Nguồn Ion Nói chung, tất cả các nguồn GDMS ion sử dụng một loại khí phóng điện phát sáng cao quý trong huyết tương duy trì ở mức khoảng 1 Torr áp lực và một vài Watts của quyền lực xả. Một mẫu thực hiện vững chắc cho GDMS phân tích các hình thức cực âm cho phóng điện phát sáng DC (Hình 1). | sis has matured rapidly and has become more widely available since the recent introduction of commercial GDMS instrumentation. Basic Principles Ion Sources In general all GDMS ion sources use a noble gas glow-discharge plasma sustained at about 1 Torr pressure and a few Watts of discharge power. A conducting solid sample for GDMS analysis forms the cathode for a DC glow discharge Figure 1 . Atoms are sputtered nonselectively from the sample surface by ions accelerated from the plasma onto the surface by the cathode voltage. The sputtered atoms diffuse into the plasma and are mosdy ionized by collision with metastable discharge gas atoms so-called Penning ionization but also in small part by electron impact. Penning ionization more so than electron impact ionization provides similar ionproduction efficiencies for the majority of the elements. Plasma ions extracted through the exit aperture including the analyte ions are electrostatically accelerated into a mass analyzer for measurement. Ion sources for GDMS have undergone significant evolution ultimately resulting in discharge cells exposing only the sample cathode surface and the metal interior of the Ta discharge cell anode to the plasma a design that minimizes contamination and enhances reliability. The glow-discharge cells accept a variety of shapes and surface conditions requiring only sufficient length or diameter of the sample. Typically pin- or wafer-shaped samples are required. It is very helpful to include cryocooling into the design of the discharge cell to enable the analysis of materials having low melting point and to reduce the density of molecular ions created from atmospheric gas related contaminants in the glow-discharge plasma. At the current time analytical glow-discharge sources incorporate a DC glow discharge. Efforts have been underway to develop glow-discharge sources appropriate for the analysis of electrically insulating materials . glass and ceramic which comprise a very important class
