Probe method, heated plasma

The electron temperature (Tg), electron density (ng) and electron energy distribution function for a plasma sustained in an argon/benzene mixture were measured by double and triple plasma-probe methods. Each probe was heated up to 1000 K with a sheathed heater, which was inserted into the probe, in order to prevent... 

Cl in conjunction with a direct exposure probe is known as desorption chemical ionization (DCI). [30,89,90] In DCI, the analyte is applied from solution or suspension to the outside of a thin resistively heated wire loop or coil. Then, the analyte is directly exposed to the reagent gas plasma while being rapidly heated at rates of several hundred °C s and to temperatures up to about 1500 °C (Chap. 5.3.2 and Fig. 5.16). The actual shape of the wire, the method how exactly the sample is applied to it, and the heating rate are of importance for the analytical result. [91,92] The rapid heating of the sample plays an important role in promoting molecular species rather than pyrolysis products. [93] A laser can be used to effect extremely fast evaporation from the probe prior to CL [94] In case of nonavailability of a dedicated DCI probe, a field emitter on a field desorption probe (Chap. 8) might serve as a replacement. [30,95] Different from desorption electron ionization (DEI), DCI plays an important role. [92] DCI can be employed to detect arsenic compounds present in the marine and terrestrial environment [96], to determine the sequence distribution of P-hydroxyalkanoate units in bacterial copolyesters [97], to identify additives in polymer extracts [98] and more. [99] Provided appropriate experimental setup, high resolution and accurate mass measurements can also be achieved in DCI mode. [100]... 

In both of these two cases, the heat of evaporation is greater than the energy of the thermal degradation of the molecules. Therefore, methods omitting evaporation prior to ionization had to be looked for. Several attempts were made to overcome this problem . Today, the most promising methods using ionization of the sample in the solid state directly from a probe surface are field desorption (FD), desorption chemical ionization (DCI), Cf-plasma desorption technique, and laser-induced desorption technique. 

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