CS239131B1 - Method of measurement by potentiometric titration - Google Patents

Abstract

A potentiometric titration measuring method based on the addition of a titrant to a titration vessel in which a liquid sample and a camouflage solution are dispensed. The potential is scanned by a combined glass electrode. The constant titrant feed is discontinued before the potential corresponding to the equivalence point is reached. For this interruption, the amount of titrant consumption is subtracted and, after stabilization, the potential value. Subsequently, a constant volume of titrant is added to the titration vessel, and after stabilization, the potential value is subtracted, and the resulting titrant consumption is then calculated. The method is suitable for determining the acidity or sizing of samples in automated analyzers.

Description

The present invention provides a potentiometric titration measurement method based on the addition of a titration agent to a titration vessel, which, in addition to the bulk liquid sample, also contains a solution of masking agents, the potential being sensed by a combined glass electrode.

So far, two measurement methods have been used for potentiometric titration. The second derivative of the titration curve is calculated, where for the inflection point of the titration curve, i.e. the equivalence point, the second derivative is zero or the flow rate of the titrating agent slows near the equivalence point. The titration reagent consumption, which is proportional to the sample concentration, is then subtracted at the point of equivalence.

The disadvantage of the first method is the complicated evaluation method consisting in the calculation of the second derivative of the titration curve, while the second method is again complicated in mechanical terms, since it requires a variable flow of titrating agent.

This is largely eliminated by the method of measurement according to the invention, which consists in interrupting the constant flow of titrating agent into the titration vessel before reaching the potential of the equivalence point. For this interruption, the amount of titration reagent consumption and, after stabilization, the potential value are subtracted. A constant volume of titrant is then added to the titration vessel and the potential value is read again after stabilization. The resulting titration reagent consumption is then calculated.

An advantage of the measurement method according to the invention is that it is simple to evaluate, without changing the titration agent flow rate.

Exemplary embodiment

A titration vessel containing a liquid sample and a solution of masking agents is added to the titration vessel.

239 131 reagent. The constant titration of the titrating agent into the titration vessel is interrupted before reaching the equivalence point, i.e., U _BE + U. Thereafter, the titration agent flow is restored for a constant period of time, thereby supplying a constant amount of titrating agent ΔΧ. Again, the potential value is allowed to stabilize to obtain a potential value of U ₂ . In this case, it is necessary to satisfy the inequality> ^u BB ^ ^{> U} 2 », which is achieved by a suitable choice of the constants U and Δ X based on the experiment. The resulting consumption of titration reagent X, which corresponds to the point of equivalence, is then calculated from the formula:

X

reagents

Uj = steady state potential after the first titration interruption

U ₂ = steady state potential after the second titration interruption

The volume of titrating agent consumed in the first titration section

ΔΧ = constant titration volume added in the second titration section

The attached drawing shows the course of the potential versus time corresponding to the measurement method according to the invention.

The drawing shows the potential U in volts on the X-axis and the time in seconds on the y-axis. The drawing shows the course of potential over time. The section 1 corresponds to a steady-state value of the potential Ujjj, the solution of the masking agents, in which the titration usually takes place. Section 2 captures the bulk dispensing of the sample into the titration vessel. Section J is the intrinsic titration to Ugg * U at which, · | is consumed of a titrating agent. The value stabilizes during the section. Section 2 records the addition of a constant volume ΔΧ to the titration vessel. After the addition, the potential value U ₂ stabilizes in section 6. In section 2, the titration vessel is drained and filled with a new masking solution and the cycle is repeated.

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The method of measurement according to the invention is particularly suitable for determining the acidity or alkalinity of samples in automated operating and laboratory analyzers.

Claims (1)

SUBJECT OF THE INVENTION 239 131 Potentiometric measurement method based on the addition of a titrating agent to a titration vessel, in which, in addition to a liquid-metered liquid sample, a masking solution, the potential is sensed by a combined glass electrode, characterized in that the constant titration or reagent flow to the titration vessel is interrupted. before reaching the potential corresponding to the equivalence point, subtract the titration reagent consumption for this discontinuity and, after stabilization, the potential value, then add a constant volume of titrating agent to the titration vessel and read off the potential value again after stabilization, then calculate the resulting consumption of a titrating agent.