The formation of ICP is the ionization process of working gas. In order to form a stable ICP torch flame, four conditions are required: a high-frequency and high-intensity electromagnetic field, a working gas, a quartz torch tube that maintains a stable gas discharge, and an electron ion source.
The rectangular tube is composed of a triple concentric quartz tube with a diameter of 20 mm. The same 10-20L/min argon gas between the quartz outer tube and the middle tube is used as a working gas to form plasma and cool the quartz rectangular tube, which is called plasma gas or cooling gas. The middle tube and the center tube are filled with 05~1.5L/min argon gas, called auxiliary gas, to assist the formation of plasma. The central tube is used to introduce the sample aerosol. There is a high-frequency induction coil in the outer shell of the quartz rectangular tube, and the induction coil is generally a hollow copper tube with 2 to 4 turns.
The formation of an ICP torch is commonly referred to as ignition. Ignition is divided into three steps: the first step is to pass plasma and auxiliary gas into the outer tube and the middle tube. At this time, the central tube is not gas-passed, and an argon atmosphere is established in the rectangular tube; the second is to connect the induction coil to the high-frequency power supply , The general frequency is 27~40MHz, and the power supply is 1~1.5KW. At this time, there is a high-frequency current in the coil and a high-frequency electromagnetic field generated by it. As the argon dried at room temperature does not conduct electricity and will not induce current in the argon, other methods must be used to partially ionize the argon into a conductor. High-frequency electromagnetic field can further ionize it to form plasma. There are two methods to partially ionize argon. One is the graphite rod heating method. At present, high-voltage Tesla coils that can produce sharp discharges are often used. The sharp discharges are formed in the argon gas flow in the tube to partially ionize the argon into electrical conductors. Generate induced current. The induction current heats the gas to form a torch-shaped ICP torch flame.
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