Microwave Dissolution Research Articles

Metal-Organic Framework Supporting Fe3O4 Prepared by Microwave in Couple With NTP to Eliminate VOCs From Biofuel

In the production process of briquette biofuel, terpenes such as pinene and camphene, as well as non-terpenoid VOCs such as formic acid, acetaldehyde, and benzene, are generated during conditioning, drying and other procedures. Different catalysts of Fe3O4 supported by CoFe-ZIFs were prepared by thermal dissolution method and microwave dissolution method with changing the doping amount of iron. The structures of these catalysts were characterized by X-ray Diffraction (XRD), Fourier transform infrared spectrometer Fourier-Transformed InfraRed, thermogravimetric analysis (TG), and scanning electron microscope and the catalytic performance for α-pinene was tested on a fixed bed. The results show that, compared with the thermal dissolution method, the microwave dissolution method was easier to induce iron to form Fe3O4 grains with higher activity. At the same time, the grains did not affect the formation of CoFe-ZIFs structure. Fe3O4 supported on CoFe-ZIFs enhanced the catalytic activity and energy efficiency of the catalysts for α-pinene. Among the test samples, CoFe14-ZIF-W prepared by microwave method with Fe doping 14% mol exhibited the stable structural characteristics and the highest catalytic efficiency of 94.3% and energy efficiency of 8.11 g·kWh−1, which provided a further possibility of practical application for the removal of VOCs from biomass.

Determination of Total Silicon and SiO2 Particles Using an ICP-MS Based Analytical Platform for Toxicokinetic Studies of Synthetic Amorphous Silica.

Synthetic amorphous silica (SAS), manufactured in pyrogenic or precipitated form, is a nanomaterial with a widespread use as food additive (E 551). Oral exposure to SAS results from its use in food and dietary supplements, pharmaceuticals and toothpaste. Recent evidence suggests that oral exposure to SAS may pose health risks and highlights the need to address the toxic potential of SAS as affected by the physicochemical characteristics of the different forms of SAS. For this aim, investigating SAS toxicokinetics is of crucial importance and an analytical strategy for such an undertaking is presented. The minimization of silicon background in tissues, control of contamination (including silicon release from equipment), high-throughput sample treatment, elimination of spectral interferences affecting inductively coupled plasma mass spectrometry (ICP-MS) silicon detection, and development of analytical quality control tools are the cornerstones of this strategy. A validated method combining sample digestion with silicon determination by reaction cell ICP-MS is presented. Silica particles are converted to soluble silicon by microwave dissolution with mixtures of HNO3, H2O2 and hydrofluoric acid (HF), whereas interference-free ICP-MS detection of total silicon is achieved by ion-molecule chemistry with limits of detection (LoDs) in the range 0.2–0.5 µg Si g−1 for most tissues. Deposition of particulate SiO2 in tissues is assessed by single particle ICP-MS.

Direct precise determination of Pd, Pt and Rh in spent automobile catalysts solution by high-resolution continuum source graphite furnace atomic absorption spectrometry

This work investigates the analytical possibilities of high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS) for the determination of Pd, Pt and Rh (PGMs) in spent automobile catalysts without chemical separation. A novel approach for the microwave dissolution with the mixture of HCl and H2O2 (4:1) was developed for the further HR CS GFAAS. It was found that within 20 min at the temperature 210 °C of the PGMs quantitatively and simultaneously transferred to solution. It did not show any matrix interferences in determining Pd and Rh, when using HR CS GFAAS for determining the PGMs. When determining Pt, the matrix effect can be expressly minimized by diluting the sample or applying a corrective model. Limits of quantification (μg l−1) by HR CS GFAAS achieved were 1 (Pd), 2 (Pt), and 0.5 (Rh). Correlation coefficients were 0.9973 (Pd), 0.9995 (Pt), and 0.9983 (Rh). The relative standards deviation for PGM determination by the developed procedure was not higher than 5% in the concentration range 0.0005–0.5% weight. Moreover, validation of the developed multielement method demonstrated its robustness. The trueness of experimental results was assured by comparison with the atomic emission spectrometry with inductively coupled plasma method.

