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Determination of total arsenic, total inorganic arsenic and inorganic arsenic species in rice and rice flour by electrothermal atomic absorption spectrometry
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
The determination of inorganic arsenic species in food has become very important during the last few years, since As(III) and As(V) are considered carcinogenic and found at high concentrations in food products, such as rice. The present work describes the development of three different methods for the determination of total arsenic, total inorganic arsenic, and As(III)–As(V) in rice and rice flour food products, purchased from the local market by electrothermal atomic absorption spectrometry (ETAAS). The methods were based on the use of different selective extraction procedures and the optimization of all crucial instrumental and methodological parameters. By these new preparation procedures for the determination of arsenic species, the loss and transformation of analytes during the extraction and digestion steps was prevented. For the validation of each method, precision, accuracy, and selectivity have been assessed, as performance criteria. All developed methods were accurate and precise. The calculated recoveries ranged between 92% and 105% and the (%) relative standard deviation values, under repeatability or reproducibility conditions, were lower than 15% for all different concentration levels tested. The validated methods were applied successfully for the determination of total arsenic and total inorganic arsenic in a proficiency test organized by the International Measurement Evaluation Program (IMEP-107). The methods were also applied in rice and rice flour samples purchased from the Greek market and the obtained results indicated that in almost all samples total arsenic and total inorganic arsenic were detected at ng/g levels.
Publication year: 2013
Source:Microchemical Journal, Volume 108
The determination of inorganic arsenic species in food has become very important during the last few years, since As(III) and As(V) are considered carcinogenic and found at high concentrations in food products, such as rice. The present work describes the development of three different methods for the determination of total arsenic, total inorganic arsenic, and As(III)–As(V) in rice and rice flour food products, purchased from the local market by electrothermal atomic absorption spectrometry (ETAAS). The methods were based on the use of different selective extraction procedures and the optimization of all crucial instrumental and methodological parameters. By these new preparation procedures for the determination of arsenic species, the loss and transformation of analytes during the extraction and digestion steps was prevented. For the validation of each method, precision, accuracy, and selectivity have been assessed, as performance criteria. All developed methods were accurate and precise. The calculated recoveries ranged between 92% and 105% and the (%) relative standard deviation values, under repeatability or reproducibility conditions, were lower than 15% for all different concentration levels tested. The validated methods were applied successfully for the determination of total arsenic and total inorganic arsenic in a proficiency test organized by the International Measurement Evaluation Program (IMEP-107). The methods were also applied in rice and rice flour samples purchased from the Greek market and the obtained results indicated that in almost all samples total arsenic and total inorganic arsenic were detected at ng/g levels.
Highlights
► Novel and simple procedures for inorganic As speciation in rice were developed ► Optimization and full validation of all methods were performed ► Proficiency test (IMEP-107) proved the accuracy of the proposed methods ► Application to rice and rice flour samples was performed ► Total inorganic As was equal to (64±19)% of total As in all samples.Study of modern or ancient collagen and human fossil bones from an archaeological site of middle Nile by thermal analysis and chemometrics
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
Thermogravimetric (TG-DTG) curves were recorded for 23 different samples of human fossil bones from the El Geili necropolis. An accurate analysis of mass loss of the samples examined at different temperatures during a linear thermal scan between 25°C and 1000°C in dynamic air afforded a data set consisting of the thermal parameters of the decomposition processes of collagen and carbonate; this data set was then processed by standard chemometric techniques. The results obtained are discussed and attention is focused in particular on the old or modern collagen thermal breakdown and the possibility of formulating an “archaeometric” assessment that takes into account the often untied conclusions reported in the literature.
Publication year: 2013
Source:Microchemical Journal, Volume 108
Thermogravimetric (TG-DTG) curves were recorded for 23 different samples of human fossil bones from the El Geili necropolis. An accurate analysis of mass loss of the samples examined at different temperatures during a linear thermal scan between 25°C and 1000°C in dynamic air afforded a data set consisting of the thermal parameters of the decomposition processes of collagen and carbonate; this data set was then processed by standard chemometric techniques. The results obtained are discussed and attention is focused in particular on the old or modern collagen thermal breakdown and the possibility of formulating an “archaeometric” assessment that takes into account the often untied conclusions reported in the literature.
