(19)
(11)EP 2 995 941 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
05.04.2017 Bulletin 2017/14

(21)Application number: 15002854.6

(22)Date of filing:  14.02.2012
(51)International Patent Classification (IPC): 
G01N 27/42(2006.01)
G01N 31/16(2006.01)
G01N 27/44(2006.01)

(54)

KARL FISCHER TITRATION METHOD

KARL-FISCHER-TITRATIONSVERFAHREN

PROCÉDÉ DE TITRAGE KARL FISCHER


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 18.02.2011 JP 2011033621

(43)Date of publication of application:
16.03.2016 Bulletin 2016/11

(62)Application number of the earlier application in accordance with Art. 76 EPC:
12746665.4 / 2677310

(73)Proprietor: Kyoto Electronics Manufacturing Co., Ltd.
Kyoto-shi, Kyoto 601-8317 (JP)

(72)Inventors:
  • KUROSE, Ikumi
    Kyoto-shi, Kyoto 601-8317 (JP)
  • ISHIKURA, Masaaki
    Kyoto-shi, Kyoto 601-8317 (JP)

(74)Representative: Grünecker Patent- und Rechtsanwälte PartG mbB 
Leopoldstraße 4
80802 München
80802 München (DE)


(56)References cited: : 
US-A- 4 211 614
US-A- 5 296 193
  
  • TORSTENSSON L G ET AL: "Controlled-potential back-titration with electrogenerated iodine as an intermediate", TALANTA, ELSEVIER, AMSTERDAM, NL, vol. 20, no. 12, 1 December 1973 (1973-12-01), pages 1319-1328, XP026706195, ISSN: 0039-9140, DOI: 10.1016/0039-9140(73)80099-2 [retrieved on 1973-12-01]
  • SCHALCH E: "A modern Karl Fischer titrator", INTERNATIONAL LABORATORY, vol. 14, no. 2, 1 March 1984 (1984-03-01), pages 64-70, XP001333024,
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description


[0001] The invention relates to Karl Fischer titration method using a Karl Fischer titration apparatus, and, in particular, to a Karl Fischer titration method using a Karl Fischer titration apparatus for a titer determination by means of coulometric back titration.

[0002] As a method for measuring water content by means of Karl Fischer titration method, there are a volumetric titration method and a coulometric titration method, and there are apparatus corresponding to each method.

[0003] The volumetric titration apparatus has a basic configuration as shown in Fig. 6, wherein a titration flask 1 is provided with an injection nozzle 90 for titrating Karl Fischer reagent and an detection electrode 80 for detecting a polarization state. In such configuration, a dehydrated solvent is put in the titration flask 1, which is dehydrated by performing a preliminary titration with the Karl Fischer reagent. In this condition, a sample is put in the titration flask 1, and then drops of Karl Fisher reagent are added therein. According such process, the water contained in the sample reacts with iodine in the reagent. Since a concentration of iodine increases and a voltage detected by the detection electrode 80 falls as the reagent is added therein, a point when the detected voltage becomes a specific value is set to an end point. In this case, since the added amount of the reagent reacts quantitatively with the water content, the water content in the sample can be estimated by the added amount of the reagent.

[0004] In order to establish the above-mentioned theory, since it is based on the assumption that the water amount reacting with a specific amount (e.g. 1 ml) of Karl Fischer reagent (which is referred to titer) is known in advance, the titer of the reagent to be used is necessary to be measured previously. This measurement uses a liquid to be standard, such as a standard solution. That is, the standard solution (water produced as standard solution, sodium tartrate dihydrate, and pure water) is injected in the titration flask 1 holding the dehydrated solvent, and Karl Fischer reagent is added therein, so that the water amount reacting with the standard solution is defined as the titer.

[0005] In the above volumetric titration, the used Karl Fischer reagent is disposed as matters now standard, because it is no further use for the titer determination as described later.

