A convenient method for determining the concentration of hydrogen in water: use of methylene blue with colloidal platinum
 Tomoki Seo^{1},
 Ryosuke Kurokawa^{1} and
 Bunpei Sato^{1}Email author
DOI: 10.1186/2045991221
© Seo et al; licensee BioMed Central Ltd. 2012
Received: 21 July 2011
Accepted: 24 January 2012
Published: 24 January 2012
Abstract
A simple titration (oxidimetry) method using a methylene blueplatinum colloid reagent is effective in determining the concentration of hydrogen gas in an aqueous solution. The method performs as effectively as the more complex and expensive electrochemical method.
Keywords
Hydrogen gas hydrogen waterBackground
Molecular hydrogen is useful for various novel medical and therapeutic applications. In air, hydrogen gas is potentially explosive, whereas, in an aqueous solution, it is safe and convenient to use. Recent biomedical studies have shown that hydrogen is a physiological regulatory factor that has antioxidant, antiinflammatory, and antiapoptotic protective effects on cells and organs [1–5]. As a result, several aqueous solutions of hydrogen have been developed for use in medical applications as well as in health drinks.
Methods/Design
Preparation of MBPt reagent
MB (0.3 g) (WaldeckGmbh & Co KG, Munster, Germany) was dissolved in 98% ethanol (98.9 g) to give a solution of MB (99.2 g) in ethanol. An aqueous suspension of 2% colloidal Pt (0.8 g) (Tanaka Kikinzoku Group Company) was added to the solution and the mixture was stirred to give 100 g of MBPt reagent (MiZ Company, Kanagawa, Japan). The reagent was distributed in small plastic bottles, from each of which one drop of the reagent (17 mg or 0.02 mL) was drawn.
Preparation of hydrogenrich water samples
Hydrogensaturated water (0.8 mM) was prepared by bubbling hydrogen gas through purified water. Three concentrations of hydrogenrich water (0.3, 0.2, and 0.1 mM) were prepared by diluting hydrogensaturated water with purified water.
Determination of hydrogen concentrations
Electrochemical determination of the hydrogen concentration was performed using an electrochemical gas sensor (model DHD11, DKKTOA Corporation, Tokyo, Japan).
Results/Discussion
Similarly, if 20 ml of hydrogen water reduces three drops of the MBPt reagent, the concentration of DH is 43.6 μmol/L or 0.09 mg/L.
Concentrations of Dissolved Hydrogen in Hydrogen Water, Determined by Electrochemical and Oxidimetry Methods
HW  DH (mg/l)  MBPt  MB→DH (mg/l)  DO (mg/l)  T (centigrade) 

0.8 mM  1.60  55  1.65  0.54  24.8 
1.60  55  1.65  0.54  24.8  
1.62  56  1.68  0.45  23.7  
1.58  54  1.62  0.43  23.8  
0.3 mM  0.62  19  0.57  1.6  25.3 
0.62  20  0.6  1.6  25.3  
0.60  18  0.54  2.1  23.5  
0.62  19  0.57  2.3  23.8  
0.2 mM  0.41  12  0.36  2.1  25.1 
0.42  13  0.39  2.3  25.1  
0.41  13  0.39  2.4  23.6  
0.39  12  0.36  2.4  23.7  
0.1 mM  0.22  5  0.15  3.0  24.8 
0.22  5  0.15  3.4  24.8  
0.20  4  0.12  4.3  23.8  
0.19  4  0.12  4.4  23.7 
Although DO was degassed through the process of hydrogen bubbling for hydrogensaturated water (0.8 mmol/L), DO in purified water used for dilution was mixed with hydrogensaturated water, which caused an increase in DO in hydrogen water with dilution magnification. This seemed to cause a deviation in the DH values obtained using the oxidimetry method from those using electrochemical method at a lower concentration of DH.
Concentrations of Dissolved Hydrogen in DORegulated Hydrogen water, Determined by Electrochemical and Oxidimetry Methods
HW  DH (mg/l)  MB  MB→DH (mg/l)  DO (mg/l)  T (centigrade) 

0.8 mM  1.60  55  1.65  0.54  24.8 
1.60  55  1.65  0.54  24.8  
1.62  56  1.68  0.45  23.7  
1.58  54  1.62  0.43  23.8  
0.3 mM  0.61  21  0.63  0.62  23.7 
0.61  21  0.63  0.62  23.7  
0.61  21  0.63  0.87  25.2  
0.62  20  0.6  0.88  25.3  
0.2 mM  0.41  14  0.42  0.68  23.8 
0.41  13  0.39  0.68  23.7  
0.40  13  0.39  0.89  25.1  
0.41  13  0.39  0.87  25.1  
0.1 mM  0.19  6  0.18  0.81  23.5 
0.19  6  0.18  0.81  23.5  
0.20  6  0.18  0.88  25.1  
0.19  6  0.18  0.91  25.1 
The DH values obtained from the oxidimetry method approached those obtained using the electrochemical method. DO as an oxidant would compete with MB when molecular hydrogen reduces MB on the surface of Pt.
•Statistical analysis
Sixteen respective observed values obtained using the electrochemical and the oxidimetry methods were analyzed, premising that these values correspond to each another.
A linear relationship between the values obtained using the oxidimetry method and those obtained using the electrochemical method was shown. This relationship was found using a regression model (linear regression model) having regression coefficients, in which the values obtained using the oxidimetry method were regarded as response variables and those obtained using the electrochemical method were regarded as explanatory variables. The amount of information that can be explained by the straight line was indicated by the coefficient of determination (R^{2}).
Moreover, a secondorder component was added to the regression model to determine whether it deviates from linearity. In addition, the influence of DO and water temperature on the oxidimetry method was also determined.
•Analysis results
1. Linear relation equation
Linear regression equation for the electrochemical and the oxidimetry methods for DOregulated hydrogen water
Parameter  Regression coefficient  Standard error  t value  p value 

