Desired Impurity Research Articles

Development and validation of a simple and rapid ICP-OES method for quantification of elemental impurities in voriconazole drug substance

BackgroundThe aim of the present study was to develop and validate an inductively coupled plasma optical emission spectroscopic (ICP–OES) method for quantification of elemental impurities, i.e., Lead, Palladium, and Zinc, in voriconazole drug substance, and this method was employed for the regular sample analysis of Lead, Palladium, and Zinc in voriconazole drug substance for pharmaceutical use. The method has been validated using RF power of 1150 W, auxiliary gas of 0.5 L/min, and nebulizer flow of 0.4 L/min and plasma view at axial mode for Lead and Palladium and radial mode for Zinc. The wavelength was monitored for Lead, Palladium, and Zinc at 220.3 nm, 340.4 nm, and 213.8 nm respectively.ResultsThe method is selective and is capable of detecting desired elemental impurities with regulatory acceptance limits in the presence of other elements. The validation experiments involve the demonstration of system suitability, specificity, LOD and LOQ, linearity, precision, and accuracy experiments. The linearity results obtained ˃ 0.9990 for all three impurities.ConclusionThe proposed method is simple, sensitive quality control tool for the simultaneous quantitative determination of Lead, Palladium, and Zinc at low levels in voriconazole drug substance.Graphical abstract

Corrosion of carbon steel in simulated CCS streams

It is expected that Carbon capture and storage (CCS) may involve a large network with many sources, transportation systems and storage sites. Depending on factors like flue gas source, capturing technique and process parameters, the captured CO2 may contain various types and concentrations of other components. These components are expected to be present at low concentrations (in the ppm range) and are therefore commonly referred to as impurities. It is well known that some impurities may react and produce species that are corrosive to carbon steel. Long transport pipelines will be made of carbon steel due to cost considerations, and it is therefore essential to avoid formation of corrosive species. In the present work, corrosion of carbon steel was tested in a CO2 stream containing low levels of water and the impurities H2S, SO2, NO2 and O2 at a temperature of 25 °C and a pressure of 99 bar. The experiment was carried out in a custom-made autoclave with transparent windows that allowed for in-situ observation of any chemical reactions or corrosion processes. Each impurity, including water, was pre-mixed with CO2 at a high concentration (impurity stock solutions) and continuously injected through individual feed lines into the autoclave. This ensured that all impurities were injected fully dissolved in the CO2 phase and that no reactions could take place before the impurities were mixed inside the autoclave. The impurity injection rate was adjusted relative to the to the total CO2 rate, to get the desired impurity concentration in the autoclave. Exhaust CO2 was continuously removed from the autoclave and analysed for impurity content by laser spectroscopy. Comparison of the injected and exhaust impurity concentration made it possible to identify chemical reactions as concentration changes. The experiment demonstrated that there were no corrosion reactions when the impurities were at the target concentrations. However, chemical reactions between the impurities did take place. An episode with clogging of the vent line, which resulted in a temporarily increase of the impurity concentrations, resulted in formation of a separate liquid phase containing sulfuric and nitric acid formed. This also started corrosion of the carbon steel coupon.

Isolation of oxidative degradation products of atorvastatin with supercritical fluid chromatography.

The isolation of four oxidative degradation products of atorvastatin using preparative high-performance liquid chromatography applying at least two chromatographic steps is known from the literature. In this paper it is shown that the same four impurities could be isolated from similarly prepared mixtures in only one step using supercritical fluid chromatography. The methods for separation were developed and optimized. The preparation of the mixtures was altered in such a way as to enhance the concentration of desired impurities. Appropriate solvents were applied for collection of separated impurities in order to prevent degradation. The structures of the isolated impurities were confirmed and their purity determined. The preparative supercritical fluid chromatography has proven to be superior to preparative HPLC regarding achieved purity of standards applying fewer chromatographic as well as isolation steps.

Selective Removal of Silver Impurity from Oxaliplatin by Sorption on Functionalized Polymer

This report relates to synthesis of functionalized polymeric adsorbents for selective removal of silver ion in the presence of platinum(II) from crude oxaliplatin, thus providing an effective method for its purification with a desired impurity profile for silver. Two chelating ligands, thiourea and thiosemicarbazide, were grafted on styrene backbone cross-linked with 2% divinyl benzene (DVB) and tested by batch adsorption studies for the uptake of silver and platinum. The maximum sorption capacity values for both the adsorbents for Ag+ were 101.58 and 67.75 (mg/g), respectively, with an exceptionally high value of separation factor (α = 1155 and 231) over platinum. The experimental sorption data were fitted well with the Langmuir model. Desorption of silver from the polymer can be achieved by using 0.3 M Na2S solution for regeneration.

