Currently used for mass spectrometer calibration are calibrating gas mixtures.
The price of such mixtures is quite high.
The mixture components' concentration is preset on a standard process basis ("as per formula"), which creates certain difficulties in preparation of mixtures with very low component concentrations (at the level of dozens of ppmv).
The instrument calibration using such mixtures does not allow to test the absolute value of the sensitivity factor by direct measurement
For calibration of leak detectors and similar instruments, a commercially manufactured diffuse helium detector (Helite) is used. The main disadvantage of this instrument is that the helium diffusion through the quartz glass is continuous, and its rate depends on the ambient temperature and the helium pressure difference between the detector's gas reservoir and the vacuum volume. Therefore, the value of the helium flow gradually decreases compared to the rated value, while the rate of this decrease may only be assessed very approximately, which impairs the accuracy of calibration.
Principle of operation
The Gas Leak device, when activated, emisses a stable gas flow into vacuum. The flow rate value is preset in the range of 5 mm3Pa/s to 20,000 mm3Pa/s. When the device is disconnected, the flow stops. This allows to retain the flow value obtained in the calibration for as long as desired. This device enables to find the absolute sensitivity ratio by direct measurement.
The use of a Gas Leak device of our design with different gases makes possible a relative calibration, as well as in case of a gas mixture. An important advantage of our device is that the mixing directly precedes the analysis, therefore absorption of minor mixture components by vessel walls and minor carrier gas components is minimum, which provides a better reliability and accuracy of calibration.