Intercept  0.0229  0.0053  4.33  0.0007 
Electrochemical method  1.0459  0.0060  175.38  < 0.0001 
Coefficient of determination  Correlation coefficient  Error standard deviation  
0.9995  0.9998  0.0129 
Linear regression equation for the electrochemical and the oxidimetry methods for DOunregulated hydrogen water
Parameter  Regression coefficient  Standard error  t value  p value 

Intercept  0.0837  0.0066  12.75  < 0.0001 
Electrochemical method  1.0829  0.0074  146.47  < 0.0001 
Coefficient of determination  Correlation coefficient  Error standard deviation  
0.9993  0.9997  0.0158 
2. Examination of linearity
To examine linearity between the electrochemical and the oxidimetry methods, a secondorder term b2 was added to the linear regression model as 'y = b0 + b1 × × + b2 × x^{2}', and the significance level was determined (where b2 is regarded as significant if there is curvature with a second or a higherorder term).
Examination of curvature in the electrochemical and the oxidimetry methods for DOregulated hydrogen water
Parameter  Regression coefficient  Standard error  t value  p value 

Intercept  0.0243  0.0120  2.02  0.0647 
Electrochemical method: firstorder component  1.0508  0.0377  27.84  < 0.0001 
Electrochemical method: secondorder component  0.0026  0.0197  0.13  0.8974 
Examination of curvature in the electrochemical and the oxidimetry methods for DOunregulated hydrogen water
Parameter  Regression coefficient  Standard error  t value  p value 

Intercept  0.0790  0.0156  5.07  0.0002 
Electrochemical method: firstorder component  1.0669  0.0483  22.08  < 0.0001 
Electrochemical method: secondorder component  0.0084  0.0251  0.34  0.7429 
3. Influence of DO and water temperature on the oxidimetry method
Statistical test results of the multiple regression model having values measured by the oxidimetry method as response variables, values measured by the electrochemical method, values measured by the DO meter (mg/L), water temperature (degree Celsius), and the interaction between the electrochemical method and DO as explanatory variables
Type III  

Source  Degree of freedom  Sum of squares  Mean sum of squares  F ratio  p value 
Electrochemical method  1  2.5041  2.5041  12891.5  < 0.0001 
DO meter (mg/L)  1  0.0018  0.0018  9.18  0.0060 
Water temperature (degree Celsius)  1  0.0003  0.0003  1.67  0.2088 
Interaction between electrochemical method and DO  1  0.0014  0.0014  7.46  0.0119 
The influence of only DO on the oxidimetry method was then studied using a multiple regression model with the same response and explanatory variables mentioned above, except for water temperature.
Relationship among the oxidimetry method, the electrochemical method, and DO for DOregulated hydrogen water (multiple regression analysis)
Parameter  Regression coefficient  Standard error  t value  p value 

Intercept  0.0076  0.0074  1.02  0.316 
Electrochemical method  1.0575  0.0094  112.96  < 0.0001 
DO meter (mg/L)  0.0117  0.0041  2.82  0.0094 
Interaction between electrochemical method and DO  0.0358  0.0126  2.85  0.0088 
•Discussion
The correlation coefficient r is 0.9998, the coefficient of determination R^{2} is 0.9995, suggesting that the linear line indicates 99.95% of the information, and the deviation from the linear line or the standard deviation is 0.0129, which is almost equal to the minimum displaying unit of 0.01. The results show that the oxidimetry method has sufficient precision (accuracy) and can be used as a substitute for the electrochemical method.
Multiple regression analysis reveals that as DO increases by 1.0, the value based on the oxidimetry method drops 0.0117, and the gradient of the oxidimetry method and the electrochemical method drops 0.0358.
The measured hydrogen concentration of the solution was approximately between 0.2 and 1.6 mg/L at this time. The oxidimetry method was practically sufficient to measure the hydrogen concentration to one decimal place within this range. The oxidimetry method is inferred to be useful for a substitute for the electrochemical method.
List of abbreviations
 DH:

dissolved hydrogen
 DO:

dissolved oxygen
 H_{2}:

molecular hydrogen
 MB:

methylene blue
 MBPt:

methylene blueplatinum colloid
 Pt:

platinum.
Declarations
Acknowledgements
We thank Mr. Toshihito Furukawa at the Biostatistical Research Corporation for statistical analysis.
Authors’ Affiliations
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