[0006] In the coulometric titration apparatus, the titration flask 1 is provided with an electrolytic electrode 95 for electrolytic treatment of anolyte, and the detection electrode 80 for detecting the polarization state, as shown in Fig. 7.

[0007] In the configuration, the anolyte (solution including iodine ions) is put in the titration flask 1 and catholyte is put in a chamber of the electrolytic electrode 95. Since the anolyte absorbs humidity in the air at this time, the anolyte is dehydrated by the electrolytic treatment for generating the iodine at the electrolytic electrode 95 (the preliminary titration). In this condition, the sample is put in the anolyte, and the electrolytic treatment is carried out at the electrolytic electrode 95 to produce the iodine from the iodine ions, and make the iodine react with the water in the sample, (the titration for producing the iodine from the iodine ions is referred to the coulometric titration, hereinafter).

[0008] As the coulometric titration proceeds, the concentration of iodine in the titration flask 1 increases and the voltage detected by the detection electrode 80 reduces, therefore a point when the detected voltage becomes a specific value is set to an end point. The water content can be estimated based on the quantity of electricity consumed at this time.

[0009] The coulometric titration used here is an electric current control method for controlling voltage so as to fix the current to a constant, and the results by means of the current control method are well-matched with theoretical values, as long as the iodine is produced from the iodine ions.

[0010] In the above-mentioned volumetric titration apparatus, a back titration as described hereinafter can be carried out.

[0011] Specifically, the iodine in Karl Fischer reagent reacts with the water in the sample as described above. A specific amount of Karl Fischer reagent (water equivalent x) is added in the sample. When the reaction of the water in the sample and the iodine is terminated, the iodine that did not react with the water in the sample has remains, so that the detection electrode 80 indicates a lower value than the end point. Accordingly, when a standard water-methanol is titrated in this condition, the standard water-methanol reacts with the excessive iodine and the iodine ions are produced. When the standard water-methanol is added up to that the voltage indicated by the detection electrode 80 becomes the end point, the water content in the sample can be calculated by x-y, based on the added amount of the standard water-methanol (water equivalent y) and the amount of the Karl Fischer reagent (water equivalent x).

[0012] The titration for producing the iodine ion from the iodine in this case, however, is limited to the volumetric titration method. This kind of titration cannot be carried out in the coulometric titration apparatus due to the reasons described later, and the coulometric titration apparatus cannot be applied to the back titration. Moreover, since the coulometric titration apparatus is not provided with a burette for adding the standard water-methanol and the injection nozzle 90, it cannot carry out the back titration functionally.

[0013] The Karl Fischer titration apparatus that is incorporated with both the volumetric titration device and the coulometric titration device is put on the market. In this case, operation units such as a display, a keyboard, and the like are shared with both device, but measurement units (the injection nozzle + detection electrode, or electrolytic electrode + detection electrode: but the detection electrode can be shared) are constituted exclusively. Such device, however, is configured so that the independent two methods are merely carried out by the shared operation units, and it is not provided with a unique function like the present invention as described hereinafter.

[0014] Prior art citations are Japanese Unexamined Patent Application Publication No. 06-308113 (Patent Literature 1) that discloses a combined type of titration apparatus for carrying out the volumetric analysis and/or the coulometric analysis, and Japanese Unexamined Patent Application Publication No. 2007-278919 (Patent Literature 2) that discloses a moisture meter for measuring the water content in the sample by the volumetric titration method or the coulometric titration method.

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 06-308113

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2007-278919



[0015] US4211614 (A) discloses an apparatus and method for automatically correcting drift in automatic titrations, such as coulometric titrations of water. An endpoint detector provides a signal indicative of the state of the titration mixture and the detector signal is monitored by two comparators, responsive to titration mixture states on opposite sides of the endpoint and connected to means for controlling forward and back titration.

[0016] A controlled-potential back-titration with electrogenerated iodine as an intermediate is disclosed by Torstensson L. G. in Talanta, Elsevier, Amsterdam, NL, vol. 20, no. 12, 1 December 1973, pages 1319-1328.

