JP2011106954A - Monitoring method of concentration of polyhydric phenol - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monitoring method of a concentration of a polyhydric phenol which correctly detects the concentration of the polyhydric phenol within a polyhydric phenol-containing liquid in real time. <P>SOLUTION: There is provided the monitoring method of the polyhydric phenol which measures the concentration of the polyhydric phenol within the polyhydric phenol-containing liquid from an oxidation-reduction peak of a current generated by changing a potential applied to an electrode immersed in the polyhydric phenol-containing liquid, and containing a carbon element. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for monitoring the concentration of polyhydric phenols for electrochemically detecting polyhydric phenols in a polyhydric phenol-containing liquid.

  There is a technique for concentrating shochu and fruit juice and using it as a feed material or a food material. For example, Patent Document 1 discloses that concentration is performed by evaporating water of shochu in a concentration facility, and this is used as a feed material.

  When performing such concentration, a Kett moisture meter has been conventionally used to control the degree of concentration. However, in this method, since a time lag of 1 to 2 hours is required until the measurement is completed, the concentration cannot be monitored in real time, and it is difficult to achieve the target concentration.

  If the degree of concentration exceeds a certain level, the viscosity of the concentrated solution increases, causing problems such as being unable to be removed from the evaporator. On the other hand, if the concentration is insufficient, problems such as corruption occur and the product value decreases.

  The concentration can be tracked by tracking the concentration of a specific component in the concentrate by liquid chromatography, but the installation and maintenance of the equipment is expensive, and this method also provides full real-time monitoring. It does not make it possible.

  In order to set the concentration of the concentrate to the target concentration, it is necessary to establish a method for monitoring the concentration accurately and in real time, but there has been no such monitoring method in the past.

JP 2006-320206 A

  The present inventor pays attention to the fact that shochu and fruit juice contain relatively abundant polyhydric phenols known to have redox activity, and monitor these by electrochemical measurement. Therefore, it was studied to monitor the concentration of the concentrate.

  If it is an electrochemical measurement method, real-time monitoring is possible. However, polyhydric phenols have low redox activity at the electrode, extremely low detection sensitivity, and it has been impossible to accurately measure the concentration.

  The present inventors diligently studied to improve the detection sensitivity of polyhydric phenols in an electrochemical measurement method capable of real-time monitoring, and reached the present invention.

  Therefore, an object of the present invention is to provide a method for monitoring the concentration of polyhydric phenols that can accurately and in real time detect the concentration of polyhydric phenols in the polyhydric phenol-containing liquid.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
The concentration of polyhydric phenols in the polyhydric phenol-containing liquid is measured from the redox peak of the current generated by changing the potential applied to the electrode containing the carbon element impregnated in the polyhydric phenol-containing liquid. A method for monitoring polyhydric phenols characterized by the above.

(Claim 2)
2. The method for monitoring polyhydric phenols according to claim 1, wherein the electrode containing carbon element is made of carbon and / or graphite powder solidified by a binder.

(Claim 3)
3. The polyhydric phenol according to claim 1, wherein the potential applied to the electrode containing carbon element is changed by sweeping a potential in a range of −1.2 V to +1.2 V at maximum with respect to a hydrogen electrode. Monitoring method.

(Claim 4)
2. The concentration of polyhydric phenols is measured by eliminating interference caused by an interfering substance having oxidation and / or reduction activity at a potential overlapping with a redox peak of a current exhibited by the polyhydric phenol. The monitoring method of polyhydric phenols in any one of -3.

(Claim 5)
The interfering substance has only an oxidation or reduction activity at a potential overlapping with the redox peak of the current exhibited by the polyhydric phenol, and exclusion of interference by the interfering substance is performed on the oxidation side or the reduction side peak. 5. The method for monitoring polyhydric phenols according to claim 4, wherein the polyphenols are measured by measuring the concentration of polyhydric phenols from the current peak on the side where the interfering substance has no activity.

(Claim 6)
The interference substance has oxidation and / or reduction activity on both the electrode containing carbon element and the platinum group metal electrode, and the elimination of interference by the interference substance is a detection electrode containing carbon element; 5. The method according to claim 4, wherein a current peak at a specific electrode potential is measured with a platinum group metal electrode, and a concentration of polyhydric phenols is measured from a difference in peak heights. To monitor polyhydric phenols.

(Claim 7)
The method for monitoring a polyhydric phenol according to any one of claims 1 to 6, wherein the polyhydric phenol-containing liquid is food such as fruit juice or a fermentation residue such as food waste liquid or shochu.

  According to the method for monitoring polyhydric phenols of the present invention, the concentration of polyhydric phenols in various liquids containing polyhydric phenols can be monitored accurately and in real time.

  Moreover, according to the monitoring method of polyhydric phenols of this invention, the density | concentration of polyhydric phenols can be monitored more correctly, eliminating the interference by an interference substance.

  In addition, according to the method for monitoring polyhydric phenols of the present invention, the concentration of the concentrate containing the polyphenols can be monitored accurately and in real time, and the concentrate can be set to the target concentration. it can.

