Mariana Antunes Vieira

Determination of Trace Elements in Vegetable Oils and Biodiesel by Atomic Spectrometric Techniques—A Review

Abstract The determination of trace elements in edible oils and biodiesel using atomic spectrometric methods is reviewed. Problems related to sample pretreatment for appropriate sample introduction and calibration are addressed as well as the strategies to overcome them. Recent trends aimed at simplifying sample manipulation are presented. The applications and scope of atomic absorption spectrometry (AAS), flame optical emission spectrometry (F-OES), inductively coupled plasma–optical emission spectrometry (ICP-OES), and inductively coupled plasma–mass spectrometry (ICP-MS) techniques for the determination of trace metals in edible oils and biodiesel are discussed, as well as some current instrumental new developments.

Determination of mercury in ethanol biofuel by photochemical vapor generation

A new procedure based on exposure of ethanol biofuel samples to UV radiation in the presence of low molecular weight organic acids was developed for the determination of total Hg (inorganic and organometallic species: Hg2+, CH3Hg+ and CH3CH2Hg+) by photochemical vapor generation coupled with atomic absorption spectrometry (photo-CV-AAS). For each species, the optimum conditions for photochemical generation were investigated, including the effects of medium composition, exposure time to the UV radiation and transfer gas flow rate. The accuracy was evaluated by assessing the recoveries of species-specific spikes (91–107%) as well as by assessing recovery from a mixture of all species of the mercury added to the ethanol biofuel samples based on calibration standards prepared in high purity bidistilled ethanol. The limits of detection ranged from 0.05 to 0.09 μg L−1 for all addition and recovery tests, enabling the determination of total Hg. The proposed method is sensitive, simple (no sample pretreatment) and provides a direct approach to the generation of mercury vapor from ethanol biofuel samples while promoting “green” chemistry.

Determination of platinum originated from antitumoral drugs in human urine by atomic absorption spectrometric methods

Cisplatin and carboplatin are the most common platinum-based drugs used in cancer treatment. Pharmacokinetic investigations, the evaluation of the body burden during the treatment, as well as baseline levels of platinum in humans have attracted great interest. Thus, accurate analytical methods for fast and easy Pt monitoring in clinical samples become necessary. In the present study atomic absorption spectrometric methods for the determination of platinum in the forms of cisplatin and carboplatin in human urine were investigated. Platinum, in these different forms, could be determined in urine, after simple sample dilution. Regarding electrothermal atomic absorption spectrometry, the optimum parameters were defined by a central composite design optimization. Multiplicative matrix effects were overcome by using a mixture of HCl and NaCl as modifier. The limit of detection (LOD) was 0.004 mgL(-1) of platinum in the original sample. For the analysis of more concentrated samples, high resolution continuous source flame atomic absorption spectrometry was also investigated. Flame conditions were optimized by a multivariate D-optimal design, using as response the sum of the analyte addition calibration slopes and their standard deviations. Matrix matched external calibration with PtCl(2) calibration solutions, was possible, and the LOD was 0.06 mgL(-1) in the original sample. The results obtained by the proposed procedures were also in good agreement with those obtained by an independent comparative procedure.

Sample preparation methods for determination of Cd, Pb and Sn in meat samples by GFAAS: use of acid digestion associated with a cold finger apparatus versus solubilization methods

The aim of this study was to present three sample preparation methods for the determination of Cd, Pb and Sn in meat by Graphite Furnace Atomic Absorption Spectrometry (GFAAS): acid digestion, solubilization with tetramethylammonium hydroxide and formic acid. For the digestion with HNO3, a conventional open system with a cold finger was used. This system helped to avoid losses of analytes and reagents by volatilization, permitting to operate at high temperatures applied at a digester block and reducing the digestion time (∼1 h). Solubilizations were performed at room temperature. The slurry was left standing overnight and remained closed until achieving complete solubilization. The temperature program of the graphite furnace was optimized for each element in the different means of preparation samples using a mixture of Pd–Mg. The figures of merit were similar for all sample preparation methods evaluated. The limits of detection obtained for the acid digestion procedure were 0.0006, 0.0164 and 0.0520 μg g−1 for Cd, Pb and Sn, respectively. In order to evaluate the accuracy of the results obtained by the three sample preparation methods, recovery tests for four real meat samples were performed and the recoveries ranged from 93.7 to 109%, supporting the accuracy of the method. Also, different certified reference materials of meat were analyzed and the results obtained were in agreement with the certified value at 95% of confidence (t-test). The best results were obtained by the acid digestion procedure with the cold finger system. This procedure is faster, the system is semi-closed with no significant contamination or loss of analytes by volatilization and it provides a better signal/noise ratio.

