In Situ Transesterification from Soybean Seed Using Mechanochemical Methods toward Producing Biodiesel.

The research and development of new routes of biodiesel synthesis have been increasingly in line with the principles of green chemistry. In this sense, mechanochemistry is a promising technique, able to ally the energetic potential with reductions in the use of solvents and steps of treatment of the sample and the purification of the product. To date, this is the first work using mechanochemistry directly in extracting soybean oil from its seed and the in situ transesterification reaction by applying a reactive soybean oil extraction process. The presence of n-hexane was studied in different molar proportions (relative to the oil content), and a low solvent consumption in a 3:1 ratio was adopted. Mechanochemistry favored oil diffusion in the n-hexane solvent, resulting in a mean triglyceride content equal to 90%, against 66% obtained in the tests without spheres in the planetary ball mill. The catalyst content was also evaluated, and 4% NaOH (weight, concerning the oil) was the concentration that presented less residue of nontransesterified glycerides in the samples for ethyl ester preparation. Additionally, the protein content was determined on the residual soybean cake, with no loss of nutritional potential when subjected to the mechanochemical process.

Application of two- and multiway chemometric strategies for describing elementomic changes in pepper plants exposed to cadmium stress by multielement determination.

The objective of this work was to evaluate elemental changes in pepper exposed to Cd stress through different chemometric tools. For this purpose, pepper plants were grown under five different treatments with different Cd concentrations in the nutrient solution. Considering the hypothesis that pepper plants exposed to Cd stress during growth undergo changes in the macro- and microelemental distribution in leaves, stems, and roots, principal component analysis (PCA) and parallel factor (PARAFAC) analysis were applied to compare bidirectional and multivariate chemometric strategies to assess elemental changes in pepper plants. Since the number of variables and the data generated were large and complex, the application of chemometric tools was justified to facilitate the visualization and interpretation of results. The mineral composition, namely the Ca, Cd, Cu, Fe, K, Mg, Mn, N, and P contents, was assessed in 180 samples of leaves, stems, and roots of the cultivated peppers. Then, PCA and PARAFAC analysis were applied to compare bidirectional and multivariate chemometric strategies to assess elemental changes throughout pepper plants. The visualization of the trend on each sample and their intrinsic relationship with the variables were possible with the application of PCA. The use of PARAFAC analysis permitted the simultaneous study of all samples in a straightforward representation of the information that facilitated a quick and comprehensive understanding of the spatial distribution of elements in plants. Thus, macroelements (Ca, K, Mg, N, and P) that were found in higher concentrations in leaves did not present significant differences in the distribution along the plants under different treatment conditions. In contrast, a significant impact on the microelement (Cu, Fe, and Mn) distribution was produced between uncontaminated and contaminated samples. This analysis revealed a significant accumulation of Cd in roots and adverse effects on normal plant growth, demonstrating their level of phytotoxicity to pepper.

Evaluation of slurry sampling preparation of enteral nutrition formulations for multielement determination using inductively coupled plasma optical emission spectrometry.

An analytical procedure for the multielement determination in enteral nutrition formulations employing slurry sampling and inductively coupled plasma optical emission spectrometry (ICP OES) is proposed. A two-level full-factorial design was applied to assess the influence of the presence of stabilizing agents (HNO3, Triton X-100 and ethanol) on the composition of the slurry. Multiple response was established as a dependent variable. The experimental conditions for the preparation of the slurry were: 2.0 mL of sample and 8.0 mL of 10% (v/v) HNO3. The limits of detection (LOD) were 5; 9; and 10 µg L-1 for Cu, Fe, Zn, respectively. For P, and K, the LOD were 8 and 24 mg L-1, respectively. The method was applied for the analysis of three enteral nutrition formulation samples and the obtained concentrations ranges were (in mg L-1): 0.41-0.43 (Cu), 2.0-2.9 (Fe), 1.7-3.1 (Zn), 682-1409 (K), and 217-344 (P).

Multi-element determination in chocolate bars by microwave-induced plasma optical emission spectrometry.

