Microwave-induced Plasma Optical Emission Spectrometry Research Articles

Determination of Fe, Cu, and Pb in edible oils using choline chloride:ethylene glycol deep eutectic solvent-based dispersive liquid-liquid microextraction associated with microwave-induced plasma optical emission spectrometry

A new simple, fast and environmentally friendly deep eutectic solvent based dispersive liquid-liquid microextraction (DES-based DLLME) methodology assisted by vortex is presented for the separation and preconcentration of three elements (i.e., Fe, Cu and Pb) from edible oil samples (i.e., soybean, sunflower, rapeseed, sesame, and olive oil) prior to the determination by microwave-induced plasma optical emission spectrometry (MIP-OES). The deep eutectic solvent selected as extractant (i.e., choline chloride and ethylene glycol, 1:2) is synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR) and differential scanning calorimetry (DSC), and the extraction conditions are optimized by a two steps experimental design. Under the optimum extraction conditions (i.e., diluted sample weight: 8.6 g; DES volume: 100 μL; extraction time: 1 min; centrifugation time and speed: 3 min and 3000 rpm; and dispersion system: vortex) the analytical method presents excellent linearity (i.e., R2 values higher than 0.99) in the range 10–500 μg kg−1, repeatability (i.e., CV values lower than 9.2%), and limits of detection (LOD) values of 3, 2 and 0.7 μg kg−1 for Pb, Fe and Cu, respectively. None of the analytes displayed amounts over the upper limit permitted by law, and recovery values of all analytes evaluated in the different samples using external standard calibration were close to 100%, which excludes significant matrix effects. Finally, AGREEprep metric has been used to evaluate the method greenness (final score of 0.47) and it has been compared successfully with previous publications for the same type of analytes and matrices.

Elemental Analysis of Dietary Supplements by Microwave-Induced Plasma–Optical Emission Spectrometry (MIP-OES) With Ultrasound-Assisted Extraction (UAE)

The purpose of this study was to demonstrate the feasibility of determining metals (Cr, Mn, Zn, Fe, and Cu) in commercial dietary supplements using microwave-induced plasma optical emission spectrometry (MIP OES) after fast ultrasound-assisted extraction. Various parameters affecting the extraction process, such as the nature and concentration of the extractant solution, sonication time, and sample mass, were evaluated. Under the optimal conditions, it was possible to quantitatively extract metals from the samples by sonicating 1.0 g of the supplement dispersed throughout 25 mL of a 1.0 mol L−1 HNO3 for only 5 min. The developed method was applied to determine the analytes in four dietary supplements available in the Brazilian market. The results obtained with the extraction method were compared with the values obtained when the samples were completely mineralized with concentrated HNO3 in a microwave oven. There were no statistical differences between the developed and reference methods when the paired Student’s t-test was applied with a 95% confidence level. The application of ultrasound-assisted extraction was demonstrated to be advantageous compared to total sample digestion. This approach allowed the use of a higher mass of the sample, thereby enhancing the analytical capability of the method. Furthermore, employing less severe conditions, such as lower energy and a diluted acid solution, simplified and reduced the cost of the procedure compared to mineralization.

Low pressure closed system applied to sample preparation of instant soups for elemental determination by MIP OES

The increased consumption of ultra-processed foods has made the assessment of the presence of essential and/or potentially toxic elements more relevant. This work proposes the application and evaluation of a closed low pressure system for the acidic decomposition of instant soup samples and determination of Ba, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Pb and Zn by microwave-induced plasma optical emission spectrometry (MIP OES). The accuracy of the standard method was verified using certified reference materials and the values obtained were consistent with the certified values according to Student's t-test at 95% confidence. Addition and recovery tests were also performed, and the results varied from 86 to 119%. The concentrations varied of the 1.29 to 3.78 mg kg−1 for Ba; 414 to 6221 mg kg−1 for Ca; 0.40 to 1.13 mg kg−1 for Cr; < 0.006 to 4.16 mg kg−1 for Cu; 5.56 to 115 mg kg−1 for Fe; 48 to 444 mg kg−1 for K; 185 to 654 mg kg−1 for Mg; 0.11 to 8.39 mg kg−1 for Mn; 0.94 to 7.48 mg kg−1 for Pb and 3.01 to 42.7 mg kg−1 for Zn. For the Cd and Hg analytes, the concentration results were below their detection limits. The potentially toxic elements in this study showed concentrations below the established limit of daily intake, not offering risks to the consumer's health. As for the essential elements for the body, the concentrations were lower than those recommended for daily intake.

