Organised surfactant assemblies in analytical atomic spectrometry

The use of surfactant-based organised assemblies in analytical atomic spect roscopy is extensively and critically reviewed along three main lines: firs t, the ability of organised media to enhance detection of atomic spectrosco pic methods by favourable manipulation of physical and chemical properties of the sample solution second, the extension of separation mechanisms by re sorting to organised media and third a discussion of synergistic combinatio ns of liquid chromatography separations and atomic detectors via the use of vesicular mobile phases. Changes in physical properties of sample solution s aspirated in atomic spectrometry by addition of surfactants can be advant ageously used in at least four different ways: (i) to improve nebulisation efficiency; (ii) to enhance wettability of solid surfaces used for atomisat ion; (iii) to improve compatibility between aqueous and organic phases; and (iv) to achieve good dispersion of small particles in "slurry" techniques. Controversial results and statements published so far are critically discu ssed. The ability of surfactant-based organised assemblies, such as micelles and vesicles, to organise reactants at the molecular level has also been applie d to enhance the characteristics of chemical generation of volalite species of metals and semi-metals (e.g., hydride or ethylide generation of As, Pb, Cd, Se, Sn, and cold vapour Hg generation) used in atomic methods. Enhance ments in efficiency/transport of volatile species, increases in the reactio n kinetics, stabilisation of some unstable species and changes in the selec tivity of the reactions by surfactants are dealt with. Non-chromatographic cloud-point separations to design pre-concentration pro cedures with subsequent metal determination by atomic methods are addressed along with chromatographic separations of expanded scope by addition of su rfactants to the conventional aqueous mobile phases of reversed-phase high- performance liquid chromatography. Finally, the synergistic effect of using vesicles to improve both the separ ation capabilities of reversed-phase HPLC and the detectability of atomic d etectors by on-line vesicular hydride generation is described. In particula r, the possible separation mechanisms responsible for micellar and vesicula r mobile phases in reversed-phase chromatographies are analysed and compare d. The possible effect of modification of stationary phases by monomers of the surfactants should also be taken into account. The application of such on-line couplings to develop new hybrid approaches to tackle modern problem s of trace element speciation for As, Hg, Se, and Cd completes this revisio n of the present interface between analytical atomic spectroscopy and surfa ctant-based organised assemblies. (C) 1999 Elsevier Science B.V. All rights reserved.