高精度四极质谱检测限测试和影响因素分析

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

高精度四极质谱仪(QMS)的气体分压精确测量功能与其使用方法关系密切.采用包含有四极质谱仪、真空系统和进样系统的质谱参数测试装置,针对工作及系统参数对质谱测试结果的影响开展研究.试验结果表明:无论是扫描速率、质量数分辨率、电压和探测器等质谱工作参数,还是真空本底、工作真空和气体种类等系统参数都会对质谱测试结果尤其检测限产生一定影响.试验获得了特定条件下的最优参数并进行比较.采用获得的最优参数组合,通过测量空气中极低含量稀有氪气和氙气的同位素谱图,可获得一定条件下法拉第杯(FC)、二次电子倍增器(SEM)和离子计数器(CP)等3种探测器的最小可检浓度,分别为17.3×10-9、0.34×10-9和0.15×10-9.其中SEM和CP的检测限最低,适合用于微量气体分析.

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.