Direct-current plasma (DCP) is a type of plasma source used for

atomic emission spectroscopy Atomic may refer to: * Of or relating to the atom, the smallest particle of a chemical element that retains its chemical properties * Atomic physics, the study of the atom * Atomic Age, also known as the "Atomic Era" * Atomic scale, distances comp ...

that utilizes three

electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

to produce a

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

stream.Skoog, D. A.; Holler, F. J.; Crouch, S.R. Principles of Instrumental Analysis, 6th ed., Brooks Cole, 2007; pp. 258-259. . The most common three-electrode DCP apparatus consists of two

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

blocks and a

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

block arranged in an inverted-Y arrangement. An

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

gas source is situated between the anode blocks and argon gas flows through the anode blocks. The plasma stream is produced by briefly contacting the cathode with the anodes. Temperatures at the arc core exceed 8000 K. This three-electrode arrangement is illustrated in Figure 1.

Applications

The applications of DCP are comparable to inductively coupled plasma (ICP). Some applications include, but are not limited to: * identification of

boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...

in tissues and cells * analysis of

trace metal Trace metals are the metals subset of trace elements; that is, metals normally present in small but measurable amounts in animal and plant cells and tissues and that are a necessary part of nutrition and physiology. Many biometals are trace me ...

s in cows * synthesis of

carbon nanofiber Carbon nanofibers (CNFs), vapor grown carbon fibers (VGCFs), or vapor grown carbon nanofibers (VGCNFs) are cylindrical nanostructures with graphene layers arranged as stacked cone (geometry), cones, cups or plates. Carbon nanofibers with graphene ...

s Figure 2 shows DCP being used to grow carbon nanofibers.

Comparison to inductively coupled plasma (ICP)

DCP incurs several key disadvantages in comparison to ICP. In addition to the lower sensitivity, spectra generated by DCP generally present fewer spectral lines. DCP samples are often incompletely volatilized due to the relatively short amount of time spent in the hottest region of the plasma. Furthermore, DCP requires more regular upkeep than ICP, because the graphite electrodes wear out after a few hours and must be exchanged However, DCP is not without a few advantages over ICP. The amount of argon needed for DCP is much less than that needed for ICP. Also, DCP can analyze samples that have a higher percentage of solid in solution than can be handled by ICP.

References

{{Reflist Analytical chemistry