High-frequency oscillators for detection of end-points in volumetric chemical reactions were first used as early as 1938 in the laboratories of the Agricultural and Mechanical College of Texas [1]. When a high-frequency (radio-frequency) electromagnetic field is applied to an electrolyte solution there are an absorption of energy and a change in dielectric constant of the solution, as predicted by Debye and Falkenhagen and as shown experimentally by several workers [2]. The absorption of energy and the dielectric constant are also functions of the concentration at a particular frequency. When the electrolytic solution loads many types of high-frequency oscillators, the change in dielectric constant causes a change of frequency of the oscillator. The change of frequency of an oscillator due to the change of the electrolyte solution composition could be used to follow the titration process. For example, the frequency change plotted vs. volume of the added titration agent represents a titration curve. Maximum changes of the measured frequency occurred near the titration end-point, thus allowing to detect the end-point of the titration. Acid-base reactions, precipitation reactions, complex formation reactions and redox reactions were studied using high-frequency titration techniques.

Examples of the high-frequency titrators are shown below:

High-frequency oscillator-type titrometer [1] is shown in Figure 1.
 

Figure 1: High-frequency oscillator-type titrometer.

30-MHz Titrometer [2] is shown in Figure 2.
 

(A)

(B)(C)

Figure 2: (A) 30-MHz Titrometer. (B) Condenser unit and titration cell. (C) Coaxial junction on condenser unit for titration cell.

References:
1. K. Anderson, E.S. Betts, D. Revinson, Anal. Chem., 22, 743 (1950).
2. W.J. Blaedel, H.V. Malmstadt, Anal. Chem., 22, 734, (1950).