SURFACTANT-BASED ORDERED MEDIA IN ANALYTICAL ATOMIC SPECTROMETRY

During the last 10 years or so we have witnessed an enormous growth of interest and applications of surfactant-based ordered media in analyt ical chemistry. However, their use in analytical atomic spectroscopy ( AAS) has been rather scarce and often controversial. The utilization o f surfactants in this latter field is discussed here along two main li nes: one refers to the favourable manipulation of physical properties of the sample solutions (Part A) while the other, demonstrated very re cently, refers to the adequate manipulation of chemical reactions and/ or interactions of analytes in solution by resorting to surfactants us e (Part B). The control of physical properties of sample solutions, e. g. manipulation of the surface tension, allows three main applications of surfactants in atomic methods: possible increases of nebulization/ atomization efficiencies in flame-AAS, improvement of aqueous/organic solvent compatibility (emulsification applications) and enhancement of the wettability of graphitic solid surfaces. The facts and controvers ies existing today on this method of utilization of surfactants to enh ance atomic methodologies is critically discussed. The ability of surf actant-based ''ordered media'' to organize reactants at the molecular level has also been applied to enhance chemical generation of volatile species (e.g. hydride generation or cold Hg vapour generation) used i n atomic methods. The analytical potential and usefulness of micelles and vesicles to improve the detection power of hydride generation ICP- AES methodologies are summarized for the determination of arsenic, lea d and cadmium by plasma emission. Increases up to two-fold in the sens itivity of As and Pb have been observed by addition of organized media . A volatile Cd species is formed very easily in cationic vesicles wit h NaBH4. This Cd species can be used to increase by five times the det ectability of Cd by ICP-AES. Moreover, synergic combinations of liquid chromatography separations/atomic detection are possible by resorting to the use of micellar or vesicular mobile phases. The successful app lication of this principle to the modem problem of toxic arsenic HPLC speciation by using a vesicular solution [as mobile phase for the HPLC separation of As(III), As(V), monomethylarsonic and dimethylarsinic a cids] and ''on-line'' surfactant-enhanced arsine generation is also de scribed in detail and completes the whole picture of the present inter face between analytical atomic spectroscopy and surfactant assemblies.