Direct Current Plasma:
In direct current plasma (DCP) the external source of energy is a dc electric source. The most recently developed DCP is the three electrodes DCP or inverted -Y shaped plasma, as it is generally called and shown in Figure. It has two anodes set at an included angle of about 60o and a cathode. An anode is made up of graphite and is surrounded through ceramic sleeves. A cathode block consists of a little tungsten electrode also surrounded by a ceramic sleeve. The argon gas is introduced through the sleeves around the anodes and transfers the discharge to the cathode block.
Figure: A schematic diagram showing the positioning of the electrodes and the sample insertion in a typical DCP
The sample in the form of an aerosol is introduced at a rate of about 2 cm3 /min below the intersection of the two anodic columns. A spectral observation region is only just below this intersection. A background radiation is associatively low. However, the excitation region is relatively little, and good spatial stability is essential to avoid drifts in observed intensities. The DCP is subject to a few matrix effects and fairly severe ionisation interferences, that is enhancement or depression in intensities because of the presence of an easily ionisable element. It has been reported in which the detection limits for DCP-AES are inferior to those obtainable by ICP-AES.