JP6534264B2 - Measurement method of dissolved hydrogen concentration - Google Patents

Description

The present invention relates to a method of measuring the concentration of hydrogen molecules dissolved in clean water such as neutral hydrogen water, electrolyzed water, alkali ion water and the like, and a dissolved hydrogen concentration meter.

  Conventionally, a dissolved hydrogen concentration meter by an electrochemical measurement method using a diaphragm type polarographic electrode shown in FIG. 7 and an ORP electrode shown in FIG. 8 has been put to practical use.

In the diaphragm type polarographic electrode system, a constant potential is applied between the working electrode 14 disposed in close contact with the diaphragm 11 and the counter electrode 15 immersed in the electrolyte 13, and the sample to be measured (hereinafter referred to as a sample). When hydrogen molecules contained in the metal reach the platinum or platinum-plated working electrode 14 through the gas-permeable diaphragm 11, hydrogen molecules (H ₂ ) represented by the chemical formula 1 are formed on the electrode surface. An oxidation reaction occurs, and a reduction reaction of silver chloride (AgCl) shown in chemical formula 2 occurs in the counter electrode 15 composed of silver-silver chloride, and a microcurrent proportional to the amount of hydrogen between the working electrode 14 and the counter electrode 15 is Flow. The hydrogen concentration of the sample is determined from this current value.

  In addition, since the permeability of gas changes with the water temperature, the diaphragm 11 provides the temperature measurement part 16 in the housing 12, and performs temperature correction | amendment of a measurement result.

  The electrode configuration of the ORP electrode system is shown in FIG.

  In the ORP electrode system, the detection unit 31 is made of platinum, and the working electrode 32 detects the potential generated by the difference between the hydrogen molecules in the sample and the hydrogen ion activity (hydrogen ion concentration).

  In addition, the hydrogen concentration is calculated from the redox potential corresponding to the difference between the reference potential generated at the comparison electrode 35 which is made of silver-silver chloride and is immersed in the electrolyte 34 and the single electrode potential generated at the working electrode. I'm asking.

  Furthermore, at the lower end of the housing 36 shown in FIG. 8, a liquid junction 37 made of porous ceramic is provided to maintain the electrical connection between the sample and the comparison electrode 35.

The reference potential described above varies depending on the type of the electrolyte 34, and is, for example, 257 mV (25 ° C.) when using a 3.3 M potassium chloride solution and 219 mV (25 ° C.) when using a 3 M potassium chloride solution.
Generally, a potassium chloride solution having the above-mentioned concentration which has a known reference potential is employed, but in principle, other concentrations of potassium chloride solution which give a constant potential can also be used.

The redox potential due to the dissolved hydrogen is given by the Nernst equation according to the redox reaction shown in the above chemical formula 1 by the Nernst equation, and the concentration of hydrogen ions ([H ⁺ ]) which is an oxidant and the concentration of dissolved hydrogen molecules which is a reductant It is determined by ([H ₂ ]).

E _{H in} equation 1 is the redox potential, E _H ⁰ is the standard redox potential of hydrogen, R is the gas constant, T is the absolute temperature, n is the number of electrons delivered according to formula 1 (n = 2), F is the faraday The constant, pH, indicates the pH value of the sample. The E _H ⁰ is defined as 0 V at all temperatures by IUPAC (International Union of Pure and Applied Chemistry).

  Similarly, the Nernst equation holds for the redox reaction of dissolved oxygen.

An example of the oxidation-reduction reaction of dissolved oxygen is shown in Formula 3, and the oxidation-reduction potential given by the Nernst formula by this reaction is shown in Formula 2.

From Equation 2, the oxidation-reduction potential E _O varies with the dissolved oxygen concentration ([O _2]).
In a sample in which hydrogen and oxygen coexist, the redox potential is detected as a mixture of the aforementioned redox potential (E _H ) determined by the dissolved hydrogen concentration and pH and the redox potential of oxygen (E _O ) Dissolved oxygen will affect the measurement of dissolved hydrogen concentration.

Note that, under the condition that the dissolved oxygen and pH are constant, the redox potential of the dissolved oxygen is kept constant, and according to Equation 1, the dissolved hydrogen concentration ([H ₂ ]) to be measured and the redox potential (E _H ) are It has a correlation. Therefore, in the ORP electrode system, the dissolved hydrogen concentration is determined by measuring the oxidation-reduction potential (E _H ).