An easy and fast procedure for the determination of Ca, Cu, Fe, Mn, Mg, Na, K and Si in biodiesel by ICP OES using emulsification as sample preparation strategy

It is presented an alternative procedure for preparation of biodiesel samples for elemental determination by inductively coupled plasma optical emission spectrometry (ICP OES), based on the sample (10% m/v) emulsion formation with formic acid (15% v/v) and Triton X-100 (0.1% m/v). These concentrations were optimized and the stability of emulsified aqueous standards and samples was found to be of at least 3 h. Experimental conditions (1500 W of RF power and 0.5 L min-1 of Ar nebulizer flow rate) were optimized from those recommended by the equipment manufacturer, with a solution containing 10 mg L-1 of each analyte prepared with mineral oil in the same conditions of the emulsion. Matrix effects were investigated by observing the slopes of analyte addition curves for different biodiesel samples. Results showed that external calibration with inorganic aqueous standard solutions in the emulsion medium should be used. Limits of detection obtained (in mg kg-1) were 0.121, 0.008, 0.006, 0.001, 0.006, 0.071, 0.241 and 0.024 for Ca, Cu, Fe, Mn, Mg, Na, K and Si, respectively. The accuracy of the procedure for Ca, Mg, K and Na was assessed by the analysis of a multi-element standards B100 biodiesel (Conostan) and the recoveries ranged from 91 to 107%. The proposed procedure used low toxicity reagents and showed to be a simple and straightforward alternative of sample preparation for metal determination in biodiesel by ICP OES with limits of detection adequate for those analyses.

Determination of Na, K, Mg and Ca in biodiesel by LS F AAS and HR-CS F AAS: studies that supported the proposal of the ABNT NBR 15556 norm

Recently, ABNT (Brazilian Association of Technical Standards) has presented a set of norms related to the determination of Na, K, Mg and Ca in biodiesel, recommending procedures similar to those of the European and American norms. However, it has also introduced an alternative norm (ABNT NBR 15556) wherein these 4 elements can be determined by flame atomic absorption spectrometry (F AAS). This work presents the studies that have supported this proposal and compares the performance of linear source equipment with a continuous source one in the application of the norm. Among the optimized factors, the low aspiration rate and the use of mineral oil solution in xylene to adjust the viscosity between samples and calibration solutions are highlighted. Precision tests (repeatability and intermediary precision) have shown adequate values, confirming the robustness of the method. Limits of detection were suitably below the legislation limits. The accuracy was confirmed by recovery tests as well as by the participation in interlaboratory proficiency tests promoted by the National Agency on Oil, Natural Gas and Biofuels (ANP, Brazil). The determination of these 4 elements by F AAS brings evident economic advantages to the producer, once F AAS is less expensive to purchase and maintenance.

Evaluation of sample preparation methods based on alkaline and acid solubilization for the determination of Na and K in meat samples by atomic spectrometric techniques

Foram avaliados dois metodos diferentes de preparo de amostras de carnes baseados na solubilizacao em meios alcalino ou acido. O objetivo deste estudo foi determinar os teores de Na e K apos solubilizacao com hidroxido de tetrametilamonio (TMAH) temperatura ambiente, e com acido formico e aquecimento em bloco de digestao a 50 oC por cerca de 2 h. A solubilizacao alcalina se apresentou como uma metodologia simples e robusta e a melhor alternativa frente aos procedimentos de mineralizacao convencional, permitindo a solubilizacao completa das amostras usando pequenas quantidades de TMAH. O metodo foi validado empregando-se materiais de referencia certificada assim como pela comparacao com metodo de digestao convencional com acido nitrico. Os limites de deteccao obtidos foram de 0,8 e 2,0 mg g-1 para Na e K, respectivamente, e se mostraram adequados para o objetivo das analises.

