in EU
Basic Concepts
ORP (Oxidation-Reduction Potential): ORP is a measure of a solution's ability to either donate or accept electrons during chemical reactions. It is measured in millivolts (mV) and is often used to assess water quality, including its purity and antioxidant properties. However, ORP cannot accurately determine the presence of hydrogen in water. Let’s understand why.
Hydrogen: Hydrogen is a chemical element with the symbol H. In water, it can exist as molecular hydrogen (H₂) or hydrogen ions (H⁺).
Misconception About ORP and Health Benefits
There is a misconception that reducing ORP, such as in alkaline ionized water, is beneficial because it lowers the ORP. This is not true. Only the presence of hydrogen, not the ORP, determines the health benefits. Many low-ORP liquids are harmful to health.
Typically, these liquids are high in chemical reductants or contain toxic substances. Here are some examples:
- Spent electroplating solutions: Used in industry, these solutions contain hazardous chemicals that can be toxic.
- Industrial wastewater: May contain various reducing agents and toxic components.
- Antifreeze (ethylene glycol): Has a low ORP but is extremely toxic if ingested.
- Metal etching solutions: Contain chemicals that can be harmful to health.
- Certain household chemicals: Cleaners and solvents with strong chemical reductants.
The Issue with Using ORP to Determine Hydrogen
The problem is that ORP does not provide direct information on the presence of hydrogen. ORP measures the overall redox potential of the environment, which is influenced by many other factors and substances present in the water. Here are some examples of such substances:
- Iron (Fe²⁺ and Fe³⁺):
- Fe²⁺ can lower ORP as it is the reduced form of iron.
- Fe³⁺ can raise ORP as it is the oxidized form of iron.
- Oxygen (O₂):
- Oxygen, being a strong oxidizer, raises ORP. Dissolved oxygen increases the redox potential of water.
- Organic substances:
- Depending on the nature of the organic substances, they can either lower or raise ORP. For example, humic acids often act as reductants, lowering ORP.
- Manganese (Mn²⁺ and MnO₂):
- Mn²⁺ can lower ORP as it is the reduced form of manganese.
- MnO₂ (manganese dioxide) raises ORP as it is the oxidized form of manganese.
Thus, the influence on ORP depends on the oxidative or reductive nature of each substance:
- Oxidizers (Fe³⁺, O₂, Cl₂, MnO₂) raise ORP.
- Reductants (Fe²⁺, some organic substances, Mn²⁺) lower ORP.
Why ORP Cannot Accurately Indicate Hydrogen
ORP is a cumulative characteristic of all redox pairs present in the solution. This makes it impossible to determine a specific substance, such as hydrogen, solely based on the ORP value.
- Multiple Redox Pairs: Many redox pairs can be present simultaneously in water, such as Fe²⁺/Fe³⁺, O₂/H₂O, Cl₂/Cl⁻, contributing to the overall ORP. This makes it impossible to isolate the contribution of one pair, like hydrogen, without considering the influence of other pairs.
- pH Influence: Changes in pH directly affect ORP. For example, a decrease in pH by one unit increases the ORP of the hydrogen electrode by 59 mV at 25°C. This pH influence must be considered when interpreting ORP, complicating the task of isolating hydrogen.
- Measurement Complexity: ORP is measured at the electrode surface in contact with the solution, and this measured potential is a cumulative effect of all interactions in the solution. Therefore, even if hydrogen is present, its impact on the overall ORP may be negligible compared to other components.
Conclusion
Determining the presence of hydrogen in water solely by ORP is impossible due to the numerous factors affecting the redox potential. ORP measures the overall redox potential, which depends on all present oxidants and reductants, pH, and other conditions. Specific analytical methods, such as gas chromatography or specialized sensors, are required for accurate hydrogen determination.