Microwave-sustained inductively coupled atmospheric-pressure plasma (MICAP) for the elemental analysis of complex matrix samples

Microwave induced plasma optical emission spectrometry (MIP-OES) has gained widespread attention in the last few years for trace elemental analysis. Among the new generation of MIPs it is worth to mention the microwave-sustained inductively coupled atmospheric-pressure plasma (MICAP) for which previous works have shown similar detection capabilities to those afforded by ICP-OES. Nevertheless, this instrument has not been applied yet to complex matrix sample analysis. Therefore, the goal of this work is to evaluate MICAP-OES performance (e.g., analytical figures of merit, matrix effects, etc.) for elemental analysis of samples of different nature (e.g., environmental, food and polymers). To this end, both spectral and non-spectral interferences were investigated for 19 elements (Ag, Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, Ga, In, Mg, Mn, Ni, Pb, Sr, Tl, Zn) in the presence of inorganic acid, organic and saline solutions and compared to a 5 % w w−1 HNO3 solution. Unlike previous MIPs, experimental data showed that the optimum nebulizer gas flow rate for a given emission wavelength was mostly independent of matrix characteristics. Regarding matrix effects, this device was highly robust operating both inorganic acid and organic matrices. Interestingly, when operating saline matrices, changes on emission signal by easily ionizable elements were less significant than those early reported by alternative MIP cavities. Moreover, due to MICAP spectrometer design employed allows real-time simultaneous analysis, Rh, Pd, Sc and Y were suitable internal standards to minimize non-spectral interferences. Finally, MICAP-OES can be successfully applied to the elemental analysis of different complex matrix samples (i.e., CRM-DW1 Drinking water; BCR-146 Sewage sludge industrial; BCR-185 Bovine liver; BCR-278R Mussel tissue; NIST-1549 Non-fat milk powder; ERM-EC681k Polyethylene (high level) and BCR-483 Sewage sludge amended soil).

Evaluation of Total Concentrations and Bioaccessible Fractions of Essential and Toxic Elements in Amaranth, Quinoa and Chia by MIP OES

The total concentrations and the bioaccessible fractions of Al, B, Ba, Ca, Cu, Fe, K, Mg, Mn, Na, Ni, V and Zn were evaluated in 10 samples of pseudocereals, being 3 of amaranth, 3 of quinoa and 4 of chia. The samples were decomposed in a digester block with a reflux system under conditions optimized and the analyses were performed by microwave-induced plasma optical emission spectrometry. In all grains investigated, the highest total concentrations were found for the macroelements K, Mg and Ca, as well as the microelements Fe, Mn, and Zn. When the bioaccessible fraction was evaluated, negative correlations were observed between the content of total phenolic compounds and the bioaccessibility for most elements, in all samples. Among the elements considered essential in our diet, K (99%) and Cu (59%) presented the highest percentages of bioaccessible fraction. Among those elements considered potentially toxic, Ba did not exceed 15% bioaccessible fraction and Al presented concentrations lower than the limit of detection in all samples.

Continuation of investigation of effect of O2 in plasma gas on parameters of nitrogen microwave-induced plasma optical emission spectrometry

We studied the effect of O2 content in the range up to 80% in plasma gas on the plasma characteristics, the analyte signal and the intensity of the molecular species in the nitrogen microwave-induced plasma (MIP). The plasma temperature decrease from 3.9·103 to 3.3·103 K with increasing O2 content. Mg (II)/Mg (I) intensity ratio decrease from 1.02 to 0.18, the electron density decrease from 6.6·1012 to 4·1011 cm−3. The intensity of N2 (1+ system), N2 (2+ system), N2+, NH, NO, and OH intensities increases to a certain content, and then decrease (NH) or remain constant (OH) when O2 is added. The effect of O2 content on the intensity of several atomic and ionic emission lines (covering Esum values from 1.6 to 14.7 eV) of 22 elements has been studied. The line intensity was suppressed over the entire energy range. It was shown that the O2 addition increased the limit of detection (LOD) by 1.2–4 for lines with Esum of 1.5–4 eV and by 50–60 times for lines with Esum of 4–15 eV.

Determination of burn rate affecting elements in composite solid propellant and its ingredients by microwave-induced plasma optical emission spectrometry.

