CS253908B1 - Device for indicating the end point of the titration - Google Patents

Abstract

The solution relates to a device for indicating the end point of titration. The essence of the device is that the indicating electrode is connected to the signal input of the switch, the output of which is connected to the signal input of the sampling device, the output of which is connected to the measuring device, while the control inputs of the switch and the sampling device are connected to a timing device. The device can be used in all types of volumetric and coulometric titration analyses, especially in the area of low and very low concentrations.

Description

253908

BACKGROUND OF THE INVENTION The present invention relates to an apparatus at the end point of the titration by a pulsed integration method.

Determining the endpoint of titration is one of the major problems in the trace titration analysis. The accuracy, correctness and concentration limit of the titratability depend on the indication method. Among electrochemical methods, ipatria are among the most sensitive potentiometric indications with polarized electrodes and amperometric indications with one or two indicator electrodes. Therefore, potentiometric and amperometric units are most commonly used in titration apparatuses.

They allow titrations up to a concentration of 10 -5 to 10 -6 mole / l, and in some special cases only titrations at a concentration level of 10 µmol / l have been realized [eg: Cooke, Reily, Furman: Anal.Chem. 23 1951, Osteryong et al .: Anal. Chem.46 1974 and 50 1978), respectively, at 5 XX 10 "8 mol / l (e.g., Champion, Marinenkoa Taylor: Anal. Chem. 42 1970), using devices with amperometric indication. In all previously known devices, the limiting factor for the amperometric indication is the low current signal level at low concentration levels of the substances, the unfavorable signal / noise ratio, and the signal / background current ratio, with the most capacitive current limiting the sensitivity of the indication and the concentration interstitability.

Increasing the sensitivity of the titration endpoint indication and reducing the titratability range allows the device according to the invention to be connected to the signal input of the switch, the output of which is connected to the signal input of the sampling device. the output is connected by a measuring device, with the control inputs of the switch and the sampling device connected to the timing device. An integrator may be included between the switch output and the sampling input of the sampling device, which control input is connected to the timer device. The advantages of this device are that a laundry response is used to indicate the end point of the titration, or a temporal integral of the laundry response of the indication electrode polarized by the voltage pulses, the amplitude of which is given by the selected insertion potential and instantaneous equal potential.

The indication signal is substantially higher and, as yet known, amperometric methods and is largely suppressed, allowing for increased sensitivity and accuracy of indication. The end point of the titration may be indicated as a change in polarity of the indication signal.

These advantages make it possible to greatly increase the sensitivity of the indication and to reduce the titratability concentration down to a level of 10 < 10 > mol / l. In the case of coulometric titrations, the use of said endpoint indicating device has the additional advantage of allowing the induction of titration to be indicated by the indication Another advantage is the fact that the output signal is directly dependent on the concentration ratios in the vicinity of the indicating electrode, making it possible to utilize the described apparatus and the high-sensitivity electrochemical detector, for example in liquid chromatography and the like.

In the accompanying drawings, two examples of the connection of the indicator device according to the invention are given, wherein in Fig. 1 the direct measurement of the laundry electrode samples is connected and in Fig. 2 it is connected with the integrated integrator.

Fig. 1 shows a three-electrode indicator system consisting of an auxiliary electrode 3, a reference electrode 4 and an indicating electrode 5 connected to the potentiostat 2 in a titration vessel 1. Switch 6 connected in series with an indicator electrode The stage 5 is periodically expanded and turned on by means of a timing device 9. The indicator electrode 5 is thereby polarized by voltage pulses whose amplitude is given by the potential introduced by the potentiostatically during the switch on 6 and by the instantaneous equilibrium potential of the indicating electrode after the switch 6 is opened. the large-volume response of the indicating electrode 5 at a suitable time measured by the sampling device 7 and the meter 8.

The magnitude and polarity of the indicating signal depends on the magnitude of the insertion potential, the sampling time, and the instantaneous equal potential of the indicating electrode 5 at a given titration degree, respectively. concentration of electroactive ingredients. A preferred selected insertion potential is the end point of the titration indicated by the change in polarity of the indicating signal. In the circuit of FIG. 2, an integrator 10 controlled by a timing device 9 is placed between the switch 6 and the sampling device 7. The response response of the indicating electrode 5 to the polarization pulse is integrated with the integrator 10, e.g. the switching of the switch 6 and the output signal from the integrator 10 is measured by the sampling device 7 and the measuring device 8.

In the following, the integrator 10 is reset to the next indication cycle. The advantage of the coupling according to FIG. 2 is the better noise suppression and increase of the indication signal compared to the circuit shown in FIG. 1. As an example of the use of the device according to the invention, coulometric titration of potassium dichromate solution by coulomerically generated iron ions can be mentioned. A platinum indicator electrode was used, the input potential was 0.75 V vs.. 1 M Ag, AgCl. For concentration range 1.7 X 10_6 to 3 X

Claims (2)

SUBJECT An apparatus for indicating an end point of titration comprising a titration vessel and a potentiostat to which a three-electrode indicating system is connected, characterized in that the indicating electrode (5) is connected to a signal input of a switch (6) whose output is connected to a signal input a sampling device (7J), the output of which is connected to the meter (8), the control inputs of the switch (6J and the sampling device (7) being connected to the timing device (9). Device according to claim 1, characterized in that an integrator (10) is connected between the output of the switch (6) and the signal input of the sampling device (7), the control input of which is connected to the timing device (9).