ORP Calibration Standard.
- Thread starter luisagos
- Start date
I'd be skeptical. A pH calibration is made just for that purpose - it is a mixture of a weak acid/base pair. ORP is made of a redox couple (Fe2+/Fe3+ for example). I would worry that the ORP of the buffer is not consistent or stable.
Commercial ORP standardization solutions are available. Some are just a pH=4 buffer saturated with quinhydrone. But that is not the same as a pH=4 buffer alone.
Just to be clear - a pH probe measures a voltage but that is not the same as ORP. You must use an ORP probe for measuring ORP and a pH probe for measuring pH. Some places make a combination probe but you still have to switch between the two outputs.
Commercial ORP standardization solutions are available. Some are just a pH=4 buffer saturated with quinhydrone. But that is not the same as a pH=4 buffer alone.
Just to be clear - a pH probe measures a voltage but that is not the same as ORP. You must use an ORP probe for measuring ORP and a pH probe for measuring pH. Some places make a combination probe but you still have to switch between the two outputs.
reef_doug
Premium Member
What type of meter do you have?
For the AC3 they recommend a two point calibration, one with pH 7 & Qunihydrone and one with pH4 & Quinhydrone.
Exert from the manual:
It is not necessary to calibrate the ORP probe of the AquaController III. It has been properly calibrated at the
factory to maintain accurate ORP readings for the lifetime of the controller. However, it is possible to calibrate
the probe if so desired. Quinhydrone, pH 4.00 and pH 7.00 calibration solutions are required for the calibration.
The following procedure should be used to calibrate the ORP:
1. Create a saturated solution of Quinhydrone and pH 7.00 calibration solution.
2. Select Setup:ORP Setup:ORP Calibrate from the AquaController III’s menus.
3. Place the ORP probe into the Quin-7.00 solution. Wait for the numbers on the bottom of the
LCD screen to stop changing. It does not matter what value is displayed only that it is not
changing. When the display stops changing press the select button.
4. Create a saturated solution of Quinhydrone and pH 4.00 calibration solution.
5. Place the ORP probe into the Quin-4.00 solution. Wait for the numbers on the bottom of the
LCD screen to stop changing. It does not matter what value is displayed only that it is not
changing. When the display stops changing press the select button.
6. The ORP probe is now calibrated.
For the AC3 they recommend a two point calibration, one with pH 7 & Qunihydrone and one with pH4 & Quinhydrone.
Exert from the manual:
It is not necessary to calibrate the ORP probe of the AquaController III. It has been properly calibrated at the
factory to maintain accurate ORP readings for the lifetime of the controller. However, it is possible to calibrate
the probe if so desired. Quinhydrone, pH 4.00 and pH 7.00 calibration solutions are required for the calibration.
The following procedure should be used to calibrate the ORP:
1. Create a saturated solution of Quinhydrone and pH 7.00 calibration solution.
2. Select Setup:ORP Setup:ORP Calibrate from the AquaController III’s menus.
3. Place the ORP probe into the Quin-7.00 solution. Wait for the numbers on the bottom of the
LCD screen to stop changing. It does not matter what value is displayed only that it is not
changing. When the display stops changing press the select button.
4. Create a saturated solution of Quinhydrone and pH 4.00 calibration solution.
5. Place the ORP probe into the Quin-4.00 solution. Wait for the numbers on the bottom of the
LCD screen to stop changing. It does not matter what value is displayed only that it is not
changing. When the display stops changing press the select button.
6. The ORP probe is now calibrated.
luther1200
Premium Member
I used 400mv solution that came with my Pinpoint ORP probe. Didn't your probe come with anything to calibrate it with?
doug
Exert from the manual:
It is not necessary to calibrate the ORP probe of the AquaController III. It has been properly calibrated at the
factory to maintain accurate ORP readings for the lifetime of the controller.
Sorry but that is nonsense. The life of that controller could be for many years and the life of a ORP probe is about 1 1/2 - 2 years. It is also nonsense, in their framing of it, that a ORP probe never needs to be calibrated. And I NEVER buy into this either properly calibrated at the factory
luisagos
Something for you and others to read
ORP and the Reef Aquarium
http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm
Exert from the manual:
It is not necessary to calibrate the ORP probe of the AquaController III. It has been properly calibrated at the
factory to maintain accurate ORP readings for the lifetime of the controller.
