Asymmetrical flow field-flow fractionation technique for separation and characterization of biopolymers and bioparticles.

Field-flow fractionation (FFF) is one of the most versatile separation techniques in the field of analytical separation sciences, capable of separating macromolecules in the range 10³-10¹5 g mol⁻¹ and/or particles with 1 nm-100 µm in diameter. The most universal and most frequently used FFF technique, flow FFF, includes three types of techniques, namely symmetrical flow FFF, hollow fiber flow FFF, and asymmetrical flow FFF which is most established variant among them. This review provides a brief look at the theoretical background of analyte retention and separation efficiency in FFF, followed by a comprehensive overview of the current status of asymmetrical flow FFF with selected applications in the field of biopolymers and bioparticles.

Analysis of PAH compounds in soil with on-line coupled pressurised hot water extraction-microporous membrane liquid-liquid extraction-gas chromatography.

Pressurised hot water extraction (PHWE) was coupled on-line with microporous membrane liquid-liquid extraction (MMLLE) and gas chromatography (GC) in the analysis of polycyclic aromatic hydrocarbon (PAH) compounds in soil. The MMLLE serves as a trapping device after the PHWE. Water from PHWE is directed to the donor side of the membrane unit and the analytes are extracted to the acceptor solution on the other side of the membrane. The role of MMLLE is to clean and concentrate the extract, which is then transferred on-line to the GC via a sample loop and an on-column interface using partially concurrent solvent evaporation. Separate optimisation of MMLLE and simulations of the PHWE-MMLLE connection were carried out before the actual on-line coupling. After optimisation of the whole on-line system, the efficiencies of the PHWE-MMLLE-GC and PHWE-solid-phase trap extractions were compared. The PHWE-MMLLE-GC method allowed on-line analysis of soil samples. The method was linear, with limits of detection in the range 0.05-0.13 ng and limits of quantification 0.65-1.66 microg g(-1). Comparison of the results with those obtained by other techniques confirmed the good performance.

Oxidation of 4-chloro-3-methylphenol in pressurized hot water/supercritical water with potassium persulfate as oxidant.

4-Chloro-3-methylphenol (c = 2.0 mM), representing a model pollutant, was oxidized in pressurized hot water and in supercritical water in a continuous flow system. Potassium persulfate was used as oxidant in concentrations of 8.0 and 40.0 mM. Contact times (reaction times) were 3-59 s, temperatures 110-390 degrees C, and pressures 235-310 bar. A wide temperature range was tested to determine the range over which potassium persulfate can be used effectively. Good oxidation efficiencies for 4-chloro-3-methylphenol were obtained at both oxidant concentrations and with short contact times at temperatures clearly underthe critical temperature of water; total organic carbon content of the effluent was low under optimized conditions. Corrosion, measured as nickel and chromium concentrations of the effluent, was more severe at oxidant concentration of 40.0 mM. Sulfate was present in the effluent in high concentrations. Sulfate is the limiting factor in the use of potassium persulfate in wastewater treatment and requires further water treatment.

Pressurized hot water extraction coupled on-line with LC-GC: determination of polyaromatic hydrocarbons in sediment.

Pressurized hot water extraction (PHWE) was directly combined with a LC-GC system for the determination of polyaromatic hydrocarbons (PAHs) in sediment. The sediment sample was first extracted with pressurized hot water, and the analytes were adsorbed into a solid-phase trap. The trap also functioned as a LC column, which removed most of the interfering matrix components. The 780-microL LC fraction containing the analytes was directly transferred to the GC using an on-column interface. The whole PHWE-LC-GC analysis took place in a closed system, and no sample pretreatment was required. The sensitivity of the method was excellent due to the efficient concentration in the LC-GC system. Sensitivity was approximately 800 times better than in traditional systems. In addition, only a small amount of sample (10 mg) was required for the analysis. The PHWE-LC-GC method proved to be linear in the concentration range of 0.01-2 microg/g, the limits of quantification were below 0.01 microg/g for all the analytes, and the relative standard deviations were between 3 and 28%. LC cleanup and the improved sensitivity made detection with FID sufficient for the determination of analytes. The results were comparable to those obtained in an interlaboratory comparison study as well as to the results obtained with off-line SFE-GC-MS.

Extraction of iridoid glycosides and their determination by micellar electrokinetic capillary chromatography.

Several methods for the extraction of two iridoid glycosides, catalpol and aucubin, from the plant matrix (Veronica longifolia leaves) were compared. Pressurized hot water extraction and hot water extraction were the most efficient isolation techniques for both. Pressurized liquid extraction and maceration with various organic solvents were also tested. Relative to the amounts extracted with hot water, ethanol extracted only 22% of catalpol and 25% of aucubin and pressurized hot water extracted 83% of catalpol and 92% of aucubin. The lowest relative standard deviations, 22% for catalpol and 8% for aucubin, were achieved with hot water extraction (13 repetitions), and the highest relative standard deviations, 76% for catalpol and 73% for aucubin, with pressurized liquid extraction (five repetitions). A fast capillary electrophoretic method was developed for the quantitative determination of catalpol and aucubin.

Detection of beta-blockers in urine by solid-phase extraction-supercritical fluid extraction and gas chromatography-mass spectrometry.

The most convenient way to perform supercritical fluid extraction (SFE) of liquid sample matrices is to combine it with solid-phase extraction (SPE). beta-Blockers from urine were collected on an Empore disc, which was then placed into an extraction cell for derivatization and SFE. SPE recovery was best at pH 10. Effects of temperature, pressure and volume of pyridine on the acetylation and SFE processes were studied. Without acetylation the beta-blockers were not significantly soluble in CO2. SFE temperatures of 70 degree C and 150 degree C together with 200 microliters of acetic anhydride and 400 microliters pyridine gave the best results. With the SPE-SFE-GC-MS method developed here, beta-blockers like oxprenolol, metoprolol and propranolol could easily be detected in urine samples, and the limit of detection (LOD) for these compounds was found to be 20 ng/ml, 30 ng/ml and 40 ng/ml, respectively.