Sample Preparation Parameters Research Articles

X-ray absorption spectroscopy on light emitting porous silicon by XEOL and TEY

This paper presents an experimental investigation of the local structure of porous silicon based on X-ray absorption fine structure by two different techniques: Total electron yield (TEY) and X-ray excited optical luminescence (XEOL). The influence of the main parameters of sample preparation on both the photoluminescence and the local structure around Si atoms has been investigated. The dependence of the optical emission energy on the current density shows a saturation limit. The analysis of both the optical emission and the short range order (up to the third coordination shell) confirms the presence of crystalline cores on a scale of a few nanometers in freshly prepared porous silicon samples. Although the local structural parameters obtained by TEY are similar to those reported in recent X-ray absorption studies, a direct connection between optical emission energy and short range order has not always been found. In particular, while the role of HF concentration in determining optical and microstructural properties is clear, a change of current density affects the energy shift of the X-ray excited optical band but not the short range order properties monitored by TEY.

Electro-optical switching properties of a polymer dispersed ferroelectric liquid crystal device

A fast and high-contrast polymer dispersed ferroelectric liquid crystal (PDFLC) device was fabricated using a polymerization-induced phase separation technique which involves ultraviolet photopolymerization with an argon ion laser. The PDFLC film was oriented by the mechanical shear flow during the polymerization of an ultraviolet-curable adhesive. The switching times, contrast ratio and spontaneous polarization of the PDFLC film were investigated. The sample preparation parameters, such as the curing time and curing intensity were also reported.

Ribes host range and erratic distribution within plants of blackcurrant reversion associated virus provide further evidence for its role as the causal agent of reversion disease

SummaryReversion is the most important disease of blackcurrant crops world‐wide yet, despite research over more than 70 yr, the causal agent of this disease has not been identified. We reported recently the isolation of a new virus from reverted blackcurrant which had a very close association with the two recognised forms of blackcurrant reversion disease, and was detected in vector gall mites from reverted plants and in plants on which such mites had fed (Lemmetty et al., 1997). These data suggest that this virus, tentatively called blackcurrant reversion associated virus (BRAV), may be the causal agent of reversion disease. We now report the detection of BRAV by immuno‐capture reverse‐transcriptase PCR (IC‐RT‐PCR) in redcurrant and in the wild species, Ribes spicatum and R. alpinum, other known hosts of the reversion agent, but not in the non‐host, gooseberry, graft‐inoculated with scions from reverted blackcurrant plants. We also demonstrate the erratic distribution of BRAV in reversion‐affected blackcurrant plants, another characteristic of the reversion agent. Taken together with our earlier findings, these new data add further support to the suggestion that BRAV is the causal agent of reversion disease. We also report how changes to the various parameters of sample preparation and of the IC‐RT‐PCR protocol affect the sensitivity of BRAV detection.

Supercritical Fluid Extraction of Pesticide Residues from Strawberries

A supercritical fluid extraction (SFE) method for the determination in strawberries of a number of commonly used organochlorine insecticides, organophosphorus pesticides, and dichloroanilide fungicides is described. Gas chromatography was used to examine the extracts, with both electron-capture detection and either flame photometric or nitrogen phosphorus detection. Confirmation was performed by gas chromatography-mass spectrometry. The analytes were extracted with supercritical carbon dioxide at 4000 psi and 50 °C with a run time of 20 min, which corresponded to an extraction volume of 20-30 mL of carbon dioxide. In developing the method, the operating parameters of temperature, pressure, extraction time, collection solvent, and sample preparation were optimized. Recoveries ranged from 74 to 126% (with the exception of iprodione), and a method precision of ±3-18% was obtained for spiking levels of 0.08-3.7 mg/kg. The method was validated for the following organochlorine insecticides and organophosphorus pesticides: aldrin, dichloran, dieldrin, p,p'-DDE(TDE), p,p'-DDD, p,p'-DDT, α-endosulfan, β-endosulfan, endosulfan sulfate, diazinon, dichlorvos, ethion, malathion, methyl parathion, methyl pirimiphos, mevinphos E+Z, and parathion; and the following dichloroanilide fungicides: iprodione, procymidone, and vinclozolin. The SFE procedure was quicker, more environmentally friendly, and more cost effective than the traditional solvent extraction methods.

