Single-step coacervate-mediated preconcentration of metals and metal-chelates in supramolecular vesicular surfactant assemblies and determination by flame atomic absorption spectrometry

The use of ionic surfactant supramolecular aggregates is described, as means for accomplishing the concentration of analytes with different polarities using the same extraction pattern. The proposed method is based on the phase separation of an anionic surfactant through the formation of perplexed lamellar phases, allowing for the extraction of hydrated metal cations by complexation and metal-chelates by hydrophobic interactions. The data suggest that both extraction and phase separation are controlled by the presence of ionic surfactant as a function of the degree of phase divergence from the lamellar to bilayer phase. This again is determined by the composition of the phase-forming parameters, these are the surfactant concentration, the kind and amount of metallic counterparts and ionic strength. On the basis of these findings, the proposed method was successfully applied to the determination of metal species in natural waters. The limits of detection were easily brought down to the low microgram per liter levels by simply preconcentrating 10 mL of sample volume in the presence of at least 0.45% (w/v) of anionic surfactant. The method provided extraction recoveries higher than 94.0% with standard deviations well below 7.0%.