Mark D. Burford

Supercritical fluid extraction of cobalt with fluorinated and non-fluorinated β-diketones

Abstract Supercritical fluid extraction of cobalt ions was evaluated in terms of the ability of the process to extract, solvate, transport and to collect the metal species. The aim of the study was to ensure that a mass balance could be obtained for the metal before and after extraction with supercritical carbon dioxide (CO2). The stability of the ligand and resulting metal complex were assessed as was the synergistic effect of the presence of water in the extraction. Two widely used β-diketones, namely, acetylacetone (AcAc) and hexafluoroacetylacetone (HFAcAc) were chosen to extract spiked cobalt from the surface of stainless steel and >90% of the metal was extracted and collected using the HFAcAc ligand with supercritical CO2.

Deacidification of black cumin seed oil by selective supercritical carbon dioxide extraction

The deacidification of high-acidity oils from Black cumin seeds (Nigella sativa) was investigated with supercritical carbon dioxide at two temperatures (40 and 60°C), pressures (15 and 20 MPa) and polarities (pure CO2 and CO2/10% MeOH). For pure CO2 at a relatively low pressure (15 MPa) and relatively high temperature (60°C), the deacidification of a highacidity (37.7 wt% free fatty acid) oil to a low-acidity (7.8 wt% free fatty acid) oil was achieved. The free fatty acids were quantitatively (90 wt%) extracted from the oil and left the majority (77 wt%) of the valuable neutral oils in the seed to be recovered at a later stage by using a higher extraction pressure. By reducing the extraction temperature to 40°C, increasing the extraction pressure to 20 MPa, or increasing the polarity of the supercritical fluid via the addition of a methanol modifier, the selectivity of the extraction was significantly reduced; the amount of neutral oil that co-extracted with the free fatty acids was increased from 23 to 94 wt%.

Effect of the matrix on the kinetics of dynamic supercritical fluid extraction

A model for dynamic supercritical fluid extraction (SFE) is proposed, which contains the steps of: rapid fluid entry into the matrix; a reversible release process such as desorption from matrix sites or penetration of a biological membrane; transport, by diffusion or otherwise to the edge of a matrix particle; and removal by biological membrane; transport, by diffusion or otherwise to the edge of matrix particle; and removal by solvation in the fluid. It can explain the following kinetic features of dynamic SFE : (i) a slow initial extraction; (ii) a more rapid extraction phase; and (iii) a slow final phase, which can be so slow that it appears that extraction is complete when only a fraction of the solute present in the matrix has been recovered. The model may be used to extract values for the parameters quantifying the individual steps, to understand further the SFE process.

Prediction of retention behavior of ferrocene derivatives in supercritical fluid chromatography

Abstract The retention behavior in capillary supercritical fluid chromatography (SFC) of a range of ferrocene derivatives is demonstrated. Prediction of retention times and hence elution order of the ferrocene derivatives based on a knowledge of solute molar volume, solute solubility parameter and the physical parameters of the chromatography column system is shown to be feasible using this procedure.

Variable flow control and collection device for use with supercritical fluids

Real world samples which contain high concentrations of water and/or extractable material frequently cause intermittent or irreversible plugging of the flow control device during off-line supercritical fluid extraction (SFE). A supercritical fluid (SF) flow control/collection device has been developed which can simultaneously maintain the extraction flow-rate of the SF (±0.1 ml/min) and quantitatively (>90%) collect analytes as volatile as n-octane directly into an organic solvent. With this device, the extract is partially depressurized through a heated capillary restrictor and into a pressurized collection solvent, so that both temperature and pressure are used to maintain the solubility of the extract in the SF. The pressurized mixture is finally depressurized to atmospheric conditions using a backpressure regulator, so the extract can be recovered in the collection vial. Depending on the sample matrix, a restrictor heater temperature of 200 °C and a backpressure regulator with a heated (>5 wt% water in sample) or unheated (<5 wt% water in sample) exit tube is required to eliminate restrictor plugging. By varying the pressure of the collection solvent, a range of reversible and reproducible flow-rates were obtained at both high (400 bar, 3.5 to 0.2 ml/min liquid CO2) and low (100 bar, 0.8 to 0.1 ml/min CO2) SFE pressures using a 50 μm I.D. capillary restrictor. At low (0.2 ml/min) SF flow-rates the solubility of several metal complexes (e.g., ferrocene and Ni[C22H22N4] complex) was measured and reproducible solubility values and flow-rates (R.S.D.<8%) were obtained.