Supercritical Fluid Extraction of Metal Ions from a Solid Matrix with 8‐Hydroxyquinoline and Carbon Dioxide

Abstract 8‐Hydroquinoline (8‐HQ) was first used as a chelating agent for supercritical fluid extraction (SFE) of mixed metal ions (Cu2+, Pb2+, Zn2+, Cd2+, Cr3+, Ni2+, Co2+) from solid samples in this study. The experimental variables such as pressure, temperature, extraction time, and flow rate of supercritical CO2 were optimized, in order to maximize the recovery of the metal ions in a relatively short time. The collected analytes were analyzed by an atomic adsorption method. The results showed that the recoveries of the metal chelates were less than 50%, just with pure supercritical CO2. Using methanol as a modifier for supercritical CO2 can greatly improve the extraction efficiencies, and the addition of a surfactant can further enhance the recoveries of the metal chelates to a large degree. Quantitative extractions were obtained at 50°C, 15 MPa, 15 min dynamic extraction with methanol, and surfactant modified supercritical CO2. Cu2+, Pb2+, Zn2+, Co2+ ions can be extracted completely, and Cd2+, Cr3+, Ni2+ ions can be extracted efficiently (>80%). Also, extraction of metal ions from real solid environmental matrices, such as standard reference soil sample and river sludge, was investigated; the results were satisfactory.