A study of trace metallic elements in solid propellant and its ingredients is important and critical as they affect ballistic properties of solid rocket motor during combustion. In the present study, an attempt is made to develop a rapid, single run and cost-effective analytical technique for the routine and direct analysis of multi elements. Trace level metallic impurities (burn rate affecting elements) present in premix, cured propellant slab and propellant ingredients such as ammonium perchlorate, aluminium, aluminium oxide, dioctyladipate, hydroxy terminated polybutadiene and toluene diisoycanate sourced from different suppliers and propellant slag are determined based on a relatively recent analytical technique, microwave-induced plasma optical emission spectrometry (MIP-OES). Analytical wavelengths are selected based on the sensitivity and interference effects. Precision and accuracy of the developed test procedure for the metallic impurities are demonstrated using replicate analyses of certified calibration standards. The limit of quantification and detection of elements studied is determined. Linear regression coefficients are greater than 0.995. The results obtained demonstrate the potential of MIP-OES technique for the determination of metallic impurities of solid propellant ingredients, pre-mix, cured slab and slag of solid propellants with shortened analysis time which achieved lower detection limits, higher accuracy and better repeatability.

Determination of Essential and Non-Essential Elements in Dietary Supplements by Microwave-Induced Plasma Optical Emission Spectrometry: Method Development and Study of Non-Spectral Interferences

Dietary supplements have been used to overcome nutritional deficiencies and the knowledge concerning essential and non-essential elements is an important issue. In this work the suitability of microwave-induced plasma optical emission spectrometry (MIP OES) for the determination of essential and non-essential elements in dietary supplements was evaluated. Twelve dietary supplement samples of several classifications (vitamins/minerals, minerals, amino acids, and botanicals) were digested in their whole form for determination of essential (Ca, Co, Cu, Fe, K, Mg, Mn, Mo, Na, and Zn) and non-essential (Ag, Al, B, Ba, Be, Cd, Cr, La, Li, Ni, Pb, Sr, and V) elements by MIP OES. Potential non-spectral interferences by common concomitants (C, S, K, Na, and Ca) were evaluated, as well as those by residual acidity of digests. The study of non-spectral interferences showed that a signal suppression effect is observed with higher concentrations of Ca, Na, and K. Relatively good robustness was observed considering the presence of C and S, as well as residual HNO3. The limits of quantification (LOQs) were dependent on the sample mass used for decomposition (from 0.6 to 1.6 g in the commercial product) and on the minimum dilution factor. From the results, there was a prevalence of essential and non-essential elements in vitamins and minerals, minerals, and botanicals-based dietary supplements, whereas lower concentrations were found in the dietary supplements based on amino acids. All elements were in a concentration below the recommended dietary allowances (RDAs), exception for those with the concentration intentionally higher. Accuracy of results by MIP OES was evaluated by using standard reference materials (SRM) NIST 1572 and NIST 1575a. In addition, results showed no statistical difference by comparison with those by ICP OES. MIP OES proved to be a suitable technique for the determination of metals in dietary supplements, being a feasible alternative for the quality control of these products.

Poly(lactic acid)/β-cyclodextrin based nanoparticles bearing ruthenium(II)-arene naproxen complex: preparation and characterisation. Analytical validation for metal determination by microwave-induced plasma optical emission spectrometry

The objectives of this work are to develop nanocarrier systems for the Ru(II)-p-cymene naproxen antitumor metallodrug, [Ru(η6-p-cymene)(npx)Cl] or Rupcy, based on polymeric nanoparticles (NPs) composed by the biodegradable poly(lactic acid) (PLA) and the hydrophilic polymerised β-cyclodextrin (PolyCD); to validate an analytical method for determination of Ru incorporated into the metallodrug loaded-NPs. The PolyCD was prepared by single step condensation and polymerisation reaction and incorporated as a polymer blend during the fabrication of PLA/PolyCD blends NPs and also as a core/shell structure built by adsorption of the PolyCD onto the surface of PLA NPs to give PLA(core)/PolyCD(shell) NPs. Three different loaded-systems incorporating the metallodrug (Rupcy-PLA NPs (1), Rupcy-PLA/PolyCD blends (2), and Rupcy-PLA(core)/PolyCD(shell) NPs (3)) were prepared by nanoprecipitation. The characterisation was performed by Proton Nuclear Magnetic Resonance, Matrix Assisted Laser Desorption/Ionization Time-of-Flight, Fourier-Transform Infra-red and UV-VIS Electronic Absorption Spectroscopies, Thermogravimetric Analysis, Differential Scanning Calorimetry, Dynamic Light Scattering, and Electrophoretic Light Scattering. Ru was determined by Microwave Induced Plasma Optical Emission Spectrometry (MIP-OES) with validation of the method. The metallodrug entrapment efficiency was around 90% (w/w) and drug loading was at 3–4% (w/w). The characterised metallodrug-loaded systems exhibited monomodal size distributions and appropriate hydrodynamic diameters [218.3 ± 13.5 (1), 205.4 ± 14.4 (2), 231.5 ± 22.0 (3) nm] and zeta potential values [−31.5 ± 2.2 (1), −26.1 ± 4.5 (2), −28.8 ± 6.1 (3) mV]. The validation of the MIP-OES method by evaluating selectivity, linearity, precision, accuracy, and limits of detection and quantification succeeded. The NPs parameters are compatible with colloidally stable systems. The MIP-OES method showed to be simple, reliable, and feasible to quantify indirectly the amount of the metallodrug-loaded into the PLA NPs.