Optically Controlled Silicon MESFET Fabrication and Characterizations for Optical Modulator/Demodulator

An optically controlled silicon MESFET (OPFET) was fabricated by diffusion process to enhance the quantum efficiency, which is the most important optoelectronic device performance usually affected by ion implantation process due to large number of process induced defects. The desired impurity distribution profile and the junction depth were obtained solely with diffusion, and etching processes monitored by atomic force microscope, spreading resistance profiling and C-V measurements. With this approach fabrication induced defects are reduced, leading to significantly improved performance. The fabricated OPFET devices showed proper I-V characteristics with desired pinch-off voltage and threshold voltage for normally-on devices. The peak photoresponsivity was obtained at 620 ㎚ wavelength and the extracted external quantum efficiency from the photoresponse plot was found to be approximately 87.9%. This result is evidence of enhancement of device quantum efficiency fabricated by the diffusion process. It also supports the fact that the diffusion process is an extremely suitable process for fabrication of high performance optoelectronic devices. The maximum gain of OPFET at optical modulated signal was obtained at the frequency of 1 MHz with rise time and fall time approximately of 480 nS. The extracted transconductance shows the possible potential of device speed performance improvements for shorter gate length. The results support the use of a diffusion process for fabrication of high performance optoelectronic devices.

Photocatalysis and surface doping states of N-doped TiOx films prepared by reactive sputtering with dry air

Complex N (NO)-doped TiOx films on the glass substrate were prepared by radio-frequency (RF) magnetron reactive sputtering of Ti target in a mixed gas of argon and dry air with low oxygen concentrations. The surface doping states and energy band gap properties were studied by XPS and density-functional theory (DFT) applied to a 2×2×1 supercell of N-doped TiO2 with oxygen deficiency. Although all the films exhibit an anatase structure, the photocatalytic properties as well as other film properties (lattice parameters, grain sizes, introduced nitrogen contents, and optical properties) largely depend on the air flow ratios. The electronic bonding configurations at the nanoscale film surface are extremely important for photocatalysis, and there appears an optimal surface nitrogen amount incorporated in the anatase TiO2 lattice. Reduced Ti ions (and regions) at the nanoscale surface are proposed to play an important role by providing a local charge imbalance through the Schottky-barrier-like mechanism. Our DFT calculation shows the modified band calculation, especially for the film surface, involving both oxygen deficiency and N (NO) doping is important, due to the variation in the number and location of the impurity levels in the energy band gap. It is suggested that interstitial NOx (or substitutional NO) doping states with oxygen vacancy involving N–Ti–O or Ti–N–O bondings (linkages) are more effective on photocatalysis than the substitutional N doping states with oxygen vacancy. The seemingly desired impurity energy level(s) introduced in the electronic band gap does not necessarily improve photocatalysis, despite the desired optical properties observed, due to the active recombination sites newly produced and the complexity of the nanoscale surface science.

Single and Double Infrared Transitions in Rapid-Vapor-Deposited Parahydrogen Solids: Application to Sample Thickness Determination and Quantitative Infrared Absorption Spectroscopy

We present a convenient method for determining the thickness of a cryogenic parahydrogen (pH2) solid from its infrared (IR) absorption spectrum. Millimeters-thick pH2solids of exceptional optical clarity can be produced by the rapid vapor deposition method [M.E. Fajardo and S. Tam, J. Chem. Phys. 108, 4237 (1998)]. Doping of these pH2solids is readily accomplished by co-deposition of the desired impurities, making them excellent hosts for high-resolution matrix isolation spectroscopy. The intensities of the IR “double” transitions Q1(0) + S0(0) and S1(0) + S0(0) of the pH2host are insensitive to the matrix microstructure and to the presence of dopants, so these absorptions are especially well suited for thickness determinations. We calibrate the integrated absorption intensities of these two bands against the sample thicknesses determined from transmission interference fringes appearing in the same experimental spectra; we report: α˜[Q1(0) + S0(0)] = 4.84(±0.18) × 10−14cm3/s, and α˜[S1(0) S0(0)] = 0.35(±0.02) × 10−14cm3/s (95% confidence). We also discuss several other advantages of rapid-vapor-deposited pH2solids as hosts for quantitative IR absorption spectroscopy of dopant species.