Highlights
► Characterization of ancient and modern collagen based on kinetic data. ► Systematization of incomplete information about thermal analysis of fossil bones. ► Characterization of the different kinds of carbonates from bone mineralization.Classification of intact fresh plums according to sweetness using time-domain nuclear magnetic resonance and chemometrics
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
Time domain nuclear magnetic resonance (TD-NMR) and chemometric models were used to classify intact plums according to the total soluble solid content in percentage (% of SSC). The models were constructed using use Carr–Purcell–Meiboom–Gill (CPMG) decay (as independent variables) of intact plums. The reference values in % of SSC (as dependent variable) were obtained from the juice extracted from the same plums. The data sample was divided into two categories: class 1, up 9 to 12% of SSC and class 2, up 13 to 22% of SSC. The soft independent modeling of class analogy (SIMCA) of 171 plums correctly classified the class 1 plums approximately 89% of the total and the class 2 plums (sweeter) above 93% of the samples for both training and the validation data set, at 95% of confidence level. Therefore, the analysis of CPMG decay using SIMCA can be used to classify intact plums according to sweetness. This method is fast (seconds) and can easily be automated, allowing a better classification of each plum than the average SSC values of a lot.
Publication year: 2013
Source:Microchemical Journal, Volume 108
Time domain nuclear magnetic resonance (TD-NMR) and chemometric models were used to classify intact plums according to the total soluble solid content in percentage (% of SSC). The models were constructed using use Carr–Purcell–Meiboom–Gill (CPMG) decay (as independent variables) of intact plums. The reference values in % of SSC (as dependent variable) were obtained from the juice extracted from the same plums. The data sample was divided into two categories: class 1, up 9 to 12% of SSC and class 2, up 13 to 22% of SSC. The soft independent modeling of class analogy (SIMCA) of 171 plums correctly classified the class 1 plums approximately 89% of the total and the class 2 plums (sweeter) above 93% of the samples for both training and the validation data set, at 95% of confidence level. Therefore, the analysis of CPMG decay using SIMCA can be used to classify intact plums according to sweetness. This method is fast (seconds) and can easily be automated, allowing a better classification of each plum than the average SSC values of a lot.
Highlights
► Time domain nuclear magnetic resonance and Chemometrics models properly classify intact plums according to the sweetness. ► The model correctly classified the plums above 89% of the samples of low SSC and 93% of the samples of high SSC. ► This method is fast and can easily be automated.Direct detection of aromatic amines and observation of intermediates of Schiff-base reactions by reactive desorption electrospray ionization mass spectrometry
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
The fast, sensitive detection for 6 aromatic amines and direct observation of intermediates of Schiff-base reactions were achieved through reactive desorption electrospray ionization mass spectrometry (reactive DESI-MS). Pure acetone was electrosprayed to impact the aromatic amines on the paper, allowing two reactions, a proton-transfer reaction and a Schiff-base reaction, to occur in these experiments. The former was used to detect the aromatic amines, and the protonated analytes generated were selected for the qualitative and quantitative analysis. The false-positive signals were excluded by tandem mass spectrometry. For the 6 analytes, linear signal responses were obtained, and each had a dynamic range of 5 orders of magnitude. The relative standard deviation (RSD) and limit of detection (LOD) for all the measurements were in 1.5–5.3% and 0.03–0.2pg/mm2 range, respectively. The latter is a nucleophilic addition reaction that occurred between the aromatic amines and the acetone. The carbinolamine intermediates of these reactions were directly detected and identified by reactive DESI-MS. The data show that reactive DESI-MS is not only a reliable, sensitive tool for chemical analysis, but also a valid and promising method for studying organic reactions simultaneously, especially for heterogeneous reactions that occurred at a solution/solid interface.
