Characterization studies on the additives mixed l-arginine phosphate monohydrate (LAP) crystals

l-arginine phosphate monohydrate (LAP), potassium thiocyanate (KSCN) mixed LAP (LAP:KSCN) and sodium sulfite (Na₂SO₃) mixed LAP (LAP:Na₂SO₃) single crystals were grown by slow cooling technique. The effect of microbial contamination and coloration on the growth solutions was studied. The crystalline powders of the grown crystals were examined by X-ray diffraction and the lattice parameters of the crystals were estimated. From the FTIR spectroscopic analysis, various functional group frequencies associated with the crystals were assigned. Vickers microhardness studies were done on {1 0 0} faces for pure and additives mixed LAP crystals. From the preliminary surface second harmonic generation (SHG) results, it was found that the SHG intensity at (1 0 0) face of LAP:KSCN crystal was much stronger than that of pure LAP.     

电解分离-电感耦合等离子体质谱法测定高纯铜中的杂质元素

建立了电解分离-电感耦合等离子体质谱法测定纯铜中17种杂质元素(Be,Mg,Al,P,Ti,Cr,Mn,Co,Ni,As,se,Zr,Cd,Sn,Sb,Te和Pb)的方法.通过控制电流分离基体铜,大于99%的铜沉积至阴极,各杂质元素的回收率大于90%.研究了电解后电解液的酸效应、残余铜的影响和基体效应.结果表明,选用合...     

Effects of dimethylhydrazine on Zn, C, and H doping of GaP

Surfactants are beginning to be used during vapor-phase growth to provide control of the materials characteristics of epitaxial layers. This paper reports the effects of utilizing N, from pyrolysis of dimethylhydrazine (DMHy), as a surfactant during the organometallic vapor-phase epitaxial growth of GaP. Nitrogen is isoelectronic with the group V host element; thus, it generates no free carriers. Additionally, due to its small size, N is strongly rejected from the solid, so little incorporation is expected. This is confirmed by the determination of the very low N distribution coefficient (3.2×10⁻⁵). Using secondary ion mass spectroscopy analysis, we observe an increase in the distribution coefficient of the acceptor Zn when DMHy is added during growth, resulting in an increase in the doping efficiency by nearly an order of magnitude. Furthermore, the Zn doping efficiency increases linearly with the amount of DMHy added during growth over the range of partial pressures from 2.83×10⁻⁴ to 2.20×10⁻³ atm. The increase of doping for Zn is believed to be mainly a N surfactant effect. The addition of DMHy also leads to increases in both H and C incorporation. The concentrations of both are linear functions of DMHy concentration. Both H and C incorporation most likely arise mainly from pyrolysis of the DMHy. We propose a simple mechanism for the surfactant effect due to an increase in the Zn incorporation coefficients at the step edge induced by the presence of N (and probably H) on the surface.     

Development and validation of an analytical method for metformin hydrochloride and its related compound (1-cyanoguanidine) in tablet formulations by HPLC-UV

A simple, and stability-indicating liquid chromatographic method was developed and validated for the analysis of metformin hydrochloride and its related compound (1-cyanoguanidine) in tablet formulations. Liquid chromatography with a UV detector at a wavelength of 232 nm using a Nova-Pak silica column was employed in this study. Isocratic elution was employed using a mixture of ammonium dihydrogen phosphate buffer and methanol (21:79, v/v). This new method was validated in accordance with USP requirements for new methods for assay determination, which include accuracy, precision, specificity, linearity and range. The current method demonstrates good linearity over the range of 0.01-0.03 mg mL⁻¹ of metformin hydrochloride. The accuracy of the method is 100.4%. The precision of this method reflected by relative standard deviation of replicates is 0.30%. Validation of the same method for 1-cyanoguanidine determination was also performed according to USP requirements for quantitative determination of impurities which include accuracy, precision, linearity and range, selectivity, and limit of quantification (LOQ). Low LOQ of 1-cyanoguanidine using this method enables the detection and quantification of this impurity at low concentration.     

