Product category:
pH and conductivity meters
News Release from: QCL Scientific | Subject: Orion ORP
Edited by the Laboratorytalk Editorial
Team on 07 April 2008
Orion is a 'vast improvement' over other
standards
The ORP standard can be used with any other electrodes and meters as a calibration standard using a mV offset or relative millivolts, when the fill solution molarity is known
The Orion ORP standard is a vast improvement over other ORP standards on the market, says QCL Scientific For the user, it involves the same amount of preparation as an Orion pH buffer - just pour some out of the bottle into a beaker and calibrate
This article was originally published on Laboratorytalk on 14 Oct 2004 at 8.00am (UK)
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In addition to ease of use, this standard allows those measuring ORP to have a stable, reliable standard that they can easily use immediately each day to determine whether their samples or processes are changing or remaining constant.
ORP is used as a quick measurement of the oxidation-reduction potential (EH) of a solution.
The oxidation-reduction is a measure of solution reactivity, which is a critical parameter in industries such as water/wastewater, pulp/paper, environmental, food, and those concerned with corrosion inhibition and disinfection.
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The Orion ORP standard has been characterised with Orion electrodes at various temperatures to allow an automatic calibration for a direct reading (EH) relative to the Normal or Standard Hydrogen Electrode (SHE) from any Orion Star series meter with pH measurement mode.
The ease of use, the non-toxic composition, and other benefits of the ORP standard still make it the best ORP standard for any ORP measurement system.
Traditional ORP standards have several drawbacks.
They are not calibration solutions back to the 'gold standard' SHE, but are more for verification that the meter and electrode are functioning.
Their greatest drawback is preparation and/or shelf life constraints, making ORP measurement more tedious than it needs to be.
Specifically, the ZoBell's solution is based on the ferrocyanide/ferricyanide redox couple.
The cyanide complex solution itself is toxic and requires special handling disposal constraints.
The Light's solution is a ferrous/ferric redox couple solution.
It offers stability for a few months but oxidises and is acidic and dangerous to work with.
Quinhydrone can be added to pH4 and pH7 buffers to verify a system at two different potentials.
Quinhydrone is slow to dissolve and difficult to clean off the electrodes, stirring apparatus, and glassware.
It is also a toxic compound.
Although quinhydrone solutions give two data points, they are only stable for a few hours and must be reprepared for each calibration.
This is time consuming and creates an organic waste stream.
Temperature effects are usually unknown as these prepared by the end users and change over time as well.
The millivolt readings of the standard are dependent on the reference system (material and filling solution) of the ORP electrode and temperature of the solution.
For Orion electrodes (models 9678 and 9778) with the Orion 900011 fill solution, the standard will give a reading of 420mV relative to the Normal or Standard Hydrogen electrode at 25C.
The raw millivolts reading would be 220mV at 25C.
The Orion ORP Triode electrodes, models 9179 and 9180, which offer the benefit of built-in temperature sensors, will give the same values.
This lower ionic strength filling solution is a beneficial alternative for some applications.
The values given in the mV versus temperature tables are for Orion electrodes only.
Use with other manufacturer's electrodes which may have different reference systems will give slightly different mV values.
The mV value of the solution is stable and will not change over time so it is still an ideal standard for any ORP measurement system.
Any Orion Star meters with ORP mode offer the user simple automatic calibration to EH with the push of the calibration button in the EH mode using the Orion ORP electrodes. Request a free brochure from QCL Scientific ...
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