Study of the electrothermal atomization of phosphorus in transversely-heated graphite atomizers

Phosphorus electrothermal atomization behavior, in transversely-heated graphite furnace atomizers, in the presence of ascorbic acid, oxalic acid, palladium, magnesium nitrate, palladium+ascorbic acid, palladium+oxalic acid, and palladium+magnesium nitrate as chemical modifiers, was studied. The performance of these modifiers, with and without pyrolysis/thermal reduction, was assessed in terms of phosphorus thermal stability, and the sensitivity of the measurements. The study showed that neither organic acids alone nor magnesium nitrate alone prevent phosphorus losses. The effectiveness of palladium-based modifiers, on the other hand, was shown to depend on several factors, namely, the mass of palladium used, on the organic or inorganic nature of the secondary component in mixed modifiers, and on whether the modifier is thermally reduced or not, prior to the addition of the phosphorus solution into the atomizer. In general, the palladium+magnesium nitrate mixed modifier performed better for phosphorus than the other simple and mixed modifiers evaluated in this study. Scanning electron microscopy analysis of palladium-based modifiers deposited onto integrated platforms, and thermally reduced under different conditions points toward the possibility that the aforementioned observation could be related to the distribution and morphology of palladium onto such surfaces. It was found that palladium distribution over the platform is non-homogeneous, either when added alone or together with ascorbic or oxalic acid, and some portions of the deposition surface are devoid of modifier. This leads to partial analyte–modifier interactions, with incomplete thermal stabilization of the analyte and, as a result, phosphorus losses at different stages of the atomization program. Contrarily, magnesium nitrate helps in increasing palladium coverage of the deposition surface. Higher and more homogeneous coverage implies more effective analyte–modifier interactions and, consequently, better thermal stabilization of the former.