厦门大学 仪器分析课件第0 质谱分析法.ppt

《仪器分析》课程 第四章 质谱分析法 Mass Spectroscopy MS 质谱过程 　　　　　撞　击　　　　　　　得到 高速电子　 　 　气态分子　　　阳离子　　　 顺序谱图　　　　 质量分析器 定性结构 定量分析 §8-1 质谱仪 进样系统　离子源／电离室　质量分离器 离子检测器　　记录 动态：质量分析器采用变化的电磁场，利用空间位置将m/e分开。 静态：质量分析器采用稳定的电磁场，按照时间和空间区分m/e。 一、质谱仪主要性能指标 （一）质量测定范围：能够分析样品的相对原子（分子）质量范围，对gas范围 2—100，有机质谱几十到几千。 （二）分辨本领： 两个相等强度的相邻峰，峰谷不大于其峰高10%时，两峰已经分开。 R　=　m1/(m2-m1) = m1/⊿ m 分析本领由下面这些因素决定 　１、离子通道半径 　２、加速器和收集器的狭缝宽度 　３、离子源 　1000以下为低分辨率 Instrumentation In general a mass spectrometer consists of an ion source, a mass-selective analyzer, and an ion detector. Since mass spectrometers create and manipulate gas-phase ions, they operate in a high-vacuum system. The magnetic-sector, quadrupole, and time-of-flight designs also require extraction and acceleration ion optics to transfer ions from the source region into the mass analyzer. The details of mass analyzer designs are discussed in the individual documents listed below. Basic descriptions of sample introduction/ionization and ion detection are discussed in separate documents on ionization methods and ion detectors, respectively. 二、工作进程 样品进入电离室后，被热灯丝产生的电子流轰击，气态样品中的原子或离子被电离成正、负离子。离子被狭缝A、B加速进入磁场，而根据离子质荷比的差异，产生不同的偏转角，从而达到分离。改变A、B电压和外磁场，获得MS谱图。 Theory The ion optics in the ion-source chamber of a mass spectrometer extract and accelerate ions to a kinetic energy given by:K.E. = 0.5 mv2 = eV where m is the mass of the ion, v is its velocity, e is the charge of the ion and V is the applied voltage of the ion optics. The ions enter the flight tube between the poles of a magnet and are deflected by the magnetic field, H. Only ions of mass-to-charge ratio that have equal centrifugal and centripetal forces pass through the flight tube: mv2 / r = Hev centrifugal = centripetal forces. Where r is the radius of curvature of the ion path: r= mv / eH This equation shows that the m/e of the ions that reach the detector can be varied by changing either H or V. 三、部　件 （一）进样系统， 扩散法 适用于气体或挥发性