Comparative Study of the Determination of Parabens in Shampoos by Liquid Chromatography with Amperometric and Coulometric Detection

The simultaneous determination of four para‐hydroxybenzoic acid esters (parabens) in shampoos was studied by liquid chromatography (LC) with amperometric (LC‐AD) and coulometric (LC‐CD) detection. The parabens were separated on an ODS C18 reversed column by isocratic elution with a mobile phase based on methanol‐0.1 M acetic acid (60 : 40%, v/v) with 0.02 M NaClO₄ at a flow rate of 0.8 mL min^?1. The limit of detection (S/N>3) for the analytes was in the 15–25 pg (injected mass) range at an applied potential of 1.20 V vs. Ag/AgCl using the LC‐AD and in the 2–3 pg range at a potential of 0.790 V vs. Pd using the LC‐CD. The peak ratio of the internal standard peak (IS: 4‐hydroxybenzoic acid sec‐butyl ester) versus the analyte peak was found to be related to the amount injected from 0.1 ng to 100ng (r=0.996–0.999) with the LC‐AD and from 0.050 ng to 100 ng range (r=0.999–1.000) with the LC‐CD. The relative standard deviation (RSD, n=10) was comprised between 1.8 to 3.5% by LC‐AD ( 5 ng injected) and between 2.0 to 2.4% by LC‐CD (0.5 ng injected). The determination of four most used parabens in ten different shampoos was successfully realized.     

Degradation of hydroxymaleimide in 2-propanol by irradiation of energetic heavy ions (II)—N2-saturated system

Hydroxymaleimide was irradiated in N₂-saturated 2-propanol solutions by high-energy heavy ions over a wide range of LET values. The differential G-values of the degradation of hydroxymaleimide by irradiation with the heavier ions were lower than those of the lighter ions for the same LET value. An opposite result obtained in the air-saturated system. The degradation efficiency was 1.5 times higher, when the dose rate was 1/10 times lower. When irradiated at an LET value lower than 8 eV/nm, the G-values converged to a value less than that obtained by γ-irradiation.     

Peierls mechanism of the metal-insulator transition in ferromagnetic hollandite K2Cr8O16

Synchrotron x-ray diffraction experiment shows that the metal-insulator transition occurring in a ferromagnetic state of a hollandite K(2)Cr(8)O(16) is accompanied by a structural distortion from the tetragonal I4/m to monoclinic P112(1)/a phase with a √2×√2×1 supercell. Detailed electronic structure calculations demonstrate that the metal-insulator transition is caused by a Peierls instability in the quasi-one-dimensional column structure made of four coupled Cr-O chains running in the c direction, leading to the formation of tetramers of Cr ions below the transition temperature. This provides a rare example of the Peierls transition of fully spin-polarized electron systems.     

Enhanced JC in air-processed GdBa2Cu3O7−δ superconductor bulk grown by the additions of nano-particles

Single domain superconductor GdBa₂Cu₃O_7?δ bulks with variable additions of (ZnO + ZrO₂ + SnO₂) nano-particles was prepared in air by using top seed melt-textured growth process. The effect of nano-particle additions on superconductivity properties has been investigated. An enhancement of the critical current J_C in low and intermediate field at 77 K and trapped field was discovered by the additions of the nano-particles. At the same time, the superconductor transition temperature, T_C, slightly decreases from 93.5 K to 91.5 K. The experimental results show that the accumulation of the nano-particle inclusions may improve J_C of the specimens.     

Investigation of void formation beneath thin AlN layers by decomposition of sapphire substrates for self-separation of thick AlN layers grown by HVPE

Void formation at the interface between thick AlN layers and (0 0 0 1) sapphire substrates was investigated to form a predefined separation point of the thick AlN layers for the preparation of freestanding AlN substrates by hydride vapor phase epitaxy (HVPE). By heating 50–200 nm thick intermediate AlN layers above 1400 °C in a gas flow containing H₂ and NH₃, voids were formed beneath the AlN layers by the decomposition reaction of sapphire with hydrogen diffusing to the interface. The volume of the sapphire decomposed at the interface increased as the temperature and time of the heat treatment was increased and as the thickness of the AlN layer decreased. Thick AlN layers subsequently grown at 1450 °C after the formation of voids beneath the intermediate AlN layer with a thickness of 100 nm or above self-separated from the sapphire substrates during post-growth cooling with the aid of voids. The 79 μm thick freestanding AlN substrate obtained using a 200 nm thick intermediate AlN layer had a flat surface with no pits, high optical transparency at wavelengths above 208.1 nm, and a dislocation density of 1.5×10⁸ cm⁻².     

Change in free volume of polyvinylidene fluoride

Measurement of positron lifetime was carried out on polyvinylidene fluoride as a function of temperature ranging from 193 to 293 K. The local molecular motion, the cooperative motion of long chain, and the thermal expansion are discussed based on the change in free volume concluded with the use of positron lifetime. The different temperature dependence of motions is suggested for an amorphous area constrained by crystalline regions and a free amorphous area.