Publication year: 2013
Source:Microchemical Journal, Volume 108
The fast, sensitive detection for 6 aromatic amines and direct observation of intermediates of Schiff-base reactions were achieved through reactive desorption electrospray ionization mass spectrometry (reactive DESI-MS). Pure acetone was electrosprayed to impact the aromatic amines on the paper, allowing two reactions, a proton-transfer reaction and a Schiff-base reaction, to occur in these experiments. The former was used to detect the aromatic amines, and the protonated analytes generated were selected for the qualitative and quantitative analysis. The false-positive signals were excluded by tandem mass spectrometry. For the 6 analytes, linear signal responses were obtained, and each had a dynamic range of 5 orders of magnitude. The relative standard deviation (RSD) and limit of detection (LOD) for all the measurements were in 1.5–5.3% and 0.03–0.2pg/mm2 range, respectively. The latter is a nucleophilic addition reaction that occurred between the aromatic amines and the acetone. The carbinolamine intermediates of these reactions were directly detected and identified by reactive DESI-MS. The data show that reactive DESI-MS is not only a reliable, sensitive tool for chemical analysis, but also a valid and promising method for studying organic reactions simultaneously, especially for heterogeneous reactions that occurred at a solution/solid interface.
Highlights
► 6 suspected carcinogenic aromatic amines were qualitatively and quantitatively analyzed without sample pretreatment. ► The intermediates of the heterogeneous Schiff-base reactions were directly observed and identified. ► Acetone was verified to be another choice of the spray solvent of DESI-MS.Assay of high-purity sodium oxalate traceable to the international system of units by coulometric titration and gravimetric titration
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
Sodium oxalate is one of the key reference materials in volumetric analysis. This material and its solution are widely used as a reducing agent and as a standard to standardize oxidizing agents such as potassium permanganate; nevertheless, no certified reference material has been available until recently. The authors challenged purity assay of sodium oxalate basically with Ce(IV) which could accurately be standardized by coulometric titration. This paper describes the accurate determination of sodium oxalate through three different paths: gravimetric titration with Ce(IV) standardized by coulometric titration, gravimetric back titration using excess Ce(IV) and titrant thiosulfate both of which are standardized by coulometric titrations, and gravimetric back titration using excess Ce(IV) and titrant Fe(II) both of which are standardized by coulometric titration and gravimetric titration, respectively. Two kinds of back titrations of excess Ce(IV) mentioned above were carried out to completely proceed with the reaction between oxalate and Ce(IV). The comprehensive evaluation of the uncertainties for sodium oxalate assay was carried out, resulting in the significant improvement of accuracy of oxalate determination. Finally, sodium oxalate whose purity was traceable to the SI was developed as a certified reference material.
Publication year: 2013
Source:Microchemical Journal, Volume 108
Sodium oxalate is one of the key reference materials in volumetric analysis. This material and its solution are widely used as a reducing agent and as a standard to standardize oxidizing agents such as potassium permanganate; nevertheless, no certified reference material has been available until recently. The authors challenged purity assay of sodium oxalate basically with Ce(IV) which could accurately be standardized by coulometric titration. This paper describes the accurate determination of sodium oxalate through three different paths: gravimetric titration with Ce(IV) standardized by coulometric titration, gravimetric back titration using excess Ce(IV) and titrant thiosulfate both of which are standardized by coulometric titrations, and gravimetric back titration using excess Ce(IV) and titrant Fe(II) both of which are standardized by coulometric titration and gravimetric titration, respectively. Two kinds of back titrations of excess Ce(IV) mentioned above were carried out to completely proceed with the reaction between oxalate and Ce(IV). The comprehensive evaluation of the uncertainties for sodium oxalate assay was carried out, resulting in the significant improvement of accuracy of oxalate determination. Finally, sodium oxalate whose purity was traceable to the SI was developed as a certified reference material.