Macro- and microelement determination in chocolate bars by microwave-induced plasma optical emission spectrometry (MIP OES) was evaluated after microwave-assisted sample digestion. Optimization of the sample digestion was carried out, and the recommended conditions were obtained at a temperature of 190 °C, with a digestion time of 40 min and in a mixture constituted by 2.3 mL of nitric acid, 1.0 mL of hydrogen peroxide and 4.7 mL of water. The method was applied in the analysis of chocolate bars, and the concentration ranges of the elements determined were (in mg kg-1): Ca (653-3096); Cr (<0.6-2.8); Cu (<0.16-19.5); Fe (<1.6-227); Mg (147-2775); K (3554-8573); Mn (<0.03-25.2); Na (45.6-1095); Ni (3.2-10.2); P (1111-22594) and Zn (4.8-33.3). The association of the proposed microwave-assisted acid digestion with the MIP OES technique was adequate for multi-element determination in chocolate bars for routine analysis.

Determination of Cu, Ni, Mn and Zn in diesel oil samples using energy dispersive X-ray fluorescence spectrometry after solid phase extraction using sisal fiber.

As a natural adsorbent, sisal (agave sisalana) fibers were used to extract Cu, Ni, Mn, and Zn from diesel oil samples for posterior determination (i.e., direct analytical measurements on the solid support) of the analytes by energy dispersive X-ray fluorescence spectrometry (EDXRF). In the proposed procedure, 0.2 g of sisal fiber was directly added to 5.0 mL of diesel oil contained in a glass tube. After 5 min of contact time, the mixture was filtered, and the collected fibers were oven-dried for 30 min at 70 °C. After drying, the analytes were quantified directly by EDXRF using the sisal fibers as a solid support. The calibration curves showed linear concentration ranges of 0.09-1.00, 0.12-1.00, 0.09-1.00, 0.06-1.0 µg g-1 for Cu, Ni, Mn, and Zn, respectively. The limits of detection (LOD) for Cu, Ni, Mn, and Zn were 0.03, 0.04, 0.03, and 0.02 µg g-1, respectively. The repeatability, evaluated by performing ten measurements at a concentration of 0.50 µg g-1 for each metal, with the results expressed in terms of the relative standard deviation (RSD), was 3.2, 6.5, 6.8, and 6.1% for Cu, Ni, Mn, and Zn, respectively. The results obtained by the proposed method were compared with the results obtained by a comparative method using inductively coupled plasma optical emission spectrometry, and both results showed good agreement. The proposed method was applied for Ni, Cu, Mn, and Zn determination in diesel oil samples collected from different gas stations.

Determination of Cu, Ni, Mn, and Pb in diesel oil samples using reversed-phase vortex-assisted liquid-liquid microextraction associated with energy dispersive X-ray fluorescence spectrometry.

A method was developed based on reversed-phase vortex-assisted liquid-liquid microextraction (RP-VALLME) combined with energy dispersive X-ray fluorescence (EDXRF) spectrometry for the determination of Cu, Mn, Ni, and Pb in diesel oil samples. In this procedure, a nitric acid solution was used as the extraction phase to isolate analytes from organic samples. After a centrifugation step, the aqueous phase was added dropwise to a filter paper disc for EDXRF determinations. The following variables were optimized: type of extraction phase solution, concentration of the extraction phase, stirring time, and sample volume. Some instrumental parameters were also evaluated: atmospheric condition, irradiation energy, and irradiation time. Using 100 µL of a 0.075 mol L-1 nitric acid solution as the extraction phase for a sample volume of 5.0 mL and a stirring time of 45 s, the limits of detection were 14, 8, 10, and 7 µg L-1 for Cu, Mn, Ni, and Pb, respectively. The enrichment factors obtained were 34 (Cu), 62 (Mn), 59 (Ni), and 64 (Pb). The precisions, expressed as relative standard deviations (RSDs, %), were calculated from ten replications of the experiment under optimized conditions using standard solutions containing 200 µg L-1 and 400 µg L-1 of all four analytes and ranged between 2.1 and 6.4%. The results of recovery tests ranged from 87 to 112%. The proposed procedure was efficiently applied to the determination of the four analytes in diesel oil samples. The results were compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) after sample digestion, and no significant differences were found.

D-optimal mixture design for the optimization of extraction induced by emulsion breaking for multielemental determination in edible vegetable oils by microwave-induced plasma optical emission spectrometry.

A sample pretreatment based on an extraction process by emulsion breaking for multi-element determination in edible oils was developed. The determination of eight trace elements (Al, Ba, Cu, Cr, P, Ni, Ti, and Zn) was carried out by microwave-induced plasma optical emission spectrometry (MIP OES) after the extraction procedure. A D-optimal mixture experimental design was used to obtain the best experimental conditions for the extraction induced by emulsion breaking (EIEB). The proportion of HNO3 solution, Triton X-100 solution and sample was evaluated in a multivariate manner. The best recovery efficiency was obtained with 1.0 mL of 30% (v/v) HNO3, 1.0 mL of 30% (w/v) Triton-X 100 and 3.0 mL of the sample. The precisions, established as the relative standard deviation (RSD, %), were better than 2.5% for all analytes. The developed method was applied to the analysis of commercial vegetable oils with low limits of detection and good precision.