Sorry but that is nonsense. The life of that controller could be for many years and the life of a ORP probe is about 1 1/2 - 2 years. It is also nonsense, in their framing of it, that a ORP probe never needs to be calibrated. And I NEVER buy into this either properly calibrated at the factory
luisagos
Something for you and others to read
ORP and the Reef Aquarium
http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm
rsuplido
Member
For those calibrating using quinhydrone for the AC3, here are some options:
Marine Depot - $36: http://www.marinedepot.com/ps_ViewI...adyne~idProduct~OP3211~idCategory~FITECL.html
Pulse Instruments - $42.75: http://www.pulseinstruments.net/index.asp?PageAction=VIEWPROD&ProdID=1692
The Pulse Instruments kit is more complete and I guess a lifetime supply of quinhydrone - since you only use a small amount for every test. They also provide you a big supply of pH 4.01 and 7.01 for pH calibration.
Marine Depot - $36: http://www.marinedepot.com/ps_ViewI...adyne~idProduct~OP3211~idCategory~FITECL.html
Pulse Instruments - $42.75: http://www.pulseinstruments.net/index.asp?PageAction=VIEWPROD&ProdID=1692
The Pulse Instruments kit is more complete and I guess a lifetime supply of quinhydrone - since you only use a small amount for every test. They also provide you a big supply of pH 4.01 and 7.01 for pH calibration.
Lou
The Quinhydrone Method was developed by Senorex. I had Mike Ross here long ago for a ORP discussion with me , Randy and Habib when Randy was preparing his ORP article. Long ago Mike wrote this which is basically what the instructions say. Most Quinhydrone kits are just relabeled Senorex kits. See bold print below
Treating Water at ORP Speed
Monitoring ORP leads to successful treatment
By Mike Ross
Oxidation reduction potential (ORP), also known as redox, is the measurement of a solution's oxidizing and reducing activity. The ORP process can be likened to stock-market activity: Whenever one material is oxidized, another material is reduced (for someone to purchase a share, another person must sell that share).
Fire is an example of rapid oxidation and reduction. The carbon from a hydrocarbon combines with oxygen from the air to make CO2 while hydrogen from the hydrocarbon combines with oxygen to make H2O. The carbon and hydrogen have been oxidized while the oxygen has been reduced.
Rust is a slower example of an oxidation/reduction reaction. Oxygen combines with iron to form iron oxides. In this process, the iron is oxidized and, once again, the oxygen has been reduced.
Fire and rust illustrate the basic characteristics of oxidation/reduction processes; namely, that materials involved undergo chemical changes. More pertinent to water treatment is the oxidation/reduction potential of chlorine reacting with bacteria or algae.
Bacteria and algae essentially are hydrocarbons, and chlorine is a powerful oxidizing reagent. Even though it can't really be seen, chlorine destroys bacteria and algae by literally burning their carbon and hydrocarbon into CO2 and H2O. When all of the oxidizing and reducing materials have reacted, an equilibrium is reached and there is usually a surplus It is this surplus material that creates the oxidation or reduction potential of a solution.
Measuring ORP
ORP can be measured by colorimetric or potentiometric means. Colorimetric techniques take advantage of the fact that certain chemicals can change their color as for example, the amount of chlorine in water changes. Colorimetric kits are inexpensive but subject to errors from the color of the water. They are not well-suited for monitoring or control applications.
The principle of potentiometric operation is that whenever a metal is exposed to varying concentrations of chemicals, a millivolt level(mV) electrical potential is generated. The millivolts generated are a function of the type of metal used, the type and concentration of the chemicals in solution and the solution's temperature. By selecting a particular metal, a correlation to the chemical type and concentration can be made and useful information obtained.
In actual practice, a noble metal (a pure, elemental metal) is always used in ORP electrodes because it will not enter into unwanted chemical reactions that can lead to measurement errors. The use of a noble metal is important because the ORP value is a function of both the solution's chemicals and the type of metal in contact with that solution (even different noble metals can give different readings in the same solution).
Platinum is normally the metal of choice; however, gold and other noble metals can also be used.
The ORP potential generated at the platinum electrode varies as the chemicals in the solution change. This signal is compared to that of a reference electrode (one so constructed that its potential remains constant even when the chemicals in the solution change). The most commonly used reference electrode is a silver or silver chloride (Ag/AgCl) type.
Unlike the pH electrode which responds only to hydrogen ion activity, an ORP electrode responds to chemical reaction activity in which material is converted from one oxidized state to another through electron transfer. There are many similarities between pH and ORP measurements as shown below.