[0017] The above two conventional methods are processed by quite different steps from each other, and do not share any common components to be used except the detection electrode. This is caused by the coulometric titration apparatus and the volumetric titration apparatus that are used in general, as described hereinafter.

[0018] The titer is the water content that reacts with the iodine in the specific amount of Karl Fischer reagent. Accordingly, the water content to react with the Karl Fischer reagent is specified by means of a liquid to be a standard as water (standard solution), which is determined as the titer.

[0019]  The titer determination seems in principle to be equivalent to a measurement of the quantity of electricity when the iodine ions are produced from the iodine included in the specific amount of Karl Fischer reagent by the electrolytic treatment for the specific amount of Karl Fischer reagent, (the electrolytic treatment for producing the iodine ions from the iodine is referred to as coulometric back titration, hereinafter).

[0020] However, when the amount of iodine is calculated using the electrolytic electrodes provided to the coulometric titration apparatus based on the quantity of electricity consumed by means of the conventional current control method, the calculated amount does not match with an actual amount of the iodine.

[0021] Meanwhile, the coulometric back titration means that the iodine ions are produced from the iodine. Accordingly, even in the conventional coulometric titration apparatus, it seems to be possible to carry out the back titration, that is, the remained iodine is put back to the iodine ions by means of the coulometric back titration after the iodine ions are produced from the iodine by means of the coulometric titration.

[0022] As described above, however, when the coulometric back titration is carried out in the conventional coulometric titration apparatus by means of the current control method, the calculated water content (the amount of iodine) does not match with the theoretical value. This is very inconvenient. Therefore, in the present circumstances, when the back titration is required, it is carried out in the volumetric titration apparatus by means of the volumetric titration method. There is a disadvantage that the back titration cannot be carried out in the coulometric titration apparatus without the burette and the injection nozzle.

[0023] Moreover, in order to reproduce the Karl Fischer reagent that has been used to the volumetric titration, it is necessary to change the iodine ions back to the iodine. In this case, the reproduction of the Karl Fischer reagent can be possible theoretically by the coulometric titration for producing the iodine from the iodine ions by means of the electrolytic electrode. But, the volumetric titration apparatus is not originally provided with the electrolytic electrodes, so that the used Karl Fisher reagent is disposed in fact because it cannot be reproduced.

[0024] In view of the above-mentioned problems in the conventional arts, the present invention has an object to provide a Karl Fischer titration method for carrying out the titer determination by means of the coulometric back titration method.

[0025]  The present invention provides a Karl Fischer titration method by means of a Karl Fischer titration apparatus having a titration flask (1) provided with electrolytic electrodes (12) including an anode (12a) and a cathode (12k) with a membrane (12m) therebetween, a detection electrode (13) for detecting a polarization state of a solution in the titration flask (1), and a reference electrode (17) for detecting a potential between the anode (12a) and the reference electrode (17), the apparatus further comprising an electrolysis control unit (20), and a calculation unit (40), the method comprising the steps of:

introducing a Karl Fischer reagent into the titration flask (1) containing dehydrated solvent;

performing a coulometric back titration in a potential control method by using the electrolysis control unit (20) and the electrolytic electrodes (12); and

calculating the titer of the Karl Fischer reagent by using the calculation unit (40) based on the quantity of electricity consumed during the coulometric back titration.



[0026] After forming a state that iodine exists in a solution contained in the titration flask, iodine ions are produced from the iodine at a anode of the electrolytic electrodes by means of a coulometric back titration.

[0027] When the solution is a dehydrated solvent including Karl Fischer reagent to be used to a volumetric titration, the coulometric back titration is performed in order to determine the titer of the Karl Fischer reagent, and the titer is determined based on a quantity of electricity consumed during the coulometric back titration.

