RU2003113035A - METHOD FOR MEASURING ION ACTIVITY IN SOLUTIONS AND DEVICE FOR ITS IMPLEMENTATION - Google Patents

Claims (2)

1. The method of measuring the activity of ions in solutions, namely, that an ion-selective field effect transistor, an auxiliary electrode and a temperature sensor are placed on the surface of the ion-selective membrane of the field-effect transistor in the electrolyte under study, the potential is measured from the source of the ion-selective field-effect transistor, by which the desired activity is found, which differs the fact that additionally measure the temperature of the auxiliary electrode, and the desired ion activity is found by the ratio

where T ₁ is the temperature on the surface of the ion-selective membrane; V _D is the voltage at the drain of an ion-selective field effect transistor; I _D is the channel current; V _SD is the potential difference between the input and output of the ion-selective field effect transistor; L is the length of the channel; Z is the width of the channel; d is the thickness of the dielectric; z _i is the charge of the controlled ion in units of the proton charge;

- the relative dielectric constant of the dielectric under the control electrode; N _D is the concentration of donor impurities; a ' _j is the activity of the interfering ion in solution; F is the Faraday number; R is the universal gas constant; k is the Boltzmann constant; E - EMF of the electrochemical circuit; In - experimental coefficient; E _G (0) - the value of the band gap extrapolated to T = 0; TO $\genfrac{}{}{0ex}{}{\text{Pot}}{\text{i, j}}$ - coefficient of potentiometric selectivity; j is the index of the interfering ion; μ _n is the mobility of charge carriers, determined by the ratio

where μ _st is expressed as

Q _s is the charge in the channel, which is calculated by the dependence

E ₀ (T ₂ ) is the standard potential of the auxiliary electrode at the temperature of the electrode T ₂ , for example, for a silver chloride electrode calculated according to E _O (T ₂ ) = 0.22239-645.52 · 10 ^-6 · (T ₂ -298.15) -3.284 · 10 ^-6 · (T ₂ -298.15) ² + 9.948 · 10 ^-9 (T ₂ -298.15) ³ . 2. A device for measuring the activity of ions in solutions, containing an auxiliary electrode, an indicator ion-selective field-effect transistor, and a temperature sensor of the membrane of an ion-selective field-effect transistor, placed in the test solution, an operational amplifier constructed according to a compensation circuit, whose inverting input is connected to the drain of the ion-selective field-effect transistor, and the output is connected to the source of the ion-selective field-effect transistor, a resistor connecting the source of the ion-selective field-effect transistor and non-inv the rotary input of the operational amplifier, three current sources, the first and second are respectively connected to the inverting and non-inverting inputs of the operational amplifier, and the third is connected to the output of the operational amplifier, the voltage source, the first output of which is connected to the first and second current source, the second output to the third current source and the third output is connected to the auxiliary electrode, a switch, the two inputs of which are connected to the drain and the source of the ion-selective field-effect transistor, and the third and fourth inputs with sensing the outputs of the temperature sensor, a second amplifier, the input of which is connected to the output of the switch, an analog-to-digital converter, the input of which is connected to the output of the second amplifier, a microprocessor, a control unit, an indicator device, moreover, the first input of the microprocessor is connected to the fifth input of the switch, the second input of the microprocessor connected to the output of the analog-to-digital converter, the control input of the voltage source is connected to the third input of the processor, the remaining inputs of the microprocessor are connected to the control unit and an indicator, characterized in that it further comprises a temperature sensor placed on an auxiliary electrode, two outputs of which are connected to the sixth and seventh input of the switch.