Both are examples of electrochemical measurements
Both are forms of batteries and have limited lives
Both require a special high impedance mV input circuit
Both use the same Ag/AgCl reference electrode design
pH electrodes are designed to respond to hydrogen ion activity, while ORP electrodes respond to all ions that have oxidizing or reducing activities
pH measuring electrodes are constructed of hydrogen ion sensitive glass. ORP electrodes are constructed of a noble metal.
pH measuring electrodes can be made to automatically compensate for temperature changes, but the effect of temperature on ORP is not known
Why Measure?
Many industries can benefit from the use of ORP measurements, including waste water treatment applications and the pulp and paper industry. From a water treatment perspective, use of ORP for controlling water disinfection or the growth of algae with chlorine, chlorine dioxide, bromine and ozone in applications such as cooling towers, swimming pools, potable water supplies and a multitude of other sterile water applications is of prime interest. Other oxidizers include fluorine and hydrogen dioxide.
ORP measurement can be done in a variety of ways. A pH meter with a mV scale can be used simply by connecting an ORP electrode in place of the pH electrode. The mV signal generated by the electrode is representative of, for example, the residual chlorine in solution. This ORP potential is temperature-dependent; however, temperature compensation is not used because the compensation would vary for each different oxidation/reduction reaction occurring, and it is likely that several reactions are taking place at the same time.
Another factor to consider when making ORP measurements is that they can be pH- dependent (remember that pH is a measure of hydrogen ions). For example, chlorine exists in solution as hypochlorous acid (OCl- ). Depending on the pH, this hypochlorous acid will shift its equilibrium to provide more or less free chlorine (this accounts for chlorine reacting more strongly at low pH values-as pH is lowered, more free chlorine is generated).
Even though the concentration of chlorine remains constant, its oxidizing power is pH-dependent. To obtain accurate residual chlorine information, the pH must either be constant or adjusted.
ORP measurement is slow when compared to a pH measurement. Whereas a pH electrode will respond in seconds, a new or cleaned ORP electrode can take several hours to initially equilibrate or re-equilibrate to a sample. Once equilibrated, an electrode's response time is measured in minutes, not seconds.
ORP measurements can be defined as a measurement of oxidant demand relative to whatever ORP value needed to accomplish a particular disinfection goal. Actual ORP levels required for bacteriological control will vary with use of different oxidizers and makeup waters. Both concentration and activity of the oxidizer will affect the ORP levels. In addition, water chemistry-which may inhibit an oxidizer's performance-can affect the ORP levels and affect the choice of oxidizing agents.
For example, cyanuric acid is used in swimming pools to minimize the loss of chlorine. The cyanuric acid reacts with the hypochlorous acid to bind it in a form that reduces the free available chlorine. This chemical binding has the net effect of lowering the concentration of chlorine detected by the ORP electrode.
Verifying Electrode Operation
Calibration is not normally required. In fact many ORP meters do not have calibration adjustments. However, measurement error can occur due to contamination or coatings on the electrode. Even though the meter cannot be adjusted, calibration verification can be helpful.
To verify the operation of an ORP electrode, quinhydrone is added to pH buffers 4.0 and 7.0. When added to these buffers, two known, stable ORP solutions will be created. A 7.0 buffer with quinhydrone will produce a solution which will generate 90mV with a platinum ORP electrode. A 4.0 buffer with quinhydrone will produce a solution of 265mV.
If the electrode responds correctly in the samples, no further steps are required. If the values are incorrect, clean the electrodes measuring surface and reference junction with 5% hydrochloric acid. Scratches to the metal surface should be avoided. However, if acid treatment is not effective, very lightly abrade the metal measuring surface with a 600-grit wet silicon carbide sandpaper using a circular polishing motion. After such abrasive cleaning the electrode may require several hours of soaking in a quinhydrone solution before providing stable readings.
If these cleaning procedures do not restore the electrode's calibration, the electrode will need to be replaced.
The Quinhydrone Method was developed by Senorex. I had Mike Ross here long ago for a ORP discussion with me , Randy and Habib when Randy was preparing his ORP article. Long ago Mike wrote this which is basically what the instructions say. Most Quinhydrone kits are just relabeled Senorex kits. See bold print below
Treating Water at ORP Speed
Monitoring ORP leads to successful treatment
By Mike Ross
Oxidation reduction potential (ORP), also known as redox, is the measurement of a solution's oxidizing and reducing activity. The ORP process can be likened to stock-market activity: Whenever one material is oxidized, another material is reduced (for someone to purchase a share, another person must sell that share).
