Superheated water extraction of cholesterol from solid food.

A method based on superheated water extraction has been developed for the removal of cholesterol from solid food thus providing a clean approach by avoiding the use of organic solvents. A preconcentration step was also studied with the aim of solving the problem derived from low-cholesterol-content samples and dilution effect. The research also involved the optimisation of the parameters affecting the extraction process by a central composite experimental design as well as a univariate study of the optimisation of the preconcentration step. The time required for total removal of the target compound was 60 min. The method was validated using a certified reference material (NIST-CRM 1845) and was used to analyse food samples within a wide range of cholesterol concentrations. The efficiency for the CRM was 105%. The precision of the method yielded values less than 6.5% (expressed as relative standard deviation) in all instances.

Micelle formation for improvement of continuous subcritical water extraction of polycyclic aromatic hydrocarbons in soil prior to high-performance liquid chromatography-fluorescence detection.

A new method for the extraction-individual separation-determination of polycyclic aromatic hydrocarbons (PAHs) in soil is reported. The method is based on the integration of three steps: continuous subcritical extraction, solid-phase clean-up/preconcentration, and HPLC separation with post-column fluorimetric determination. Sodium dodecyl sulfate (SDS) was added to the water for favouring the extractability of the low-polarity analytes. Soil samples spiked with the target PAHs were subjected to static-dynamic extraction with SDS-water at 50 bar, 150 degrees C, for 15 min of static extraction and 10 min dynamic extraction at a flow-rate of 3 ml/min. Recoveries from 73.6 to 110.4% were obtained in the presence of SDS versus 30 to 80% obtained with water as extractant. The calibration graphs provided by HPLC-fluorimetric detection were run between 0.031 and 0.375 microg/ml for each analyte with regression coefficients between 0.917 and 0.999 and precision, expressed as RSD, between 1.2 and 11.5%. The method was applied to a certified reference material [CRM 524, BCR (Community Bureau of Reference), industrial soil/organic] for validation and the results obtained were in agreement with the certified values.