Liquid carbon dioxide for improvements in online preconcentration and sample introduction in AAS,

Abstract

In this work liquid carbon dioxide in a flow system for better sample introduction and online preconcentration of copper, by means of Thermospray Flame Furnace-Atomic Absorption Spectrometry (TS-FF-AAS) has been used. Liquid carbon was used as pressure pump, liquid carrier, eluting solvent and nebulizer gas in the flow system. The flow restrictor consisted of a fused silica capillary (optimal i.d. 75 μm, 5 cm length) which is used for maintaining carbon dioxide in liquid state under subcritical conditions (58.5 bar and room temperature). Regarding the aerosol formation mechanism by aqueous samples, the CO₂-saturated sample is decompressed from 58.5 to 1 bar producing CO₂ vaporization which expands the liquid jet and forms a conic wet aerosol cloud that is rapidly vaporized in the atomizer. In other cases, by elution of preconcentrated complexed metals from a column (C18), CO₂-dissolved compounds became rapidly desolvated by CO₂ vaporization, forming a dry aerosol of gaseous metal complexes which became thermally decomposed and atomized in the Ni-tube. The detection limit by means of liquid carbon dioxide have improved by a factor ca. 3 and 10, in comparison with TS-FF-AAS and Flow Injection Flame Atomic Absorption Spectrometry (FI-FAAS), respectively. Preconcentration of copper 8-hydroxyquinoleine complex in a C18 mini column and its elution with liquid carbon dioxide resulted in an enrichment factor of 24 and a detection limit of 2 μg L⁻¹. This innovative system of sample pretreatment and nebulization envisages novel applications in atomic spectrometry avoiding the use of organic solvents and consequently the generation of toxic residues.