HPLC study for evaluating the significance of pH in the inhibiting effect of phosphate buffer on the leaching pattern of resin composites

An HPLC method was applied to evaluate the inhibiting effect of phosphate buffer on the leaching pattern of resin composites and the significance of pH levels during the storage period in the solutions. Ten (10) disk-shaped specimens (2?mm?×?12?mm diameter) from Evetric restorative resin composite were immersed by means of a silk string in each of the following solutions: Distilled water (solution A), phosphate buffer of pH?=?4.5 (solution B) and phosphate buffer of pH?=?6.8 (solution C). After storage for 7, 30 and 60 days’ period, the eluates were examined by means of High Performance Liquid Chromatography (HPLC) at each time interval. The storage of the resin composite specimens in the phosphate buffer solution demonstrated an inhibiting effect on the leaching pattern compared to the distilled water solution. The results of this study suggest that HPLC is a useful tool to investigate the effect of the pH value of phosphate buffer solution, which resembles saliva, on the leaching pattern of resin composites.     

Comparison between different leaching tests for the evaluation of metal release from fly ash

Comparison of three different leaching tests, each characterized by different conditions, e.g. liquid/solid ratio, pH, leachant, stirring conditions, duration time, has been performed within the activities of Analeach, financed by the European Union in the "Cooperation with third Countries" programme (INCO). The comparison was performed on four highly homogenized fly ash reference materials, of different origin, provided by the Joint Research Centre of Ispra. Seven different elements (Cd, Cr, Cu, Ni, Pb, V, and Zn) were considered in this study. The influence of the main experimental conditions and of the matrix on metal release was studied. Basic characterization of the materials was also performed.     

The application of long wavelength radiation in X-ray analysis

The authors used long wavelength X-ray radiation excited by low energy electrons for analytical purposes. Low energy electron excitation was achieved with an open window tube. The authors used a type that was developed in Philips laboratories. The electron source was a glow discharge from which the electrons ( 15 keV) are extracted and directed towards the anode. A photon spectrum of “Bremsstrahlung” and characteristic peaks is generated at a gold anode. In addition about half of the impinging electrons is reflected and may, thanks to the open window, be used to irradiate a specimen in spite of a partial loss of energy due to the collisions.The authors mention the following attractive characteristics: the tube is simple to operate and may easily be exchanged for a closed tube; no high vacuum is needed, a feature which, however, at the same time inhibits the determination of traces of O, N, C; about 7 cm² of the specimen, which may be an insulator, is irradiated. A discussion of applications illustrates the usefulness of the tube.     

HPLC study of the inhibiting effect of phosphate and bicarbonate buffers on the leaching pattern of dental resin composites

A high-performance liquid chromatographic method was applied to evaluate the effect of bicarbonate (NaHCO₃) and phosphate (NaH₂PO₄, Na₂HPO₄) buffers on monomer leachability of dental resin composites. Evetric was the restorative resin composite that was investigated in current study. Forty disk-shaped resin composite specimens (n?=?40) were immersed by means of a silk string in the following solutions: Distilled water (A), phosphate buffer (B), bicarbonate buffer (C), artificial saliva (D). After seven (7) and fourteen (14) days, the eluates were analyzed by means of High Performance Liquid Chromatography (HPLC). Subsequently, new specimens were fabricated and immersed in fresh solutions in which methanol 12% (v/v) was added. After seven and fourteen days of storage, the leaching of monomers was examined by means of HPLC, which was proved to be an effective tool to buffers demonstrate the inhibiting effect of phosphate and bicarbonate ions on the leaching pattern of dental resin composites.     

Leaching tests on immobilised waste from monolithic bodies Formulation, appraisal and use of radioanalysis

Assessment of environmental risks of granular wastes, immobilised in monolithic bodies implies at least three independent, preferably standardised, tests: Weight variations during drying and wetting; leaching with water or dilute acid and determination of the available fraction of the micro-constituent involved. Their accuracy, precision and minimal turn-over time depend on the dimensions of the test specimen and the experimental procedure. They are considered here in relation to the inevitable underlying assumptions and the practical limitation of the turn-over time. Two standard geometries of test aliquots are considered in detail. The use of radioanalysis in the determination of some of the characterising parameters is summarised.     