Fire is an example of rapid oxidation and reduction. The carbon from a hydrocarbon combines with oxygen from the air to make CO2 while hydrogen from the hydrocarbon combines with oxygen to make H2O. The carbon and hydrogen have been oxidized while the oxygen has been reduced.
Rust is a slower example of an oxidation/reduction reaction. Oxygen combines with iron to form iron oxides. In this process, the iron is oxidized and, once again, the oxygen has been reduced.
Fire and rust illustrate the basic characteristics of oxidation/reduction processes; namely, that materials involved undergo chemical changes. More pertinent to water treatment is the oxidation/reduction potential of chlorine reacting with bacteria or algae.
Bacteria and algae essentially are hydrocarbons, and chlorine is a powerful oxidizing reagent. Even though it can't really be seen, chlorine destroys bacteria and algae by literally burning their carbon and hydrocarbon into CO2 and H2O. When all of the oxidizing and reducing materials have reacted, an equilibrium is reached and there is usually a surplus It is this surplus material that creates the oxidation or reduction potential of a solution.
Measuring ORP
ORP can be measured by colorimetric or potentiometric means. Colorimetric techniques take advantage of the fact that certain chemicals can change their color as for example, the amount of chlorine in water changes. Colorimetric kits are inexpensive but subject to errors from the color of the water. They are not well-suited for monitoring or control applications.
The principle of potentiometric operation is that whenever a metal is exposed to varying concentrations of chemicals, a millivolt level(mV) electrical potential is generated. The millivolts generated are a function of the type of metal used, the type and concentration of the chemicals in solution and the solution's temperature. By selecting a particular metal, a correlation to the chemical type and concentration can be made and useful information obtained.
In actual practice, a noble metal (a pure, elemental metal) is always used in ORP electrodes because it will not enter into unwanted chemical reactions that can lead to measurement errors. The use of a noble metal is important because the ORP value is a function of both the solution's chemicals and the type of metal in contact with that solution (even different noble metals can give different readings in the same solution).
Platinum is normally the metal of choice; however, gold and other noble metals can also be used.
The ORP potential generated at the platinum electrode varies as the chemicals in the solution change. This signal is compared to that of a reference electrode (one so constructed that its potential remains constant even when the chemicals in the solution change). The most commonly used reference electrode is a silver or silver chloride (Ag/AgCl) type.
Unlike the pH electrode which responds only to hydrogen ion activity, an ORP electrode responds to chemical reaction activity in which material is converted from one oxidized state to another through electron transfer. There are many similarities between pH and ORP measurements as shown below.
Both are examples of electrochemical measurements
Both are forms of batteries and have limited lives
Both require a special high impedance mV input circuit
Both use the same Ag/AgCl reference electrode design
pH electrodes are designed to respond to hydrogen ion activity, while ORP electrodes respond to all ions that have oxidizing or reducing activities
pH measuring electrodes are constructed of hydrogen ion sensitive glass. ORP electrodes are constructed of a noble metal.
pH measuring electrodes can be made to automatically compensate for temperature changes, but the effect of temperature on ORP is not known
Why Measure?
Many industries can benefit from the use of ORP measurements, including waste water treatment applications and the pulp and paper industry. From a water treatment perspective, use of ORP for controlling water disinfection or the growth of algae with chlorine, chlorine dioxide, bromine and ozone in applications such as cooling towers, swimming pools, potable water supplies and a multitude of other sterile water applications is of prime interest. Other oxidizers include fluorine and hydrogen dioxide.
ORP measurement can be done in a variety of ways. A pH meter with a mV scale can be used simply by connecting an ORP electrode in place of the pH electrode. The mV signal generated by the electrode is representative of, for example, the residual chlorine in solution. This ORP potential is temperature-dependent; however, temperature compensation is not used because the compensation would vary for each different oxidation/reduction reaction occurring, and it is likely that several reactions are taking place at the same time.
Another factor to consider when making ORP measurements is that they can be pH- dependent (remember that pH is a measure of hydrogen ions). For example, chlorine exists in solution as hypochlorous acid (OCl- ). Depending on the pH, this hypochlorous acid will shift its equilibrium to provide more or less free chlorine (this accounts for chlorine reacting more strongly at low pH values-as pH is lowered, more free chlorine is generated).