Highlights
► The purity of sodium oxalate was first determined with the linkage to the SI units. ► The determination methods were examined through three different paths. ► The determination methods with the highest accuracy were presented. ► High accuracy of each titration reaction was newly ascertained. ► The measurement methods presented enable analysts to obtain reliable results.Simultaneous determination of quality parameters in biodiesel/diesel blends using synchronous fluorescence and multivariate analysis
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
An analytical method was developed to determine four quality parameters (Biodiesel percentage, Cetane Number, Heat of Combustion Gross and Color) in biodiesel/diesel blends through a simple synchronous fluorescence spectrum of the samples. For this purpose, chemometrics models based on fluorescence spectra and PetroSpect data obtained from mixtures of biodiesel/diesel were built. A variable selection by the successive projections algorithm (SPA) was used in order to obtain simple multiple linear regression (MLR) models based on a small subset of wavelengths. The SPA-MLR results were compared with a partial least squares (PLS) full spectrum regression. The best values found for the root mean square error of prediction using external validation were 0.37% (w/w) for the biodiesel in diesel, 0.5 for cetane number, 0.013MJ/kg for heat of combustion and 0.1 for color.
Publication year: 2013
Source:Microchemical Journal, Volume 108
An analytical method was developed to determine four quality parameters (Biodiesel percentage, Cetane Number, Heat of Combustion Gross and Color) in biodiesel/diesel blends through a simple synchronous fluorescence spectrum of the samples. For this purpose, chemometrics models based on fluorescence spectra and PetroSpect data obtained from mixtures of biodiesel/diesel were built. A variable selection by the successive projections algorithm (SPA) was used in order to obtain simple multiple linear regression (MLR) models based on a small subset of wavelengths. The SPA-MLR results were compared with a partial least squares (PLS) full spectrum regression. The best values found for the root mean square error of prediction using external validation were 0.37% (w/w) for the biodiesel in diesel, 0.5 for cetane number, 0.013MJ/kg for heat of combustion and 0.1 for color.
Highlights
► Chemometric models are useful to determine parameters with a simple synchronous fluorescence spectrum of the fuel sample. ► The proposed method is rapid and inexpensive compared to official methods. ► The quality parameters are fatty acid methyl esters (FAME), cetane number, gross heat of combustion and color.Extraction and detection of organoarsenic feed additives and common arsenic species in environmental matrices by HPLC–ICP-MS
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
Organoarsenic compounds, such as roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) and p-arsanilic acid (ASA), are widely used as animal feed additives, while animal wastes bearing these compounds are often used to fertilize agricultural land, which can cause arsenic pollution of soil, surface water, and groundwater. Determination of a number of inorganic and organic arsenic species in a variety of environmental matrices is necessary to study the environmental fate of organoarsenic feed additives and to assess their risk. A robust analytical method was developed in this work for precise and accurate quantification of ROX, ASA, dimethyl arsenic acid (DMA), monomethyl arsenic acid (MMA), arsenate [As(V)], and arsenite [As(III)] by HPLC–ICP-MS with gradient elution. Extraction conditions for recovering the inorganic and organic arsenic species from soils and sediments were also optimized, and the best results were obtained with 0.5mol·L−1 H3PO4 under constant shaking for 16h. This method was applied in determining the levels of inorganic and organic arsenic species in sediments, soils, and surface water surrounding several swine farms in the Pearl River Delta in southern China and the results showed that the environmental media were already impacted by organoarsenic feed additives.
Publication year: 2013
Source:Microchemical Journal, Volume 108
Organoarsenic compounds, such as roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) and p-arsanilic acid (ASA), are widely used as animal feed additives, while animal wastes bearing these compounds are often used to fertilize agricultural land, which can cause arsenic pollution of soil, surface water, and groundwater. Determination of a number of inorganic and organic arsenic species in a variety of environmental matrices is necessary to study the environmental fate of organoarsenic feed additives and to assess their risk. A robust analytical method was developed in this work for precise and accurate quantification of ROX, ASA, dimethyl arsenic acid (DMA), monomethyl arsenic acid (MMA), arsenate [As(V)], and arsenite [As(III)] by HPLC–ICP-MS with gradient elution. Extraction conditions for recovering the inorganic and organic arsenic species from soils and sediments were also optimized, and the best results were obtained with 0.5mol·L−1 H3PO4 under constant shaking for 16h. This method was applied in determining the levels of inorganic and organic arsenic species in sediments, soils, and surface water surrounding several swine farms in the Pearl River Delta in southern China and the results showed that the environmental media were already impacted by organoarsenic feed additives.
