CH648933A5 - METHOD AND DEVICE FOR ANALYZING CHEMICAL SOLUTIONS. - Google Patents

Description

The present invention avoids these disadvantages and relates to a method for analyzing chemical solutions by means of sensors by measuring the parameters that occur when adding a suitable reagent, and is characterized in that an amount of the reagent with excess concentration during a short time interval in the manner of an impulse function is added to the sample solution or a reaction vessel so that the concentration of the reagent which arises as a result of the abrupt addition and the subsequent steady decrease is measured by means of sensors, and that a parameter which is used for the course of the reaction between the moment of Addition of the reagent until an at least approximately original state of the analyzed sample solution is characteristic, measured and evaluated as a measure of the original concentration of a component of the sample solution.

The invention also relates to a device for carrying out the method and comprises a metering device which adds a predetermined reagent volume to the sample stream, a measuring chain with sensors for determining the concentration of the reagent in the sample solution and a measuring device for determining a characteristic parameter within the period between the addition of the reagent and reaching the at least approximately original state of the sample solution.

The invention is explained in more detail with the aid of the description and the figures. It shows

FIG. 1 shows schematically the principle of the analysis method,

FIG. 2 shows a diagram of the time course of the decrease in concentration as a function of time,

FIG. 3 shows a further diagram for changes in concentration,

Figure 4 is a diagram of experimental results.

According to the schematic arrangement in FIG. 1, the sample solution 3 is fed to a reaction vessel 1 from a line 2. An outflow or overflow 4 leads away the inflowing amount and the sample solution displaced by any added reagent. The reagent 5 is added to the sample solution 3 from a container 6 via a metering device 7 in such a way that a predetermined reagent volume is released by the metering device 7 within a short time interval and poured into the sample solution. An agitator 8 ensures rapid mixing of sample solution and reagent in a known manner. The concentration of the amount of reagent added is to be selected so that there is an excess at the moment of addition. Any suitable elements, for example solenoid valves or injectors, can be used as metering devices 7.

The chemical state or its changes are detected by means of sensors 11, 12 and evaluated in a display and / or control device 13. The type of sensors is determined by the intended type of state change detection; if the pH is monitored, these sensors are glass electrodes; If the redox potential of the mixture of sample solution and reagent is observed, appropriate metal electrodes 11.12 must be selected as sensors. The monitoring of electrochemically active substances requires amperometric sensors. If the heat generated by the reaction of the sample solution and the reagent is evaluated, sensors 11, 12 with thermo-sensitive properties are required. Reactions between sample solution 3 and reagent 5 with colorimetric effects are recorded by photodetectors.

As soon as the specified amount of reagent 5 has been added to the sample solution 3, the pH value suddenly increases to a certain value:

A + n.B - »C

c | vR

10th

-n.CA

VR + VG

in which

15 A B n

20 ^ o substance to be measured reagent stoichiometric factor

Cg concentration of the solution at time t0

.R

2s Cg concentration of the reagent 5

30th

VG CA

Amount of reagent added 5 Volume of the reaction vessel 1 = amount of sample solution 3 concentration to be determined.

35

The concentration CB in the reaction vessel 1 now decreases in accordance with the flow of the sample solution 3 to be analyzed. At the same time, CB also decreases as a result of the reaction with the sample solution. After a while all CB will be implemented, i.e. the solution in the reaction vessel 1 is located in the so-called equivalence point and the potential provided by the sensors 11, 12 will indicate the equivalence jump known per se. This time 45 is called the equivalence time teq. It is obvious that with constant flow and constant quantity VR, teq is dependent on the desired concentration Ca.

The logarithmic dependence of the equivalence time teq on the concentration CA of the sample solution 3 results in such a wide range of concentrations that can be covered with one and the same reagent 5.