Assessment of radioactive materials and heavy metals in the surface soil around uranium mining area of Tongliao, China

Natural and artificial radionuclides and heavy metals in the surface soil of the uranium mining area of Tongliao, China, were measured using gamma spectrometry, flame atomic absorption spectrophotometry, graphite furnace atomic absorption spectrophotometry and microwave dissolution atomic fluorescence spectrometry respectively. The estimated average activity concentrations of 238U, 232Th, 226Ra, 40K and 137Cs are 27.53±16.01, 15.89±5.20, 12.64±4.27, 746.84±38.24 and 4.23±4.76Bq/kg respectively. The estimated average absorbed dose rate in the air and annual effective dose rate are 46.58±5.26nGy/h and 57.13±6.45μSv, respectively. The radium equivalent activity, external and internal hazard indices were also calculated and their mean values are within the acceptable limits. The heavy metal concentrations of Pb, Cd, Cu, Zn, Hg and As from the surface soil were measured and their health risks were then determined. Although the content of Cd is much higher than the average background in China, its non-cancer and cancer risk indices are all within the acceptable ranges. These calculated hazard indices to estimate the potential radiological health risk in soil and the dose rate are well below their permissible limit. In addition the correlations between the radioactivity concentrations of the radionuclides and the heavy metals in soil were determined by the Pearson linear coefficient.

Evaluation of PGE Liberation and Chromium Isolation in a Solid UG2 Chromitite Concentrates at Moderate Temperatures Using ICP-OES

Complete sample digestion is a prerequisite in achieving accurate and reproducible results in wet chemical analysis as well as effective element recovery in hydrometallurgical beneficiation processes. Inductively coupled plasma-optical emission spectroscopy was used to evaluate the efficiency of (NH4)2HPO4/(NH4)H2PO4, Na2HPO4/NaH2PO4·H2O (800°C), NH4F·HF flux (250°C), microwave dissolution using HCl and aqua regia acids (240°C) to dissolve and liberate the platinum group metals (PGE) in a Upper Group 2 (UG2) chromitite concentrate sample. Complete digestion of the UG2 chromitite ore was achieved using Na2HPO4/NaH2PO4·H2O and (NH4)2HPO4/(NH4)H2PO4 flux mixtures and average PGE (Ru, Os and Pt) yields of 1.90 g/kg (Ru), 0.88 g/kg (Os), 2.52 g/kg (Pt) were obtained using Sc as internal standard. Fusion with NH4F·HF yielded 0.85 g/kg (Ru), 0.72 g/kg (Os) and 0.95 g/kg (Pt) whilst microwave dissolution using HCl and aqua regia yielded an average of 0.77 g/kg (Ru), 0.08 g/kg (Os) and 0.35 g/kg (Pt). Sodium phosphate flux, however, introduced Na+ ions as easily ionised elements, which affected the emission intensities to yield slightly inflated PGE (Ru, Os and Pt) yields. The use of ammonium phosphate and sodium phosphate at 800°C (after the selective removal of Na+ ions) proved to better the fluxes and produced higher and consistent PGE yields. The use of ammonium phosphate flux was also shown to facilitate the isolation of a green chromium precipitate with a 98.9% purity, which may assist in a hydrometallurgical beneficiation process of the UG2 chromitite concentrate ore and may also have important implications for the ferro-chrome industry.

Analysis of uranium in the insoluble residues after decomposition of soil samples by various techniques

A comparison of different dissolution techniques for determination of uranium in soil samples was made. Conventional wet dissolution with mixtures of HNO3, HClO4 and HF acids, microwave dissolution using HNO3 and HF, and alkaline fusion with Na2CO3 and Na2O2 were evaluated. For testing the effectiveness of the dissolution procedures, two reference materials and six soil samples from the surroundings of a former uranium mine were investigated. It was observed that the content of uranium in the residues determined by INAA represents a significant contribution to its total concentration in the sample, especially in the case of microwave dissolution.

Microwave-assisted dissolution of ceramic uranium dioxide in TBP–HNO3 complex

Microwave-assisted dissolution of ceramic uranium dioxide in tri-n-butyl phosphate (TBP)–HNO3 complex was investigated. The research on dissolution of ceramic uranium dioxide in TBP–HNO3 inclusion complex under microwave heating showed the efficiency of the use of this method. Nitric acid present in the inclusion complex participates both dissolution of UO2, and oxidation of U(IV)–U(VI), the resulting UO2(NO3)2 extracted with tri-n-butyl phosphate. Dissolution rate depends on both temperature of microwave dissolution process, and concentration of nitric acid present in the inclusion complex. The most intensive dissolution process is when the concentration of nitric acid ≥2 mol/L and the temperature of 120 °C. From the experimental data obtained by two kinetic models activation energies were calculated. At the average activation energy of UO2 dissolution in TBP–HNO3 complex equal 70 kJ/mol, and reaction order is close to one, i.e. the reaction takes place in an area close to kinetic.

