Doping profile techniques for Si epitaxial layers

Various methods (e.g. spreading resistance and C-V measurements, neutron activation analysis, SIMS) have been used to determine concentration distributions of antimony dopant and charge carriers in single and double epitaxial silicon layers. Comparing the results obtained by the methods, an increased dopant diffusion process could be observed in the epitaxial layer during neutron irradiation of the sample, which arose as a systematic error in the NAA method. The origin of the deviations is discussed. 6th Colloquium on Microwawe Communication, Budapest, 29th August-1st September 1978.     

The Dynamical Structure Function of the One‐Component Plasma Revisited

We present high precision Molecular Dynamics simulations for the dynamical structure function, S (k, ω), of the classical Coulomb One Component Plasma (OCP), for a wide range of the coupling parameter Γ (from 0.05 to 10 000). We follow the positive‐to‐negative transition of the slope of the ω (k) dispersion curve at small wave numbers caused by the onset of correlations with increasing coupling. The high signal‐to‐noise ratio of the data over several orders of magnitude allows examination of a wide dynamical range of S (k, ω), including extreme values of ω and k, and the identification of waves at higher harmonics of the plasma frequency. Sum rules are found to be accurately satisfied. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Linear Fluid Theory for Weakly Inhomogeneous Plasmas with Strong Correlations

Linearized fluid equations for the collective modes of weakly inhomogeneous plasmas including strong coupling effects are derived from a recent kinetic theory based on an extended Singwi‐Tosi‐Land‐Sjölander (STLS) ansatz [H. Kählert, G. J. Kalman, and M. Bonitz, Phys. Rev. E 90 , 011101(R) (2014)]. The equations are analogous to the equations of linearized elasticity theory with space dependent elastic moduli that correspond to those of a bulk system with the local fluid density. The identification of the latter as infinite‐frequency elastic moduli shows that the present version of the extended STLS theory accounts for the elastic properties of the fluid but does not capture the viscous behavior. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On-line photo-oxidation for the determination of organoarsenic compounds by atomic-absorption spectrometry with continuous arsine generation

A method has been developed for on-line conversion of organoarsenicals into arsenate, which is readily detected by atomic-absorption spectrometry with continuous arsine generation. The photoreactor consists of a mercury lamp wrapped with 5 m of PTFE tubing (0.5 mm i.d.). The photo-oxidation conditions were optimized, with a flow-injection analysis procedure, for arsenobetaine, monomethylarsonic acid, dimethylarsinic acid, o-arsanilic acid, and phenylarsonic acid, all organoarsenicals of biological and environmental importance. Solutions were continuously pumped at a flow-rate of 2.0 ml/min and combined with a stream of potassium persulfate (flow-rate 0.6 ml/min) before entering the photo-reactor. With reactor dwell times of 36 sec, conversion efficiencies for these compounds were above 95% under these conditions. Interfacing of this flow-through conversion and detection system with a chromatographic inlet permits real-time analysis of mixtures of these organoarsenic compounds, in a manner suitable for environmental or biomedical samples.     

Determination of vitamin B5 in a range of fortified food products by reversed-phase liquid chromatography-mass spectrometry with electrospray ionisation

Methods for Vitamin B5 determination in food products remain limited by their low sensitivity and poor selectivity. Here, we have developed a liquid chromatography-mass spectrometry (LC-MS) method for Vitamin B5 determination in wide range of fortified food products. Vitamin B5 was extracted from food samples by heat treatment and analysed by LC-MS in the positive mode using electrospray ionisation (ESI). Vitamin B5 was quantified using hopantenic acid (HOPA) as internal standard after their separation on a C18 narrow-bore column with a gradient of mobile phase made of water/acetonitrile and trifluoroacetic acid (TFA) 0.025%. MS with single ion monitoring mode at mass m/z 220 was used for Vitamin B5 quantification. Calibration curve between 0.5 and 10 microg/ml of Vitamin B5 was linear (r2=0.9993) and the detection limit was determined to be 800 pg. The overall quantitative efficiency of the method was evaluated using Nestle reference sample (infant formula). The intra-assay RSD was 4.8% (n=8), the inter-assay RSD 6.4% (n=4) and the recoveries of the spiked samples were above 95%. Application of the LC-MS method to Vitamin B5 determination in wide range of fortified food products including three US National Institute of Standards and Technology (NIST) reference samples (RM 8435, RM 8415 and SRM 1546) shows consistent results with those obtained by microbiology and recoveries of Vitamin B5 between 93 and 104% for the spiked samples.     

Determination of pantothenic acid in foods by optical biosensor immunoassay

An optical biosensor inhibition immunoassay was developed using a specific pantothenic acid-binding protein for the quantitation of free pantothenic acid (vitamin B5) in foodstuffs. Samples were prepared by a simple extraction procedure in buffer, and vitamin content was estimated against authentic calibrants in the same buffer. Performance parameters included a working range of 10-5000 ng/mL, a limit of detection of 4.4 ng/mL, precision relative standard deviation of 5.4-7.1% over a range of concentrations, and recoveries > 95% in the matrixes tested. A wide range of foodstuffs, including National Institute of Standards and Technology reference samples, were tested in 3 independent laboratories and the results were compared with microbiological assay and liquid chromatography/mass spectrometry (LC/MS) methods. The results indicate that the biosensor technique is appropriate for the estimation of pantothenic acid in a wide range of foodstuffs.     

Full and fractionated experimental designs for robustness testing in the high-performance liquid chromatographic analysis of codeine phosphate, pseudoephedrine hydrochloride and chlorpheniramine maleate in a pharmaceutical preparation

This paper describes the testing of a saturated factorial design using a full factorial design. Saturated factorial designs are often used to test the robustness of high-performance liquid chromatography (HPLC) methods, however they are based on several assumptions. A full factorial design relies on fewer assumptions and hence could be used to evaluate the effectiveness of the saturated design. Both designs were used to test a gradient HPLC method for the assay of codeine phosphate, pseudoephedrine hydrochloride and chorpheniramine maleate. Six HPLC conditions, including wavelength, mobile phase pH and ion pairing reagent concentration were tested using the saturated design. Three of these factors were selected for full evaluation using a full factorial design. The results showed that the main effects calculated by each design were comparable. However, the saturated design showed higher standard errors, probably due to the effects of changing several more factors. One interaction effect was indicated as a confounding effect by the saturated design and this was confirmed by the calculation of the same interaction effect using the full design. Overall the method was shown to be robust under the variety of HPLC conditions tested.