Studies of polymer ball type polymer dispersed liquid crystal films

Abstract ‘Reverse’ or ‘polymer ball’ polymer dispersed liquid crystal (PDLC) samples were prepared by a photopolymerization induced phase separation method. A detailed study of the effects of the sample preparation parameters, such as curing time, curing intensity, and liquid crystal concentration are reported. It was found that by adjusting these parameters, we were able to change the morphology of these ‘polymer ball’ PDLC samples and thus change their optical characteristics. Incomplete polymerization of the PDLC samples results in a higher threshold voltage and a lower ON state transmission. When the amount of monomer is too low, the shape of the resulting polymer ball becomes irregular, and the sample has a larger threshold voltage and a larger saturation voltage.

Optimization of Plant Sample Preparation and ICP Parameters for Analysis of Phosphorus

Abstract Parameters of HNO3-H2O2 wet digestion sample preparation method and inductively coupled plasma atomic emission spectrometer

Influence of DNA preparation and application on specificity of a 3′-end labelled oligonucleotide probe in a dot blot assay

Optimization of the parameters of sample preparation, sample application, probe concentration and also membrane suitability have a considerable influence on the specificity of 3′-end labelled oligonucleotides.

Determination of quartz in kaolins by x-ray powder diffractometry

Depending upon their origin, naturally occuring kaolins contain various accessory minerals including micas, feldspars and quartz. These minerals may be partially removed, but rarely eliminated, by refining. When determining quartz by x-ray diffractometry, serious problems are encountered even with refined kaolins due to overlapping peaks from micas, feldspars and kaolinite itself. This paper discusses the peak overlap and other problems and describes how optimisation of sample preparation and diffractometer parameters, together with the use of profile fitting techniques permits the determination of crystalline quartz in bulk samples to ±0.015 wt.% (1σ absolute) at the 0.1 wt.% level. A detailed examination of the errors involved in the analysis shows that counting and particle statistics are the most important error sources. For the samples examined in this study, counting statistics is the major contributor to the observed 15% relative error. Preliminary results on the use of a laboratory air classifier to generate “large” respirable dust samples from bulk powders for quartz analysis are given.

Determination of concentration and distribution of (CuO) + in high- Tc superconducting La 2− xSr xCuO y pellet by flow-coulometry

The novel wet-chemical method for the analysis of the concentration and the distribution of constituent(s) at a higher oxidation state, [CuO] +, in superconducting La 2− x Sr x CuO y was developed. The sample pellet was dissolved in a flow of acid solution containing Fe 2+, and the solution was introduced continuously into a flow-coulometric system composed of two-step column electrodes of glassy carbon fibers as working electrodes. Fe 3+ generated in the solution through the stoichiometric redox between [CuO] + and Fe 2+ was detected at the first column electrode, and Cu 2+ in the dissolving solution was detected at the second column. It was obvious that the [CuO] + concentration in the surface region of ca. 200 μm in depth from the surface was lower than that of the bulk pellet and the distribution of [CuO] + near the surface was dependent on such sample-preparation parameters as sintering time, annealing atmosphere and storage time of the pellets, etc.

Direct determination of impurities in powdered silicon carbide by electrothermal atomic absorption spectrometry using the slurry sampling technique

A direct method of analysis of powdered silicon carbide for the determination of Al, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Ti, V and Zn based on electrothermal atomic absorption spectrometry (ETAAS) using the slurry sampling technique is described. Possible spectral interferences caused by the refractory matrix components were studied. The technique was optimized with regard to sample preparation, dispensing, thermal pre-treatment and atomization parameters. The accuracy was checked by comparison of the results with those obtained by ETAAS and inductively coupled plasma atomic emission spectrometry involving decomposition of the sample, and by instrumental neutron activation analysis. For most of the elements investigated the achievable limits of detection are at the sub-microgram per gram level.