Studies on leaching behaviour of sodium borosilicate glasses by neutron activation: Effects of groundwater composition,pH, surface area to volume ratio,and temperature

Static leaching experiments have been conducted to evaluate the durability of sodium borosilicate glass as the host matrix for immobilized high-level radioactive wastes. Simulated granitic groundawater, synthetic Grande Ronde basaltic groundwater and distilled deionized water have been used. The results indicated a strong influence of the leachant composition through both its pH and nature as well as concentrations of the ions present on the leach rate. The roles of silicon, boron and a few other elements on leaching have been examined. Three surface area to volume ratios (SA/V) and two temperatures were investigated. Total mass loss and normalized elemental mass loss results showed that the rate of release decreased with increased SA/V ratio in the three leachants at both temperatures. The rate of leaching at 90 °C was 5–30 times higher than that at 40 °C. Activation energies for the glass at three SA/V ratios have been calculated.     

A new standardized leaching test on stabilized wastes

A new long-term leaching test on stabilized and solidified waste material have been developed and standardized in the frame of the Standards, Measurements and Testing (SMT, formerly BCR) programme of the European Union (EU). The project was coordinated by Dr. H. A. Van der Sloot from ECN (Energy Research Foundation, The Netherlands). Twenty-five European laboratories from EU and EFTA countries participated in the intercomparison exercise. The solidification/stabilization treatment of municipal solid waste incinerator fly ashes, using cement as a matrix, was performed by INTRON B. V. (The Netherlands). The resulting solidified waste material was then used to produce the requested specimens for the intercomparison study. Before distribution to participants, specimen homogeneity was tested according to the state-of-the-art technology for physical-mechanical testing of cement samples as well as for consistency of chemical composition of the solid and stabilized waste. The results of tank leaching test for the above mentioned interlaboratory study are reported and the advantages of this new procedure for the study of the environmental impact of solidified wastes are discussed.     

The Influence of Experimental Leaching Conditions for the Determination of the Soluble Element Content of Soil and Stream Sediment Samples

The Hungarian Geological Survey - Geological Institute of Hungary participated in an INCO-Copernicus project which was aimed at the harmonisation of analytical methods and finished recently. In the first phase, participating geological laboratories entered the International Soil Exchange (ISE) scheme. Laboratories determined total and leachable element contents of soil (and stream sediment) samples, using their own methods. This article in intended to summarise the problems and conclusions regarding the determination of leachable (mobile) elements. Using their own methodologies, laboratories obtained fairly divergent results, especially for some elements. In order to eliminate the variance originating from applying different methodology, a standardised common method was designed for aqua regia leaching. The spread of the results did not improve significantly because of the insufficient control of the applied open vessel method. The final conclusion was: in order to produce internationally comparable results, the use of well-defined and well-controllable digestion methods is strongly recommended. A typical example might be the use of the microwave assisted digestion methods for all geological institutes participating in international geochemical programmes.     

Determination of phenolic compounds in grape skin by capillary electrophoresis with simultaneous dual fluorescence and diode array absorption detection after dynamic superheated liquid leaching

A fast method for the analysis of 10 of the characteristic compounds of the phenolic fraction in grape skin is proposed here. The method is based on a leaching step by superheated ethanol-water at 120 degrees C and 80bar, which enables to maintain the leachant in liquid state and wide the range of leachable compounds (polar, mid-polar and relatively non-polar compounds) by decrease of the dielectric constant; thus, allowing high leaching efficiencies to be achieved in 30min. After leaching, the target analytes were separated by capillary electrophoresis using a 50mM sodium tetraborate with 10% methanol (pH 8.4) solution as background electrolyte. Determination was performed by simultaneous dual diode array absorption and fluorescence detection, the combination of which increased the selectivity of the overall method, particularly interesting taking into account the complexity of the leachate as no additional concentration and/or clean-up steps were required prior to electrophoretic separation, which lasted only 10min. The short time of the electrophoretic step makes it useful as a screening tool of the target analytes in commercial and non-commercial extracts belonging to the pharmaceutical, cosmetic, nutraceutical or food fields.     

