ORP meter

Content
1. What is ORP meter?
2. Application of ORP meter
3. ORP meter working principle
4. Performance characteristics of ORP meter
5. ORP meter specifications
    5.1. Benchtop ORP meter
    5.2. Portable ORP meter
6. How to understand the accuracy of ORP meter values?
7. How to prepare the standard solution for ORP meter?
8. How to repair ORP meter compound electrode?
9. Precautions for using ORP meter
10. How to order ORP meter?

ORP meter is the abbreviation of oxidation-reduction potential meter, which indicates the oxidation-reduction potential of a solution. ORP electrode is a kind of electrode that can only absorb or release electrons on the surface of its sensitive layer without a chemical reaction with the solution, it is an noble metal, usually made of both platinum and gold. Reference electrode is the same silver/silver chloride-based electrode as the pH electrode.

ORP meter is widely used in industry, agriculture, scientific research, environmental protection and other fields. The instrument is also a necessary inspection equipment for QS and HACCP certification in food factories and drinking water factories. Also widely used in thermal power, chemical fertilizer, metallurgy, environmental protection, pharmaceutical, biochemical, food and tap water and other solutions in the continuous monitoring of potential value.

Industrial wastewater treatment
The redox system of oxidation-reduction potential meter used in water treatment is mainly for the reduction of chromic acid and the oxidation of cyanide. If sodium disulfide or sulfur dioxide is added to the wastewater, the hexavalent chromium ions can be turned into trivalent chromium ions. If you add chlorine or sodium hypochlorite can be used to oxidize the qingide, followed by the hydrolysis of the qingide cyanide, the formation of cyanate. This chemical reaction process is called redox reaction system. Redox potential is the measurement of electron activity, which is very similar to the measurement of hydrogen ion activity.

Water disinfection and applications
ORP measurement’s redox electrodes can measure the disinfection of swimming pool water, mineral water and tap water. Because the bactericidal effect of coliform bacteria in water is influenced by the redox potential, the redox potential is a reliable indicator of water quality. If the redox potential in pool water and mineral water is equal to or higher than 650mv, the bacteria content is acceptable.

Observe the dynamic changes
ORP meter also can observe the dynamic changes of ORP in the soil, for example, after the rice soil is irrigated with water to grow rice, the redox condition of the soil has changed dramatically. One kind of rice soil from the tillage layer, generally maintained at 450-650mV before irrigation. irrigation ORP declined rapidly, to the organic matter decomposition period ORP fell to negative 200mV to 100mV, when applying a large amount of fresh green manure, even down to negative 300mV. later rebounded, generally maintained at 0-200mV. before the rice harvest, the soil fell dry, ORP rose again to 450mV or more.

Applications in other fields
Marine exploration, biological engineering, environmental protection, brewing industry, and other sectors of the national economy have been widely used.

The working principle of oxidation-reduction potential meter is the direct measurement method using platinum electrode, which mainly consists of two parts: measuring electrode and high resistance millivoltmeter (or ion meter).

The primary cell is composed of the measuring electrode, the reference electrode and the measured solution. The electrode potential of the reference electrode does not change with the concentration of the measured solution.

The ORP value is determined by the electron activity in the solution, because free electrons do not exist in the solution, and in fact ORP can be seen as the ease with which a substance binds or loses electrons. the determination of ORP is a measurement of potential potential energy, and there is no actual current passing through the aqueous solution during the potential measurement.

During ORP formation, electrons can flow from the electrode to the redox system, or vice versa. The precipitation of charge on the metal surface leads to the formation of a potential, which in turn resists further electron migration. When the equilibrium state is reached, the electrochemical (potential) and chemical (oxidation or reduction) forces balance each other so that the ORP of the solution increases or decreases proportionally to its oxidation capacity, and the measured ORP value is typically linear. Therefore, the electric potential of the primary cell has a one-to-one correspondence with the activity of the ion to be measured. It can be seen that the role of the primary cell is to convert a chemical quantity (ionic activity), which is difficult to measure directly, into an electrical quantity (electric potential of the measuring cell), which is easy to measure.

In water, each substance has its redox properties, the higher the redox potential, the stronger the oxidation, the lower the potential, the weaker the oxidation. A positive potential indicates the oxidizing nature of the solution, a negative one shows the reducing nature.