Assessing the internal standardization of the direct multi-element determination in beer samples through microwave-induced plasma optical emission spectrometry.

An evaluation of different elements (Be, Ga, In, Sc, and Y) as internal standards was performed to determine the content of Al, Ba, Co, Cr, Cu, Fe, Mn, Ni, Sr, Zn, Ca, Mg, Na, K in beer samples through microwave induced plasma optical emission spectrometry. The analytes were determined after simple dilutions of the samples with a 1.0 M nitric acid solution at a 1:4 ratio (sample: acid solution) with the addition of the IS. The analytical performance for each potential IS was established based on the limit of detection, limit of quantification, addition and recovery tests and accuracy obtained in the determination of each analyte. Each analyte responded differently when internal standardization was applied, and as such, the evaluation of each IS is important in the development of the method. In the presence of the recommended internal standard, the limit of detection varied, in µg L-1, from 0.23 to 4.6 for the microelements and between 10 and 620 for the macroelements. The limit of quantification, in µg L-1, was between 0.78 and 15.4 and between 30 and 970 for the microelements and macroelements, respectively. The precisions of the measurements, expressed as the relative standard deviation (n = 10; 0.50 and 3.0 mg L-1 of each analyte), were lower than 1.0% for all analytes. The proposed method was applied for the multi-element determination in commercial beer samples and the results were compared with those obtained by inductively coupled plasma optical emission spectrometry after sample digestion.

Multiple response optimization of alkaline pretreatment of sisal fiber (Agave sisalana) assisted by ultrasound.

A procedure for the alkaline pretreatment of sisal fiber assisted by ultrasound was optimized to obtain a higher solubilization of hemicellulose and the removal of lignin with cellulose fraction maintenance. A full factorial design 23 was used for the evaluation of the effects of the variables (sonication time, NaOH concentration, and sonication amplitude) on the pretreatment. The optimal values for the variables using the Doehlert matrix for the sonication time, NaOH concentration, and sonication amplitude were 27 min, 4.1% (m/v), and 50%, respectively. The X-ray diffractometry and scanning electron microscopy analyses, after pretreatment, showed changes in chemical structure and morphology due to the removal of 82% of hemicellulose and 86% of lignin from sisal fiber. The soft reaction conditions and relatively short times demonstrated the effectiveness of the combined action of ultrasound with alkaline pretreatment to improve the accessibility to cellulose in this important step of the ethanol production process from biomass.

Multivariate optimization of ultrasound-assisted extraction using Doehlert matrix for simultaneous determination of Fe and Ni in vegetable oils by high-resolution continuum source graphite furnace atomic absorption spectrometry.

A method for simultaneous determination of Fe (232.036 nm) and Ni (232.195 nm) in vegetable oil samples by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) after an acid extraction of the analytes is proposed. In the extraction step, hydrochloric, nitric and acetic acid solutions were tested. The optimization of the procedure was performed by applying Doehlert matrix, and multiple response was used for simultaneous evaluation of the performance of the extraction. The optimum conditions were: extraction time of 17 min, extraction temperature of 39 °C and sonication amplitude of 42%, employing 0.5 mol L-1 HCl as the extracting solvent. The limits of quantification were 60 and 160 ng g-1 for Fe and Ni, respectively. The method was applied to the analysis of vegetable oil samples and the results were compared with a method employing inductively coupled plasma optical emission spectrometry (ICP OES).

Multivariate data analysis of trace elements in bivalve molluscs: Characterization and food safety evaluation.

Four species of bivalve molluscs (Anomalocardia brasiliana, Iphigenia brasiliana, Lucina pectinata and Trachycardium muricatum) were collected in the Todos os Santos Bay (TSB), Bahia, Brazil, in order to evaluate As, Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Se, V and Zn levels and, consequently, the risk of bivalve mollusc consumption in humans. The samples were analyzed by inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) after closed-vessel microwave digestion. The accuracy was confirmed using the certified reference materials of oyster tissue (NIST 1566b) and mussel tissue (NIST 2977), and the results were statistically equivalent to the certified values. Application of principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a tendency to form two groups between samples of Lucina pectinata and Trachycardium muricatum. All species showed As and Cr concentrations higher than the maximum tolerable limit specified in Brazilian legislation.

