Characterization of the vapor-phase molecular and atomic absorption from sea water matrices in electrothermal atomic absorption spectrometry

Vaporization of sea water was investigated by molecular and atomic absorption spectrometry. Using the combination of an ultraviolet spectrometer with multi-channel detector and an electrothermal atomizer, vapor-phase absorption was monitored in the wavelength region between 200 and 400 nm. The effects of the vaporization temperature, thermal pretreatment, internal gas flow and use of nitric acid as matrix modifier on the composition of the vapor phase were investigated using tube, platform and filter furnaces. Moreover, solutions of the main components of sea water (chlorides and sulfates of sodium, magnesium and calcium) were vaporized to clarify the contribution of each salt to the overall absorption. The addition of nitric acid to sea water led to partial suppression of the intense NaCl bands and to the appearance of oxygen containing species. Total suppression of chlorides could not be attained even with high concentration of nitric acid (more than 8% m/m). Molecular bands attributed to NaCl, NaOx, MgCl, CaCl, SOx and NO species were observed at different stages of the vaporization process. In the filter furnace, the bands of the oxygen containing molecules were less intense due to the reaction with carbon. An intense spectral continuum, attributed to light scattering, was decreased with the filter furnace relative to that observed for the tube and platform furnaces with the gas stop mode of operation. (C) 1998 Elsevier Science B.V. All rights reserved.