Glow Discharge Optical Spectroscopy and Mass Spectrometry

Abstract

AbstractGlow discharge (GD) sources provide analytically useful gas‐phase species from solid samples. These sources can be interfaced with a variety of spectroscopic and spectrometric instruments for both quantitative and qualitative analysis. Optical (atomic absorption spectroscopy, AAS; atomic emission spectroscopy, AES; atomic fluorescence spectroscopy, AFS; and optogalvanic spectroscopy) and mass spectrometric (magnetic sector, quadrupole mass analyzer, QMA; quadrupole ion trap, QIT; Fourier transform ion cyclotron resonance, FTICR; and time‐of‐flight, TOF) instrumentation are well suited for coupling to the GD.The GD is a relatively simple device. A potential gradient (500–1500 V) is applied between an anode and cathode. In most cases the sample is also the cathode. A noble gas (e.g. Ar, Ne, Xe) is introduced into the discharge region prior to power initiation. When a potential is applied, electrons are accelerated toward the anode. As these electrons accelerate they collide with gas atoms. A fraction of these collisions are of sufficient energy to remove an electron from a support gas atom, forming an ion. These ions are, in turn, accelerated toward the cathode. These ions impinge on the surface of the cathode, sputtering sample atoms from the surface. Sputtered atoms that do not redeposit on the surface diffuse into the excitation/ionization regions of the plasma where they can undergo excitation via a number of collisional processes.GD sources offer a number of distinct advantages that make them well suited for specific types of analyses. These sources afford direct analysis of solid samples, thus minimizing the sample preparation required for analysis. The nature of the plasma also provides mutually exclusive atomization and excitation processes that help to minimize the matrix effects that plague so many other elemental techniques. Unfortunately, the GD source functions optimally in a dry environment, making analysis of solutions difficult. These sources also suffer from difficulties associated with analyzing nonconducting samples.In this article, the principles of operation of the GD plasma will first be reviewed, with an emphasis on how those principles relate to optical spectroscopy and mass spectrometry. Basic applications of the GD techniques will next be considered. These include bulk analysis, surface analysis, and the analysis of solution samples. The requirements necessary to obtain optical information will be addressed following the analytical applications. This section will focus on the instrumentation needed to make optical measurements using the GD as an atomization/excitation source. Finally, mass spectrometric instrumentation and interfaces will be addressed as they pertain to the use of a GD plasma as an ion source.