Sample state and preparation for glow-discharge sampling

Sample state and preparation for glow-discharge sampling 

Clearly, the principal use of GD is for solid analysis. At a time when many complex procedures are being examined for introducing solid samples into plasmas that are, by nature, better suited to solution injection, GD sputter sampling provides a simple procedure for conversion of a solid into an atomic vapour. 

Samples obtained from animal or plant tissue must be processed prior to GD analysis. The sample may either be dried in an oven or ashed. The dry residue is homogenized and ground, after which it can be handled in the same manner as particulate matter. 

The variables that influence performance in GD sampling can be classified according to whether they are shared by the source and detector or pertain exclusively to one or the other. The optimum value for each variable depends on the particular aim of the work at hand (e g. quantitation in homogeneous samples, surface and depth profiling studies in layered samples). 

The most influential parameters in dcGD are the current intensity that circulates between the electrodes, the applied voltage and the pressure of the plasma gas. In 1993, Payling and Jones devised a method for separating the contributions of the three key variables in these sources and proposed a quantitative approach in which the emission yield was assumed to depend on pressure alone [171]. This hypothesis was shown to hold for the rfGD mode as well [172]. 

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