Determination of volatile aromatic hydrocarbons in estuarine and coastal sediments using gas syringe injection of headspace vapours and gas chromatography with flame-ionisation detection

A simple, low cost flame-ionisation detection method for the determination of volatile aromatic compounds in estuarine and coastal sediments is described. Headspace vapours are drawn from a modified sample vessel at 80 °C and injected by means of a gas-tight syringe with a valved needle. The method eliminates the difficulties normally encountered with solvent extraction and dynamic “non-equilibrium” headspace methods. The effect of varying the sample preparation parameters is discussed and results giving the optimised values are presented. Relative standard deviations of less than 2% were achieved for a variety of sub-marine and tidal sediments and the results were found to be superior to those given by an existing solvent extraction method. The limits of detection of the method are below 0.5 µg kg–1(dry mass) for ten key volatile organic aromatic compounds and the response is linear up to at least 200 µg kg–1.

An investigation of the effect of sample preparation on the thermal behavior and the small‐angle x‐ray scattering of a polyurethane block copolymer

AbstractThe effect of varying sample preparation parameters on the thermal behavior and on the small‐angle x‐ray scattering (SAXS) properties of a polyether polyurethane were investigated. The polyurethane studied was a methylene bis(p‐phenyl isocyanate) (MDI)/butanediol/poly(tetramethylene oxide) (PTMO) system synthesized in a 6/5/1 mole ratio by a two‐step solution polymerization. The PTMO had a nominal molecular weight of 2000. The samples were compression molded under different conditions for the SAXS experiments. The preparation parameters studied included molding time and temperature, sample thickness, and quenching rate from the molding temperature. The molding temperature has the greatest effect on the SAXS data. In this case the domain size was observed to increase as the molding temperature increased from 130 to 200°C. The thermal properties were also found to be strongly dependent on the molding temperature, as measured by differential scanning calorimetry (DSC). An endotherm related to the annealing that occurs during the molding process appears in each sample near the molding temperature. The other preparation parameters have little or no effect on the SAXS and thermal properties of this sample.

The detection of quartz in clay minerals by differential thermal analysis

Differential thermal analysis (DTA) has proven to be a sensitive, specific and relatively rapid technique for the detection of small amounts of free crystalline quartz in clay minerals. The method utilizes the thermal transition representing the reversible alpha—beta crystal inversion of quartz at 573°C. On heating, the latent heat of inversion gives rise to an endothermic reaction; on cooling, an exothermic transition is obtained. The mineral is first calcined at approximately 800°C for the purpose of inducing irreversible thermal transitions characteristic of that mineral and its impurities. The cooling curve then shows a flat baseline, thus improving detectability for quartz. With the use of standard prepared samples of quartz in talc, the minimum level of detection of quartz by DTA was determined to be 0.5% by weight. If sample preparation and experimental parameters are standardized, DTA provides a definitive technique for detection of quartz in clay minerals. The method has also been applied for the detection of quartz in industrial dust and in respirable particle size material such as might be taken from personnel air samplers.

Pseudo-Kikuchi maps of Nb-diffused LiTaO3 thin-film optical waveguides

Electron diffraction phenomena which naturally occur in scanning electron microscopy are applied to the study of the crystal structure of LiTaO3 surface layers following Nb diffusion. Kikuchi maps, which relate to the reciprocal lattice of the crystal, are given for LiTaO3 oriented along the (01.0) and (00.1) crystal axis. Details on sample preparation and microscopy parameters are given along with a brief discussion as to how Kikuchi maps are predicted for this crystal. The techniques used allow observation of only the surface layer; the results are not masked by diffraction effects due to the substrate.

Ammonium Perchlorate Combustion: Effects of Sample Preparation; Ingredient Type; and Pressure, Temperature and Acceleration Environments

Abstract Differences in ammonium perchlorate (AP) combustion behavior as evidenced by the effects of pressure, sample temperature and acceleration environments on burning rate are shown for samples prepared in various manners. The sample preparation parameters investigated include pellet compaction time and pressure, the particle sizes of the AP powder from which samples were pressed, and the type of AP (ultra-pure, propellant grade, and propellant grade with conditioners) from which the pellets were made.