Even though the concentration of chlorine remains constant, its oxidizing power is pH-dependent. To obtain accurate residual chlorine information, the pH must either be constant or adjusted.
ORP measurement is slow when compared to a pH measurement. Whereas a pH electrode will respond in seconds, a new or cleaned ORP electrode can take several hours to initially equilibrate or re-equilibrate to a sample. Once equilibrated, an electrode's response time is measured in minutes, not seconds.
ORP measurements can be defined as a measurement of oxidant demand relative to whatever ORP value needed to accomplish a particular disinfection goal. Actual ORP levels required for bacteriological control will vary with use of different oxidizers and makeup waters. Both concentration and activity of the oxidizer will affect the ORP levels. In addition, water chemistry-which may inhibit an oxidizer's performance-can affect the ORP levels and affect the choice of oxidizing agents.
For example, cyanuric acid is used in swimming pools to minimize the loss of chlorine. The cyanuric acid reacts with the hypochlorous acid to bind it in a form that reduces the free available chlorine. This chemical binding has the net effect of lowering the concentration of chlorine detected by the ORP electrode.
Verifying Electrode Operation
Calibration is not normally required. In fact many ORP meters do not have calibration adjustments. However, measurement error can occur due to contamination or coatings on the electrode. Even though the meter cannot be adjusted, calibration verification can be helpful.
To verify the operation of an ORP electrode, quinhydrone is added to pH buffers 4.0 and 7.0. When added to these buffers, two known, stable ORP solutions will be created. A 7.0 buffer with quinhydrone will produce a solution which will generate 90mV with a platinum ORP electrode. A 4.0 buffer with quinhydrone will produce a solution of 265mV.
If the electrode responds correctly in the samples, no further steps are required. If the values are incorrect, clean the electrodes measuring surface and reference junction with 5% hydrochloric acid. Scratches to the metal surface should be avoided. However, if acid treatment is not effective, very lightly abrade the metal measuring surface with a 600-grit wet silicon carbide sandpaper using a circular polishing motion. After such abrasive cleaning the electrode may require several hours of soaking in a quinhydrone solution before providing stable readings.
If these cleaning procedures do not restore the electrode's calibration, the electrode will need to be replaced.
Thank you Boomer.
What type of ORP reading would someone read, when a tank has been newly setup, like in one week.
Just sand, rock, and no real lights yet.
PH is at 8.05
Temps at 79.1
Conductivity is at 1.0213
ORP at 140mv
My return pump are running like 800 gph.
I have great flows with my two MP40w Vortech.
What type of ORP reading would someone read, when a tank has been newly setup, like in one week.
Just sand, rock, and no real lights yet.
PH is at 8.05
Temps at 79.1
Conductivity is at 1.0213
ORP at 140mv
My return pump are running like 800 gph.
I have great flows with my two MP40w Vortech.
About what you got. New water or systems always have a lower ORP. What really raises the ORP are rate reactions that take place in the tank with time. In a well run aged system, months old, with clean water and good maintenance, good skimming, 30 % WC / month that ORP will rise into the high 300's
Please read this
ORP and the Reef Aquarium
http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm
Conductivity is at 1.0213
You mean Specific Gravity. And that is to low, needs to be 1.0264 unless it is a fish only tank.
Please read this
ORP and the Reef Aquarium
http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm
Conductivity is at 1.0213
You mean Specific Gravity. And that is to low, needs to be 1.0264 unless it is a fish only tank.
Billybeau1
Premium Member
The ORP reading of 140 mv does not surprise me in a new tank like that. As Boomer said, ORP is very complicated.
You should see it slowly rise, day by day for another month or so.
Without ozone, it should settle somewhere between 260 and 320mv.
When you do a water change, it will lower temporarily as the ORP of freshly mixed salt water is around 220 mv or so. When you feed it will lower and recover within 12 hrs or so. As pH rises, ORP will lower and as pH lowers ORP will rise.
This is the nature of the beast that is................. ORP.
You should see it slowly rise, day by day for another month or so.
Without ozone, it should settle somewhere between 260 and 320mv.
When you do a water change, it will lower temporarily as the ORP of freshly mixed salt water is around 220 mv or so. When you feed it will lower and recover within 12 hrs or so. As pH rises, ORP will lower and as pH lowers ORP will rise.
This is the nature of the beast that is................. ORP.