Cyclodextrin-MEEKC for the analysis of oxybutynin and its impurities

The development of a cyclodextrin-MEEKC method for the analysis of oxybutynin and five related impurities is described. Experimental design strategies were applied in order to reach baseline separation of the compounds in a short analysis time. Mixture design made it possible to find the best composition for the microemulsion acting as pseudostationary phase, which was constituted by 89.1% 10 mM borate buffer pH 9.2, 1.7% n-heptane, 9.2% SDS/n-butanol in 1:2 ratio. The addition of (2-hydroxypropyl)-β-cyclodextrin to the background electrolyte was found to improve analysis performance. A Doehlert design, for the factors cyclodextrin concentration and voltage, was carried out and Derringer desirability function led to the identification of 18 mM and 29 kV as the optimal values. Applying the optimum conditions, separation of all the compounds, including the enantiomers of impurity 1, was obtained in less than 12 min. The method was validated according to ICH guidelines for drug assay and determination of impurities and was applied to oxybutynin tablet analysis.     

Transport properties of surface acoustic wave based single electron transport device in the presence of an impurity potential

We report the transport properties of a surface acoustic wave based single electron transport device, which contains an unintentional quantum dot induced by background impurity potential fluctuations. It is found that the presence of the impurity potential can cause a deviation of the acoustoelectric current from its quantized value. Through the charging effect of the quantum dot induced by the impurity, we get an approximate relationship between the applied gate voltage and its corresponding electrostatic potential barrier height, together with the Coulomb charging energy needed to add a second electron into the dynamic quantum dot. Moreover, the amplitude of the surface acoustic wave is also estimated within a simple model.     

ICP-AES用于硅溶胶中杂质元素的直接测定

通过直接称取适量硅溶胶样品稀释于水中,采用超声配制成悬浮液,无需加入额外的分散剂,然后直接进样进行ICP-AES分析,将所获得的结果与传统的样品处理方法所获得的测定结果进行比较,发现两种不同样品处理方法得到的分析结果相一致。该方法无需消解样品,避免了腐蚀性酸的使用,降低了对环境的危害,同时减少了预处理过程。方法的回收率在92%—103%之间,且具有良好的准确度和精密度。     

Impurity proton NMR signals from common "proton-free" laboratory materials

For the study of small samples (tens of microns cubed) by NMR, impurities from the environment and construction materials (Teflon, Kel-F, glass NMR tubes, etc.) can dominate the signal, in particular for proton NMR. Using pulsed NMR with a resolution of several microseconds, we have studied a number of common construction materials considered to be proton-free and find considerable proton impurity. We present results in terms of impurity proton spins per milligram and discuss procedures to minimize the effects of impurity signal.     

Binding of3He atoms to liquid helium

Summary We calculate the³He−⁴He chemical potential and change in volume in bulk liquid⁴He employing integral equation and Monte Carlo procedures. Detailed numerical results on these quantities and their dependence on bulk density and on the isotopic-mass difference are presented and discussed. This work has been supported by the Deutsche Forschungsgemeinschaft under grant Ri 267 and by the U.S. Department of energy under contract DE-AC 02-76 ER03077 and by the NSF under grant DMR-77-18329.     

Nitride bonded silicon nitride as a reusable crucible material for directional solidification of silicon

Nitride bonded silicon nitride (NBSN) has the potential of a reusable crucible material for directional solidification of silicon. This is demonstrated in this work by reusing a NBSN crucible six times for the directional solidification of undoped multicrystalline (mc) silicon ingots. The progress of the ingot contamination at subsequent use of the NBSN crucible was studied systematically. Minority carrier lifetime, electrical resistivity as well as impurity content were analyzed after each solidification run. The results were compared to those obtained from ingots which were crystallized by using identical directional solidification process parameters in standard fused silica crucibles with silicon nitride coating. The impurity content of the ingots can be clearly correlated to the impurity content of the NBSN crucible. The main impurity is the acceptor B. Its concentration in the ingots decreases from about 10¹⁷ atoms/cm³ to 10¹⁶ atoms/cm³ with continued reuse. The contamination mechanism is most likely due to outdiffusion from the crucible wall into the Si melt.