Determination of phospholipids in soybean lecithin samples via the phosphorus monoxide molecule by high-resolution continuum source graphite furnace molecular absorption spectrometry.

This paper presents a method for determining phospholipids in soybean lecithin samples by phosphorus determination using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) via molecular absorption of phosphorus monoxide. Samples were diluted in methyl isobutyl ketone. The best conditions were found to be 213.561nm with a pyrolysis temperature of 1300°C, a volatilization temperature of 2300°C and Mg as a chemical modifier. To increase the analytical sensitivity, measurement of the absorbance signal was obtained by summing molecular transition lines for PO surrounding 213nm: 213.561, 213.526, 213.617 and 213.637nm. The limit of detection was 2.35mgg-1 and the precision, evaluated as relative standard deviation (RSD), was 2.47% (n=10) for a sample containing 2.2% (w/v) phosphorus. The developed method was applied for the analysis of commercial samples of soybean lecithin. The determined concentrations of phospholipids in the samples varied between 38.1 and 45% (w/v).

Multivariate optimization of ultrasound-assisted extraction for determination of Cu, Fe, Ni and Zn in vegetable oils by high-resolution continuum source atomic absorption spectrometry.

An assisted liquid-liquid extraction of copper, iron, nickel and zinc from vegetable oil samples with subsequent determination by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was optimized by applying a full factorial design in two levels and the response surface methodology, Box-Behnken. The effects of the acid concentration and the amplitude, cycle and time of sonication on the extraction of the analytes, as well as their interactions, were assessed. In the selected condition (sonication amplitude = 66%, sonication time = 79 s, sonication cycle = 74%), using 0.5 mol L(-1) HCl as the extractant, the limits of quantification were 0.14, 0.20, 0.21 and 0.04 µg g(-1) for Cu, Fe, Ni and Zn, respectively, with R.S.D. ranging from 1.4% to 3.6%. The proposed method was applied for the determination of the analytes in soybean, canola and sunflower oils.

Determination of cadmium in biodiesel using microemulsion and electrothermal atomization atomic absorption spectrometry.

This work aimed to prepare biodiesel microemulsions for the subsequent quantification of cadmium via graphite furnace atomic absorption spectrometry (GFAAS). The biodiesel samples were prepared using n-propanol as an emulsifier, 10% (v/v) nitric acid as the aqueous phase, and biodiesel. Pseudoternary phase diagrams were constructed to determine the microemulsion region with the specified components. The optimized conditions for microemulsion formation were 57.6% (v/v) n-propanol, 21.2% (v/v) biodiesel, and 21.2% (v/v) nitric acid solution. The stability of the microemulsified system was investigated using aqueous and organic standards, and the system was found to be stable for at least 240 min. The applied pyrolysis and atomization temperatures were 800 and 2000 °C, respectively, and 5 µg of aluminum was used as the chemical modifier. The obtained limits of detection and quantification were 0.2 and 0.5 µg kg(-1), respectively, and the characteristic mass was 1.6 pg. The precision, expressed as the relative standard deviation (% R.S.D., n = 10), was 2.5% for a sample with a cadmium concentration of 6.5 µg kg(-1). The accuracy was determined from addition and recovery experiments, with results varying from 93 to 108% recovery. This study demonstrates that the proposed method based on the use of a microemulsion formation in sample preparation can be applied as an efficient alternative for the determination of cadmium in biodiesel by GFAAS. Cadmium determination in biodiesel samples of different origins (soybean, corn, cotton, and sunflower) was evaluated after acid digestion using the inductively coupled plasma-mass spectrometry (ICP-MS) technique, and the obtained results were compared to the results obtained using the proposed method. The paired t test (95% confidence level) did not show significant differences. The concentrations of cadmium found ranged from 5.3 to 8.0 µg kg(-1).

Multi-element determination of Cu, Fe, Ni and Zn content in vegetable oils samples by high-resolution continuum source atomic absorption spectrometry and microemulsion sample preparation.