Advantageous Effects of Invention



[0028] According to the above, the Karl Fischer reagent to be used to the volumetric titration is put in the dehydrated solvent, and the solvent is subjected to the coulometric back titration to produce the iodine ions from the iodine. According the quantity of electricity consumed during the coulometric
back titration, the titer of the reagent can be determined. The system does not require the standard solution to be used in conventional art.

[0029] In order to carry out the back titration by means of the conventional volumetric titration, the apparatus must be provided with a burette that contains the reagent (water-methanol) having a determined titer, but the present invention does not require it.

[0030] When the apparatus is configured to be provided with the electrolysis control unit for changing the coulometric titration and the coulometric back titration as necessary, the titration that has been used in usual or the above-mentioned each kinds of titrations can be performed independently or changing to another titration.

Fig. 1 is a perspective view showing an apparatus to be used in the present invention.

Fig. 2 is a sectional view of an apparatus to be used in the present invention.

Fig. 3 is a graph showing a principle of the present invention.

Fig. 4 is a graph showing a status that the titer is measured in the present invention.

Fig. 5 is a graph showing a voltage change at the detection electrode when the coulometric titration is changed to the coulometric back titration.

Fig. 6 is a conventional volumetric titration apparatus.

Fig. 7 is a conventional coulometric titration apparatus.


<Principle>



[0031] In the coulometric titration by means of a popular Karl Fischer titration apparatus as shown in Fig. 7, a side of the anolyte is an anode, and a side of catholyte through a membrane is a cathode. As long as the coulometric titration is carried out by applying a positive voltage on the anode and a negative voltage on the cathode, that is to say, as long as the iodine is produced from the iodine ions, the amount of the produced iodine can be calculated based on the quantity of electricity obtained by the appropriate current control.

[0032] Where the iodine ions are produced from the iodine by means of the coulometric back titration applying the negative voltage on the anode and the positive voltage on the cathode, the amount of the iodine ions produced by the current control does not match with the theoretical value, so that it cannot be applied to the titer determination as described hereinafter.

[0033] The coulometric back titration is carried out using a specific solution containing a known amount of iodine (the anolyte or dehydrated solvent). The current is measured while changing the potential between the electrodes. A relation between the current and the potential for every iodine concentration (10-10M, 10-7M, 10-6M : M = mol / L) is shown in Fig. 3. Here, the current is a current that flows between a cathode (12k in Fig. 2) and an anode (12a in Fig. 2), and the potential is a potential between a reference electrode (17 in Fig. 2) and the anode.

[0034] It can be understood that an area where the current between the cathode and the anode is kept constant regardless of the potential change (-0.1 V to -0.5V) exists in an area where the negative potential between the reference electrode and the anode is low, and the current changes suddenly against the potential when the negative potential gets higher. In addition, the value of the constant current gets large in a negative direction when the concentration of the iodine increases, however, a range of potential corresponding to the constant current does not change according to the concentration of the iodine.

[0035] The potential area where the current is constant is considered as a potential area where the iodine is reacting at a constant speed and changing to iodine ions according to the applied quantity of electricity, while the area where the current changes suddenly against the potential is considered as an area where negative ions except the iodine ions are produced.

[0036] Therefore, in order to use the coulometric back titration, the coulometric back titration should employ the potential control method using the area where the current is constant against the change of the potential (the current control to keep the potential constant or to keep the potential be in the above-mentioned area). In fact, by applying the potential control method to the titer determination as described hereinafter, it is possible to ensure the matching between the produced amount of iodine ions and the applied quantity of electricity.

[0037] Even in the potential control method, when using the potential existing out of the area where the constant current is kept against the change of the potential, the produced amount of the iodine ions does not match with the theoretical value, which is not suitable to the titer determination, like the conventional art.

<Apparatus> (not embraced by the present invention)



[0038] Based on the above confirmations, the present invention is constituted as shown in Fig. 1.

[0039] Fig 1 is a perspective view of Karl Fischer titration apparatus designed based on the above described facts. Fig. 2 is a sectional view of the apparatus.