  Furthermore, when the polyphenols are recovered as valuables from the polyhydric phenol-containing liquid by a known method, the polyphenols concentration is measured in advance by the polyphenols concentration monitoring method of the present invention. Since the recovery amount can be predicted by performing the step, the polyhydric phenols can be recovered efficiently.

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  Embodiments of the present invention will be described below.

  In the method for monitoring the concentration of polyhydric phenols of the present invention, polyhydric phenols are obtained from the redox peak of the current generated by changing the potential applied to the electrode containing the carbon element impregnated in the polyhydric phenol-containing liquid. Polyhydric phenols in the contained liquid are detected.

  The polyhydric phenols refer to compounds having a plurality of phenolic hydroxy groups (hydroxy groups bonded to an aromatic ring such as a benzene ring and a naphthalene ring) in the molecule, for example, flavans, chalcones, flavanones, Flavonoids such as flavones, flavonols, flavonols, flavanols (catechins), isoflavones, anthocyanidins, stilbenoids, lignans, coumarins, curcumins, chlorogenic acids, ellagic acids, tannins, phenylcarboxylic acids (gallic acid) Acid) and the like, and further, anthraquinones, which have redox activity.

  The polyhydric phenol-containing liquid is a liquid containing at least the polyhydric phenols, and preferable examples thereof include foods such as fruit juice, food waste liquids, and fermentation residues such as shochu.

  The electrode containing carbon element is preferably made of carbon and / or graphite powder solidified by a binder. Those having a carbon content of 50% or more on the electrode surface can be preferably used.

  When an electrode containing such a carbon element is used as a detection electrode, it has a property that polyhydric phenols are easily adsorbed to carbon. The amount of polyphenols to be performed is increased, and the detection sensitivity is dramatically improved.

  In addition, the amount of polyhydric phenols adsorbed on the electrode containing carbon element varies with the amount of polyhydric phenols in the liquid due to adsorption equilibrium. Therefore, it is possible to monitor the concentration of polyhydric phenols in the liquid by detecting the redox peak of the current exhibited by the polyhydric phenols adsorbed on the electrode.

  As a method of changing the potential applied to the electrode containing carbon element, either a potential sweep method in which the potential is continuously changed or a potential step method in which the potential is changed in steps may be used. For example, a cyclic voltammetry method can be preferably exemplified.

  The potential applied to the carbon element-containing electrode can be changed by sweeping the potential in the range of −1.2 V to +1.2 V, preferably −1.0 V to +1.0 V, based on the hydrogen electrode. preferable. The peak of current exhibited by polyhydric phenols is usually detected at a potential within this range.

  Since the peak height of the obtained redox peak is proportional to the concentration of polyhydric phenols, the concentration of polyhydric phenols can be quantified by referring to a calibration curve or the like. When using a calibration curve, it is preferable to use one prepared under the same temperature conditions in order to eliminate the temperature dependence of the peak height.

  Moreover, a peak can be measured more clearly by using the differential curve of a voltammogram. This further improves the accuracy of concentration monitoring.

  By the way, when an interfering substance having oxidation and / or reduction activity exists at a potential overlapping with the current peak of the polyhydric phenol in the liquid, a large amount of electric current is caused by the current resulting from the electrode electron transfer reaction of the interfering substance. In some cases, currents represented by polyhydric phenols interfere with each other, making accurate measurement difficult. In such a case, it is preferable to measure the concentration of polyhydric phenols by eliminating interference caused by interfering substances. The specific method will be described below.

  First, it is conceivable that the interfering substance has only oxidation or reduction activity at a potential overlapping with the current peak exhibited by the polyhydric phenols. As such an interfering substance, for example, ascorbic acid showing only oxidation activity can be mentioned.

  The redox reaction of ascorbic acid is very complicated, and the oxide (dehydroascorbic acid) shows high stability. It is not easy to reduce this oxide back to ascorbic acid. Because of such characteristics, ascorbic acid shows a current peak only on the oxidation side in the electrode electron transfer reaction. Furthermore, when the potential sweep is repeated, the concentration of ascorbic acid in the vicinity of the electrode is changed to an oxide and the concentration thereof is reduced. Along with this, the peak of current due to oxidation is also reduced. This change in current due to oxidation occurs regardless of the concentration. In particular, the tracking of the degree of concentration requires that a certain correlation is established between the concentration of the concentrate and the current peak. However, an interfering substance having only either an oxidation or reduction activity, such as ascorbic acid, reflects a change caused by a reduction in reduced or oxidized form as described above, in addition to a change caused by concentration. This is a mechanism of interference by an interfering substance having only an oxidation or reduction activity at a potential overlapping with a current peak exhibited by polyhydric phenol.

  Such interference is eliminated by measuring the concentration of polyphenols from the observed peak on the oxidation side or reduction side on the side where the interference substance has no activity. It can be carried out.