The measurement of impurities in silicon for solar cell production

The power conversion efficiency of solar cells is largely dependent on impurity levels in silicon. In the current investigations two sample preparation methods of silicon had been used before analysis - acid dissolution at atmospheric pressure and pressured microwave assisted technique. Quantification of impurities in solar silicon was done by inductively coupled plasma mass spectrometry and electrothermal atomic spectrometry. Microwave assisted dissolution of solar silicon was more effective compared to the traditional dissolution method on the hot plate, but complete dissolution of impurities and silicon matrix was achieved with a nitric and hydrofluoric acid mixture. The mass of solar silicon for the microwave dissolution is about 0.5 g and optimal ratio of HF and HNO3 acids mixture is 3 to 5.

Comparison of sample preparation methods for the ICP-AES determination of minor and major elements in clarified apple juices

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of minor and major elements present in apple juices. Prior to ICP-AES measurement, samples were diluted with nitric acid or digested in a microwave assisted digestion system. The differences in the measured element concentrations after application of different types of sample preparation procedures are discussed. The direct measurement compared to closed microwave dissolution was found to be the best sample preparation procedure. Prior to the measurements the ICP-AES method was validated and optimized for the determination of elements in apple juices. For diluted apple juice samples the lowest limits of detection (LOD) were obtained for Ba and Cd (<20μgL−1), moderate ones for Cu, Mn, Ni, Fe, Ag, Ca, Cr, Zn, Mg, and Sr (20–100μgL−1), and the highest LODs for K, Pb, Na, and Al (>110μgL−1). The results obtained for the repeatability (<0.9%), the intermediate precision (<4.5%), the day-to-day reproducibility (<5.2%), and the overall uncertainty of measurement (approx. 4–7%) for all elements analyzed demonstrated the good applicability of the proposed method. Differences in major element content in fresh and commercial apple juice are discussed.

Preparation of PES Ultrafiltration Membrane using Novel Modified Microwave Casting Solution Technique

In this study the influence of anhydrous lithium fluoride (LiF) and the novel modified microwave casting solution technique on membrane performance are investigated. The polyethersulfone (PES) asymmetric membrane was prepared by the dry/wet phase inversion process. In order to observe the effect of microwave dissolution technique on membrane performance, PES concentration in the dope solutions was kept to 20 wt.% through out the experiments. The concentration of lithium fluoride was varied from 1-5 wt.% and N, N-dimethylformamide (DMF) is used as the solvent. Viscosities of the dope solutions were measured and membrane performance was characterized in terms of pure water permeation (PWP), permeation rate (PR) and solute separation of PEG solutions of different molecular weights ranging from 600-35000 Da. The molecular weight cut off (MWCO), mean pore size and pore size distribution of the membranes were subsequently determined. Results disclosed that the addition of lithium fluoride to the PES/DMF solution and the microwave irradiation technique increases the membrane permeability while maintaining their separation properties. However, the LiF concentration was best kept to 2 wt.% concentration.

Multivariate optimization of the synthesis and of the microwave dissolution of biomorphic silicon carbide ceramics

Biomorphic silicon carbide ceramics are a new class of materials that are used for various industrial applications owing to its attractive properties. The efficiency of the synthesis and the partly extreme properties of the biomorphic ceramic depend decisively on the synthesis parameters and on the impurities of the final ceramic. In the present article the synthesis as well as the decomposition of these materials is optimized using a multivariate methodology for the design of experiments. Three variables (initial amount of Si, infiltration temperature and reaction time) were considered as factors in the synthesis optimization and six variables (digestion time, ramp time, microwave power, volumes of concentrated HF, HNO 3 and H 2SO 4) in the microwave dissolution optimization. Interactions, between analytical factors and their optimised levels were investigated using full factorial, Plackett–Burman and central composite designs. The synthesis parameters that found higher percentage of SiC (quantified by FTIR) and the digestion procedure that found higher concentrations of metals (Co, Cr and Ni, determined by FI-ETAAS) were considered the optimum.

The optimization of microwave digestion procedures and application to an evaluation of potentially toxic element contamination on a former industrial site

The optimization of a microwave dissolution procedure for potentially toxic elements in a contaminated soil sample has been evaluated using a central composite design approach. By considering the operating parameters of temperature, digestion time, microwave power and acid volume it was possible to identify the following optimum conditions: temperature, 160 °C; power, 750 W; digestion time, 25 min; and, an aqua regia volume of 13 mL. These microwave digestion conditions were then applied to 19 samples obtained from a former industrial site in Newcastle upon Tyne. Of the range of potentially toxic elements present at the site as a consequence of former industrial activity (As, Cd, Cr, Cu, Mo, Ni, Pb and Zn), the majority of topsoil samples indicated elevated concentrations of one or more of these elements. In particular, data obtained using either inductively coupled plasma mass spectrometry or flame atomic absorption spectroscopy indicates the high and wide concentration of Pb on the site (188–60300 mg/kg). Comparing the resulting potentially toxic elements data with UK soil guidelines values (SGVs) suggests at least parts of the site represent areas of potential human health risk. It was found that lead soil values exceeded the SGV on 17 out of the 19 sampling sites; similarly for As 6 out of 19 sampling sites exceeded the SGV. While for Cd, Cr and Ni the soil levels were below the stated SGVs.

