Analyte Collection in Off-Line Supercritical Fluid Extraction

• Published in: Analytical chemistry (Washington) 1999-02, Vol.71 (4), p.905-909
• Main Authors: Vejrosta, Jiří, Karásek, Pavel, Planeta, Josef
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemical and thermal methods; Chemistry; Exact sciences and technology; Fluids
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac980744j

A new analyte collection method for off-line supercritical fluid extraction (SFE), based on mixing of expanding supercritical effluent with overheated organic solvent vapor, is described. The mixing process takes place in a fused-silica capillary (i.d. < 500 μm). The model, describing the trapping mechanism, is validated by the collection of n-alkanes into n-hexane. Spike experiments were performed with selected PAHs (acenaphthene, fluorene, phenanthrene, pyrene, and chrysene) and with the mixture of acetophenone, N,N-dimethylaniline, and naphthalene. In the case of PAHs, from 12 common organic solvents used, quantitative recoveries (>90%) were achieved for 10 of them, the exceptions being cyclohexane and diethyl ether. The minimum solvent flow rates were found to be in the 25 (ethanol)−90 μL/min (acetone) range. Recoveries of acetophenone, N,N-dimethylaniline, and naphthalene were found to be quantitative to a CO2 flow rate of 420 mL/min (a.c.) at a 70 μL/min toluene flow rate into the collection device. In comparison with existing collection methods, the total solvent consumption was considerably reduced, and resulting extracts were concentrated more than 10 times without preconcentration. There is not a problem of analyte stripping by gaseous CO2 from the collection vial. Due to the efficient heating of the restrictor end (∼150 °C), no restrictor plugging was observed.