1. ORP meter adopts high-performance CPU chip, high-precision AD conversion technology and SMT chip technology, it completes multi-parameter measurement, temperature compensation and instrument self-test with high precision and good repeatability.

2. ORP analyzer can automatically store measurement data every 5 minutes, and can continuously store ORP value for one month.

3. Oxidation-reduction potential meter adopts electromagnetic compatibility (EMC/RFI) design: designed and manufactured according to European standard EN50081/50082. Multiple calibration methods, E0, S query, monitor electrode performance.

4. ORP meter can realize 25℃ commutation: Canst electrode slope temperature compensation, pure water and ammonia added ultrapure water 25℃ commutation.

In the natural body of water, there are a variety of variable ions and dissolved oxygen, when some industrial wastewater is discharged into the water, the water contains a large number of ions and organic substances, due to the different nature between ions, redox reactions occur in the water body and tend to equilibrium, so in the natural body of water is not a single redox system, but a mixed system of redox. What the measuring electrode reacts with is also a mixed potential, which has a large experimental error. In addition, the pH of the solution also affects the ORP value. Therefore, the redox potential is a qualitative determination of the redox capacity of a solution, which reflects a relative condition, or it can also be described as a trend and state of the equilibrium state of the redox reaction and the degree of completion of the reaction process, rather than a theoretical quantitative projection. Therefore, it is meaningless to emphasize the absolute potential of the solution in the actual measurement process. We can say that the ORP value of a solution around a certain value point indicates a reduction or oxidation state of the solution or indicates a certain property of the solution (such as the degree of hygiene, etc.), but this value will vary widely and you cannot make a quantitative determination of it, which is a different concept from the accuracy in pH testing. In addition, the temperature coefficient that affects the ORP value is also a variable that cannot be corrected, so ORP meters generally do not have a temperature compensation function.

Quinone hydroquinone standard solution can be used for the calibration of ORP meter. The method of preparing quinone hydroquinone standard solution and the standard value is as follows: pour about 50mlpH4.00 standard buffer solution into a small beaker, add an appropriate amount of quinone hydroquinone reagent and stir, dissolve until saturation (when it is cold, the solution can be heated to 30~40℃ to accelerate the dissolution of quinone hydroquinone reagent to saturation, and then cool to room temperature). The same day use.
The value of ORP standard solution is related to the concentration of potassium chloride used in the silver/silver chloride reference electrode. mV value of ORP standard solution of 3.3 mol/L KCl solution is shown in the table. The error is 256±15mV (25℃).

In the OPR meters, ORP measuring electrode (platinum or gold), the surface should be bright, the rough surface of the redox potential response than the surface of the bright electrode to be much slower. In addition, ORP electrodes after long-term use, platinum or gold surface contamination will also lead to inaccurate measurement and slow response, when the following methods are available for cleaning and activation:
For inorganic contamination, the electrode can be immersed in 0.1 mol/L dilute hydrochloric acid for 30 minutes, cleaned with pure water, and then immersed in the electrode soaking solution for 6 hours and then used.

For organic oil and oil film contamination, use detergent to clean the platinum or gold surface after cleaning with pure water, and then immerse into the electrode soaking solution for 6 hours before use.

For platinum surface pollution with the serious surface formation of oxide film, use toothpaste to polish the platinum or gold surface, then clean with pure water, and then immerse into the electrode soaking solution for 6 hours before use.

In oxidation-reduction potential meter, ORP electrodes are prone to fouling. The presence or absence of any material on the electrode, whether organic or inorganic, visible or invisible - can lead to false readings. The measurement result will reflect the ORP of the fouled material rather than the overall solution. Therefore it is important to keep the sensor clean and its surface smooth.

The results of two ORP sensors measuring the same solution will usually differ. The difference usually stems from different amounts and types of contamination on the electrodes and possibly potential variations at the reference electrode. This effect is amplified in waters where fewer species are involved in the redox reaction.

The redox potential of a solution is partly a function of temperature, which is reflected in the Nernst equation. Since almost all components of natural water are never accurately known or quantified, the relationship between ORP and temperature cannot be determined on a practical basis. However, it is recommended and encouraged to use ORP results to record water temperature to facilitate comparison of measurements.

If you are interested in our ORP meter or have any questions, please write an e-mail to [email protected], we will reply to you as soon as possible.