The air flow in the chamber optical doesn't pass wavelengths shorter than 190 nm , because oxygen and water vaporin the air have high absorption power for wavelengths shorter than 190 nm. A number of important elements that have wavelengths shorter than 190nm :
"C": 133nm, 136nm,159nm, 165 nm, "N": 149 nm, "P": 177nm, 178nm , "S": 180.7nm
For the measurement of the optical elements we need to remove the oxygen and water vapor in the optical chamber , this is possible in two ways :
1- Cleanup optical system by a permanent establishment gas flow , such as Argon or Nitrogen
2- Stablishment vacuum in the chamber optic
Use vacuum pump to remove the air inside of the chamber optics. This method has been used in spectrometers for a long time and have lots of advantages , including :

• Lack of continued use of Argon or other inert gas , resulting in problems such as the lack of high quality, high purity gas use , the instability of the terms of the optics chamber , in purities in the gas flow
• Save stability of spectrometer device after turning on the spectrometer
• The stability and reproducibility of results analysis of samples
• Increase accuracy and precision in the measurement of the elements , especially the elements of the short wavelength , in the range of UV wavelength , such as Carbon , Sulfur , Phosphorus.
• Create an stable and fixed environment in the optics chamber