A simple method for the determination of toxicologically relevant arsenic species in urine by hydride generation microwave-induced plasma optical emission spectrometry for health risk assessment

This analytical note presents a simple and economic analytical method for quantifying toxicologically relevant arsenic species in urine—the sum of As (III), As (V), monomethylarsonic acid, and dimethylarsinic acid—by hydride generation microwave-induced plasma atomic emission spectrometry (HG-MIP-AES).The accuracy of the method was in the range of 95%–97%; the intra-assay precision was within the range of 1.8%–6.2% expressed as the relative standard deviation, and the interassay precision was within 6.9%–15%. The limits of detection and quantification were 1.8 and 5.4 μg L−1, respectively.The validated method resulted very helpful to assess the health risk of As exposure through drinking water and was successfully applied in urine samples collected from wood impregnation plant workers. The methodology can be postulated as a viable alternative to expensive techniques, such as liquid chromatography (HPLC) in combination with inductively coupled plasma mass spectrometry (ICP-MS), for biomonitoring studies.

Fit-for-Purpose MIP OES Method to Meet the Requirements of the Brazilian Regulations for K and Na in Coconut Water, and Nutritional Assessment

The Brazilian regulations for processed coconut water establish the range concentrations of Na and K, being necessary high-throughput analytical methods, as microwave-induced plasma optical emission spectrometry (MIP OES) for quality control. Samples of natural (green and mature) and processed coconut water were treated by acid decomposition assisted by microwave radiation before their MIP OES analysis. Recoveries for Na and K were 103 and 95%, whereas the relative standard deviation (RSDs) were 7.6 and 1.3%, respectively. The limit of detection (LOD) was 1.77 mg kg-1 for K and 2.31 mg kg-1 for Na. Sodium and K were determined in the ranges of, respectively, 27-490 and 1,600-3,500 mg L-1 in natural samples, whereas in processed samples the ranges were 26-168 and 814-2,054 mg L-1. K-means cluster analysis identified a group of processed samples with compositions similar to green coconut water. All the processed samples were in accordance with the established regulation, except one dehydrated sample for which K content was below the accepted range. Natural coconut water is an excellent source of K in the diet as its daily consumption can supply more than 20% of the recommended daily ingestion of K for adults and 30% for children.

Exploratory Analysis of South American Wines Using Artificial Intelligence.

In this work, microwave-induced plasma optical emission spectrometry was applied for multielement determination in South American wine samples. The analytes were determined after acid digestion of 47 samples of Brazilian and Argentinian wines. Then, logistic regression, support vector machine, and decision tree for exploratory analysis and comparison of these algorithms in differentiating red wine samples by region of origin were carried out. All wine samples were classified according to their geographical origin. The quantification limits (mg L-1) were P: 0.06, B: 0.08, K: 0.17, Mn: 0.002, Cr: 0.002, and Al: 0.02. The accuracy of the method was evaluated by analyzing the wine samples by ICP OES for results' comparison. The concentrations in mg L-1 found for each element in wine samples were as follows: Al (< 0.02-1.82), Cr (0.15-0.50), Mn (< 0.002-0.8), P (97-277), B (1.7-11.6), Pb (< 0.06-0.3), Na (8.84-41.57), and K (604-1701), in mg L-1.