[0040] A titration flask 1 is configured to be provided with a sample injection port 14 (not shown in Fig. 2) as well as an injection nozzle 11 for the volumetric titration, electrolytic electrodes 12 for the coulometric titration, a detection electrode 13 for detecting the polarization state and an end point, and a reference electrode 17 for the potential control. A reagent supplied from a burette 15 is put in the titration flask 1 via the injection nozzle 11, and the reagent in the burette 15 is supplied from a reagent bottle (not shown). The apparatus is provided with a switching cock 16 for changing a path from the reagent bottle to the burette 15 with a path from the burette 15 to the injection nozzle 11. The apparatus is provided with a burette control unit 10 for controlling the amount of reagent to be supplied from the burette 15 to the injection nozzle 11.

[0041] The electrolytic electrodes 12 are arranged so that an anode 12a and a cathode 12k face each other across a membrane 12m. The anode 12a is released in the titration flask 1 and the cathode 12k is contacting with catholyte.

[0042] The detection electrode 13 and the reference electrode 17 are formed in one unit as shown in Fig. 1, but Fig. 2 shows them separately in order to be easily understandable, whereby the relations between the above-mentioned electrodes are defined clearly.

[0043] In the configuration, the anolyte is put into the titration flask 1, and the catholyte is put into the electrolytic electrodes 12. When the positive voltage is applied on the anode 12a and the negative voltage is applied on the cathode 12k (the coulometric titration), the iodine is produced from the iodine ions in the anolyte. The produced iodine reacts with the water in the sample added to the anolyte, which is controlled by an electrolysis control unit 20.

[0044] The detection electrode 13 detects the concentration of the iodine in the titration flask 1. That is to say, when the sample including the water is put in the solution (the volumetric titration: the dehydrated solvent, the coulometric titration: the anolyte) in the titration flask 1, the concentration of the iodine reduces, the voltage at the detection electrode 13 increases. On the contrary, when the concentration of the iodine in the solution increases by the titration, the voltage at the detection electrode 13 reduces.

[0045] Therefore, it is possible to determine the status of the titration based on the voltage indicated by the detection electrode 13. When the voltage indicated by the detection electrode 13 becomes a value indicating the end point of the titration, the burette control unit 10 or the electrolysis control unit 20 stops the titration, and the voltage or the end-point voltage at the detection electrode 13 during the titration is displayed on a display 50 or printed out by a printer 60.

[0046] It is nevertheless to say that the volumetric titration and the coulometric titration can be performed by means of the apparatus having the above-mentioned configuration, in the same manner as the conventional apparatus. In addition, it is possible to perform processing unique to the present invention as described hereinafter.

<Titer determination>



[0047] Karl Fischer reagent has a property of reducing its titer during storage. Accordingly, it is necessary to measure the water content (titer) reacting with the specific amount (1 ml) of the Karl Fischer reagent in advance of the titration.

[0048] The previous titration operation is usually done by using the standard solution as described above, but the above-mentioned coulometric back titration using the electrolytic electrodes 12 is employed here. That is to say, when the coulometric back titration is carried out by applying the negative voltage on the anode 12a and the positive voltage on the cathode 12k of the electrolytic electrodes 12, the iodine in Karl Fischer reagent is changed to the iodine ions.

[0049] As a result, the voltage indicated by the detection electrode 13 increases gradually (Fig. 4, (a)) and the flowing current reduces (Fig. 4, (b)) as shown in Fig. 4. The calculation unit 40 can calculate the titer based on the quantity of electricity obtained by the electrolysis control unit 20 before a point when the voltage indicated by the detection electrode 13 becomes the specific value XmV.

[0050] As described in the above <Principles>, the potential control method is employed here, and the current between the cathode 12k and the anode 12a is controlled so that the potential at the reference electrode 17 be in a specific range (e.g. -0.5 to -0.1V as shown in Fig. 3). When the potential is out the range, the obtained titer does not match with the theoretical value. It is very inconvenient.

