Sample entraining multi-electrode plasma sources for atomic emission spectroscopy.

摘要

lasma sources with multiple electrodes have been developed and characterized in this research for atomic emission spectroscopy. Multi-electrode plasma sources use electrodes to shape the plasma in order to continuously entrain a sample stream in the center of hot plasma, in a manner similar to an inductively coupled plasma (ICP) source. By changing the electrode spacings, the residence time can be readily adjusted even during plasma operation. For a 25-mm plasma length, a relatively long residence time of the analyte species (23 msec) in the plasma was calculated, indicating sufficient time for desolvation, vaporization, and atomization of the sample.;When current, gas flow rate, and plasma length are varied, the spatial emission profiles reflect many of the characteristics associated with an ICP. The short term stability of the plasma with a blank solution is better than 2% (relative standard deviation). A total of less than 6 L/min of argon gas is required to operate the plasma. With the vertical 4-electrode plasma source, 4 to 5 orders of magnitude of linear dynamic range are obtained and detection limits for 12 elements are comparable to those obtained with an ICP.;For a 30-mm plasma length, the interference effect of either phosphate or aluminum on calcium emission at 393.37 nm is insignificant over the entire vertical region of the plasma. The effect of an easily ionized element (EIE) is to generally enchance Ca(II) emission in the lower regions, and to depress the emission in the higher regions in the plasma, which is in general agreement with observations in an ICP. Under an assumption of local thermal equilibrium (LTE), the Fe excitation temperature and the electron number density in the center of the plasma at 8 mm above the top of the quartz tube are 5000 K and 1.0