Greening microwave-assisted acid digestion of animal feeding samples

Nowadays it is well-established that microwave-assisted digestion of organic matrices can be efficiently performed in closed vessels using dilute nitric acid solutions. In this work microwave-assisted sample preparation procedures compatible with green chemistry recommendations were developed for grains and cereals used to raise swine. Digestion efficiency was evaluated by determining the residual carbon content, which was lower than 3.5%. Residual acidity was also evaluated and was lower than 0.65 mol L−1. Calcium, Co, Cu, Fe, K, Mg, Mn, Mo, Na, P, Sr, and Zn were determined using either ICP OES or ICP MS depending on respective concentrations. Certified reference materials were evaluated and most determined concentrations were between 80 and 120% compared to certified values. Finally, after analytical measurements an apparatus for recovering nitric acid by sub-boiling distillation was used. To the best of our knowledge, this is the first application of sub-boiling distillation for recovering nitric acid of digests. Then, the purified acid could be reused in further digestions. This is a promising alternative for increasing the green chemistry attributes of trace inorganic analysis. The combination of these strategies, i.e. dilute nitric acid digestion followed by recovery of the acid digests, represents steps towards green chemistry approaches: “reduce the use, recycle and reuse”, strictly following the major green chemistry recommendations.Fil: Savio, Marianela. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Fialho, Lucimar L.. Universidade Federal do São Carlos; BrasilFil: Nobrega, Joaquim A.. Universidade Federal do São Carlos; Brasi

Exploiting Mn(III)/EDTA complex in a flow system with solenoid micro-pumps coupled to long pathlength spectrophotometry for fast manganese determination

The formation of the Mn(III)/EDTA complex in a flow system with solenoid micro-pumps was exploited for fast manganese determination in freshwater. Manganese(II) was oxidized in a solid-phase reactor containing lead dioxide immobilized on polyester. Long pathlength spectrophotometry was exploited to increase sensitivity, aiming to reach the threshold limit established by environmental legislation. A linear response was observed from 25 to 1500 mu g L(-1), with a detection limit of 6 mu g L(-1) (99.7% confidence level). Sample throughput and coefficient of variation were 36 samples/h and 2.6% (n = 10), respectively. EDTA consumption and waste generation were estimated as 500 mu g and 3 mL per determination, respectively. The amount of Pb in the residue corresponds to 250 mu g per determination and a solid-phase reactor could be used for up to 1600 determinations. Adsorption in active charcoal avoided interferences caused by organic matter and the developed procedure was successfully applied for determination of manganese in freshwater samples. Results were in agreement with those attained by GFAAS at the 95% confidence level. (C) 2010 Elsevier B.V. All rights reserved.FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)[2008/01045-0]CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico)INCTAA (INCT-MCT/CNPq)[573894-2008-6

ASSESSMENT of POLYATOMIC INTERFERENCES ELIMINATION USING A COLLISION REACTION INTERFACE (CRI) FOR INORGANIC ANALYSIS of FUEL ETHANOL BY ICP-QMS

The effectiveness of a collision-reaction interface (CRI) as instrumental device and the addition of oxygen in the composition of auxiliary gas were evaluated to minimize polyatomic species generated in plasma gas caused by direct introduction of fuel ethanol samples through spray chambers in inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The oxygen flow-rate was optimized as a compromise among signal counts, signal to background ratio (SBR), and background equivalent concentration (BEC). For 12.5mL min(-1) O-2, ethanol samples diluted 20 times were introduced into the plasma and deposits of carbon compounds on the sampler and/or skimmer cones were not observed. The performance of CRI using H-2 and He inserted through the sampler or skimmer cones was evaluated. Hydrogen gas added through the skimmer cone was more efficient to reduce blank and BEC values. This strategy was necessary to eliminate spectral interferences caused by (Ar12C+)-Ar-40, Ar-40(16) O+, (CO+)-C-12-O-16, C-12(2)+ at isotopes Cr-52(+), Fe-56(+), Si-28(+) and Mg-24(+), respectively. Using matrix-matching calibration and Y internal standard, the optimized method was applied to the determination of Al, Ba, Co, Cr, Cu, Fe, Mg, Mn, Mo, Na, Ni, Pb, Sb, Si, V, and Zn in fuel ethanol. Accuracy of developed method was checked after addition/recovery tests. Recoveries and RSD (n = 12) for all elements varied within the 78-114% and 0.4-2% ranges, respectively. Limits of detection for all elements obtained by combining CRI and ICP-QMS were always better than 0.80 mu g L-1 except for Si at 14 mu g L-1.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Direct determination of iron in sand using solid sampling graphite furnace atomic absorption spectrometry