[0051] Table 1 shows results that the titer is measured by the coulometric back titration of the present invention. Regarding Karl Fischer reagent with titer 3.0 (H2Omg/mL) and Karl Fischer reagent with titer 1.0, the titers were measured by using the conventional method (using the standard solution) in advance, and these were marked as a reacting weight 100. Next, the reagent is injected in the titration flask 1 (0.3mL and 0.2mL regarding titer 3.0; 1.0 mL; and 0.5mL regarding titer 1.0), and the iodine ions are produced from the iodine by means of the coulometric back titration. The results obtained by the processing are shown in Table 1. As understood by Table 1, the titer determination by means of the potential control method is well-matched with that by using the conventional standard solution. It is understood that using the potential control method is correct.

[0052] Besides, as a matter of course, the specific amount of Karl Fischer reagent to be measured is put into the titration flask which contains the dehydrated solvent previously dehydrated.
Table 1
 Karl Fischer reagent Titer 3.0 (H2Omg/mL) Karl Fischer reagent Titer 1.0 (H2Omg/mL)
Injection Amount0.3mL0.2mL 1.0mL0.5mL
Frequency 1 99.8 100.1   98.2 99.7
2 100.1 99.0   99.6 100.5
3 98.4 99.9   102.5 100.2

< Coulometric back titration >



[0053] The apparatus to be used in the present invention is possible to perform the back titration by means of the electrolytic electrodes.

[0054] As shown in Fig. 5, after a point (time t1) when the sample is put in the titration flask 1 that contains the anolyte, the coulometric titration using the current control method is performed in response to an instruction to start the coulometric titration from the operation board 80, and supplies a constant current to the electrolytic electrodes 12 (time t2), and then forms a state that a specific amount of iodine exists in the sample (in the anolyte). The reaction of the iodine with the water in the sample proceeds so that the voltage reaches the end point voltage (XmV) (time t3). At this time, the coulometric titration is continued to form a state that the iodine is excessively existed (time t4). Next, like the titer determination, the iodine ions are produced from the iodine by performing the coulometric back titration using the potential control method. Gradually, the concentration of the iodine reduces and the voltage at the detection electrode 13 increases. When the detected voltage becomes the specific end point voltage (VmX) (time t5), the titration is terminated.

[0055] Where the quantity of electricity consumed at constant current during the coulometric titration is defined as Y, the quantity of electricity flowed during the coulometric back titration is defined as Z, and the quantity of electricity corresponding to the water content in the sample is defined as X, it becomes X = Y - Z, which can find the water content converted from the quantity of electricity X.

[0056] Table 2 shows the quantity of electricity consumed at the coulometric back titration, where the quantity of electricity consumed at the coulometric titration (producing iodine from iodine ions) for a specific time (in the current control method) is defined as 100. It is understood according to Table 2 that the quantity of the electricity at the coulometric back titration is well-matched with the quantity of the electricity at the coulometric titration.

[0057] In the measurement by means of the coulometric titration, there is a possibility that it takes a long time to react the iodine with the water content in the sample because the water content in the sample is hard to be dissolved in the anolyte. In the titration by means of the coulometric back titration, however, after the iodine excessively added by the coulometric titration is fully reacting with the water in the sample, the remained iodine is put back to the iodine ions, so that it is possible to carry out the quick and high-precise measurement.

[0058] The titration by means of this coulometric back titration is available to the volumetric titration method for forming the state that the specific amount of iodine exists in the sample. That is, the specific amount of Karl Fischer reagent is put into the titration flask 1 that contains the dehydrated solvent and the sample, which forms a state (time t4, Fig. 5) that the specific amount of iodine exists in the sample in the dehydrated solvent. After that, the coulometric back titration is carried out by means of the potential control method using the electrolytic electrodes 12, whereby the iodine ions are produced from the iodine. According to the production of the iodine ions, the voltage at the detection electrode 13 increases. The detected voltage at this time becomes the specific end point (time t5), and the titration is terminated. Therefore, the processing does not require the standard water-methanol.
Table 2
 The percentage (Y/Z)of the quantity of electricity (Y) during the coulometric back titration, when the quantity of electricity (Z) during the coulometric titration is 100
Frequency 1 98.4
2 97.7
3 98.4


[0059] The present invention allows Karl Fischer titration apparatus to carry out the titer determination by the electrolytic treatment and the back titration, as described above, so that the industrial applicability is very high.