The aim of this work was to evaluate the microemulsification as sample preparation procedure for determination of Cu, Fe, Ni and Zn in vegetable oils samples by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry (HR-CS FAAS). Microemulsions were prepared by mixing samples with propan-1-ol and aqueous acid solution, which allowed the use of inorganic aqueous standards for the calibration. To a sample mass of 0.5g, 100µL of hydrochloric acid and propan-1-ol were added and the resulting mixture diluted to a final volume of 10mL. The sample was manually shaken resulting in a visually homogeneous system. The main lines were selected for all studied metals and the detection limits (3σ, n=10) were 0.12, 0.62, 0.58 and 0.12mgkg(-1) for Cu, Fe, Ni and Zn, respectively. The relative standard deviation (RSD) ranged from 5% to 11 % in samples spiked with 0.25 and 1.5µgmL(-1) of each metal, respectively. Recoveries varied from 89% to 102%. The proposed method was applied to the determination of Cu, Fe, Ni and Zn in soybean, olive and sunflower oils.

Uranium determination using atomic spectrometric techniques: an overview.

This review focuses on the determination of uranium using spectroanalytical techniques that are aimed at total determination such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma optical emission spectrometry (ICP-OES); and inductively coupled plasma mass spectrometry (ICP-MS) that also enables the determination of uranium isotopes. The advantages and shortcomings related to interferences, precision, accuracy, sample type and equipment employed in the analysis are taken into account, as well as the complexity and costs (i.e., acquisition, operation and maintenance) associated with each of the techniques. Strategies to improve their performance that employ separation and/or preconcentration steps are considered, with an emphasis given to solid-phase extraction because of its advantages compared to other preconcentration procedures.

Indirect determination of chloride and sulfate ions in ethanol fuel by X-ray fluorescence after a precipitation procedure.

This paper proposes an alternative analytical method using energy dispersive X-ray fluorescence (EDXRF) to determine chloride and sulfate ions in ethanol fuel samples after precipitation procedure. The preconcentration methodology involved the precipitation of the analytes as silver chloride and barium sulfate followed by filtration through a paper filter, which demonstrated to be a convenient substrate for EDXRF measurements. The elements were determined directly on the filters using silver and barium lines for the indirect determination of chloride and sulfate ions, respectively. The precisions calculated from 20 consecutive measurements and defined as the coefficient of variation of standard solutions containing 1.0 microg mL(-1) of Cl(-) and SO(4)(2-) were 7.3% and 5.9%, respectively. The limits of detection (LOD), defined as the analyte concentration that gives a response equivalent to three times the standard deviation of the blank (n=10), were found to be 25 microg L(-1) and 30 microg L(-1) for Cl(-) and SO(4)(2-), respectively. The proposed method was applied to chloride and sulfate ions determination in hydrated ethanol fuel samples collected from different gas stations.

A green analytical procedure for sensitive and selective determination of iron in water samples by flow-injection solid-phase spectrophotometry.

A greener analytical procedure based on flow-injection solid-phase spectrophotometry is proposed for iron determination. Iron(II) is reversibly retained on 1-(2-thiazolylazo)-2-naphthol immobilized on C18-bonded silica, yielding a brown complex. The metal ion is eluted as iron(II) with a small volume of a diluted acid solution without removing the immobilized reagent, which can be used for at least 100 determinations. Other chemicals (buffer and reducing agent) were carefully selected taking into account the analytical performance and toxicity. The developed procedure is 10-fold more sensitive in comparison to the analogous procedure based on measurements in solution, being suitable for the determination of iron in water samples with good accuracy and precision. The detection limit (99.7% confidence level), sampling rate and coefficient of variation (n=10) were estimated as 15mugL(-1), 25 measurements per hour and 4.0%, respectively. The proposed procedure involves a reduced effluent generation (3.6mL per determination) and consumes micro amounts of reagents.

Simultaneous determination of copper and iron in automotive gasoline by X-ray fluorescence after pre-concentration on cellulose paper.

This paper proposes an alternative analytical method using energy dispersive X-ray fluorescence (EDXRF) to determine Fe and Cu in gasoline samples. In the proposed procedure, samples were distilled and the distillation residues were spotted on cellulose paper disk to form a uniform thin film and to produce a homogeneous and reproducible interface to the XRF instrument. The disks were dried at 60 degrees C for 20min and copper and iron were determined directly in the solid phase at 6.40 and 8.04keV, respectively. The calibration curves showed linear response in the 20-800mugL(-1) concentration range of each metal. The precisions (repeatability) calculated from 15 consecutive measurements and defined as the coefficient of variation of solutions containing 100mugL(-1) of Fe and Cu were 7.8 and 8.1%, respectively. The limits of detection (LOD), defined as the analyte concentration that gives a response equivalent to three times the standard deviation of the blank (n=10), were found to be 10 and 15mugL(-1) for Fe and Cu, respectively. The proposed method was applied to copper and iron determination in gasoline samples collected from different gas stations.