Ultrasound and surfactant-assisted dispersive liquid–liquid microextraction prior to poly(ethylene oxide)-mediated stacking in CE for highly sensitive determination of barbiturates in human fluids

This study developed a facile, highly sensitive technique for extracting and quantifying barbiturates in serum samples. This method combined ultrasound and surfactant-assisted dispersive liquid–liquid microextraction with poly(ethylene oxide)-mediated stacking in capillary electrophoresis. Factors influencing the extraction and stacking performance, such as the type and volume of extraction solvents, the type and concentration of surfactant, extraction time, salt additives, sample matrix, solution pH, and composition of the background electrolyte, were carefully studied and optimized to achieve the optimal detection sensitivity. Under the optimized extraction (injecting 140 μL C₂H₄Cl₂ into 1 mL of sample with pH 4 (5 mM sodium phosphate containing 0.05 mM Tween 20 and sonication for 1 min) and separation conditions (150 mM tris(hydroxymethyl)aminomethane-borate with pH 8.5 containing 0.5% (m/v) poly(ethylene oxide)), the limits of detection (signal-to-noise ratio = 3) of five barbiturates ranged from 0.20 to 0.33 ng/mL, and the calculated sensitivity improvement ranged from 868- to 1700-fold. The experimental results revealed excellent linearity (R² > 0.99), with relative standard deviations of 2.1%–3.4% for the migration time and 4.3%–5.7% for the peak area. The recoveries of the spiked serum samples were 97.1% –110.3%. Our proposed approach offers a rapid and practical method for quantifying barbiturates in biological fluids.     

An Anion-Switchable Dual-Function Rotaxane Catalyst

In situ switching of the associated anions of a rotaxane catalyst between Cl⁻ and TFPB⁻ exposes its dialkylammonium and imidazolium stations, respectively, thereby selectively catalyzing the reactions of a mixture of trans-cinnamaldehyde and an aliphatic thiol to yield the Michael adduct and the thioacetal product, respectively.     

New organosoluble polyimides with low dielectric constants derived from bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl] diphenylmethylene

A new kink diamine with trifluoromethyl group on either side, bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]diphenylmethane (BTFAPDM) , was reacted with various aromatic dianhydrides to prepare polyimides via poly (amic acid) precursors followed by thermal or chemical imidization. Polyimides were prepared using 3,3′, 4,4′-biphenyltetracarboxylic dianhydride(1), 4,4′-oxydiphthalic anhydride(2), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (3), 4,4′-sulfonyldiphthalic anhydride(4), and 4,4′-hexafluoroisopropylidene-diphathalic anhydride(5). The fluoro-polyimides exhibited low dielectric constants between 2.46 and 2.98, light color, and excellent high solubility. They exhibited glass transition temperatures between 227 and 253°C, and possessed a coefficient of thermal expansion (CTE) of 60-88 ppm/°C. Polymers PI-2, PI-3, PI-4, PI-5 showed excellent solubility in the organic solvents: N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridkie and tetrahydrofuran (THF). Inherent viscosity of the polyimides were found to range between 0.58 and 0.72 dLg-1. Thermogravimetric analysis of the polyimides revealed a high thermal stability decomposition temperature in excess of 500°C in nitrogen. Temperature at 10 % weight loss was found to be in the range 506-563°C and 498-557°C in nitrogen and air, respectively. The polyimide films had a tensile strength in the range 75-87 MPa; tensile modulus, 1.5-2.2 GPa; and elongation at break, 6-7%.