JP 2002-195975 A

  In the conventional diaphragm type polarographic electrode system, since the working electrode is separated from the sample by the diaphragm, it is difficult to be affected by impurities, and the current value flowing according to the oxidation reaction of hydrogen molecules is measured. High accuracy measurement can be realized.

  However, in order to correct the change in gas permeability of the diaphragm due to the sample temperature, it is necessary to mount a temperature measuring unit in the electrode.

  In addition, a power supply circuit that supplies a constant potential constantly between the working electrode and the counter electrode, an amplification circuit for determining changes in minute current and noise control are required, and a complex control circuit is required, so a large and expensive measurement is required. It is a bowl.

  In addition, in a sample containing a large amount of micro bubbles such as electrolyzed water, a gas permeates into the electrode, and a bubble that affects the electrode response is formed in the electrolyte solution in a short period of time. And complicated maintenance such as replacement.

  On the other hand, in the ORP electrode method, since the potential generated at the electrode is directly replaced with the dissolved hydrogen concentration, a measuring instrument with an extremely simple configuration can be realized, but the electrode potential is large due to the pH of the sample and the coexisting dissolved oxygen. to be influenced.

As described above, the redox potential E _H of Formula 1 indicates the potential corresponding to the dissolved hydrogen concentration under the conditions of the dissolved oxygen concentration and the constant pH, but the dissolved oxygen concentration and the pH indicate the water temperature and free carbonic acid concentration of the sample, etc. In the ORP electrode system, the water quality of the sample that can be measured has become extremely limited.

  In particular, it was not possible to measure the dissolved hydrogen concentration of the hydrogen water or the alkaline ionized water prepared using electrolysis in which the fluctuation of the dissolved oxygen concentration or pH is remarkable.

In order to solve the above-mentioned problems, appropriate amounts of glucose oxidase and catalase are added to samples of various pH including dissolved hydrogen and dissolved oxygen, and hydrogen phosphate having pH buffer function of glucose and neutral region is combined. Add a liquid reagent that contains sodium and potassium dihydrogen phosphate.
The appropriate amounts of glucose oxidase and catalase correspond to addition amounts such that the former activity is 5 kU / L or more, preferably 10 kU / L or more and the latter activity is 0.5 MU / L or more after addition to the sample. The unit of activity (U / L) represents the reactivity of glucose oxidase or catalase in one liter, and in the case of glucose oxidase, glucose and oxygen are reacted at 25 ° C. and pH 7, gluconic acid δ-lactone The reactivity of glucose oxidase capable of producing 1 μmol is 1 U. In the case of catalase, the reactivity of catalase capable of decomposing 1 μmol of hydrogen peroxide in 1 minute at 25 ° C. and pH 7 is 1 U.

  ORP consisting of a working electrode with a platinum-black plated platinum electrode (hereinafter referred to as a platinum-black-plating electrode) and a reference electrode in which a silver-silver chloride electrode is immersed in an electrolyte consisting of a potassium chloride solution The redox potential of the sample subjected to the above-mentioned pretreatment is measured using an electrode, and converted to the concentration of dissolved hydrogen.

  The catalytic action of glucose and glucose oxidase, catalase decomposes the dissolved oxygen affecting the redox potential, and the buffer function of disodium hydrogen phosphate and potassium dihydrogen phosphate can keep the pH of the sample constant. .

  In addition, since glucose oxidase and catalase selectively exert a catalytic function, stable measurement can be realized without affecting the redox potential even under reagent-rich conditions.

  In addition, by adopting a platinum black plating electrode having an extremely large specific surface area, the hydrogen storage capacity can be increased, and a stable potential response to dissolved hydrogen can be obtained.

  In addition, the conventional ORP electrode which used the platinum electrode for the working electrode by the dissolved hydrogen concentration meter of the above-mentioned structure can also be utilized. In this case, the stability of the electrode response is slightly reduced compared to the platinum black plated electrode, but high merits can be created in terms of maintainability and cost as described later.

  According to the present invention, it is possible to realize a small-sized and inexpensive densitometer capable of measuring dissolved hydrogen concentration with high accuracy even to electrolyzed water such as hydrogen water or alkaline ion water showing various dissolved oxygen concentrations and pH.