Ultrasound-assisted extraction and silylation prior to gas chromatography-mass spectrometry for the characterization of the triterpenic fraction in olive leaves

One of the most important fractions of bioactive compounds isolated from plants is that formed by triterpenic compounds, which have proved to be anti-bacterial, antifungal, anti-inflammatory, cytotoxic and anti-tumour. A method for leaching and determination of the main triterpenic compounds (oleanolic acid, ursolic acid, uvaol, erythrodiol) in olive leaves is here presented. Quantitative leaching was obtained with ethanol as leachant and ultrasonic assistance for 20 min, a very short time as compared to conventional procedures by maceration, which usually requires at least 5 h. After isolation, an aliquot of the ethanolic leachate was silylated to derivatize the analytes prior to gas chromatography-mass spectrometry analysis. Silylation reaction was also assisted with ultrasound in order to accelerate the derivatization step, which only required 5 min--a dramatic shortening in comparison to conventional silylation of terpenic compounds with derivatization times ranging from 30 min to 3 h. The proposed method has demonstrated to be useful for isolation and characterization of the triterpenic fraction in plants; the capability of ultrasound to assist sample preparation (acceleration of leaching and derivatization) has also been proved.     

Microwave digestion of biological samples with tetramethylammonium hydroxide and ethylenediaminetetraacetic acid for element determination

A microwave-digestion system with a closed PTFE vessel was used to improve the leaching of inorganic constituents from biological samples with tetramethylammonium hydroxide (TMAH) and ethylenediaminetetraacetic acid (EDTA). The effects of microwave parameter settings and the quantities of TMAH and EDTA used on leaching efficiency were evaluated. This new digestion method has been applied to the standard reference materials NIST SRM 1577 B Bovine Liver 1515 Apple Leaves and NIES CRM No. 1 Pepperbush, No. 3 Chorella, No. 6 Mussel and No. 7 Tea Leaves. The major and minor elements in the digests were analyzed by flame atomic absorption spectrometry or graphite furnace atomic absorption spectrometry. Good agreement of the analytical results with the certified values was obtained.     

Methods for Concentration of Hydrogen Peroxide To Obtain It in Anhydrous Form

Methods for concentrating hydrogen peroxide and obtaining this compound in anhydrous form, based on removal or binding of water from the surface of solution in an open vessel or in a closed volume and also on binding of water directly in a H₂O₂ solution, are described.     

Comparison of digestion procedures for the determination of mercury in soils by cold-vapour atomic absorption spectrometry

Five digestion procedures were investigated for the determination of mercury in soils by cold-vapour atomic absorption spectrometry. These methods included three acid leaching procedures in open systems and two acid digestion procedures in closed decomposition vessels. The closed vessels were heated in a conventional laboratory oven or a laboratory microwave oven. In the open systems, digestion with concentrated acids at elevated temperatures led to considerable losses of (organo) mercury compounds, while digestion at ambient temperature gave incomplete oxidation of the sample matrix. To prevent any losses of mercury and to obtain complete oxidation, the use of a closed decomposition system at elevated temperatures appeared to be necessary. The results obtained with these closed systems were in good agreement with those obtained by neutron activation analysis. Heating in a microwave oven appeared to be a considerable improvement over conventional thermal heating.     

Influence of sample pre-treatment on the determination of trace silver and cadmium in geological and environmental samples by quadrupole inductively coupled plasma mass spectrometry

The suitability of three different digestion procedures has been evaluated with regard to the quantitative determination of trace amounts of silver and cadmium in geological and environmental samples. Procedure A: extraction with aqua regia in an open vessel system; Procedure B: extraction with aqua regia in a closed pressurized vessel system; Procedure C: digestion with HF + HNO₃ in a closed pressurized vessel system. It was found that procedure A represented an effective way of extracting analytes from different types of geological samples while the effect of extracting interfering metals is low. Because it is interference-free, poses a low risk of contamination and is time-saving, sample treatment procedure A was preferred. For this digestion procedure, a series of Chinese geological reference materials was determined by ICP-MS, the results of which were found to be in reasonable agreement with the certified values.     

DSC and FTIR Analyses of The Curing Behavior of Epoxy/dicy/solvent Systems on Hermetic Specimens

The curing characteristics of adicyandiamide-cured epoxy system under the influence of solvents in a closed environment were studied by means of isothermal differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The DSC analyses revealed that the presence of solvent results in decreases in the curing exotherm, the initial curing rate, the glass transition temperature, the reaction rate and the reaction order of the epoxy resin. The greatest decreases were caused by the solvent with the highest boiling temperature. A change in temperature-dependent curing route due to the heat absorbed during solvent evaporation is responsible for the difference. The FTIR analyses confirmed that the composition of the cured resin is affected by the solvent, the curing temperature and the specimen configuration. As compared with those obtained from open systems, specimens produced in a closed environment have an enhanced curing exotherm, initial curing rate, glass transition temperature, reaction rate and reaction order because of the retention of volatile catalytic by-products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Imaging and Microanalysis in Environmental Scanning Electron Microscopy