Analysis of Ge distribution in Si 1 − xGe x single crystal fibers by the micro-pulling down method

The Ge distribution in both melt and crystal was analyzed for the growth of Si 1 − x Ge x ( x = 0.05) single crystal fibers by the micro-pulling down (μ-PD) method. The solute accumulation volume in the vicinity of the interface comprises the molten zone (zone I) next to the interface and the capillary zone (zone II) leading to the bulk melt. A steady-state solution was given for each of these two zones and the initial transient analysis lead to the equilibrium partition coefficient, k 0 and diffusion constant, D, for Ge in the Si 1 − x Ge x ( x = 0.05) melt to be 0.43 and 5.6 × 10 −5cm 2s −1, respectively. A sudden change of either the growth velocity or the molten zone volume size during steady-state growth yields an abrupt change of Ge distribution, and its change mode is interpreted in terms of the degree of imbalance of the Ge mass flow between zone I and zone II at the zone boundary. It is, therefore, suggested that the desired impurity distribution in a Si single crystal fiber can be designed by the manipulation of the imbalance of the impurity mass flow at the zone boundary.

Synthesis of Chlorhexidine Digluconate Impurities

Five new biguanides, found as impurities in chlorhexidine digluconate solutions, were synthesized by addition of amines to aminonitriles. Nonstoichiometric additions required to prepare the unsymmetrical biguanides resulted in low yields of the desired impurities, which were isolated by flash chromatography and characterized by HPLC-UV, HPLC-MS, and 1 H NMR.

Energetic ion population formed in close collision with fusion alpha-particles

Close collisions of fusion alpha-particles with thermal plasma ions (both of impurities and of main component) give rise to formation of high energy "halo" in the ion velocity space, extending to the energies of MeV-range even for rather heavy ions, like iron. The implications of this process for the diagnostics of the burning plasmas have been discussed. There seem to be possible two versions of the diagnostics: (i) measurement of Doppler contours of the lines radiated by noncompletely stripped impurity ions; (ii) detection of prompt losses of light impurities. In both versions the spatial resolution can be attained by injecting into the plasma the pellets containing the desired impurities. Another option is to detect the prompt losses of 7MeV alpha-particles formed by collisions between 3.5 MeV alpha-particles.

Dynamic polarization technique by use of the overhauser effect in Li metal - magnetic moment of short-lived β emitter 28Al -

Abstract A new dynamic polarization technique has been successfully applied to determine the magnetic moment and the sign of β-decay asymmetry factor for short-lived β emitter 28Al ( I τ = 3 + , T 1 2 =136 sec, EMax.β=2.9 MeV ), utilizing the Overhauser effect in a Li metal at 1.5 K and 4.2 K. The magnetic moment was determined as ( 3.242±0.005 ) nm and the asymmetry factor was found negative. This technique showed wider applicabilities to any desired impurity with the lifetime longer than a few seconds.

Metastable Phases in Metals Produced by Ion Implantation

Metallic alloys are usually produced by equilibrium or quasiequilibrium methods. The constituents of the alloy including any desired impurities can be mixed together, melted, and the resultant liquid allowed to solidify and cool. Because the cooling rates are normally fairly slow, the final alloy is usually stable against thermal annealing at operating tempera­ tures and times. In some cases, an alloy may be rapidly cooled or quenched in order to produce a material with a particular physical property. This alloy is metastable with respect to thermal annealing, and the property will be lost if the material is heated to a sufficiently high temperature. The alloy was produced, however, from an equilibrium phase, perhaps a liquid, at a higher temperature. This limits conventional studies of metastable alloys to those that can be formed by quenching from an equilibrium phase. Ion implantation is a method for introducing impurities into the surface layer of a solid in a nonequilibrium fashion. Ions of the desired impurity are accelerated to an energy (generally in the range of 20-200 keY) related to the desired depth of the implanted layer and directed onto the surface of the material to be implanted. The ions penetrate the surface of the material and come to rest some distance below the surface. The impurity concentration distribution in depth is usually almost Gaussian with the peak of the distribution at a depth of a few hundred to a few thousand angstroms, depending on the ion-target combination and the

Optimal summation of Gaussians for ion implantation profile control

A method is described for selecting appropriate ion implantation energies and fluences to synthesize desired impurity profiles in semiconductor device fabrication. An optimization routine utilizing Rosenbrock's algorithm allows computation of a set of implantation parameters which result in close approximation to the preselected distribution.

