A Contactless Impedance Probe for Simple and Rapid Determination of the Ratio of Liquids with Different Permittivities in Binary Mixtures

Abstract

Simple contactless cells with planar or tubular electrodes have been designed for measurement of the permittivity of solutions. The cells, connected to an integrated circuit of astable multivibrator, respond primarily to the capacitance component of the cell impedance, the multivibrator frequency depends in a defined manner on the solution permittivity and is readily used as the analytical signal in determinations of the ratios of components in binary liquid mixtures; water solution of methanol, ethanol and dioxane have been tested. The response of the cell with planar electrodes satisfies well the simple theoretical model and both the cells provide results with a sufficient sensitivity, a low LOD value (units of %vol) and a good precision (around 1%rel). The cell simplicity, small dimensions, long-term stability and the possibility of powering them from a battery make them suitable for hand-held meters. As an example of application in practice, the content of ethanol was determined in the car fuel petrol.

Capacitively coupled contactless conductivity detection for microseparation techniques – recent developments

“…Total organic carbon was determined by Tian and Dasgupta 112 also after conversion to CO 2 using a sequential injection analysis system and a detector similar to a C 4 D. Opekar et al . 113 used a contactless impedance probe for the determination of the composition of binary mixtures of solvents with different permittivity. Ghaini et al .…”

Contactless Impedance Sensors and Their Application to Flow Measurements

“…The analytical signal is then represented by the multivibrator frequency. This type of detector has been used for determinations of organic solvents in binary mixtures [35,36]. This approach permits extremely simple, rapid and cheap analyses of binary liquid mixtures; however, it suffers from a serious limitation in that the overall electric conductivity of the mixture must be low, as has already been mentioned above.…”

Some Possibilities and Limitations of Contactless Impedimetric Determinations of Organic Liquids in Aqueous Solutions. The Interference from Ionic Compounds

“…The insulating layer thickness, l , equalled 0.24 mm (the epoxy and glass, 0.12 mm each). The cell is depicted in 5. For the electric equivalent circuit of the cell see Figure 1A; the C x values are the capacities between the metal electrodes and the test solution, the glass and epoxy constituting the dielectric, the C i value is the capacitance between the electrodes (the test solution being the “dielectric”) and R i is the ohmic resistance between the electrodes, depending on the solution conductivity.…”

“…5 that detector cell designs making the capacitance component the predominating signal factor can also be readily used in batch analyses. A detection cell of this type, combined with a simple electronic circuitry, has been successfully applied 5 to batch determinations of organic solvents in aqueous solutions. These practically attractive, extremely simple, rapid and cheap analyses of binary liquid mixtures (e.g., dioxane in water, ethanol in car petrol, etc.)…”