What is the principle of a trace oxygen analyzer? Detailed explanation of the principle of trace oxygen analyzer

Trace oxygen analyzerIt is a commonly used analytical instrument that uses a sealed fuel pool oxygen sensor, which is currently one of the advanced methods for measuring oxygen. It consists of highly active oxygen electrodes and lead electrodes, immersed in KOH solution.Trace oxygen analyzerWhat is the principle behind it? Below, the editor will provide a specific introduction, hoping to help everyone.
Trace oxygen analyzerThe principle of
Trace oxygenThe analysis methods mainly include colorimetric method, chemical cell method, yellow phosphorus luminescence method, concentration cell method, and gas chromatography method. Among them, colorimetric method is an early adopted analytical method. It is a method specified by national standards, which uses copper ammonia solution for colorimetric analysis. Due to its complex operation, accuracy is difficult to guarantee, and automatic online analysis cannot be achieved. It is now rarely used, but it is still an arbitration method. The yellow phosphorus luminescence method uses oxygen and yellow phosphorus oxidation combustion for analysis, which has the characteristics of fast analysis speed and continuous analysis. However, the yellow phosphorus used in this method is a hazardous chemical, and the generated products are corrosive with low detection limits, so it is rarely used now. Here, we mainly introduce the chemical battery method, concentration cell method, and gas chromatography method. 1. Chemical battery method
The Chemical Battery MethodTrace oxygen analyzerRefers to the use of the principle of redox batteriesTrace oxygen analysisIts sensor (detector) is a chemical primary battery, mainly composed of a cathode, an anode, and an electrolyte. The above components are sealed in an inert shell. Oxygen in the measured gas enters the battery near the cathode to obtain electrons from O2. The anode is made of lead metal and loses electrons by oxidation. The electrons generated by the battery are extracted by the circuit and compensated, corrected, and amplified to measure the oxygen content in the measured gas. The reaction equation is as follows:

O2+2H2O+4e - → 40H cathode

Pb+2OH - → Pbo+H2O+2e anode

The total reaction equation is 2pb+O2 → 2pbO

Due to different implementation methods, it can be divided into primary cell method, fuel cell method, and Hertz cell method.

2. Concentration battery method

The concentration cell method, also known as the zirconia cell method, uses zirconia elements as key components of the detector to form an oxygen measuring cell. It includes zirconia tubes, molybdenum electrodes coated at the bottom of the tubes, and electrode leads, which can lead out signals; The heating furnace is used to heat the zirconia tube, keeping it constant at the set temperature (780 ± 10 ℃); The standard gas tube is used to connect the standard gas and calibrate the probe; Thermocouples are used to measure the temperature in oxygen cells and are connected to the transmitter temperature control system; The wiring board is equipped with three pairs of terminals for signals, thermocouples, and heating furnaces, as well as filters, mounting flanges, and probe housings. As shown in Figure 1, there are two platinum electrodes on the inner and outer surfaces of the bottom of the zirconia tube, namely the reference electrode and the measuring electrode, each with two platinum leads, forming a zirconia oxygen cell, namely the oxygen concentration cell. Its reaction principle at the platinum electrode is O2+4e → 2O2-; 2O2- → O2+4e, thus, a potential difference is formed between the two electrodes, forming a concentration cell (2).
The main disadvantage of zirconia concentration batteries is that reducing impurities have an impact on the analysis of trace oxygen. Because at temperatures between 500-800 degrees Celsius, reducing substances can react with oxygen, consuming oxygen and resulting in lower analysis results. Its main advantages are a wide range of measurement, covering analysis of oxygen content from constant to trace amounts, easy to use, and long service life.

3. Gas chromatography method

The advantage of gas chromatography for trace oxygen analysis is that multiple impurities can be detected simultaneously, as the separation of impurities in air separation gases is relatively easy, making the configuration of the chromatographic column system simple. When detecting various impurities containing trace amounts of oxygen, chromatographic analysis is more appropriate. The available chromatographic detectors include thermal conductivity detector, electron capture detector, helium ionization detector, argon ionization detector, discharge ionization detector, atomic emission detector (AED), etc.
The disadvantage of using chromatography for trace oxygen analysis is that it cannot achieve true online analysis, which means real-time monitoring of trace oxygen cannot be achieved, intermittent detection is required, and the equipment system is complex, requiring carrier gas, auxiliary gas, etc.