Which variables have an affect on an Oxidation Reduction Potential (ORP) measurement?
Factors influencing ORP measurements
Oxidation Reduction Potential (ORP) is not an ion specific measurement, but a "sum parameter" as it is affected by all ionic activity and expresses the relationship between all of the oxidants and reductants in the sample matrix being analyzed. If the ORP reading is to be correlated to chlorine concentration (or any other oxidant/reducer) in the sample, the variations in temperature, pH, ionic strength, as well as each ion's relationship to the ORP measurement would have to be known and accounted for (controlled), or completely eliminated as variables. The ORP reading alone cannot accurately represent the concentration of chlorine (or any other oxidant/reducer) because these variables all have direct influence on the ORP measurement.