Direct-current plasma source

In a direct-current plasma source (DCP) initial heating of an inert gas, usually argon, is produced by a dc-arc. Experimentally it is arranged for the plasma to be established in a high-velocity gas stream. When the edges of the plasma are cooled with an inert gas vortex, the cooler outer parts have... 

Figure 5. Analytical working curve for potassium. The curve was obtained using a RCA 53612 CCD with a direct current plasma source.

The principle of the direct current plasma source (Gerdien and Lotz)... 

Direct-current circuits, 26,27 Direct-current plasma source, 258-259... 

There are two popular types of plasma sources l) the direct current plasma (DCP), and 2) the inductively coupled plasma (ICP). In the commercial version of the former plasma source (marketed by Spectrometries, Inc.), the sample is aspirated with argon through a small orifice into a chamber where the large droplets settle out and the fine mist is conveyed by the argon stream through a chimney to the vertex of a plasma which is in the form of... 

Microwave-induced plasma (MIP), direct-current plasma (DCP), and inductively coupled plasma (ICP) have also been successfully utilized. The abundance of emission lines offer the possibility of multielement detection. The high source temperature results in strong emissions and therefore low levels of detection. Atomic absorption (AA) and atomic fluorescence (AF) offer potentially greater selectivity because specific line sources are utilized. On the other hand, the resonance time in the flame is short, and the limit of detectability in atomic absorption is not as good as emission techniques. The linearity of the detector is narrower with atomic absorption than emission and fluorescence techniques. 

For special applications direct current plasma (DCP) (Leis et al., 1989) and micro-wave-induced plasma (MIP) may be used. The MIP first became widely used as a spectroscopic radiation source after a stable discharge at atmospheric pressure had been obtained (Beenakker, 1977 Beenakker et al., 1978). The MIP is not capable of taking up wet aerosols, but is useful for the excitation of dry aerosols, produced by electrothermal evaporation from a graphite furnace (Aziz et a ., 1982). Direct sample insertion has been discussed recently by Blain and Savin (1992). 

PACVD method is another typical way of making diamond films. Precursor gas molecules can be decomposed into radicals under the effect of plasma. There are three plasma sources commercially available (Davis 1993). Microwave plasma typically uses excitation frequencies of 2.45 GHz. Radio frequency (RF) plasma excitation typically employs frequencies of 13.56MHz (or less commonly 450kHz). Direct current plasmas can be run at low electric powers, named as cold plasma, or at high electric powers, which create an arc, named as thermal plasma. Microwave PACVD method is the most common one among the three methods. 

Direct-current plasma jets were first described in the 1920s and have been systematically investigated as sources for emission spectroscopy. In the early 1970s, the first commercial direct current plasma (DCP) was introduced. The source was quite popular, particularly among soil scientists and geochemists for multielement analysis. 

During the 1980s, a rapidly increasing number of methods have been published for mercury determination by AES (often called OES = optical emission spectrometry) after excitation/ionization in a gas plasma, usually argon. The plasma source most frequently used is an ICP, but also other kinds of plasma sources are used, e.g. alternating current plasma (ACP), direct current plasma (DCP), and microwave-induced plasma (MIP). AES has a wide multi-element capability the linear range extends over 4-6 orders of magnitude. 

The use of atomic emission spectrometry expanded markedly when the first commercial plasma atomic emission spectrometers came on the market in the middle of the seventies. The principle of the direct current plasma (DCP) source was reported in the twenties and the first DCP instrument was constructed at the end of the fifties. The first microwave plasma source was... 

Alan Gray first suggested the connection of a plasma source and a mass spectrometer in 1975. The direct current plasma jet was first applied in this new technique. Later it was shown that the inductively coupled plasma (ICP) met the requirements better than the DCP for an ionization source of mass spectroscopic analysis. The pioneering work of ICP-MS was mainly conducted by three research groups (Fassel, Gray, and Date). 

Direct current plasma (DCP). A spectroscopic source in which plasma is maintained by an electric field (a direct current arc between three electrodes). 

The analytical plasmas are classified according to the method of power transmission to the working gas. There are three dominant types of plasma source in use today (i) Inductively coupled plasmas, ICPs (ii) Direct current plasmas, DCPs (current carrying DC plasmas and current-free DC plasmas) (iii) Microwave plasmas (microwave induced plasmas, MIPs, and capacitively coupled microwave plasmas, CMPs). 

---