Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements.

Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600° C. The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q=(2.70±0.11) eV and preexponential factor D_{0}=(5.5_{-3.7}^{+11.1})×10^{-2} cm^{2} s^{-1}. Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.025901).

Determination of biogenic amines in infusions of tea (Camellia sinensis) by HPLC after derivatization with 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl).

The reagent 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) was used for the pre-column derivatization of the biogenic amines (BAs) cadaverine (Cad), histamine (Him), octopamine (Ocp), phenylethylamine (Pea), putrescine (Put), spermidine (Spd), spermine (Spm), tyramine (Tym) and the internal standard 1,6-diaminohexane (Dhx). The resulting Fmoc-derivatives were resolved by high-performance liquid chromatography on a Superspher(©) C(18) column using a binary gradient generated from sodium acetate and acetonitrile. For quantification, the fluorescence of derivatives was used at 263 nm excitation and 313 nm emission wavelength. This approach was applied to free BAs extractable with boiling water from 14 black, 5 green, 1 Oolong, and 1 instant tea. Infusions were prepared by adding 35 ml boiling water to one gram of tea and extracted for 20 min. In the Oolong tea and two black teas, no BAs could be detected. Limits of detection were 0.07-1.0 pmol for BAs at signal-to-noise ratio 3:1. Besides most abundant Tym and Spm lower quantities of Pea, Put, and Spd were detected, albeit not in all teas. Quantities of Tym ranged from 16 to 431 µg Tym/L infusion (1.1-25.3 µg Tym/g tea) and 31 to 319 µg Spm/L infusion (1.5-16.9 µg Spm/g tea). In none of the teas, Him was detected. Owing to the low amounts of free BAs in tea infusions, no health risks are to be expected even on consumption of large quantities of tea as beverage.

Analysis of medium-range order based on simulated segmented ring detector STEM-images: amorphous Si.

Properties of amorphous materials are connected to the local structure at the nanoscale, which is typically described in terms of short- and medium-range order (SRO, MRO). Variable resolution fluctuation electron microscopy (VR-FEM) is a sensitive method to characterize the underlying characteristic length scale of MRO of amorphous samples (Voyles, Gibson and Treacy, J. Electron Microsc. 49 (2000) 259). VR-FEM data was acquired using scanning transmission electron microscopy (STEM), collecting a large number of nano-beam diffraction patterns (NBDPs) with various probe sizes. Here we present an advanced method to accelerate the calculation of simulated FEM normalized variance profiles using a newly developed simulation and analysis approach with segmented ring detectors using the program STEMcl (Radek et al., Ultramicroscopy 188 (2018) 24). VR-FEM simulations are based on structures obtained from molecular dynamics (MD) simulations. A comparison between simulated and experimental VR-FEM profiles with respect to peak position, ratio and shape (and intensity) show good agreement. Moreover, a crystalline cluster of 1 nm in size was embedded into the MD box to test the validity of the paracrystalline approximation with the pair-persistence analysis suggested by Gibson et al. (Gibson, Treacy and Voyles, Ultramicroscopy 83 (2000) 169). The corresponding VR-FEM simulation and calculation of MROs yield close results to the size of the initially embedded crystalline cluster, which supports both the paracrystalline approach and the validity of the segmented detector simulation. Additionally, we conclude that continuous random network (CRN) amorphous silicon models contain a higher degree of MRO than experimentally expected.

Liquid chromatographic determination of biogenic amines in fermented foods after derivatization with 3,5-dinitrobenzoyl chloride.

The reagent 3,5-dinitrobenzoyl chloride (DNBZ-Cl) was tested for pre-column derivatization of biogenic amines (BAs). Samples were derivatized within 3 min in 1 M NaOH at ambient temperature by adding 2-propanole and 50 mM DNBZ-Cl in acetonitrile. The reaction was terminated by addition of 2 M HCl. For high-performance liquid chromatography an encapsulated stationary reversed-phase and gradient elution using a ternary gradient system were used. The DNBZ derivatives were quantified by their UV-absorption at 260 nm. The structures of the derivatives were elucidated using coupling of HPLC with electrospray ionization mass spectrometry. Detection limits of BAs were approximately 124-864 microg l(-1) (injected amounts 203-1410 pg) at a signal-to-noise ratio of 3:1. The coefficients of determination were 0.989-0.996, with the exceptions of cadaverine (0.976) and serotonin (0.965). The method was applied to the quantitative determination of agmatine, cadaverine, histamine, octopamine, 2-phenylethylamine, putrescine, serotonin, spermidine, spermine, tryptamine and tyramine, in fermented cabbage juices, soy sauces, Misos (soy pastes), fermented fish sauces, and anchovy paste.

Differential borohydride assay for conjugated ketosteroids: improvement with propylene glycol.

A previously developed differential UV assay for 3-one-4-ene steroids involving reduction with sodium borohydride was frequently found to be less than 100% complete. Such incomplete reduction can be mimicked by additions of sodium metaborate, a product of the hydrolysis of sodium borohydride, to the reaction system. Complete reduction can be achieved by adding propylene glycol to the reduction system. The phenomenon was studied using halcinonide as a model.

