Conductive powder

In 1979, Diaz et al. produced the first flexible, stable polypyrrole (PPy) film with high conductivity (1(X) Scm ). The substance was polymerized on a Pt-electrode by anodic oxidation in acetonitrile. The then known chemical methods of synthesis " usually produced low conductivity powders from the monomers. By contrast, electropolymerization in organic solvents formed smooth and manageable films of good conductivity. Thus, this technique soon gained general currency, stimulating further electropolymerization experiments with other monomers. In 1982, Tourillon... 

SSMS can be classified among the milliprobe techniques (Figure 8.3), i.e. it is a unique link between microprobe techniques and macroanalytical methods that are characterised by poor lateral and in-depth resolutions (as in OES), or that have no lateral resolution whatsoever (as in NAA). Also, the achievable precision and accuracy are poor, because of the irreproducible behaviour of the r.f. spark. Whereas analysis of metals, semiconductors and minerals is relatively simple and the procedures have become standardised, the analysis of nonconducting materials is more complex and generally requires addition of a conducting powder (e.g. graphite) to the sample [359]. Detection limits are affected by the dilution, and trace contamination from the added components is possible. These problems can be overcome by the use of lasers [360]. Coupled with isotope dilution, a precision of 5% can be attained for SSMS. 

Conductive powder composites Carbon-black composites... 

Remote sampling of up to 20 m makes the system attractive for the analysis of large items. On the other hand, the system is also useful for precision analyses both by atomic absorption and plasma spectrometric methods. The analysis of electrically non-conductive powders is also possible, where a mixture of the powder to be analyzed and copper powder in a ratio of about 1 5 can be made and briquetted into a pellet. This can be realized by using pressures of up to 80 Torr/cm2, as has been described for glow discharge work by El Alfy et al. [210], The mass ratio of analyte to copper may, however, differ considerably from one sample base to another. 

Spark AES has also been used for oil analysis. Here the oil is sampled by a rotating carbon electrode. Also electrically non-conducting powders can be analyzed after mixing them with graphite powder and briquetting. 

Electrically non-conducting powder samples can be analyzed after mixing with a metal powder such as Cu, Ag or Au and briquetting, as is known from experience with GD-OES. However, degassing and oxygen release may necessitate long preburn times and introduce instabilities. Also blanks arising from the metal powder may be considerable, e.g. for Pb in the case of copper powder. 

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