It is a figure which shows the relationship between the detection electric potential of the dissolved hydrogen concentration meter of this invention, and dissolved hydrogen concentration. It is a figure which shows the change of the dissolved oxygen concentration with respect to the activity of glucose oxidase. It is a figure which shows the activity of catalase, and the relationship of a detection potential. It is a figure which shows the electrode structure of the dissolved hydrogen concentration meter of this invention. It is a figure which shows the result of having measured the dissolved hydrogen concentration using a platinum electrode. It is a figure which shows the result of having measured the dissolved hydrogen concentration in the working electrode provided with the platinum black plating electrode using the liquid reagent I stored refrigerated for six months. It is a figure which shows the structure of the diaphragm type polarographic electrode of a prior art. It is a figure which shows the structure of ORP electrode of a prior art. It is a figure which shows the structure of a hydrogen electrode. It is a figure which shows an example of the electrode response of the dissolved hydrogen concentration meter of this invention.

  In the dissolved hydrogen concentration meter of the present invention, the decomposition reaction of dissolved oxygen used for the pretreatment of a sample is represented by Formula 4.

As shown in chemical formula 4 (1), dissolved oxygen in the sample generates gluconic acid and hydrogen peroxide (H ₂ O ₂ ) when glucose is added in the presence of glucose oxidase.

Also, as shown in chemical formula 4 (2), hydrogen peroxide generated in the presence of catalase forms oxygen (O ₂ ) and water (H ₂ O), and as shown in chemical formula 4 (3), the total reaction Then, gluconic acid is produced from oxygen and glucose, and the dissolved oxygen is eliminated.

  The dissolved oxygen can also be eliminated by the addition of sulfite, ascorbic acid, iron (II) ions, etc. However, when sulfite is used, the pH shifts to the acid side as the dissolved oxygen is recovered. In addition, when ascorbic acid is used, when it is dissolved in water, it exhibits an acidity of about pH 2 to 3, and any of them causes a large positive error to the redox potential.

On the other hand, iron (II) ions react with dissolved oxygen to form alkaline iron (II) hydroxide, and iron (II) hydroxide further forms iron (III) hydroxide to form colloids. . For this reason, a negative error of the redox potential occurs due to the pH increase, or the fouling by the colloid causes a decrease in the sensitivity of the electrode.
Due to the above problems, it is difficult to apply any of the components described above to the measurement of hydrogen concentration using the redox potential.

  On the other hand, glucose is said to exhibit reducibility because it has an aldehyde group (-CHO), but it does not exhibit the function of eliminating dissolved oxygen alone when the strong alkaline region is removed at normal temperature, which is stable is there. For this reason, even when an excessive amount of glucose is added to the dissolved oxygen concentration, no pH fluctuation occurs and the redox potential is not affected.

  In addition, since glucose oxidase acts as a catalyst for selectively promoting the reaction of glucose and oxygen, the reaction with excess glucose does not proceed after dissolved oxygen is eliminated, and there is no effect on the redox potential.

  FIG. 2 shows changes in dissolved oxygen concentration of samples prepared to have different activities by changing the amount of glucose oxidase added to hydrogen water generated by electrolysis.

  It has been confirmed that when the addition amount (activity) of glucose oxidase decreases, the decrease rate of the dissolved oxygen concentration tends to decrease. Since it takes time to stabilize the redox potential of the sample as the rate of decrease of the dissolved oxygen concentration slows down, in the present invention, the activity of glucose oxidase is 5 kU / L or more, preferably 10 kU / L or more for practical use. Prepare to.

  As shown in the chemical formula 4 (3), since the reaction proceeds with 2: 1 stoichiometrically, glucose and oxygen are required to be applied to saturated oxygen water (about 40 mg / L, 25 ° C.) The concentration needs to be about 2.5 mM or more, but as shown in FIG. 1 described later, it has been confirmed that the measurement of the dissolved hydrogen concentration is not affected even under a large excess condition.

  After adding glucose oxidase 10 kU / L, glucose 0.045 M and disodium hydrogen phosphate as a pH adjuster to 0.025 M each to hydrogen water produced by electrolysis in Fig. 3 and then adding catalase It shows the change of the redox potential of the samples prepared by changing the addition amount to have different activities.

  As shown in FIG. 3, since the redox potential of the sample is almost constant when the catalase activity is in the range of 0.7 to 4.5 MU / L, it is possible to measure the dissolved hydrogen concentration even if an excess amount of catalase is present like the above-mentioned glucose. Has confirmed that it will not affect.

  In order to secure a measurement accuracy of about 0.1 mg / L, it is necessary to suppress the fluctuation of the redox potential to 2 mV or less, and according to the test results of FIG. 3, the activity of catalase is at least 0.5 MU / L or more. Is desirable.

