Molecular Dynamics Simulation of Distribution and Diffusion Behaviour of Oil⁻Water Interfaces.

The distribution and diffusion behaviors of microscopic particles at fluorobenzene-water and pentanol-water interfaces are investigated using molecular dynamics simulation. The influences of Na+/Cl- ions and the steric effects of organic molecules are examined. The concentration distributions of different species, the orientations of oil molecules at the interface, and oil-water interface morphology as well as the diffusion behaviors of water molecules are explored and analyzed. The results indicate that a few fluorobenzene molecules move into the water phase influenced by Na+/Cl- ions, while the pentanol molecules at the interface prefer orientating their hydrophilic groups toward the water phase due to their large size. The water molecules more easily burst into the pentanol phase with larger molecular spaces. As the concentration of ions in the water phase increases, more water molecules enter into the pentanol molecules, leading to larger interface roughness and interface thickness. In addition, a lower diffusion coefficient for water molecules at the fluorobenzene-water interface are observed when introducing Na+/Cl- ions in the water phase, while for the pentanol-water system, the mobility of interfacial water molecules are enhanced with less ions and inhibited with more ions.

Simultaneous determination of thirty non-steroidal anti-inflammatory drug residues in swine muscle by ultra-high-performance liquid chromatography with tandem mass spectrometry.

An ultra-high-performance liquid chromatography with tandem mass spectrometric detection (UHPLC-MS/MS) method was established for the simultaneous determination of residues of thirty non-steroidal anti-inflammatory drugs (NSAIDs) in swine muscle. The samples were extracted with acetonitrile and phosphoric acid. The extracts were defatted with n-hexane, and then purified by HLB solid-phase extraction cartridge. Analysis was carried out on UHPLC-ESI-MS/MS working with multiple reaction monitoring mode with polarity switching. Limits of detection were between 0.4 µg/kg and 2.0 µg/kg, and limits of quantification were between 1.0 µg/kg and 5.0 µg/kg. The recoveries of NSAIDs were between 61.7% and 125.7% at spiked levels of 1.0-500 µg/kg. The repeatability was less than 8% and the within-laboratory reproducibility was not more than 12.3%. The method was reliable, convenient and sensitive.