Highlights
► Organoarsenic compounds are widely used as feed additives to animals. ► Unmetabolized organoarsenic feed additives are released into the environment. ► A method was developed to measure these additives and environmental arsenic species. ► Conditions for extracting these As compounds from soils and sediments were optimized. ► The method can help study the environmental distribution and fate of these additives.Optimization and application of headspace liquid-phase microextraction coupled with gas chromatography–mass spectrometry for determination of furanic compounds in coffee using response surface methodology
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
A simple and accurate method for determination of furanic compounds in coffee samples using headspace liquid-phase microextraction (HS-LPME) combined with gas chromatography–mass spectrometry (GC/MS) was developed and validated. In addition to furan, other furanic compounds such as 2-methylfuran, 2,5-dimethylfuran, 2-vinyl furan, 2-(methoxymethyl) furan and furfural were also determined. The effective parameters in HS-LPME process, including ionic strength, stirring rate, temperature and time of extraction process were optimized using response surface methodology (RSM) based on central composite design. The results of optimization study showed that stirring rate, temperature and time of extraction parameters have positive effect on the efficiency of microextraction process but the effect of salt addition on response was negative. The optimal extraction conditions using a quadratic model were: stirring rate 700rpm, extraction temperature 43°C, extraction time 15min and without salt addition. The calibration curves showed good linearity (R2 >0.99) for all the furanic compounds in the range of 0.2–400ngml−1. Repeatability varied from 4.2% to 9.5%. The method accuracy was acceptable with recoveries ranging from 79.6% to 102%. Good enrichment factors were obtained e.g. 1270 for furan. The limits of detection (LOD) and limits of quantification (LOQ) ranged from 0.02 to 10ngg−1 and 0.06 to 39ngg−1, respectively. The comparison of validated method with two other methods for furan analysis showed comparable merit figures and proved the applicability of HS-LPME followed by GC/MS for extraction and determination of furanic compounds in coffee samples.
Publication year: 2013
Source:Microchemical Journal, Volume 108
A simple and accurate method for determination of furanic compounds in coffee samples using headspace liquid-phase microextraction (HS-LPME) combined with gas chromatography–mass spectrometry (GC/MS) was developed and validated. In addition to furan, other furanic compounds such as 2-methylfuran, 2,5-dimethylfuran, 2-vinyl furan, 2-(methoxymethyl) furan and furfural were also determined. The effective parameters in HS-LPME process, including ionic strength, stirring rate, temperature and time of extraction process were optimized using response surface methodology (RSM) based on central composite design. The results of optimization study showed that stirring rate, temperature and time of extraction parameters have positive effect on the efficiency of microextraction process but the effect of salt addition on response was negative. The optimal extraction conditions using a quadratic model were: stirring rate 700rpm, extraction temperature 43°C, extraction time 15min and without salt addition. The calibration curves showed good linearity (R2 >0.99) for all the furanic compounds in the range of 0.2–400ngml−1. Repeatability varied from 4.2% to 9.5%. The method accuracy was acceptable with recoveries ranging from 79.6% to 102%. Good enrichment factors were obtained e.g. 1270 for furan. The limits of detection (LOD) and limits of quantification (LOQ) ranged from 0.02 to 10ngg−1 and 0.06 to 39ngg−1, respectively. The comparison of validated method with two other methods for furan analysis showed comparable merit figures and proved the applicability of HS-LPME followed by GC/MS for extraction and determination of furanic compounds in coffee samples.