Determination of rare earth elements in tomato plants by inductively coupled plasma mass spectrometry techniques

In recent years identification of the geographical origin of food has grown more important as consumers have become interested in knowing the provenance of the food that they purchase and eat. Certification schemes and labels have thus been developed to protect consumers and genuine producers from the improper use of popular brand names or renowned geographical origins. As the tomato is one of the major components of what is considered to be the healthy Mediterranean diet, it is important to be able to determine the geographical origin of tomatoes and tomato-based products such as tomato sauce. The aim of this work is to develop an analytical method to determine rare earth elements (RRE) for the control of the geographic origin of tomatoes. The content of REE in tomato plant samples collected from an agricultural area in Piacenza, Italy, was determined, using four different digestion procedures with and without HF. Microwave dissolution with HNO3 + H2O2 proved to be the most suitable digestion procedure. Inductively coupled plasma quadrupole mass spectrometry (ICPQMS) and inductively coupled plasma sector field plasma mass spectrometry (ICPSFMS) instruments, both coupled with a desolvation system, were used to determine the REE in tomato plants in two different laboratories. A matched calibration curve method was used for the quantification of the analytes. The detection limits (MDLs) of the method ranged from 0.03 ng g(-1) for Ho, Tm, and Lu to 2 ng g(-1) for La and Ce. The precision, in terms of relative standard deviation on six replicates, was good, with values ranging, on average, from 6.0% for LREE (light rare earth elements) to 16.5% for HREE (heavy rare earth elements). These detection limits allowed the determination of the very low concentrations of REE present in tomato berries. For the concentrations of REE in tomato plants, the following trend was observed: roots > leaves > stems > berries.

Microwave digestion—ICP-MS for elemental analysis in ambient airborne fine particulate matter: Rare earth elements and validation using a filter borne fine particle certified reference material

NIST standard reference material SRM 2783 was employed to validate a high temperature, high pressure, two-stage microwave assisted acid digestion procedure using HNO 3, HF and H 3BO 3 developed for the analysis of trace elements (including rare earths) in atmospheric fine particulate matter (PM 2.5) prior to inductively coupled plasma mass spectrometry (ICP-MS). This method quantitatively solubilized Na, Mg, Al, K, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sb, Cd, Cs, Ba, Pb, Th, U and several rare earth elements (REEs) (La, Ce, Pr, Nd, Gd, Dy, Er, Sm and Eu) from SRM 1648 and SRM 2783. A small amount of HF in the first stage was required to dissolve silicates necessitating the corresponding addition of H 3BO 3 in second stage to dissolve fluoride precipitates of Mg, La, Ce and Th. The optimized microwave dissolution—ICP-MS method detected Na, Mg, Al, K, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Cd, Mo, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Gd, Pb, Th and U at trace to ultra-trace levels in ambient airborne fine particles from three sites in North Carolina. La to light lanthanide signature ratios suggested that soil and motor vehicles are the dominant REE sources in SRM 2783 and PM 2.5 samples collected during this study.

Multivariate optimization of a microwave-assisted leaching procedure using dilute acid solutions, for FAAS determination of Cu, Fe, Mn, and Zn in multivitamin/multimineral supplements

This paper reports the development of a microwave-assisted procedure for leaching of copper, iron, manganese, and zinc from multivitamin/multimineral supplements by use of dilute acid before determination by flame atomic absorption spectrometry (FAAS). A Doehlert design was used to find optimum conditions for the procedure by use of response-surface methodology. Three variables (acid concentration in the leaching solution, irradiation time, and irradiation power) were used as factors in the optimization study for two acids, HCl and HNO(3). Final working conditions were established as a compromise between the optimum values for each analyte, taking into consideration the robustness of the procedure. The best leaching results were obtained with HNO(3) and the acid concentration, irradiation time, and irradiation power used were 0.70 mol L(-1), 15 min and 360 W, respectively. The accuracy of the optimized procedure was evaluated by comparison with a well-established closed-vessel microwave dissolution technique.