Analysis of captopril and hydrochlorothiazide combination tablet formulations by liquid chromatography.

A reverse-phase, high-performance liquid chromatographic (HPLC) procedure was developed for the simultaneous assay of captopril and hydrochlorothiazide in a combination tablet formulation. Gradient elution was used to quantify these two drugs, as well as the oxidized form of captopril, the disulfide. Tablets were extracted with methanol and, after centrifugation, were chromatographed. Initially, a methanol-0.05% aqueous phosphoric acid (25:75, v/v) solution was pumped at 2 mL/min into a phenyl column. After 8 min, the flow rate was increased to 4.5 mL/min and the methanol content of the mobile phase was increased to 45% to elute the disulfide. Detection was at 210 nm. Linearity and repeatability of all constituents were satisfactory. The hydrolytic degradation product of hydrochlorothiazide, 4-amino-6-chloro-1,3-benzene disulfonamide (also called the disulfonamide ), could be resolved in test solutions but was not visible in chromatograms of tablets carried through the gradient procedure even after storage at elevated temperatures for prolonged time periods prior to assay. The method can be automated.

Homogeneity of Pasteurella avicida bacterin.

A simple rapid procedure is described for determining whether an emulsified bacterin is homogenous by measuring the UV absorbances of chloroform-washed centrifugates. These absorbances appear to depend on nucleic acid content.

High-performance liquid chromatographic analysis of nadolol and bendroflumethiazide combination tablet formulations.

A reverse-phase high-performance liquid chromatographic (HPLC) method was developed for the simultaneous assay of nadolol and bendroflumethiazide in tablet formulations. The tablets were extracted with methanol and, after centrifugation, were chromatographed. A phenyl column was used with a mobile phase of aqueous acetate buffer with sodium chloride-methanol (60:40); detection was at 270 nm. Linearity of both drugs was satisfactory. The procedure can be automated and also applied to bendroflumethiazide formulations and bulk material.

High-pressure liquid chromatography of nadolol and other beta-adrenergic blocking drugs.

A high-pressure liquid chromatographic assay was developed for the analysis of the beta-adrenergic blocking agent nadolol as a bulk material or formulated in a tablet. Other beta-adrenergic blocking drugs such as acebutolol, alprenolol, atenolol, metoprolol, oxprenolol, pindolol, practolol, propranolol, sotalol, and timolol can be chromatographed in this system. An ethylsilane column and a mobile phase consisting of 35% methanol-65% aqueous 0.0005 M hydrochloric acid-0.05 M sodium chloride are used. Detection is either at 254 nm with a variable-wavelength detector. As exemplified by nadolol, the drug content can be quantitated with or without atenolol as an internal standard.

Inter-laboratory transfer of HPLC methods: problems and solutions.

As high-performance liquid chromatography (HPLC), the premier analytical technique in the pharmaceutical industry, becomes more ubiquitous, methods are more frequently being transferred from one laboratory to another. This review will discuss sources of failures to reproduce HPLC procedures, ranging from sample handling and preparation, through mobile phase, injector, column, detector and data manipulation problems. Also to be considered will be the precautions that should be taken, when initially developing a method, to obviate future problems. These precautions include using stable, well-defined analytical columns, buffered mobile phases, low wavelengths (or a mass-sensitive detector) and internal tests for accuracy; based on the author's experiences. Since the laboratory that originally developed the procedure has the moral obligation and, perhaps, the regulatory responsibility to "guarantee" that the method will perform successfully elsewhere, a series of increasingly comprehensive steps will be given, based on practice, to be followed by the laboratory that could not reproduce the procedure. Also to be discussed are approaches for treating methods that were initially successful but have slowly deteriorated and now fail, and several examples of procedures that were not reproducible in some other laboratories.

Liquid chromatographic resolution of the isomers of tipredane and phenylthioproline using urea-solubilized beta-cyclodextrin in the mobile phase.

Two LC assays were developed using urea-solubilized beta-cyclodextrin (beta-CD) as a mobile phase additive in combination with reversed-phase columns. A methylsilane column gave optimal resolution of the steroid tipredane from its epimer. An investigation of the effects of beta-CD concentration, column temperature, column type, and addition of ethanol on the chromatographic separation is detailed. The enantiomer and diastereoisomers of L-cis-phenylthioproline were best resolved by urea-solubilized beta-cyclodextrin and a trimethylsilane column. The elution order of L-cis-phenylthioproline relative to its stereoisomers was reversed after adding ethanol to the beta-CD containing mobile phase or by changing from a beta-CD to an acetylated beta-CD column. The resolution factors for these separations obtained using the beta-CD mobile phase were larger than those obtained using beta-CD columns. Mobile phases containing up to 0.15 M beta-CD and 8 M urea were investigated. The separation of these isomers are dramatically affected by column polarity.

Dermabrasion on scars.

Dermabrasion utilizing wire brushes and Fluro-Ethyl refrigerant anesthesia is an effective way of ameliorating a variety of epidermal and dermal defects. Familiarization with proper equipment and technique is imperative. The overall incidence of troublesome complications is relatively low and is offset by the considerable value of the procedure. The patient is spared the hazards of general anesthesia and hospitalization.