Closed Microwave System Research Articles

Determination of Total Iodine in Food Samples Using Inductively Coupled PlasmaMass Spectrometry

A method was developed and validated for the extraction and determination of total iodine (I) in food composite samples, representing different foods available on the Canadian market, by inductively coupled plasma-mass spectrometry (ICP-MS). Prior to analysis, samples were digested in a closed microwave system using a mixture of nitric acid and perchloric acid. The detection limit for iodine determination was 29 nglg and precisions of 10 and 1.3% were obtained for 10 replicate measurements of 100 and 1000 ng/g standards, respectively. The method was validated using Certified Reference Materials and spike recovery measurements in food samples and was applied for the determination of iodine in a variety of food composite samples from the Canadian Total Diet Study. The high sample throughput of ICP-MS makes the method suitable for analysis of large numbers of food samples with varying matrixes, such as for Total Diet Studies.

The evaluation of Cr, Ni, Cu, and Co contents in bottom sediments of the Supraśl River and its tributaries

Abstract The aim of this study was to evaluate the total and soluble forms of Cr, Ni, Cu, and Co contents in bottom sediments of the Supraśl River and its tributaries. Studies were carried out in August 2005 and March 2006. The total contents of metals were determined, following the digestion of the sediments in nitric acid in a MARS 5 closed microwave system. Soluble forms of metals were extracted with 1 mol dm-3 HC1 at the ambient temperature. The bottom sediments of the Supraśl and its tributaries are slightly contaminated with chromium. Copper, nickel, and cobalt occur mainly at a geochemical background level. A positive linear correlation between total forms of metal contents and their soluble forms was found.

Comparison of various digestion procedures in chemical analysis of spent hydrodesulfurization catalyst

Four digestion procedures have been tested to verify their applicability to the determination of major and trace elements (Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, Ti, V, Zn) in a spent catalyst by inductively coupled plasma optical emission spectrometry (ICP-OES). Two digestion procedures have been carried out in a closed microwave system using: (1) HCl + HNO 3 + H 2O 2; (2) HNO 3 + HF, whereas the remaining two in an open system using: (1) aqua regia + NH 4F, HNO 3, H 2SO 4; (2) HF + HClO 4, H 3BO 3, HCl. Among these four procedures the microwave digestion system (1) gave the best recovery results. The quality of the analytical results has been evaluated by the analysis of the CTA-FFA-1 Fine Fly Ash Certified Reference Material. A good agreement between the measured and reference values was found for almost all elements. The precision was assessed from the replicate analyses of microwave digestion (1) system and was found to be less than 5% of the relative standard deviation (R.S.D.).

Cu determination in crude oil distillation products by atomic absorption and inductively coupled plasma mass spectrometry after analyte transfer to aqueous solution

Cu was determined in a wide range of petroleum products from crude oil distillation using flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma mass spectrometry (ICP-MS). Different procedures of sample preparation were evaluated: (i) mineralization with sulfuric acid in an open system, (ii) mineralization in a closed microwave system, (iii) combustion in hydrogen–oxygen flame in the Wickbold's apparatus, (iv) matrix evaporation followed by acid dissolution, and (v) acidic extraction. All the above procedures led to the transfer of the analyte into an aqueous solution for the analytical measurement step. It was found that application of FAAS was limited to the analysis of the heaviest petroleum products of high Cu content. In ICP-MS, the use of internal reference method (with Rh or In as internal reference element) was required to eliminate the matrix effects in the analysis of extracts and the concentrated solutions of mineralized heavy petroleum products. The detection limits (in original samples) were equal to, respectively, 10, 86, 3.3, 0.9 and 0.4 ng g − 1 in procedures i–v with ETAAS detection and 10, 78, 1.1 and 0.5 ng g − 1 in procedures i–iii and v with ICP-MS detection. The procedures recommended here were validated by recovery experiments, certified reference materials analysis and comparison of results, obtained for a given sample, in different ways. The Cu content in the analyzed samples was: 50–110 ng g − 1 in crude oil, < 0.4–6 ng g − 1 in gasoline, < 0.5–2 ng g − 1 in atmospheric oil, < 6–100 ng g − 1 in heavy vacuum oil and 140–300 ng g − 1 in distillation residue.

Simultaneous microwave-assisted extraction of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phthalate esters and nonylphenols in sediments

A new method was developed for the simultaneous extraction of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phthalate esters (PEs), nonylphenols (NPs) and nonylphenol mono- and diethoxylates (NP1EOs and NP2EOs, respectively) in sediment samples by means of a closed microwave system. The extractions were carried out at 21 psi and 80% of microwave power and 15 ml of acetone were used as the common extraction solvent. The filtered extract was further fractionated in two groups using Florisil ® cartridges: PAHs and PCBs were eluted with n-hexane:toluene (4:1) and the PEs, NPs and ethoxylates were eluted with ethyl acetate. All the compounds were analysed by gas chromatography–mass spectrometry (GC–MS). In case of PAHs and PCBs, the developed method was validated by comparison of the results obtained for the certified reference material NIST 1944 with the certified values. In the absence of a reference material for phthalate esters and nonylphenols, one sediment sample was extracted twice under the optimal conditions in order to check than an exhaustive extraction of the analytes occurred. This method is currently used in the study of the distribution of those organic contaminants in the estuaries of the Bay of Biscay (Spain).

