Detection Limit Calculation and Influencing Factors Analysis of High-Precision Quadrupole Mass Spectrometry

An excellent usage is quite important for a high resolution quadrupole mass spectrometer (QMS) especially in the detection of the accurate partial pressure of gas. The mass spectral parameters testing device including QMS, vacuum system and sample injection system was used to study the influence of working and system parameters on mass spectral test results. Comparative experiments were carried out by changing one parameter each time. The result revealed that not only the scan speed, mass resolution, multiplier voltage and detectors, but also the vacuum background, work pressure and gas species can more or less influence the output spectrum particularly the detection limit of the instrument. Adopting the optimum parameters combination, minimum detectable concentrations of the three detectors were acquired under a certain condition by measuring the mass spectra for extremely low content krypton and xenon in atmosphere, including the Faraday cup(FC), secondary electron multiplier(SEM) and ion counter preamplifier(CP). It is concluded that the SEM and CP have much lower detection limits of 0.15×10^-9 and 0.34×10^-9, which are suitable for trace gas analysis, while the FC detector has a relative higher value of 17.3×10^-9.