Synthesis of general impurity profiles using a two-step diffusion process

By optimizing selected characteristics, the performance of modern semiconductor devices and integrated circuits could be improved if it were possible to control the impurity profile in given regions of the material. However, present methods used for fabricating planar devices by diffusion techniques invariably produce profiles which are approximately either Gaussian or complementary error functions. The purpose of this paper is to demonstrate the feasibility of obtaining a general impurity profile in semiconductor material compatible with the two-step diffusion process. The general boundary value problem for the two-step diffusion process is solved and the impurity concentration in the solid is determined as a function of the impurity concentration of the carrier gas in the diffusion tube. An optimization routine using linear programming techniques is developed which, for a given diffusion time, determines the necessary control function producing a best-fit approximation to the desired impurity profile. The optimum control functions governing the diffusion of boron in silicon for two examples are synthesized. The numerical results clearly indicate that a best-fit approximation to a given impurity profile can be realized by controlling the impurity concentration in the carrier gas during the gaseous phase of a two-step diffusion process.

Pair Spectra Involving the Shallow Acceptor Mg in GaP

Type II donor-acceptor pair spectra involving the shallow group IIA acceptor Mg and the group VI donors S and Te have been observed from GaP crystals grown from Ga solution in an open-tube furnace system. Magnesium can be an optically active inadvertent contaminant in high-purity GaP. Crystals containing ∼1017 cm−3 of these desired impurities, added intentionally, exhibited sharp structure due to electron-hole recombinations at discrete donor-acceptor pairs, with negligible contamination from unwanted spectra. The transition energies in these spectra can be closely fitted for shell numbers m≳20 (pair separation ≳17 Å) by an expression which includes only the coulomb monopole term for the final state interaction and a van der Waals term for the initial state interaction, using low-temperature static dielectric constant. This analysis yields the activation energy of the Mg acceptor in GaP, (EA)Mg=53.5±1 meV, substantially different from previous estimates derived from electrical transport and impurity Raman scattering measurements. Trends in the activation energies of the three Ga-site acceptors and three P-site acceptors known in GaP are discussed qualitatively.

Trends in silicon device technology

The present status of silicon device technology is reviewed in order to point out its limitations. The combination of melt-doping, epitaxial growth, and oxide-masked diffusion allows, at least in principle, the construction of about any desired impurity configuration within the silicon crystal. Our present understanding of the silicon-silicon oxide surface allows the design and control of the important surface properties and makes available such important devices as MOS transistors. The limitations of most concern in these areas of wafer fabrication technology are those associated with improving process control and minimizing defects. Effort in this area takes the form of relating cause to effect followed by appropriate detailed process changes. It represents a direction of extreme importance in maximizing the impact of silicon devices through greatly reduced cost.

Silicon Vapour Epitaxy

The technique of vapour epitaxial growth has found widespread usage in semiconductor device technology. From the time it was used to improve the high frequency performance of transistors in the early 1960's, the technique has become a very important part of the silicon integrated circuits today. The advantage which vapour epitaxy offers over techniques like diffusion is in providing alternate P, N layers without any impurity compensation. The technique is also very useful in incorporating desired impurity concentrations in alternate layers. An attempt has been made by the authors to grow epitaxial layers of silicon by the hydrogen reduction of silicon tetrachloride. The paper presents the results obtained, after describing the set-up employed for the growth experiments.

Kinetics of Epitaxial Silicon Deposition by a Low Pressure Iodide Process

This report is primarily a study of the factors which control the vapor transport process of silicon in a modified closed tube low pressure cyclic iodide process. The kinetics of transport from the source to the substrate are examined and are found to agree with a diffusion controlled mechanism. The model is useful for estimating the deposition rate under a variety of conditions. The process is found capable of depositing silicon on silicon substrates at relatively high deposition rates. Impurity doping with this process is accomplished by incorporating the desired impurity into the source silicon.

Doping of Crystals by Ion Bombardment to Produce Solid State Detectors

Ion bombardment was used to produce silicon charged particle detectors because of two advantages over diffusion methods: the quantity of the desired impurity introduced can be precisely controlled by monitoring the ion beam current, and the undesirable impurities can be avoided; further, if the ions are accelerated to only very low energies, the junction will be shallow, and owing to the discrete range of the ions, the depth will be well-defined. The resulting detector will have a very thin window, or dead layer, and, for sufficiently high impurity con centration, the thickness of the window will be independent of the bias voltage applied to the detector. Preliminary results indicate that this method permits construction of detectors that have an energy resolution comparable to that obtained with diffused devices. (L.T.W.)

Impurity Introduction during Epitaxial Growth of Silicon

In this note it has been shown that the silicon iodide disproportionation process for growing epitaxial layers of silicon is also capable of transporting and codepositing desired impurities. Certain Group I11 and V elements such as B, P, As and Sb, can be introduced controllably into epitaxial layers of silicon during the growth. Impurity concentrations obtained cover 4 orders of magnitude, reaching far into the degenerate region. Therefore the process as described by Wajda et a1 is a new tool for the fabrication of various silicon semiconductor structures.