Multivariate technique for optimization of digestion procedure by focussed microwave system for determination of Mn, Zn and Fe in food samples using FAAS

This article describes the development by response surface methodology (RSM) of a procedure for iron, zinc and manganese determination by flame atomic absorption spectrometry (FAAS) in food samples after digestion employing a focussed microwave system. A Doehlert matrix was used to find optimal conditions for the procedure through response surface study. Three variables (irradiation power and time and composition of oxidant solution—HNO 3 + H 2O 2) were regarded as factors in the optimization study. The working conditions were established as a compromise between optimum values found for each analyte taking into consideration the robustness of the procedure. These values were 12 min, 260 W and 42% (v/v) for irradiation time, irradiation power and percent of H 2O 2 in solution, respectively. The accuracy of the optimized procedure was evaluated by analysis of certified reference materials and by comparison with a well-established closed vessel microwave dissolution methodology.

Determination of Trace Noble Metals in Natural Samples Using Hyphenated Methods

An approach was proposed to analyzing platinum-containing materials. It involves the high-temperature dissolution of samples in acids under the action of microwave radiation, the sorption preconcentration of noble metals on complexing adsorbents, and their instrumental determination after the microwave dissolution of the concentrate.

Inductively coupled plasma optical emission spectrometric determination of minerals in catfish frame.

The concentration of 14 major and trace elements in catfish (Ictalurus punctatus) frames was determined and analyzed for differences. Three frames were obtained each week for five consecutive weeks in the spring and the fall of 2000. The frames were freed of remaining flesh, dried, treated by microwave dissolution technique and the minerals determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The mean calcium concentration (mg/kg, dry basis) in the spring (140400) was not significantly (P > 0.05) different from that in fall (167000). Among the heavy metals (Cd, Pb, and Al) the concentration of Cd varied significantly (P < 0.05) from week to week but not from season to season. The concentration of all the above-mentioned heavy metals did not exceed the critical level for human consumption.

Determination of Cr in certified reference material HISS-1, marine sediment, by cold plasma isotope dilution ICP-MS and INAA: comparison of microwave versus closed (Carius) tube digestion

The recovery of Cr from National Research Council Canada (NRCC) certified reference material HISS-1 sediment was investigated by non-destructive instrumental neutron activation analysis (INAA) and isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) after two different chemical treatments: (1) microwave dissolution using HNO3, HF, and HClO4, followed by reflux with concentrated HClO4, and (2) a closed system method using sealed Carius tube digestion with HNO3 and HCl at high temperature (240 °C) and high pressure (1 × 107 Pa, ∼100 atm). The first chemical treatment gave recoveries of only ∼50% in agreement with observations of Yang et al. of NRCC. Samples digested in Carius tubes gave recoveries that ranged from 79 to 110% which may reflect heterogeneity in the samples rather than differing recoveries. This is supported by the excellent agreement of the mean value determined by INAA of 31.4 ± 4.5 µg g−1, and the mean value of 28.1 ± 3.9 µg g−1 by Carius tube digestion and the observation that these standard deviations are essentially equal and much larger than the measurement precisions. The results from this study are also in excellent agreement with the certified value of 30.0 ± 6.8 µg g−1. This preliminary study demonstrates that chemical treatment of this sediment with HNO3 and HCl acids in closed system Carius tubes is an efficient and capable preparation method for the determination of Cr in silicate materials which typically contain refractory Cr-bearing minerals. This study also demonstrates the unique advantage of using two independent methods for the determination of Cr in a complex matrix which has a high potential for low chemical recovery.

An example of abnormal glow curves identification in personnel thermoluminescent dosimetry

The personal Dosimetry Service Seibersdorf analyses monthly a large number of thermoluminescent dosimeters (TLD). The dosimeters consist of LiF chips, and the readout is carried out with an automated Harshaw 8800 reader system. In some cases, the luminescent glow curves of the routine analysis do not have the expected form as a result of external chemical contamination, hardware problems, poor heat transfer, etc. It is therefore necessary to investigate the reasons for the irregularity of these curves. An algorithm for the investigation of the routine curves was developed. It is based on the fact that the shape of an abnormal glow curve differs from the shape of a normal one. An interesting type of abnormal glow curves in the routine service was found. Some dosimeters of a certain client, a steel industry, exhibit glow curves with an untypical shape and very high signals. In those dosimeters, a possible chemical contamination in the form of a powder was discovered, which interferes with the dosimetric signal. A quantitative analysis of that powder was made by means of inductively coupled plasma emission spectroscopy (ICP-OES) after microwave dissolution. Elements like aluminium, barium, calcium and others were found. Such elements are used in different combinations as thermoluminescent materials.