REFERENCE SIGNS LIST



[0060] 
1
Titration flask
11
Injection nozzle
12
Electrolytic electrode
13
Detection electrode
14
Electrolysis control unit
17
Reference electrode



Claims

1. A Karl Fischer titration method by means of a Karl Fischer titration apparatus having a titration flask (1) provided with electrolytic electrodes (12) including an anode (12a) and a cathode (12k) with a membrane (12m) therebetween, a detection electrode (13) for detecting a polarization state of a solution in the titration flask (1), and a reference electrode (17) for detecting a potential between the anode (12a) and the reference electrode (17), the apparatus further comprising an electrolysis control unit (20), and a calculation unit (40), the method comprising the steps of:

introducing a Karl Fischer reagent into the titration flask (1) containing dehydrated solvent;

performing a coulometric back titration in a potential control method by using the electrolysis control unit (20) and the electrolytic electrodes (12); and

calculating the titer of the Karl Fischer reagent by using the calculation unit (40) based on the quantity of electricity consumed during the coulometric back titration.


 


Ansprüche

1. Karl-Fischer-Titrationsverfahren mittels einer Karl-Fischer-Titrationsvorrichtung mit einem Titrierkolben (1) mit elektrolytischen Elektroden (12) mit einer Anode (12a) und einer Kathode (12k) mit einer Membran (12m) dazwischen, einer Detektionselektrode (13) zur Detektion eines Polarisationszustands einer Lösung in dem Titrierkolben (1), und einer Referenzelektrode (17) zur Detektion eines Potentials zwischen der Anode (12a) und der Referenzelektrode (17), wobei die Vorrichtung ferner eine Elektrolyse-Steuereinheit (20) und eine Berechnungseinheit (40) umfasst, wobei das Verfahren folgende Schritte umfasst:

Einführen eines Karl-Fischer-Reagens in den Titrierkolben (1), der ein dehydratisiertes Lösungsmittel enthält,

Durchführen einer coulometrischen Rücktitration in einem Potentialkontrollverfahren unter Verwendung der Elektrolyse-Steuereinheit (20) und der elektrolytischen Elektroden (12); und

Berechnen des Titers des Karl-Fischer-Reagens unter Verwendung der Berechnungseinheit (40), basierend auf der während der coulometrischen Rücktitration verbrauchten Elektrizitätsmenge.


 


Revendications

1. Procédé de titrage Karl Fischer au moyen d'un appareil de titrage Karl Fischer comprenant un vase de titrage (1) équipé d'électrodes électrolytiques (12) incluant une anode (12a) et une cathode (12k) avec une membrane (12m) entre les deux, d'une électrode de détection (13) destinée à détecter un état de polarisation d'une solution dans le vase de titrage (1) et d'une électrode de référence (17) destinée à détecter un potentiel entre l'anode (12a) et l'électrode de référence (17), l'appareil comprenant, en outre, une unité de commande d'électrolyse (20) et une unité de calcul (40), le procédé comprenant les étapes consistant à :

introduire un réactif Karl Fischer dans le vase de titrage (1) contenant un solvant déshydraté ;

réaliser un rétrotitrage coulométrique selon une méthode à potentiel contrôlé en utilisant l'unité de commande d'électrolyse (20) et les électrodes électrolytiques (12) ; et

calculer le titre du réactif Karl Fischer en utilisant l'unité de calcul (40) sur la base de la quantité d'électricité consommée pendant le rétrotitrage coulométrique.


 




Drawing


























Cited references

REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description




Non-patent literature cited in the description