A convenient method for determining the concentration of hydrogen in water: use of methylene blue with colloidal platinum

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, anti-inflammatory, 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.A method for determining the concentration of hydrogen in water is very desirable, particularly if it is simpler and more inexpensive than the current state-of-the-art method involving expensive electrochemical gas sensors. Accordingly, we investigated a simple oxidimetry method that involves a redox reaction of methylene blue (MB) oxidant in the presence of a colloidal platinum (Pt) catalyst. MB is well known to react with an equimolar amount of hydrogen in the presence of Pt or palladium to produce colorless reduced MB (leucomethylene blue, leucoMB), as follows:On the basis of the above equation, we used a volumetric analysis method called oxidimetry to determine the concentration of hydrogen in water by a titration by using the MB-Pt reagent (Figure 1).MB (0.3 g) (Waldeck-Gmbh & 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 MB-Pt 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.Hydrogen-saturated water (0.8 mM) was prepared by bubbling hydrogen gas through purified water. Three concentrations of hydrogen-rich water (0.3, 0.2, and 0.1 mM) were prepared by diluting hydrogen-saturated water with purified water.Electrochemical