Advances of nitrogen microwave plasma for optical emission spectrometry and applications in elemental analysis: a review
The present review deals with microwave-induced plasma optical emission spectrometry (MIP OES) with focus on MIP sustained by N2. Advances of MIP OES as an analytical tool and N2-MIP OES application in elemental analysis are highlighted. The novel microwave inductively coupled atmospheric-pressure plasma (MICAP) is also presented and the N2-MICAP is discussed. The assertion of MIP OES as an atomic spectrometry technique for elemental analysis occurred mainly due to the development of N2-MIP generated in a cavity embedded in a narrow width waveguide. The precise location of the cavity as a function of the wavelength associated with the 2450 MHz frequency maximizes the magnetic field and generates H-type excitation almost entirely, and is similar to that occurring in argon inductively coupled plasma (Ar-ICP). Microwave induced plasma optical emission spectrometry based on the use of N2-MIP is in general more sensitive in terms of detection limit than the flame atomic absorption spectrometry (FAAS) and almost comparable to inductively coupled plasma optical emission spectrometry (ICP OES). Since the introduction of a commercial N2-MIP OES instrument in the last decade, which allows metals and non-metal determination, applications of the technique for the analysis of samples with different matrices have increased as demonstrated in the present review.