Short-chain fatty acids (SCFAs) have attracted much attention recently because of their positive physiological effects. In this work, a rapid and reliable gas chromatographic method for determination of eight SCFAs, in colonic and faecal samples from rats and humans has been developed and validated. The methodology involves extraction of the SCFAs in water before a direct injection procedure on a FFAP capillary column. A stock standard solution containing acetic acid, propionic acid, n-butyric acid, i-butyric acid, n-valeric acid, i-valeric acid, n-caproic acid and n-heptanoic acid was prepared and used. A high linearity (r2 > 0.9990), low quantification limit (2.38-30.14 microm) and high recovery for most acids were obtained. Acidification of faecal samples was found to be crucial for quantitative determination of the SCFAs, and adjustment of pH to 2-3 was regarded as necessary. Glass wool inserted in the glass liner of the injection port proved effective in preventing the contamination of the column by non-volatiles, and 12% formic acid reduced the ghost peak that appeared gradually after several injections. After validation, the methodology was applied on two faecal samples from rats fed diets containing different amount of dietary fibre and one faecal sample from human fed a normal diet to test the accuracy of the developed method.

Room-temperature ionic liquids (ILs) are gaining wide recognition as novel solvents in chemistry. Their application in analytical chemistry, especially in separating analytes, is merited because ILs have some unique properties, such as negligible vapor pressure, good thermal stability, tunable viscosity and miscibility with water and organic solvents, as well as good extractability for various organic compounds and metal ions. This review gives a brief overview of the application of ILs in analytical chemistry, including sample preparation, chromatographic/capillary electrophoretic (CE) separation, and detection. ª

The preemptive scheduling of systems of periodic tasks on a platform comprised of several identical processors is considered. A scheduling algorithm is proposed for staticpriority scheduling of such systems; this algorithm is a simple extension of the uniprocessor rate-tnonotonic scheduling algorithm. It is proven that this algorithm successfully schedules any periodic task system with a worst-case utilization no more than a third the capacity of the multiprocessorplatform. It is also shown that no static-priority multiprocessor scheduling algorithm (partitioned or global) can guarantee schedulability for a periodic task set with a utilization higher than one halfthe capacity of the multiprocessor platform.

BackgroundIn soils contaminated by hydrophobic organic compounds, the concentrations are less indicative of potential exposure and distribution than are the associated chemical activities, fugacities and freely dissolved concentrations. The latter can be measured by diffusive sampling into thin layers of polymer, as in, for example, solid phase micro-extraction. Such measurements require equilibrium partitioning of analytes into the polymer while ensuring that the sample is not depleted. We introduce the validation of these requirements based on parallel sampling into polymer layers of different thicknesses.ResultsEquilibrium sampling devices were made by coating glass vials internally with 3–12 μm thick layers of polydimethylsiloxane (PDMS). These were filled with slurries of a polluted soil and gently agitated for 5 days. The concentrations of 7 polycyclic aromatic hydrocarbons (PAHs) in the PDMS were measured. Validation confirmed fulfilment of the equilibrium sampling requirements and high measurement precision. Finally, chemical activities of the PAHs in the soil were determined from their concentrations and activity coefficients in the PDMS.ConclusionPAHs' thermodynamic activities in a soil test material were determined via a method of uptake into PDMS. This can be used to assess chemical exposure and predict diffusion and partitioning processes.

No abstract