A variety of gas cascade amplification and signal detection strategies have evolved for use in low vacuum and environmental scanning electron microscopy on poorly conducting specimens. These detectors have been optimized to perform well under various limitations on the range of gas pressure and working distance which may be imposed by experimental requirements. All of the detectors must produce high gains, low backgrounds, and generate a sufficient positive ion flux to the specimen to enable charge neutralization. The underlying principles of operation of each detector type are discussed, along with the range of experimental conditions appropriate to each.     

Evaluation of hybrid laser-cut and cast miniature fracture specimens

This paper presents a new hybrid laser-cutting method for producing fracture test specimens from thermosetting materials. The hybrid approach combines casting of a sheet of material with subsequent laser-cutting of the test specimens. The new approach was compared to the traditional casting method using a fracture toughness test. For this study, a compact version of the tapered double cantilever beam (cTDCB) was used as a specimen geometry for both manufacturing methods. The cTDCB specimen is crack length independent, and crack length investigations were performed to ensure the crack length independence of the cTDCB specimens. The specimens that were made by the hybrid laser-cut method were found to be comparable to the specimens obtained by the traditional casting method. Moreover, the laser-cut method provides a fast and accurate method to make a significant number of samples in a reasonable time. These tests show that the hybrid laser-cut method could be a good alternative to the traditional casting method.     

Doubly labeled water analysis using cavity ring-down spectroscopy

The doubly labeled water method provides an objective and accurate measure of total energy expenditure in free‐living subjects and is considered the gold‐standard method for this measurement. Its use, however, is limited by the need to employ isotope ratio mass spectrometry (IRMS) to obtain the high‐precision isotopic abundance analyses needed to optimize the dose of expensive ¹⁸O‐labeled water. Recently, cavity‐ring down spectroscopy (CRDS) instruments have become commercially available and may serve as a less expensive alternative to IRMS. We compared the precision and accuracy of CRDS with those of IRMS for the measurement of total energy expenditure from urine specimens in 14 human subjects. The relative accuracy and precision (SD) for total body water was 0.5 ± 1% and for total energy expenditure was 0.5 ± 6%. The CRDS instrument displayed a memory between successive specimens of 5% for ¹⁸O and 9% for ²H. The memory necessitated carefully ordering of specimens to reduce isotopic disparity, performance of several injections of each specimen to condition the analyzer, and use of a mathematical memory correction on subsequent injections. These limited the specimen throughput to about one urine specimen per hour. CRDS provided accuracy and precision for isotope abundance measurements of urine that were comparable with those of IRMS. The memory problems were easily recognized by our experienced laboratory staff, but future efforts should be aimed at reducing the memory of the CRDS so that it would be less likely to result in poor reproducibility in laboratories using doubly labeled water for the first time. Copyright © 2010 John Wiley & Sons, Ltd.     

An adaptable flexural test fixture for miniaturised polymer specimens

An adaptable flexural test fixture is proposed to characterise the mechanical properties of miniature beam specimens (≤10 mg) at ambient conditions or in the presence of fluids at elevated temperatures. The fixture is validated using representative amorphous and semi-crystalline polymers. The response of miniature specimens is compared against that of medium-sized specimens (≤1 g) on the same fixture and on conventional test equipment. Good agreement is found between the specimen sizes for all materials, but the comparisons highlight small differences attributed to factors such as specimen dimensional accuracy, crystallinity and span-to-thickness ratios. Flexural tests in water at 37 °C using both specimen sizes were performed to investigate the evolution of mechanical behaviour of hydrolytically degraded polylactides. Here, specimen size influences the diffusion timescale of acidic by-products which can reduce or enhance autocatalysis.     

Leaching behavior of137Cs in cement

To assess the safety of disposal of a radioactive waste-cement composite, the leaching of¹³⁷Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA.¹ The leachability was measured as a function of bentonite clay to cement ratio. The fraction of¹³⁷-Cs leached from a specimen of Portland cement is 0.03–0.13 at a leaching time of 400 d. Results presented in this paper are examples of data obtained in a 10 y mortar and concrete testing project, which will influence the design of the engineered trench system for a future Yugoslav radioactive waste storage center.^2,3