Laser-induced fluorescence in graphite furnaces under low pressure conditions as a powerful technique for studies of atomization mechanisms: investigation of Ag

Abstract

A new method for accurate studies of atomization processes of various elements in graphite furnaces has been developed. It utilizes the highly sensitive Laser-Induced Fluorescence spectrometry technique for detection of atoms in Graphite Furnaces under Low Pressure conditions (LIF-GF-LP). The high sensitivity of the LIF technique enables the study of atomization processes at low pressures under true analytical conditions (i.e. for low analyte mass) with a minimum of influences from diffusion processes. This first work is concerned with an investigation of the atomization mechanisms of Ag. It was found that the LIF-GF signal area was linear with pressure for virtually all pressures. The LIF-GF signal shape (versus time as well as versus 1/ T) was found to vary with both pressure and concentration. The signals were, in general, found to have a shorter duration and higher appearance and peak temperatures, the higher the pressure. Activation energies could be evaluated from the LIF-GF-LP curves very accurately by the Smets method. Excellent agreements with the predicted linear relationship were obtained for a major part of the signal curve (> 50%) under many sample and furnace conditions. Studies of the activation energy dependence on pressure, analyte mass and heating rate gave valuable information about the atomization mechanisms of Ag in graphite furnaces. The findings support a picture that Ag atomizes as individual adatoms under low pressure and low analyte mass conditions. Under atmospheric conditions, repeated desorption and adsorption processes delay the appearance of the signal in time as well as being responsible for formation of 2-D and 3-D microstructures on the surface.