Comparison of Two Wet Digestion Procedures for Multi‐element Analysis of Plant Samples

Two microwave digestion systems for multi‐element analysis of leaves and fruits were compared. Samples were digested by two different methods: 1) with HNO3 (8 mL) and HClO4 (6 mL) using an open microwave system and 2) with HNO3 (5 mL) and H2O2 (3 mL) in a closed microwave system. Total concentrations of aluminum (Al), cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), leaf (Pb), magnesium (Mg), manganese (Mn), nickel (Ni), and zinc (Zn) were determined in 22 samples by inductively coupled plasma atomic emission spectrometry and by simultaneous inductively coupled plasma mass spectrometry (ICP/AES and ICP/MS). Not statistical differences for Cu, Mn, Mg, Pb, and Zn concentration between the two methods were observed. Trace elements, whose concentration is low, such as Cr and Cd, have to be determinate by ICP/MS. The accuracy of the procedures was acceptable, except for Al, Fe, and Mg using the open microwave system, as the results from certified reference materials were in agreement with certified values.

Ashing and microwave digestion of aerosol samples with a polypropylene fibrous filter matrix

Radionuclide monitoring is one of the key techniques required by the International Monitoring System (IMS) and On-Site Inspection (OSI) in the Comprehensive Nuclear Test Ban Treaty (CTBT). There shall be a global network of 80 radionuclide monitoring stations. Atmospheric aerosols are collected generally on filters in the stations. A polypropylene (PP) fibrous filter is often used in sampling atmospheric aerosols. There might be much information to be obtained by measuring aerosol samples after digestion rather than nondestructive analysis directly by γ-spectrometry. The present work focused on pretreatment of the filter samples, which includes the influence of different ashing or microwave digestion conditions on the recoveries of analytes. The inductively coupled plasma–atomic emission spectrometric detection results indicated that the recoveries of elements in the PP fibrous filters by ashing were influenced by ashing time, temperature and the properties of the elements. High recoveries of volatile elements and consistent recovery for other elements were obtained by using a closed microwave system to digest the filters. Higher sensitivity was also obtained when the intercomparison sample was measured by a HPGe well detector after pretreatment by the recommended ashing and microwave digestion procedures.

The use of numerical simulation as a cognitive tool for studying the microwave drying of softwood in an over-sized waveguide

A previously developed mathematical model, which uses a comprehensive two-dimensional heat and mass transport code coupled with a three-dimensional code for resolving Maxwell's equations in the time domain, will be used to investigate numerous aspects of the microwave enhanced convective drying of softwood in an over-sized waveguide. At first, in order to highlight the predictive capabilities of the developed model, comparisons will be made between theory and experiment for spruce heartwood. It will be shown that the model is able to identify most of the important heat and mass transfer phenomena that arise throughout the drying process. After validation of the numerical simulation results, the work focuses on using the model as a cognitive tool for investigating important issues for closed microwave systems which include the effect of varying the sample dimensions and changing the location of the material within the applicator. Finally, a study will be presented that compares the overall drying kinetics generated within two different types of applicator designs. The first design uses a wave-trap located at the end of the waveguide to prevent reflected energy from back-propagating into the over-sized section of the guide, while the second design uses a short-circuit plane to ensure that this reflected energy is back – propagated towards the material. The advantages and disadvantages of these two designs will be deliberated.

Determination of heavy metal concentrations in plants exposed to different degrees of pollution using ICP-AES.

Plant samples (Plantago lanceolata - narrow leaf plantain and Cichorium endiviae - endive) were collected in the surroundings of heavy metal emission sources and in other less contaminated areas. After digestion in a closed microwave system using HNO(3), the concentrations of Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn were determined using ICP-AES. Detection limits for all the elements of interest are given. Differences in heavy metal uptake rate between both plant species were observed. The uptake is more intensive for endive than for narrow leaf plantain. High concentrations of some heavy metals were determined in the unwashed plant samples as a result of exposure to aerosols. Tukey's statistical test was used to confirm the discrepancy of Cr concentration in plant samples from various areas. Washing the leaves with water was found to remove a large amount of water-soluble aerosols.

Field and power-density calculations in closed microwave systems by three-dimensional finite differences

A three-dimensional finite-difference scheme is used to solve Maxwell&apos;s equations in closed microwave systems. The calculation of the sinusoidal steady-state amplitude and phase of the EM-field, and the derivation of the power density are discussed. The method is tested on some canonical examples which can be solved analytically. Finally, some nontrivial three-dimensional examples are given.

New power-density calculation method by three-dimensional finite elements

A new method to calculate the absorbed power density in closed microwave systems is presented. The method, which is based on the use of a dual variational principle and three-dimensional finite elements, extracts more information from the field solution than a previously published method. The calculation of the total incident and reflected power in a microwave cavity is discussed.

Field and power-density calculations by three-dimensional finite elements

Three-dimensional finite elements are used to find the fields and the dissipated power in a closed microwave system. The material contained in the system is assumed to be linear, lossy, of arbitrary shape, isotropic and inhomogeneous. The method is tested on some examples for which the analytical solution is straightforward. In addition some nontrivial three-dimensional examples are given. Accurate numerical results are obtained provided that the correct test functions are used.