preferably housed in a reagent containing compartment of the reaction cell separated from the remainder of the electrolyte by a porous or sintered glass partition. The apparatus is preferably used for the determination of water in organic substances using the Karl Fischer method and the current pulses are counted in an electro-mechanical counter as a measure of the water content. When water is present, the voltage between a pair of measuring electrodes is high. This voltage is amplified at Al, and fed to non linearly connected meter M and to comparator A 2 where it is compared with the end-point value. The resulting error signal is fed via potentiometer W to an output for an analogue recorder. It is also fed to voltage to frequency converter X, and then via isolating transformer Y to constant width pulse generator Z. These pulses switch constant current generator T, controlled by amplifier A3 to supply current pulses to the generating electrodes. The error voltage is also fed to the supplementary current control circuit via LEDs P and photo diodes Q. Between titrations switch S is closed and the voltage at the output of integrator A4, R C builds up until enough generating current is being supplied via T2 or T3 to maintain the apparatus at the titration end-point i.e. to compensate for impurities. During titration, switch S is opened, but this supplementary current is maintained because capacitor C has a very high discharge time.