Refer to WQSensors Measurement Techniques for additional WQSensor guidelines that will help lead to best results. For the WQ-ORP Oxidation Reduction Potential Smart USB Sensor, see Figure 1 for further depiction of proper techniques.
ORP is an important chemistry parameter and provides useful information on the oxidizing or reducing nature of water. However, ORP is a non-specific measurement and ORP readings of the same sample may vary as much as 50-100mV depending on such factors as ionic composition, temperature, pH, and sensor condition. Generally, only deviations greater than 100 mV are suspect.
Differences in the sensor condition may further exacerbate the non-specificity of ORP measurements. Contaminants on the surface of the platinum electrodes, such as hard water deposits, oil/grease, or other organic matter, will slow response and cause a long time for equilibration. Cleaning the probe will help prevent interferences due to a fouled probe condition.
ORP readings typically stabilize much more rapidly in high ionic strength solutions, such as ORP standards, than in more dilute environmental water. Often, in clean environmental waters, only low concentrations of a few redox-active species are present, and readings may take many hours to stabilize. In some cases, the concentration of redox-active species may be so low that the redox influence of the species is undetectable. Under these conditions, the ORP readings will have questionable meaning and may show great variation. Any differences in sensor condition, such as deposits on the platinum electrode, will further exacerbate these variable readings.
Refer to WQ-ORP Smart USB Sensor Getting Started for steps that should be taken before measuring begins.