FIG. 2 shows the course of the concentration CB as a function of time t, the concentration being expressed, for example, by the respective pH. At the point in time t = t0 55, the reagent 5 is added, as a result of which the pH suddenly increases to the value Cg and from then on gradually drops according to one of the curves 14, 15 or 16, depending on the original concentration CA of the sample solution 3. Curve 14 corresponds to a strong, curve 15 to a medium and curve 16 to a weak original concentration CA. The equivalence points 17, 18, 19, which are reached, for example, when the pH values pass through the neutral value pH = 7, reflect the equivalence times teq for the relevant concentrations Cai, CA2, CA3.

The times teq determined from the observation of the display of the device 13 thus result in the respective values CA.

From the reaction equation

648 933

A + nB -> C

the following quantity balance can be made:

dCB

VG- ^ = - CB.VA - n.CA.VA

dt where

VG reactor volume dCB

Change in concentration in the reaction vessel

VA flow of sample solution / unit of time

CA Searched concentration of the sample solution

"-, • V °

t dwell time =

VA

Through transformations and integration one obtains t

CB = C ° -e *

or

^ eq

CA = n.C ° -e *

By logarithming and further changes teq can be isolated:

teq = 2.303 t • log (n.Cg) - 2.303-T.log CA •

R VR

if n.CA «C • -, B VG applies

4th

teq = constant - 2.303.x.logCA.

The display or control device 13 is advantageously provided with a microprocessor data processing which

5 Sensor data entered in a suitable form, transformed in this according to a specified program and output as a measured value.

FIG. 3 shows a course of a measurement signal S, which represents the rise and fall of the reaction variable after the reagent 5 has been added at time t0. The equivalence point 17 is located at the turning point of the falling branch of the measurement signal S at the time teq. Instead of a time measurement to obtain the time interval teq - t0, the course of the measurement signal S can also be measured, for which purpose i5 offers some solutions that can be easily implemented using the electrical measurement signal S. First, the peak height 26 can be observed as a parameter for determining the concentration of sample 3. A further characteristic value is obtained from the peak width 27 at a predetermined height 28 of the signal curve, for example at 63% of the peak height 26. Finally, by integrating the measurement signal S over time t from time t0 until the original signal level is reached again at t], a characteristic parameter for the original concentration of sample 3 can be obtained, by determining the area 29 for this purpose.

FIG. 4 shows the result of a series of tests with the method according to the invention. In three examples, the equivalence time teq is a function of the concentration CA of 30 HCl with different concentrations CB of NaOH

g £ 2CÌgt!

Curve 20 with 6 N NaOH

Curve 21 with 4 N NaOH

Curve 22 with 2 N NaOH.

35 The measuring points show a good linearity between time and logarithm of the concentration over at least a decade. While the theoretical slope can be calculated as 12.5 sec / decade, the experiment shows that of approx. 12 sec / decade, which means that it is in good agreement with the expectations.

C.

2 sheets of drawings

Claims (13)