Determination of elemental impurities Cd, Pb, As, Hg, Co, V, Ni, Pd, Ru, Ag, Pt, Mo, Al, and Fe in highly potent analgesic activity agent by microwave-induced plasma optical emission spectrometry (MIP OES)

Determination of elemental impurities Cd, Pb, As, Hg, Co, V, Ni, Pd, Ru, Ag, Pt, Mo, Al, and Fe in highly potent analgesic activity agent by microwave-induced plasma optical emission spectrometry (MIP OES)

Determination of elemental bioavailability in soils and sediments by microwave induced plasma optical emission spectrometry (MIP-OES): Matrix effects and calibration strategies.

In the past few years, microwave induced plasma optical emission spectrometry (MIP-OES) has generated great interest as an alternative technique to inductively coupled plasma-based techniques due to its lower operational cost. Since MIP-OES suffers from severe matrix effects due to easily ionizable elements (EIEs) (Na, Ca, etc.), it is unclear whether this technique could be employed for elemental bioavailability studies in soils and sediments since the main extractant solutions employed in such works may contain high levels of these elements. Thus, the aim of this work was to evaluate the feasibility of MIP-OES as a detector for such applications. To this end, the influence of different extractant solutions (0.25molL-1 MgCl2, 0.25molL-1 CaCl2, 0.10molL-1 acetic acid, 0.05molL-1 Na2EDTA, 0.25molL-1 NaNO3, 0.25molL-1 NaOAc/HOAc and 0.10molL-1NH2OH·HCl) on the analyte emission of several elements (As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Rh, Se, Sr and Zn) was investigated. Results were compared to those obtained using a reference solution made of 5% w w-1 HNO3 solution. For saline extractant solutions, both the optimum nebulizer gas flow rate (Qg) and analyte emission were modified with regard to the reference solution. In general, the optimum Qg was reduced by between 0.1 and 0.2Lmin-1 for both ionic and atomic lines. Under optimum Qg conditions, analyte emission was supressed by saline solutions except for atomic lines with an upper electronic state below 4eV, which were enhanced. The magnitude of matrix effects was strongly dependent on EIE ionization energy. The lower the ionization energy, the greater the matrix effects were registered. No measurable matrix effects were registered on both Qg and analyte emission within experimental uncertainties for NH2OH·HCl and acetic acid extractant solutions. Experimental data suggest that matrix effects were related to changes in plasma characteristics and the analyte excitation/ionization mechanism. To mitigate matrix effects and improve long-term MIP-OES performance, internal standardization using either Rh (343.489nm and 369.236nm) or OH molecular emission band (308.958nm) was required. This calibration methodology was successfully applied to the study of the elemental bioavailability in soil samples from a vineyard affected by copper-based fungicides and sediment samples from an area affected by mining waste.

Adsorption of Cu (II) Ions Present in the Distilled Beverage (Sugar Cane Spirit) Using Chitosan Derived from the Shrimp Shell.

Cachaça (sugar cane spirit) is a typically Brazilian distilled beverage. Copper ions can be present in craft beverages despite their acceptance in the national and international market. This study aims to evaluate the efficiency of chitosan as an adsorbent in removing copper (II) from cachaça. The structural characteristics of the obtained chitosan and the effect of adsorbed copper were evaluated by Fourier Transform Infrared Spectroscopy (ATR-FTIR), viscosimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The deacetylation reaction from chitin (shrimp shell) resulted in chitosan with a deacetylation degree of 88.9% (potentiometric titration) and 86.9% (FTIR), low crystallinity, and an estimated molecular weight of 162.96 kDa. The copper reduction rate was 84.09% evaluated by spectrophotometric titration and microwave-induced plasma optical emission spectrometry (MIP–OES). The amine groups of chitosan had adsorption affinity with copper ions, and the kinetic analysis showed a better fit of the data by the Elovich equation, suggesting that the chemosorption mechanism controlled the kinetic process. The results suggest that chitosan has the potential to improve the quality and safety of cachaça.

Greening Ultrasound-Assisted Extraction for Sorghum Flour Multielemental Determination by Microwave-Induced Plasma Optical Emission Spectrometry.