  In addition, gluconic acid produced after dissolved oxygen decomposition is weakly acidic and affects the redox potential of the sample, so that the concentration in the sample is 0.025 M each, disodium hydrogen phosphate and potassium dihydrogen phosphate The pH of the sample after reaction can be maintained at around 6.9 (25.degree. C.) to remove the influence of gluconic acid production by adding.

  Similarly, the above-mentioned phosphate may be substituted, or the above-mentioned disodium hydrogen phosphate and diphosphoric acid may be substituted for the above-mentioned phosphate so that potassium hydrogen phthalate 0.05 M having weak acid buffer function and pH 4.0 (25 ° C.) can be obtained. The addition amount of hydrogen potassium may be changed to adjust to any pH within pH 4-9.

  The structure of the electrode used to measure the dissolved hydrogen concentration is shown in FIG.

  A comparative electrode 7 provided with a working electrode 5 in which platinum black plating 4 is applied to the surface of the platinum electrode 3 at the tip in a state separated from the electrolytic solution 2 in the housing 1 and a detection unit 6 composed of silver-silver chloride Is immersed in an electrolytic solution 2 consisting of a 3.3 M or 3 M potassium chloride solution.

  Further, in order to maintain the electrical connection between the sample and the reference electrode 7, a liquid junction 8 made of porous ceramic is provided at the tip.

  Since the surface area of the electrode can be expanded by applying platinum black plating 4 to the working electrode 5, the adsorption action of hydrogen molecules works, the electrode sensitivity to hydrogen is improved, the electrode response is stabilized, and highly accurate measurement can be realized.

  Note that although platinum black plating simultaneously exhibits the adsorptive action of dissolved oxygen, the electrode response can be purely dependent on the concentration of hydrogen molecules since dissolved oxygen can be almost completely removed by adding the above-mentioned reagent. become.

  A hydrogen electrode is known as an electrode for determining a reference potential of electrochemical analysis.

  FIG. 9 shows the structure of the hydrogen electrode.

  The hydrogen electrode has a structure in which an excessive amount of hydrogen gas 22 is supplied to the surface of a platinum black-plated electrode 21 and immersed in a solution 23 having a hydrogen ion activity of 1. The pole potential is defined as 0V.

  The hydrogen electrode has many problems in terms of maintenance and safety, and as a substitute for this, a comparative electrode in which the above-described silver-silver chloride is used for the electrode and is immersed in a potassium chloride solution has been put to practical use.

  In the present invention, the potential generated at the electrode 21 fluctuates depending on the amount of adsorption of hydrogen 22 and the hydrogen ion activity of the solution 23, and the amount of adsorption of hydrogen 22 on the electrode 21 is constant when the hydrogen ion activity of the solution is constant. A platinum black-plated electrode was adopted as the working electrode under the assumption that a certain potential fluctuation occurred accordingly.

  The aforementioned glucose oxidase, glucose, catalase and pH adjuster are added to a sample containing dissolved hydrogen and dissolved oxygen, and the electrode shown in FIG. 4 described above is immersed to dissolve hydrogen from the potential between the working electrode 5 and the reference electrode 7 Determine the concentration.

  The platinum black plated electrode is also adopted in the above-mentioned diaphragm type polarographic electrode system which is the prior art, but in the same system, a constant potential is established between the working electrode and the counter electrode so as to advance the oxidation reaction of hydrogen molecule shown in chemical formula 1. Is continuously given, and the working surface of the working electrode maintains the adsorption state of hydrogen molecules according to the concentration of dissolved hydrogen.

  On the other hand, in the dissolved hydrogen concentration meter of the present invention, since the decomposition reaction of hydrogen molecules is not intentionally performed, adsorption of hydrogen molecules on the electrode surface progresses with time, and an electrode response having a correlation with dissolved hydrogen concentration However, the inventors confirmed that the electrode response that can realize the determination of the dissolved hydrogen concentration.

  After preparing electrolytic water samples with different dissolved hydrogen concentration, glucose oxidase 13 kU / L, glucose 0.045 M, catalase 2.7 MU / L, disodium hydrogen phosphate as pH adjuster, and potassium dihydrogen phosphate as 0.025 M each The results of measuring the electrode response are shown in FIG.

  In addition, the 3.3 M potassium chloride solution was utilized for the electrolyte solution of an electrode for this verification. In addition, a working electrode in which platinum black plating was performed on a round platinum electrode of φ3 mm was used.

  The detected potential was correlated with the concentration of dissolved hydrogen, and when the concentration of dissolved hydrogen was in the range of 0.2 to 1.6 mg / L, a redox potential of -565 to -595 mV was given.