648 933 2 PATENT CLAIMS 14. Device according to speech 13, characterized thereby- 1. Method for the analysis of chemical solutions by means of net that a time measurement for determining the time interval of sensors is carried out by measuring the parameters occurring when adding a suitable and calculating the concentration (CA) by means of micro-reagents, characterized by processors. that a quantity of the reagent (5) with a concentration surplus. 5. Device according to claim 13, characterized in that during a short time interval in the manner of an internet that a solenoid valve is used as the metering device (7). Pulse function in the sample solution (3) or in a reaction 16. Device according to claim 13, characterized in vessel (1) is added that by means of sensors (11, 12) the net that an injector is used as the metering device (7). as a result of the volatile addition and the steadily decreasing concentration of the 10th Reagent (5) is measured, and that a parameter which is necessary for the course of the reaction between the moment of addition for the analysis of chemical substances or for the of the reagent (5) until the concentration of certain substances in a product is at least approximate to the original state of the analyzed sample solution benstrom, the classic method is to take a (3) characteristic, measured and as a measure of the original - 15 predefined amount of the sample, which in turn is spent in a sudden concentration of a component of the sample solution provided with the necessary facilities (3). and undergo the appropriate reactions there. This 2. The method according spoke 1, characterized, however, the process is very complex and time-consuming; The greatest that the time interval between the addition of the disadvantage as a parameter is that during the reagent (5) required for the analysis and reaching the equivalence point (17, 18, 20 time, the concentration of the monitored sample stream is still 19). is not known and therefore no documents for any- 3. The method according to claim 1, characterized in that there are corrective measures. that the peak height (26) of the measurement signal (25) is used as a parameter. In process engineering there is therefore a desire to be checked. determination of the concentration as continuously as possible, at least 4. The method according to claim 1, characterized in 25 at least in short time intervals and directly in the area of the ver-that as a parameter to perform the peak width (27) at a predetermined height. A continuous concentration (28) of the measurement signal (25) is considered. determination with short time required for sample removal 5. The method according spoke 1, characterized, take, analysis and evaluation only makes sense that the peak area (29) of the measurement signal (25) full concentration control is considered by metering the addition as a parameter. 30 of substitute chemicals. 6. The method according to claim 1, characterized, in particular in the large-scale industry that the reagent (5) in a flow of the sample flow, automation of the work processes, an automatic control branch branched from the main sample flow into a secondary flow, for example galvanic baths, is essential, reaction vessel (1) is injected. equivalent products are to be delivered for a long time 7. The method according spoke 1, characterized, 35 be. that the concentration is determined by measuring the pH-known analysis method, including those with an automatic value and using glass electrodes as their own workflow, use metering pumps with which to set. take exactly measured amounts of sample and reagent 8. The method according to claim 1, characterized in that it is mixed in a mixing chamber and by means of a suitable method that the concentration determination is monitored by measuring the measuring devices. The apparatus has an on-dox potential and, as sensors for the metal-electric wall, this method is large in that pumps and ones are used. set filters need to be maintained constantly. The aspirations 9. The method according to spoke 1, characterized, gene therefore go to the analysis without the necessity - that the concentration determination by evaluating the speed of a dosed removal of the sample is carried out directly in the unaffected heat which occurs during the reaction and to carry out the process stream , whereby, of course, only a minimal part of the process solution used for thermo-sensitive measuring elements becomes a reak. branched with the necessary measuring elements 10. The method according to claim 1, characterized. that the concentration determination of electrochemically active substances is carried out by means of amperometric sensors in accordance with one of the German Auslegeschrift 2,716,560, the analysis method disclosed is carried out with a constant 11. The method according to spoke 1, characterized in that the volume velocity of the sample with a time determined by the concentration determination by evaluating colo with increasing volume / time unit, which occurs during the reaction, resulted in an amount suitable for the measurement Reagent over and for this photodetectors are used. titrated, and then the supplied reagent stream again 12. The method according spoke 1, characterized in that the 55 is continuously reduced to zero. The changes that take place in the reaction that the concentration is determined by measuring the mixture of ions and the ion concentration are carried out, and the ion-specific concentration of the sample is used as sensors by comparing the electrodes between the electrodes. Occurrence of the two chemical equivalence points 13. Device for performing the method determined after genen time. This method therefore presupposes a set-up claim 1, characterized by a predetermined reaction, which enables a programmed addition of reagent in gene volume into the sample stream (3) to be added to the sample stream, and means for monitoring (7) a measuring chain with sensors (11, 12) for determining a time interval, the beginning of which is undetermined, ie only the concentration of the reagent (5) in the sample solution is obtained in the course of the method. Furthermore, this (3) and a measuring device for determining a method have the disadvantage that a large consumption of characteristic parameters can be recorded within the period between 6 seconds of reagent, and also that the measuring range for the addition of the reagent (5) and the achievement of a certain reagent as a result of the linear relationship - at least approximately the original state - of the progression between the time interval and the concentration of the solution to be measured (3). the component of the sample is narrowly limited. An extended 648 933 This range can only be achieved by using different reagents.