Highlights
► A simple method was proposed to determine of furanic compounds from coffee. ► The method is based on HS-SPME combined with GC–MS. ► The effective parameters in HS-LPME were optimized using RSM based on CCD. ► The absence of matrix effect using the HS-LPME has been demonstrated. ► The figures of merit for furans in coffee using the proposed method were perfect.Evaluation of drying conditions of fish tissues for inorganic mercury and methylmercury speciation analysis
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
The influence of drying conditions on the behavior of Hg species (Hg2+ and CH3Hg+) present in fish tissues was evaluated. Drying conditions were evaluated for six fish species using air circulation drying oven in different temperatures (50 to 175°C) and lyophilization (0.25mm Hg, −2°C). Evaluation of drying step was based on losses and conversions of original Hg species after each drying condition. The extraction efficiency was determined by comparing the concentration of total Hg in digested samples (wet digestion in closed system using HNO3) with extracted Hg using l-cysteine solution. Chemical vapor generation-inductively coupled plasma mass spectrometry (CVG-ICP-MS) and liquid chromatography-chemical vapor generation-inductively coupled plasma mass spectrometry (LC-CVG-ICP-MS) were used for the determination of total Hg and Hg species, respectively. The accuracy was evaluated using certified reference materials and an agreement better than 97% with certified values was obtained for CH3Hg+ and total Hg. The relative standard deviation of the proposed method was below 5.5%. Limit of detection of 1.7 and 2.3ngg−1 as Hg was obtained for Hg2+ and CH3Hg+, respectively. Results showed that with drying temperatures above 100°C losses and conversions of CH3Hg+ to Hg2+ can occur for some fish species.
Publication year: 2013
Source:Microchemical Journal, Volume 108
The influence of drying conditions on the behavior of Hg species (Hg2+ and CH3Hg+) present in fish tissues was evaluated. Drying conditions were evaluated for six fish species using air circulation drying oven in different temperatures (50 to 175°C) and lyophilization (0.25mm Hg, −2°C). Evaluation of drying step was based on losses and conversions of original Hg species after each drying condition. The extraction efficiency was determined by comparing the concentration of total Hg in digested samples (wet digestion in closed system using HNO3) with extracted Hg using l-cysteine solution. Chemical vapor generation-inductively coupled plasma mass spectrometry (CVG-ICP-MS) and liquid chromatography-chemical vapor generation-inductively coupled plasma mass spectrometry (LC-CVG-ICP-MS) were used for the determination of total Hg and Hg species, respectively. The accuracy was evaluated using certified reference materials and an agreement better than 97% with certified values was obtained for CH3Hg+ and total Hg. The relative standard deviation of the proposed method was below 5.5%. Limit of detection of 1.7 and 2.3ngg−1 as Hg was obtained for Hg2+ and CH3Hg+, respectively. Results showed that with drying temperatures above 100°C losses and conversions of CH3Hg+ to Hg2+ can occur for some fish species.
Highlights
► Critical evaluation of drying conditions for mercury speciation analysis in fish. ► Dependence of temperature for losses or conversion of mercury species in fish. ► Feasibility of selected drying conditions for further LC-CVG-ICP-MS determination of Hg species.Durability of Nafion-hydrophilic silica hybrid membrane against trace radial species in polymer electrolyte fuel cells
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
Durability of an organic–inorganic nanocomposite electrolyte membrane prepared by mixing hydrophilic fumed silica particles of an average size of 7nm with Nafion ionomer was studied for the mitigation of chemical degradation of the membrane caused by trace radial species in polymer electrolyte fuel cells (PEFCs). Infrared (IR) spectroscopy indicated that the peak of C−F, S−O and C−O−C bands were not shifted to the higher wavenumber with an addition of 1wt.% hydrophilic silica to the Nafion matrix. This suggests that hydrophilic silica had a catalyst activity for the decomposition of hydrogen peroxide and reduced the membrane degradation by trace radicals attack. Quantum chemical calculations (QCCs) using a model ionomer of trifluoromethanesulfonate (TFMS) and a model nanoparticle of Si(OH)4 also implied that the nanoparticle was able to trap H, OH and OOH radical species before attacking the ionomer. The hydration of TFMS that induces deprotonation of sulfonic acid group in TMFS and formation of hydronium anion was confirmed also in the presence of trace radicals due to the ability of Si(OH)4 to trap H radical.
