Oxidation Reduction Potential (ORP) is a commonly-used measure in physical chemistry for denoting the oxidation or reduction power of a substance, usually a liquid.  It is measured in millivolts (mv.) on a scale from -1,200 (most strongly reducing) to +1,200 (most strongly oxidizing).   A reading at or below approximately zero (0) strongly, although indirectly, indicates an increasing concentration of the negative hydrogen ion.  For example, a reading of -800 mv. would often indicate a strongly reducing solution, often with strong antioxidant properties, and could indicate the presence of large amounts of H-minus ions in the solution. 

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A Quick Note: Relative Hydrogen Score, aka rH Score, an Absolute 
Measure of Hydrogen Reducing Power Calculated
from ORP and pH Measures

For a brief tutorial on the Relative Hydrogen Score, or rH score, please see the on-site page devoted to that topic! rH score is an absolute measure of hydrogen reducing power (and of oxidizing power) which is independent of changes in pH, and which is calculated from measures of ORP and pH.

So, we have seen above that ORP (ORP) is a commonly-used measure in physical chemistry for denoting the oxidation or reduction power of a substance, usually a liquid.  It is measured in millivolts (mv.) on a scale from -1,200 (most strongly reducing) to +1,200 (most strongly oxidizing).  However, notice that this is a "sometimes" correlation which  does not always hold true in either direction.  Thus, a water solution of a compound with a strongly negative ORP may show no reducing and antioxidant activity, and a water solution (of certain compounds dissolved in the water) with  strong antioxidant (reducing) activity may show a modestly positive ORP.

Here are some quick points on the whole topic:

• a aqueous product does not need to have a strongly negative ORP to have nutritional antioxidant properties (reducing ability) in biochemical systems.  Witness vitamin C, vitamin E, beta carotene, citric acid, and a host of other biologically active substances with higher molecular weights (that that of H or O).  Indeed, a number of these substances named herein show a pretty strongly positive ORP, and yet, in certain specific biochemical situations, will indeed donate an electron to a molecule ( a free radical) needing one, thus acting as an antioxidant. 
• conversely, a strongly negative ORP does not necessarily say anything at all about antioxidant properties. It is OFTEN correlated to antioxidant properties, but not always.  Some examples follow: 
1. 1)  If you bubble hydrogen gas (H2) from a commercial storage tank through water, the ORP will drop to about -690 or even further.  However, any standard assay of chemical or biochemical antioxidant properties, or of chemical reduction properties, will show ZERO activity. 
2. 2)  On the other hand, ERW ionized water and water containing  MegaHydrin™ (aka Active H- or MegaH™) not only show a strongly negative ORP, but also strong reducing and antioxidant effects in both chemical and biochemical (life-type) reactions, as determined by a number of standard assays of such activity.
• Just as some substances with strongly positive ORP are highly toxic (witness chlorine bleach and hydrogen peroxide), so it is true that some substances with strongly negative ORP are toxic as well.  For example, dissolve sodium hydroxide in water (CAREFULLY! or YOU WILL BE BURNED OR BLINDED!), and the ORP becomes modestly negative, but yet it is toxic due to its alkalinity.  Another great example is lithium hydride.  This substance shows a strongly negative ORP, and yet is incredibly toxic. 
• the ORP correlation with antioxidant activity tends, among other limitations and qualifications, to apply only to substances with very small molecular weight.  Thus, water and the negative hydrogen ion may be in the ballpark, but larger molecules with molecular weight in the hundreds or thousands (vitamin C, vitamin E, citric acid, beta carotene, alpha lipoic acid, pycogenol) hold onto their free electron in another way, and so it is no apparent or available in a simple aqueous solution. 

But this leads us to the next point: How can one easily tell if a solution which shows a strongly negative ORP truly has reducing properties?  As mentioned above, there are a number of standard chemical and biochemical assays, or tests, which can be performed in any well-equipped lab, to measure just that quality.  But. . . .  what if you just need a quick indication, and do not have access to a lab? Well, here are two quick tests:

• A water solution with a strongly negative ORP but which demonstrates no true chemical reducing activity must therefore contain large amounts of dissolved diatomic hydrogen (H2) gas.  Therefore, one quick test for any solution showing strongly negative ORP is to place it in a laboratory de-gasser (a type of ultrasonic bath) and drive off any dissolved gases for an hour.  After the de-gassing prrocedure, if the water still exhibits a strongly negative ORP, then it is likely a truly reducing medium, whereas if the ORP has regressed to the positive range, then the low ORP was due only to dissolved H2 gas.

• for various quirky reasons, the phenols and other compounds which cause the bright (red/purple) coloring of grape juice can be easily bleached (resulting in loss of color intensity) by solutions with true reducing activity, but not by substances with strong oxidizing activity (within certain reasonable limits, that is.)  Nor will the color intensity of grape juice be easily bleached by pH changes, as in the case of strongly acidic or alkaline solutions.  Therefore, this author has demonstrated that frozen grape juice concentrate can act as a quick indicator of true reducing activity.  Normally, one would add about one ounce of water to each of five or six empty beakers.  Next, one would add about ten drops of grape juice concentrate to the one ounce of water in each beaker, and stir well. The water will turn reddish-purple.  Then, one would add 3 ounces of distilled water to one beaker as a control, and to each of the other beakers, add 3 onces of whatever substances (dissolved in water) which one wished to test.  If any beakers, now each full to the 4 ounce mark, shows strongly lessened color intensity, this is a good indicator of reducing activity. However, this test will not work easily unless the reducing water solution added to the beakers for testing has an ORP of about -500 mv or stronger.  Substances which are more weakly reducing will exhibit such small effects in color intensity that differentiation may become difficult without a spectrophotometer.

For a brief tutorial on the Relative Hydrogen Score, or rH score, please see the on-site page devoted to that topic! rH score is an absolute measure of hydrogen reducing power (and of oxidizing power) which is independent of changes in pH, and which is calculated from measures of ORP and pH.

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