A fast and reliable method for the direct determination of iron in sand by solid sampling graphite furnace atomic absorption spectrometry was developed. A Zeeman-effect 3-field background corrector was used to decrease the sensitivity of spectrometer measurements. This strategy allowed working with up to 200 mu g of samples, thus improving the representativity. Using samples with small particle sizes (1-50 mu m) and adding 5 mu g Pd as chemical modifier, it was possible to obtain suitable calibration curves with aqueous reference solutions. The pyrolysis and atomization temperatures for the optimized heating program were 1400 and 2500 degrees C, respectively. The characteristic mass, based on integrated absorbance, was 56 pg, and the detection limits, calculated considering the variability of 20 consecutive measurements of platform inserted without sample was 32 pg. The accuracy of the procedure was checked with the analysis of two reference materials (IPT 62 and 63). The determined concentrations were in agreement with the recommended values (95% confidence level). Five sand samples were analyzed, and a good agreement (95% confidence level) was observed using the proposed method and conventional flame atomic absorption spectrometry. The relative standard deviations were lower than 25% (n = 5). The tube and boat platform lifetimes were around 1000 and 250 heating cycles, respectively

Determination of Ca, Mg, and Zn in biodiesel microemulsions by FAAS using discrete nebulization

In this work an analytical procedure was developed for calcium, magnesium, and zinc determination in biodiesel samples using flame atomic absorption spectrometry based on microemulsion formation for sample preparation and discrete aspiration for sample introduction. The microemulsions were composed by biodiesel, Triton X-100, HNO3 20% (v v (1)), and n-propanol 10:5:5:80 (v v (1)). External calibration was carried out employing inorganic standards and light mineral oil was used for simulating the matrix of biodiesel samples. Relative standard deviations (RSD) were lower than 4.0%, 2.2% and 5.7% (n = 10) for Ca, Mg and Zn, respectively. Matrix effects were not observed when the standard additions method was applied. Sensitivities by using discrete aspiration for Ca, Mg and Zn were 2.5, 6.1, and 7.0-fold, respectively, better than those obtained when employing conventional continuous aspiration. Accuracy was checked by addition and recovery experiments for different types of biodiesel samples (African oil palm, castor beans, palm, and soybeans), and recoveries ranged from 90.8% to 115%. (C) 2011 Elsevier Ltd. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Evaluation of the use of multiple lines for determination of metals in water by inductively coupled plasma optical emission spectrometry with axial viewing

Inductively coupled plasma optical emission spectrometers (ICP DES) allow fast simultaneous measurements of several spectral lines for multiple elements. The combination of signal intensities of two or more emission lines for each element may bring such advantages as improvement of the precision, the minimization of systematic errors caused by spectral interferences and matrix effects. In this work, signal intensities for several spectral lines were combined for the determination of Al, Cd, Co, Cr, Mn, Pb, and Zn in water. Afterwards, parameters for evaluation of the calibration model were calculated to select the combination of emission lines leading to the best accuracy (lowest values of PRESS-Predicted error sum of squares and RMSEP-Root means square error of prediction). Limits of detection (LOD) obtained using multiple lines were 7.1, 0.5, 4.4, 0.042, 3.3, 28 and 6.7 mu g L(-1) (n = 10) for Al, Cd. Co, Cr, Mn, Pb and Zn, respectively, in the presence of concomitants. On the other hand, the LOD established for the most intense emission line were 16. 0.7, 8.4, 0.074. 23, 26 and 9.6 mu g L(-1) (n = 10) for these same elements in the presence of concomitants. The accuracy of the developed procedure was demonstrated using water certified reference material. The use of multiple lines improved the sensitivity making feasible the determination of these analytes according to the target values required for the current environmental legislation for water samples and it was also demonstrated that measurements in multiple lines can also be employed as a tool to verify the accuracy of an analytical procedure in ICP DES. (C) 2009 Elsevier B.V. All rights reserved

Determination of macro- and micronutrients in plant leaves by high-resolution continuum source flame atomic absorption spectrometry combining instrumental and sample preparation strategies