  On the other hand, based on the electrode dependency of redox activity, interference by an interference substance can be eliminated by a method different from the above method. Interfering substances to which this method is applied are those that have oxidation and / or reduction activity on both the carbon element-containing electrode and the platinum group metal electrode, and as described above, either oxidation or reduction activity. It is possible to eliminate interference not only in the case of having only oxidant but also in the case of having both oxidation and reduction activities.

  That is, polyhydric phenols are active for electrodes containing carbon elements, but are inactive for platinum group metal electrodes. On the other hand, if the interference substance has activity in both of these electrodes, the interference by the interference substance can be eliminated by using a detection electrode containing a carbon element and a platinum group metal electrode. The measurement can be carried out by measuring the current peak at the potential and measuring the concentration of the polyhydric phenols because the difference in peak height corresponds to the current peak of the polyhydric phenols.

  According to the method for monitoring the concentration of polyphenols of the present invention, the concentration of polyphenols in a liquid containing polyphenols can be measured accurately and in real time.

  For example, if the method for monitoring the concentration of polyhydric phenols of the present invention is used, polyhydric phenols in a concentrated liquid containing polyhydric phenols can be detected with high sensitivity and in real time. By monitoring the concentration of the liquid, the concentration can be accurately controlled, and the concentrated solution can have the target concentration.

  Further, for example, when polyhydric phenols are recovered as valuables from a polyhydric phenol-containing liquid by a known method, the concentration of the polyhydric phenols is previously measured by the polyhydric phenol concentration monitoring method of the present invention. Since the recovery amount can be predicted by performing the measurement, the polyhydric phenols can be efficiently recovered.

  Examples of the present invention will be described below, but the present invention is not limited to such examples.

  Cyclic voltammetry measurement was performed on the shochu concentrate collected from the evaporator, and in parallel, the solid content concentration was measured by a dry weighing method.

  The conditions for the cyclic voltammetry measurement are as follows. At 15 ° C., cylindrical graphite (1 mmφ) is used for the detection electrode, and the potential window is −0.9 V to +0.9 V (vs Ag / AgCl) (approximately converted to hydrogen electrode standard). −0.7 V to about +1.1 V), and the sweep speed was 0.1 V / sec.

  The voltammogram after concentration is shown in FIG. Moreover, the differential curve of the voltammogram in FIG. 1 is shown in FIG. Furthermore, the correlation between the peak height of the current on the reducing side in FIG. 1 and the solid content concentration is shown in FIG.

<Evaluation>
From the results shown in FIG. 1, it can be seen that the peak height at the current peak on the reduction side increases with the solid content concentration.

  From the results shown in FIG. 2, it can be seen that the peak of the current on the reduction side becomes clearer by representing it as a differential curve.

  From the result shown in FIG. 3, a proportional relationship is recognized between the peak height of the current on the reduction side and the solid content concentration. That is, it is possible to monitor the solid content concentration, that is, the concentration, from the peak height of the current on the reduction side. In the concentrated liquid, the change in the solid content concentration is proportional to the concentration of the polyhydric phenols. Therefore, it can be seen that the peak height of the current on the reduction side and the concentration of the polyhydric phenols are also proportional. Furthermore, the concentration of the polyhydric phenols can be quantified by referring to the measured peak height of the polyhydric phenols with a calibration curve prepared in advance.

Claims (7)

  The concentration of polyhydric phenols in the polyhydric phenol-containing liquid is measured from the redox peak of the current generated by changing the potential applied to the electrode containing the carbon element impregnated in the polyhydric phenol-containing liquid. A method for monitoring polyhydric phenols characterized by the above.   2. The method for monitoring polyhydric phenols according to claim 1, wherein the electrode containing carbon element is made of carbon and / or graphite powder solidified by a binder.   3. The polyhydric phenol according to claim 1, wherein the potential applied to the electrode containing carbon element is changed by sweeping a potential in a range of −1.2 V to +1.2 V at maximum with respect to a hydrogen electrode. Monitoring method.   2. The concentration of polyhydric phenols is measured by eliminating interference caused by an interfering substance having oxidation and / or reduction activity at a potential overlapping with a redox peak of a current exhibited by the polyhydric phenol. The monitoring method of polyhydric phenols in any one of -3.   The interfering substance has only an oxidation or reduction activity at a potential overlapping with the redox peak of the current exhibited by the polyhydric phenol, and exclusion of interference by the interfering substance is performed on the oxidation side or the reduction side peak. 5. The method for monitoring polyhydric phenols according to claim 4, wherein the polyphenols are measured by measuring the concentration of polyhydric phenols from the current peak on the side where the interfering substance has no activity.   The interference substance has oxidation and / or reduction activity on both the electrode containing carbon element and the platinum group metal electrode, and the elimination of interference by the interference substance is a detection electrode containing carbon element; 5. The method according to claim 4, wherein a current peak at a specific electrode potential is measured with a platinum group metal electrode, and a concentration of polyhydric phenols is measured from a difference in peak heights. To monitor polyhydric phenols.   The method for monitoring a polyhydric phenol according to any one of claims 1 to 6, wherein the polyhydric phenol-containing liquid is food such as fruit juice or a fermentation residue such as food waste liquid or shochu.

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