A Simple Sensor for Determining the pH of Solutions
Abstract Generated abstract
This paper describes a simple electrochemical sensor for approximate pH determination using pairs of solid electrodes without liquid junctions. Measurements showed that nickel, graphite, silicon carbide, and stainless steel electrodes maintain nearly constant potentials over a middle pH range, while tungsten, antimony, and some other electrodes exhibit potentials that vary linearly with pH. On this basis, several two-electrode sensors, such as tungsten with silicon carbide, nickel, graphite, or stainless steel, were tested and found to preserve a linear emf response over specified pH intervals with moderate deviations. The authors suggest that the low-resistance, simple design can be read with a suitable millivoltmeter and may be applicable for approximate pH assessment of food products.
Full Text
N. V. Podbornov, V. N. Titov
A SIMPLE SENSOR FOR DETERMINING THE pH OF SOLUTIONS
(Presented by the scientific seminar of the departments)
By measuring the potentials of various electrodes in solutions, it was found that electrodes made of nickel, graphite, silicon carbide, and stainless steel in the middle pH range have a constant potential value and do not change with changes in the pH of the solution. Thus, an electrode made of silicon carbide in solutions containing calcium and potassium cations and the anions of hydrochloric and sulfuric acids has a potential, relative to a calomel electrode, equal to 310 mV when the pH changes from 3.0 to 10.0. Changes in potential due to changes in the concentration of cations and anions and a number of other factors did not exceed 40 mV.
The potentials of antimony, tungsten, and a number of other electrodes vary linearly with changes in the pH of the solution. This served as the basis for creating sensors of simple design. The sensor consisted of two solid electrodes without any liquid connections—for example, a tungsten electrode and a stainless-steel electrode. Tests of such sensors in solutions (see the table) showed that they can be used for an approximate assessment of pH.
Table 1
| No. | Sensor electrodes | pH limits within which the linear dependence of emf on pH is preserved | Slope angle of the line | Absolute deviations of experimental points from the line |
|---|---|---|---|---|
| 1 | Tungsten–silicon carbide | 3.5–9 | 27 | 20 |
| 2 | Tungsten–nickel | 3.5–6 | 100 | 80 |
| 3 | Tungsten–graphite | 4.5–6.5 | 200 | 90 |
| 4 | Tungsten–stainless steel | 3–8 | 65 | 70 |
In the experiments, the pH of the solutions was measured with an LP-58 instrument (with a glass electrode), and the emf was measured with a vacuum-tube potentiometer; however, owing to the low resistance of the sensor, a millivoltmeter with increased input resistance may be used. During operation of such a sensor, no products harmful to the organism are formed; therefore it can be used to assess the pH of food products.