  FIG. 10 shows an example of the electrode response.

  As shown in FIG. 10, the electrode response at any concentration shows a tendency for the potential to drop sharply after measurement starts and to rise again after reaching the predetermined lower limit potential, but the lower limit potential corresponding to each concentration It has been confirmed that it is effective to use the lower limit potential as determination information of the dissolved hydrogen concentration because of the characteristic that it can be maintained for several minutes.

  In addition, in realizing the measuring instrument, the electrode characteristics in FIG. 1 are stored in advance as a calibration curve, or an approximate expression of the electrode characteristics is stored in hardware, and the lower limit potential reached by the detected potential is read. Equipped with detection and calculation functions to be replaced.

  As described above, in the dissolved hydrogen concentration meter of the present invention, by adding an enzyme catalyst and a pH adjuster that do not affect the detection potential, and adopting a platinum black plating electrode having high sensitivity response to hydrogen molecules, A stable measurement of dissolved hydrogen concentration can be realized without being influenced by the dissolved oxygen concentration and pH.

  In addition, since there are many types of pretreatment reagents added to the sample for practical use, and it takes time and effort to measure and dissolve, liquid reagent I and glucose in which an appropriate amount of glucose oxidase and catalase are dissolved in clean water Prepare a liquid reagent II in which a predetermined amount of pH adjuster such as disodium hydrogen phosphate or potassium dihydrogen phosphate is dissolved in clean water, and use the method of quantitatively adding each liquid reagent with a syringe etc. It is valid.

  The electrode used for the dissolved hydrogen concentration meter of the present invention has a small diameter rod structure provided with a platinum black plating electrode as a detection unit as shown in FIG. Immersion and measurement of dissolved hydrogen concentration can be performed.

For example, when the sample volume is 15 mL and glucose oxidase having activity of 200 kU / g and catalase at 10 MU / g are used as a raw material, 0.25 g or more of glucose oxidase, more preferably 0.5 g or more, 0.5 g or more of catalase, pure water The aforementioned liquid reagent I is prepared by dissolving in 1 L.
At this time, the activity of glucose oxidase of liquid reagent I is 50 kU / L or more, more preferably 100 kU / L or more, and the activity of catalase is 5 MU / L or more.

Further, a liquid reagent II is prepared by dissolving 3 g or more of glucose, 23.8 g of disodium hydrogen phosphate, and 22.8 g of potassium dihydrogen phosphate in 1 L of pure water.
At this time, the glucose concentration of the liquid reagent II is about 17 mM or more, and the concentrations of disodium hydrogen phosphate and potassium dihydrogen phosphate are each about 0.17 M.

  By adding 2 mL of liquid reagent I and 3 mL of liquid reagent II to 15 mL of the sample, the glucose oxidase activity of the sample is 5 kU / L or more, more preferably 10 kU / L, and the catalase activity is 0.5 MU / L or more. The concentration of glucose is 2.5 mM or more, and the concentrations of disodium hydrogen phosphate and potassium dihydrogen phosphate each are 0.025 M, and the dissolved oxygen of the sample can be decomposed and the pH can be adjusted.

  The activity of the raw material of glucose oxidase and catalase used in the above-mentioned liquid reagent I, and the activity, concentration and addition amount of each component of liquid reagent I and liquid reagent II are one example, and in the sample after addition of both liquid reagents Any conditions may be set for the raw material activity, the activity of the liquid reagent I, the concentration of each component of the liquid reagent II, and the addition amount of the liquid reagent I and the liquid reagent II so that the component .

  In addition, the stability of the enzyme in an aqueous solution is not sufficiently known, and in particular, cryopreservation with glucose oxidase alone is common, but even when stored under refrigeration for 6 months at the verification stage of the present invention It has been confirmed that the function of the liquid reagent I described above does not deteriorate, and it can be treated as a reagent with sufficient practicality.

  FIG. 6 shows the measurement results of the dissolved hydrogen concentration using liquid reagent I stored refrigerated for 6 months.

  The results in FIG. 6 were obtained by investigating the deviation from the reference concentration using a measuring device incorporating the above-described approximate expression of the electrode characteristics, and stable concentration measurement even when using liquid reagent I after storage for 6 months in a refrigerator Indicates that can be achieved.

  Furthermore, glucose oxidase used in the present invention, catalase is a protein, and glucose is a saccharide, both of which are biodegradable, and phosphate of a pH adjusting agent is also contained in general environmental water Can be provided as a safe and environmentally friendly reagent.