A method for determination of B, Ca, Cu, Fe, K, Mg, Mn, Mo, P. S and Zn in plant tissues by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) is proposed. This method is based on special features of HR-CS-AAS, such as side pixel registration, wavelength integrated absorbance, and molecular absorption bands, for determining macro- and micronutrients in foliar analysis without requiring several different strategies for sample preparation and adjustment of the analytes concentration ranges. Plant samples were analyzed and results for certified materials were in agreement at a 95% confidence level (paired t-test) with reference values. Recoveries of analytes added to plant digests varied within the 82-112% interval. Relative standard deviations (n = 12) were lower than or equal to 5.7% for all analytes in all concentration ranges. (C) 2010 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Cloud point extraction to avoid interferences by structured background on nickel determination in plant materials by FAAS

An analytical procedure based on microwave-assisted digestion with diluted acid and a double cloud point extraction is proposed for nickel determination in plant materials by flame atomic absorption spectrometry. Extraction in micellar medium was successfully applied for sample clean up, aiming to remove organic species containing phosphorous that caused spectral interferences by structured background attributed to the formation of PO species in the flame. Cloud point extraction of nickel complexes formed with 1,2-thiazolylazo-2-naphthol was explored for pre-concentration, with enrichment factor estimated as 30, detection limit of 5 mu g L(-1) (99.7% confidence level) and linear response up to 80 mu g L(-1). The accuracy of the procedure was evaluated by nickel determinations in reference materials and the results agreed with the certified values at the 95% confidence level.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP

Direct analysis of biodiesel microemulsions using an inductively coupled plasma mass spectrometry

An analytical procedure for direct introduction of biodiesel samples into an inductively coupled plasma mass spectrometer (ICP-MS) by using microemulsion for sample preparation was developed here. Cadmium, Co, Cu, Mn, Ni, Pb, Ti, and Zn were determined in biodiesel microemulsified samples prepared from different oleaginous sources (African palm, castor beans, palm, soybeans and an unknown oleaginous). Microemulsions were prepared using 0.25 mL Triton X-100, 0.25 mL 20% v v(-1) HNO(3), 0.50 mL biodiesel sample and 4.0 mL n-propanol. Argon-oxygen mixture was added to the plasma as auxiliary gas for correcting matrix effects caused by the high carbon load due to biodiesel microemulsions. The oxygen gas flow rate was set in 37.5 mL min(-1). The accuracy of the developed procedure was evaluated by applying addition-recovery experiments for biodiesel samples from different sources. Recoveries varied from 76.5 to 116.2% for all analytes but Zn in castor beans biodiesel sample (65.0 to 76.2%). Recoveries lower than 86.6% were obtained for palm biodiesel sample, probably due to matrix effects. Detection limits calculated by using oxygen in the composition of the auxiliary gas added to the plasma were higher than those calculated without using it, probably due to the highest formation of oxides. Despite oxides formation, best analytical performance was reached by using oxygen as auxiliary gas and by proper correction of transport interferences. The developed procedure based on microemulsion formation was suitable for direct introduction of biodiesel samples in ICP-MS. (C) 2010 Elsevier B.V. All rights reserved

Microwave-assisted digestion procedures for biological samples with diluted nitric acid: Identification of reaction products

Microwave-assisted sample preparation using diluted nitric acid solutions is an alternative procedure for digesting organic samples. The efficiency of this procedure depends on the chemical properties of the samples and in this work it was evaluated by the determination of crude protein amount. fat and original carbon. Soybeans grains, bovine blood. bovine muscle and bovine viscera were digested in a cavity-microwave oven using oxidant mixtures in different acid concentrations. The digestion efficiency was evaluated based on the determination of residual carbon content and element recoveries using inductively coupled plasma optical emission spectrometry (ICP OES). In order to determine the main residual organic compounds, the digests were characterized by nuclear magnetic resonance (1 H NMR). Subsequently, studies concerning separation of nitrobenzoic acid isomers were performed by ion pair reversed phase liquid chromatography using a C18 stationary phase, water:acetonitrile:methanol (75:20:5, v/v/v) +0.05% (v/v) TFA as mobile phase and ultraviolet detection at 254 nm. Sample preparation based on diluted acids proved to be feasible and a recommendable alternative for organic sample digestion, reducing both the reagent volumes and the variability of the residues as a result of the process of decomposition. It was shown that biological matt-ices containing amino acids, proteins and lipids in their composition produced nitrobenzoic acid isomers and other organic compounds after cleavage of chemical bonds. (C) 2009 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundacao de Amparo A Pesquisa do Estado de Sao Paulo (FAPESP)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenacao de Aperfeicoamento de Nivel Superior (CAPES