Why choose argon as the working gas for ICP spectrometer?

The working gas used in ICP spectrometer is high-purity argon (99.999%). In the analysis process, the role of argon is very important. Its role is to produce ionized gas for plasma. The electromagnetic energy is coupled to argon by inductive coupling. The gas is ionized into plasma. The plasma itself can release various spectra or interact with objects to emit characteristic spectra of objects. The spectrometer analyzes these emitted spectra, and the obtained spectral distribution can be used for various analyses.

But you don’t know that in the development of ICP spectroscopy technology, molecular gases (nitrogen, air, oxygen, argon-nitrogen mixture) have been discussed many times to replace argon as working gas. Although molecular gases can also form plasma torches at higher powers, the excitation temperature of the plasma formed is also lower than that of argon plasma. The physical properties of the working gas, such as resistivity, thermal melting and thermal conductivity, are another important reason that affects the formation of stable plasma. Argon has low resistivity, thermal melting and thermal conductivity. Low thermal conductivity can reduce the energy loss caused by thermal heat dissipation; improve the thermal efficiency of plasma, and the high or low thermal conductivity is extremely important for the formation of stable plasma.

According to the test, when the gas flow rate of the outer tube is 5L/min argon, the heat conduction of the quartz tube loses 60%, 43% and 20% of the total energy respectively. Due to the above reasons, argon is easier to form a stable ICP.

ICP spectrometers all use argon as the working gas for two reasons:

1. Argon ICP light source has good analytical performance, high analytical sensitivity and low spectral background;

2. It is easy to form a stable ICP using argon as plasma, and the required high-frequency power is also low.

3. Argon is an inert gas and will not react chemically with the material being measured. Moreover, argon has little cooling effect on the arc, so when the arc burns in argon, the heat loss is small and the stability is better. At the same time, the positive ions after argon decomposition have a large volume and mass, and the impact force on the cathode is very strong, which has a strong cathode crushing effect. Therefore, argon can make the spectrometer perform better.

The quality of the gas source of the ICP spectrometer directly affects the importance and reproducibility of the instrument's measurement data. Especially when measuring trace and ultra-low content elements, it is necessary for the gas source to meet the requirements of high-purity argon (99.999%). If the gas source purity does not meet the requirements, an argon gas purifier is required to ensure the purity of the argon.