Sorghum is the fourth most important cereal produced in Argentina and the fifth worldwide. It has good agronomic characteristics and could be developed in arid areas, allowing a wide geographic distribution. Its starch content, higher than 70%, makes it possible to obtain a good yield of flours. Nutritionally, it should be noted that the grain does not have the protein fraction called prolamins, which makes it suitable for consumption by people with celiac disease. The multielemental composition constitutes an important indicator of the nutritional profile of the grains and allows, together with other parameters, to select the most suitable varieties for human consumption. In its determination, the preanalytical stage is decisive to obtain a reliable result. Organic samples are a challenge for sample introduction systems that use plasma-based techniques. As an alternative to conventional pretreatment with a microwave-assisted digestion (MWAD), a greener, quick, and simple treatment is proposed, using ultrasound-assisted extraction (UAE) in diluted acid media. The UAE method accelerates analysis times, improves performance and productivity, and was applied to sorghum samples cultivated in the province of La Pampa (Argentina). Microwave-induced plasma optical emission spectrometry (MIP OES) was employed for the determination of Cu, K, Mg, Mn, P, and Zn. The detection limits found ranged from 0.6 (Cu) to 89 (P) mg kg−1, and the precision expressed by the relative standard deviation (RSD) was ≤7.7% (Zn). For validation, a maize reference material (NCS ZC 73010) was evaluated. The principal component analysis revealed three different groupings related to the sorghum varieties' mineral profile.

Photochemical vapor generation combined with headspace solid phase microextraction for determining mercury species by microwave-induced plasma optical emission spectrometry

A new and simple photochemical vapor generation (PCVG) technique utilizing UVC irradiation combined with headspace solid phase microextraction (HS SPME) is developed for the unified separation and preconcentration of mercury species followed by their determination through miniaturized thermal desorption argon microwave-induced plasma optical emission spectrometry (TD–MIP–OES). Inorganic mercury (Hg2+), methylmercury, and ethylmercury are decomposed and reduced to mercury cold vapor in 2% formic acid through combined UVC irradiation and thermochemical reduction. The mercury vapor is subsequently liberated from the liquid phase and transported to the headspace. Without any tedious sample pretreatments, HS SPME using DVB/CAR/PDMS fiber affords clean and convenient one-step extraction followed by direct desorption into the injection port of the detection system. The 15 min-long UVC irradiation, thermal reduction of mercury species, and preconcentration of mercury vapor resulted in low limits of detection between 0.08 and 0.10 ng mL−1 for all mercury species. The method performance was validated by determining the total mercury and MeHg concentration in a tuna fish certified reference material (ERM CE464) and total mercury in sediment ERM CC580, and the results agreed well with the certified values.

Multiple response optimization of ultrasound-assisted procedure for multi-element determination in Brazilian wine samples by microwave-induced plasma optical emission spectrometry

In the present work, a method was developed, optimized, and validated for the determination of aluminum, manganese, lead, copper, cadmium, and zinc by microwave-induced plasma optical emission spectrometry of wine samples from the São Francisco Valley, northeastern Brazil. The samples were subjected to a sonochemical treatment aiming at the degradation of the sample matrix. To optimize the analytical procedure, initially, a two-level fractional factorial design was used to study five experimental variables and determine which ones significantly affected the analytical response. In a second step, the significant variables were optimized using the Doehlert matrix as the response surface methodology and the desirability function as a strategy to optimize multiple responses. The optimum conditions established were concentrations of nitric acid (2.3 mol L−1) and hydrogen peroxide (9%). The developed method is simple, fast, and precise, has a low operational cost and low limits of detection and quantification. The accuracy confirmed by spike tests with recoveries ranging from 104 to 118% and comparative analysis of the results obtained using the proposed method and digestion total procedure. The method was applied for multi-element determination in three wine samples.

In vitro bioaccessibility of Cu and Zn in cooked beef cuts

Cu and Zn bioaccessibility was studied in two different beef cuts (rib plate and top sirloin), through the development of an in vitro assay. Samples were cooked at two degrees of doneness (medium and well-done) as usually consumed locally, to establish the contribution to the recommended daily allowance (RDA). Simulated gastrointestinal conditions were optimized and trueness of the method was evaluated by performing mass balances. Analytical determinations were performed by atomic absorption spectrometry and microwave-induced plasma optical emission spectrometry. No significant differences were found between the studied cuts nor between the degrees of doneness evaluated. Mean bioaccessible fraction (BF) of Zn was 83%, for both cuts and both degrees of doneness. In the case of Cu, rib plate presented a mean BF of 20%, while for top sirloin was of 38%. However, these differences found between cuts and degrees of doneness were not statistically significant. The contribution of Cu and Zn to the RDA for adults over 19 years was estimated, as an example, considering a 200 g portion. Results showed that the RDA of Zn would be completely covered, while the contribution to the RDA of Cu would be up to 33%.

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.