Publication year: 2013
Source:Microchemical Journal, Volume 108
Durability of an organic–inorganic nanocomposite electrolyte membrane prepared by mixing hydrophilic fumed silica particles of an average size of 7nm with Nafion ionomer was studied for the mitigation of chemical degradation of the membrane caused by trace radial species in polymer electrolyte fuel cells (PEFCs). Infrared (IR) spectroscopy indicated that the peak of C−F, S−O and C−O−C bands were not shifted to the higher wavenumber with an addition of 1wt.% hydrophilic silica to the Nafion matrix. This suggests that hydrophilic silica had a catalyst activity for the decomposition of hydrogen peroxide and reduced the membrane degradation by trace radicals attack. Quantum chemical calculations (QCCs) using a model ionomer of trifluoromethanesulfonate (TFMS) and a model nanoparticle of Si(OH)4 also implied that the nanoparticle was able to trap H, OH and OOH radical species before attacking the ionomer. The hydration of TFMS that induces deprotonation of sulfonic acid group in TMFS and formation of hydronium anion was confirmed also in the presence of trace radicals due to the ability of Si(OH)4 to trap H radical.
Highlights
► Decomposition test is applied by immersing Nafion in hydrogen peroxide at 80°C for 0, 1, 4 and 8h. ► Vibrational frequencies and IR intensities show Nafion/Aerosil 380 (1 wt.%) is better for chemical durability. ► Using DFT to study the mechanism of durability by calculating the optimization structure and energies. ► Si(OH)4 as a model of hydrophilic silica acts as radical scavenger for H·, ·OH and ·OOH. ► The entropy of Si(OH)4 to make a conjugation with H·, ·OH and ·OOH is 0.092, 0.134, 0.130kJ·mol−1·K−1, respectively.Vanadium fractions determination in asphaltite combustion waste using sequential extraction with ICP-OES
05 February 2013,
10:07:08
May 2013
Publication year: 2013
Source:Microchemical Journal, Volume 108
Asphaltite derives from petroleum origin solid fossil fuel. It contains many elements in different forms which may change during combustion process. A true understanding of the dynamics of elements in the natural environment requires an expanded knowledge of its oxidation–reduction cycling. This study presents a sequential extraction method for the fractionation of vanadium (V) from asphaltite combustion waste (ACW) in seven forms (water soluble, exchangeable, carbonate, reducible, oxidizable, sulfide, and residual) and their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The 292.464nm line was used because it offers better detectability and was free from major spectral interferences. Two-stage microwave acid digestion was used to preparation of samples. Total V concentration in the ACW is 546.15mgkg−1 dry weight (d.w). The most abundant vanadium in studied ACW sample was found as sulfide fraction of V (307.50mgkg−1d.w.). Relative abundances of the remaining V fractions in ACW are as follows: Oxidizable (86.19mgkg−1d.w.)>reducible (64.18mgkg−1d.w.)>carbonate (32.79mgkg−1 d.w.)>residual (32.18mgkg−1d.w.)>exchangeable (14.25mgkg−1d.w.)>water soluble (9.04mgkg−1d.w.). The results were found to be in good agreement with the certified value. The advantages of the technique include a high degree of automation, good reproducibility, and short analysis time and thus make it the method of choice for the fractionation of V.
Publication year: 2013
Source:Microchemical Journal, Volume 108
Asphaltite derives from petroleum origin solid fossil fuel. It contains many elements in different forms which may change during combustion process. A true understanding of the dynamics of elements in the natural environment requires an expanded knowledge of its oxidation–reduction cycling. This study presents a sequential extraction method for the fractionation of vanadium (V) from asphaltite combustion waste (ACW) in seven forms (water soluble, exchangeable, carbonate, reducible, oxidizable, sulfide, and residual) and their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The 292.464nm line was used because it offers better detectability and was free from major spectral interferences. Two-stage microwave acid digestion was used to preparation of samples. Total V concentration in the ACW is 546.15mgkg−1 dry weight (d.w). The most abundant vanadium in studied ACW sample was found as sulfide fraction of V (307.50mgkg−1d.w.). Relative abundances of the remaining V fractions in ACW are as follows: Oxidizable (86.19mgkg−1d.w.)>reducible (64.18mgkg−1d.w.)>carbonate (32.79mgkg−1 d.w.)>residual (32.18mgkg−1d.w.)>exchangeable (14.25mgkg−1d.w.)>water soluble (9.04mgkg−1d.w.). The results were found to be in good agreement with the certified value. The advantages of the technique include a high degree of automation, good reproducibility, and short analysis time and thus make it the method of choice for the fractionation of V.
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