  On the other hand, the dissolved hydrogen concentration meter of the present invention can also use the platinum electrode shown in FIG. 8 as a working electrode. In this case, since the hydrogen storage function of the working electrode is lower than that of the platinum black plated electrode, the measurement result has slight variations, but the electrode response equivalent to the case of using the platinum black plated electrode shown in FIG. The determination of the dissolved hydrogen concentration using the lower limit potential can be realized, and the practicality as a simple measuring instrument can be satisfied.

  The measurement result at the time of using a platinum electrode as a working electrode in FIG. 5 is shown.

  Although a measurement error of both positive and negative is confirmed with respect to a reference concentration in the range of 0.2 to 0.4 mg / L of dissolved hydrogen concentration, an accuracy of about ± 0.1 mg / L can be secured.

  In addition, since platinum black plating has a very large surface area, it can not be cleaned with a surfactant, and in addition, its strength is poor, so it can not be cleaned by brushing, but platinum electrodes can easily be initially polished by the user. It is possible to create the merit of providing a lower cost electrode because it can be regenerated and plating is not required.

  By using the dissolved hydrogen concentration meter of the present invention, it is possible to measure the dissolved hydrogen concentration contained in hydrogen water containing abundant dissolved oxygen and alkaline ionized water having a pH of about 10 by a simple operation.

  In addition, while the electrode configuration is simple, the potential fluctuation per dissolved hydrogen concentration of 0.1 mg / L can be detected as a change of several millivolts, so electrical discrimination is easy and highly accurate measurement can be realized.

  In addition, since the potential generated by the dissolved hydrogen concentration and hydrogen ion concentration of the sample is detected, a power source for detection is unnecessary, so the measuring instrument has a very simple configuration of only the input circuit and the arithmetic circuit. It can be realized.

  Furthermore, since the working electrode is in direct contact with the sample, the mixing of air bubbles into the electrolytic solution does not occur, and a measuring instrument that does not require complicated maintenance can be configured.

Reference Signs List 1 housing 2 electrolyte 3 platinum electrode 4 platinum black plating 5 working electrode 6 detection unit made of silver-silver chloride 7 comparison electrode 8 liquid junction

Claims (7)

A working electrode having a platinum electrode exposed to the housing bottom, and immersed in an electrolytic solution consisting of potassium chloride solution having a predetermined concentration, isolated silver - a reference electrode having a silver chloride electrode, before xylo gold electrode using an electrode having a liquid junction formed of porous ceramic which is parallel in the housing lower end spaced apart from the, 5kU / L or more as an active glucose oxidase, 0.5 mU / L over the activity of catalase, 2.5 mM as the concentration of glucose A measurement method of dissolved hydrogen concentration characterized by measuring the oxidation-reduction potential of the sample which added the pH adjuster which can be adjusted to the fixed value in pH 4-9 each as above, and determined the lower limit electric potential. . The method for measuring the concentration of dissolved hydrogen according to claim 1, wherein the working electrode is a platinum electrode with platinum black plating . The method of measuring the concentration of dissolved hydrogen according to claim 1 or 2, wherein the concentration of the potassium chloride solution is 3.3M or 3M. A liquid reagent I prepared by dissolving an appropriate amount of glucose oxidase and catalase in clean water so that the activity after addition to the sample is 5 kU / L or more glucose oxidase and 0.5 MU / L or more catalase, and after addition to the sample It is characterized by using a pretreatment reagent comprising a liquid reagent II in which a pH adjuster capable of adjusting the sample to a constant value of 2.5 mM or more and a neutral region or a weakly acidic region is dissolved in clean water. The method for measuring the concentration of dissolved hydrogen according to any one of claims 1 to 3. The method is characterized in that disodium hydrogen phosphate and potassium dihydrogen phosphate each having a concentration of 0.025 M after addition to the sample are added, and a pH adjuster capable of adjusting the sample to around pH 6.9 is used. The measuring method of the dissolved hydrogen concentration in any one of 1 thru | or 4. A pH adjuster capable of adjusting the sample to a constant pH within 4 to 9 is used by adding an appropriate amount of disodium hydrogen phosphate and potassium dihydrogen phosphate to the above-mentioned sample. The measuring method of the dissolved hydrogen concentration in any one of-. The method is characterized in that potassium hydrogen phthalate whose concentration after addition is 0.05 M is added to the sample, and a pH adjuster capable of adjusting the sample to a constant pH around 4.0 is used. The measuring method of the dissolved hydrogen concentration in any one of-.