Aspects of indirect atomic-absorption determinations based on molybdenum heteropoly acid chemistry
Molybdenum heteropoly acid chemistry with its inherent amplification factor has been used to improve the sensitivities and detection limits of methods for phosphorus and germanium determination, using both flame and electrothermal atomization atomic absorption spectrometry to determine the molybdenum. Phosphorus extracted as 12-molybdophosphoric acid, was used as a model element for the study of certain aspects of the procedure. Solvent extraction was used for the separation of the heteropoly species from the considerable excess of molybdate (added to drive the reactions to completion), which usually produces high blank values in both flame and electrothermal atomization work. A considerable improvement in blank levels, to below the instrumental detection limits has been achieved by careful drying of the extract. In addition to the chemistry of formation and extraction, the flame atomization of molybdenum has been investigated with view of improving sensitivity and detection limit. Modifications to the flame gas composition by the addition e.g. possible additional reducing agents, have been investigated. Variation of the particle microenvironment in the flame by varying the salt composition of the solution was also studied. Improvement in the nebulization process by combining flow injection sample introduction with modification of the solution physical properties was investigated.