Determination of Ca, Cu, Fe and Mg in fresh and processed meat treated with tetramethylammonium hydroxide by atomic absorption spectrometry

Um metodo simples para o tratamento de amostras de carne fresca e processada com hidroxido de tetrametilamonio (TMAH) e proposto para a determinacao de Ca, Fe e Mg por espectrometria de absorcao atomica com chama (FAAS) e Cu por espectrometria de absorcao atomica com forno de grafite (GFAAS). A exatidao foi avaliada por comparacao dos resultados usando outros dois procedimentos de preparo de amostra e por analise de materiais de referencia certificados. Nao houve diferenca significativa entre os resultados obtidos, em um nivel de confianca de 95%. Os limites de deteccao para Ca, Cu, Fe e Mg foram 45,0, 0,2, 16,0 e 0,3 µg g -1 , respectivamente. A espectrometria de absorcao atomica de alta resolucao com fonte continua em forno de grafite (HR-CS GFAAS) foi empregada para avaliar as interferencias espectrais na determinacao de Cu. Entretanto, nenhuma interferencia foi encontrada. O metodo proposto e simples, rapido e confiavel para analise de produtos carneos e nao requer o uso de equipamentos especiais nem de acidos fortes no preparo das amostras. A simple method for treating fresh and processed meat with tetramethylammonium hydroxide (TMAH) is proposed for the determination of Ca, Fe and Mg by flame atomic absorption spectrometry (FAAS) and Cu by graphite furnace atomic absorption spectrometry (GFAAS). The accuracy was evaluated by comparison of the results by using two other sample preparation procedures and by the analysis of certified reference materials. No significant differences between the results were found at the 95% confidence level. Limits of detection for Ca, Cu, Fe and Mg were 45.0, 0.2, 16.0 and 0.3 µg g -1 , respectively. High-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) was employed to evaluate the spectral interference in the determination of Cu. However, no interference was found. The proposed method is simple, fast and reliable for meat products analysis and does not require especial equipment, neither strong acid for sample preparation.

Acid Decomposition of Yerba Mate (Ilex paraguariensis) Using a Reflux System for the Evaluation of Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Pb and Zn Contents by Atomic Spectrometric Techniques

In the first part of this paper, two acid decomposition procedures for the determination of Al, Ca, Fe, Mg, Mn and Zn contents in yerba mate samples by inductively coupled plasma optical emission spectrometry (ICP OES) were compared. Using a reflux system, the samples were treated with a mixture of HNO3 and H2O2 for 3 hours at 220 °C in the digester block. The results from five commercial yerba mate samples were compared with the results obtained from microwave digestion. Good agreement between the procedures at a 95% confidence level was obtained with relative standard deviation (RSD) values lower than 10.0%. The accuracy was evaluated using addition and recovery experiments (80.5 to 112.8%). In the second part, Ca, Cd, Cr, Cu, Fe, K, Mg, Na, Pb and Zn concentrations were evaluated in the yerba mate infusion. The results showed that elements such as Na, K, Mg and Zn are easily transferred to the hot water used for the infusion. For Pb and Cd, the concentrations found in the analyzed samples were lower than the values established by Brazilian legislation.

Evaluation of the use of a reflux system for sample preparation of processed fruit juices and subsequent determination of Cr, Cu, K, Mg, Na, Pb and Zn by atomic spectrometry techniques

The acid decomposition method was applied for the sample preparation of processed fruit juice. The decomposition of 15mL of juice sample using HNO3 and H2O2 was performed in a digester block with reflux system and heated at 200°C for 150min. The limits of detection were 0.03; 0.24; 0.8; 0.008; 0.026 and 0.056mgL-1 for Cr, Cu, K, Mg, Na and Zn, respectively and for Pb was 0.99μgL-1. The accuracy was evaluated by spiked experiments (80 to 119%). Four processed fruit juice samples commercialized in Brazil (strawberry, mango, peach, and orange) were analyzed and indicated the absence of Cr, Zn and Cu in the samples, except for Cu in strawberry juice. Pb was found in the mango juice sample (17.8±0.9μgL-1) and the concentration is below the maximum values recommended by Brazilian legislation for juices of citric fruits (0.3mgkg-1).