ORP should not be used to estimate or compare concentrations of aqueous H2: An in silico analysis and narrative synopsis

Abstract

Oxidation reduction potential (ORP) has become a commonly used measurement to characterize functional beverages, specifically alkaline ionized water and hydrogen water. Numerous health benefits including antioxidant effects have been attributed to a negative ORP value. A greater negative ORP value is often incorrectly interpreted to mean a greater degree of health benefits and/or a high concentration of H 2 . Some hydrogen meters use the Nernst equation to calculate the concentration of H 2 based on the measured ORP value. Unfortunately, due to the fundamental issues with the ORP meter, the calculated H 2 value may be very inaccurate. Using the Nernst equation, we performed an in silico analysis of the ORP as a function of pH, temperature, and H 2 concentration. Our analysis shows that a one unit increase in pH (e.g., 7–8) influences the ORP by as much as increasing the H 2 concentration by 100 times (e.g., 1–100 mg/L). Similarly, at a saturated H 2 concentration (1.57 mg/L) and pH 7, every ∆T of 20 °C changes the ORP by ≈ 30 mV. This is comparable to changing the H 2 concentration by a factor of 10 (0.1 mg/L to 1 mg/L). Finally, to measure H 2 within 0.1 mg/L, ORP meters need to have an accuracy of about 0.8 mV. However, ORP meters have an error range of at least ±10 mV, which corresponds to a potential error in measured H 2 concentration of nearly 2 mg/L (≈125% error). This analysis shows that pH, temperature, and the intrinsic ORP errors can individually influence the ORP greater than the entire contribution of dissolved H 2 within normally used ranges. In fact, this can easily result in a water sample with a greater negative ORP than another despite having significantly less H 2 . This makes it impossible to consistently determine if one water sample has more H 2 than another water sample. Therefore, we can only conclude, based on a negative ORP reading, that, excluding the possibility of other reductive redox couples, some level of dissolved H 2 is present in the water. Accordingly, ORP and ORP-based H 2 meters are not recommended for testing or comparing the concentration of H 2 in water. Experimental studies are warranted to determine if the ORP error is as great as or greater than what is predicted via this in silico analysis.

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