Microwave-induced combustion for further determination of potentially toxic elements in honey by ICP-MS

Microwave-induced combustion (MIC) was proposed in this study for honey decomposition aiming for As, Cd, Hg, and Pb determination by inductively coupled plasma mass spectrometry (ICP-MS). Sample mass (up to 1.0 g), absorbing solution (0.5 to 14.4 mol L-1 HNO3, and H2O), heating program, and combustion aids were evaluated. The Eurachem guidelines were used for method validation. The proposed method enabled combustion of a high sample mass (0.8 g of honey, with 0.4 g of microcrystalline cellulose and 100 µL of 6 mol L-1 NH4NO3) using 6 mL of an absorbing solution consisting of 1 mol L-1 HNO3, which resulted in low residual carbon in solution (< 25 mg L-1). Honey samples from different geographical origins were analyzed. Results showed no significant difference in comparison to other two microwave decomposition methods, based on microwave-assisted wet digestion with single reaction chamber (MAWD-SRC) and microwave-assisted wet digestion (MAWD). Standard addition experiments resulted in recoveries higher than 98%. The limits of detection ranged from 1.10 (As) to 4.60 ng g-1 (Pb). In addition to using only diluted reagents and resulting in digests virtually free of interferences, the proposed method was faster (< 30 min) than most of those presented in the literature.

Low cost sample preparation method using ultrasound for the determination of environmentally critical elements in seaweed

In this study, ultrasound (US) was evaluated for As, Cd, Pb, Mn, Sr and V extraction from seaweed samples. The following parameters of ultrasound-assisted extraction (UAE) using an US bath were: frequency (25 to 130 kHz), amplitude (30 to 100%), temperature (30 to 80 °C), sample mass (50 to 200 mg), extractant concentration (1 to 3 mol L-1 of HNO3) and treatment time (5 to 30 min). Acoustic density and power density distribution were calculated using the calorimetric method and mapping of the acoustic pressure distribution was also evaluated. The optimized UAE conditions were 200 mg of sample in 10 mL of 2 mol L-1 HNO3 and 30 min of sonication in a 25 kHz US bath (37.2 ± 4.0 W L-1) at 70% of amplitude and 70 °C. Analytes were quantified using inductively coupled plasma mass spectrometry and results were compared with values obtained using "silent" conditions (magnetic or mechanical stirring at 500 rpm, and without stirring), and a reference method based on microwave-assisted wet digestion (MAWD). The UAE method demonstrated the best extraction efficiency (higher than 95%) for all analytes, especially for As, Cd and V, with lower standard deviations (up to 5%) and lower blank values in comparison with the silent conditions. The proposed UAE method was more advantageous than the reference method, being faster, simpler, safer, more environmentally friendly, and with higher detectability (lower limits of quantification, from 0.0033 to 1.34 µg g-1). In addition, negligible blank values were obtained for UAE and no interference were observed in the determination step. Furthermore, the optimized UAE method was applied for Antarctic seaweed samples and comparison with results obtained by MAWD was satisfactory. In this sense, UAE is demonstrated to be a suitable option for sample preparation of seaweed samples and further determination of environmentally critical elements avoiding the use of concentrated reagents as in the MAWD reference method.

New Analytical Strategy for Bioaccessibility Evaluation of Bromine and Iodine from Edible Seaweeds

A strategy for determining the bioaccessibility of bromine and iodine from edible seaweeds was proposed for the first time using microwave-induced combustion (MIC) and ion chromatography coupled to mass spectrometry (IC-MS) after in vitro digestion. The concentrations of bromine and iodine in edible seaweeds using the proposed methods (MIC and IC-MS) were not statistically different from those using MIC and inductively coupled plasma mass spectrometry (p > 0.05). Trueness was assessed by recovery experiments (101-110%, relative standard deviation <10%). Following an in vitro digestion protocol, MIC was proposed as sample preparation for bioaccessible and residual fractions. Using this strategy, the mass balance totaled from 97 to 111%. No statistical difference (p > 0.05) was observed between the total concentration of bromine or iodine and their concentration in bioaccessible and residual fractions for three edible seaweed species, indicating full analyte quantification in the fractions.

A single step ultrasound-assisted nitrocellulose synthesis from microcrystalline cellulose

Nitrocellulose is a nitrated cellulose polymer with a broad application in industry. Depending on the nitrogen content, this polymer can be used for manufacturing explosives, varnishes, clothes, and films, being considered a product of high value-added. In this work, the use of ultrasound was investigated for the intensification of nitrocellulose synthesis from microcrystalline cellulose. The ultrasound-assisted nitrocellulose synthesis (UANS) was carried out using several ultrasound systems, such as baths and cup horns, allowing the evaluation of the frequency (from 20 to 130 kHz) and delivered power (from 23 to 134 W dm^-3) to the reaction medium. The following parameters were evaluated: acid mixture (H₂SO₄, H₃PO₄, CH₂O₂ or CH₃COOH with HNO₃, 2 to 14.4 mol L^-1), ultrasound amplitude (10 to 70%) and reaction time (5 to 50 min). Better nitrocellulose yield (nitrogen content of 12.5% was obtained from 1 g of microcrystalline cellulose employing a cup horn system operating at 20 kHz, 750 W of nominal power with 60% of amplitude, 25 mL of acid solution (13.6 mL of 18.4 mol L^-1 H₂SO₄ + 9.2 mL of 14.4 mol L^-1 HNO₃ + 2.2 mL H₂O), at 30 °C for 30 min. At silent conditions (mechanical stirring ranging from 100 to 500 rpm), the nitrogen content was lower than 11.8% which demonstrate the ultrasound effects for nitrocellulose synthesis.

Advances in Sample Digestion Using Microwave-ultraviolet Radiations: Phosphorus and Sulfur Determination in Animal Feed

Background:

Conventional analytical methods for phosphorus and sulfur determination in several matrices present normally analytical challenges regarding inaccuracy, detectability and waste generation.

Objective:

The main objective is proposing a green and feasible analytical method for phosphorus and sulfur determination in animal feed.

Methods:

Synergic effect between microwave and ultraviolet radiations during sample preparation was evaluated for the first time for the animal feed digestion associated with further phosphorus and sulfur determination by ion chromatography with conductivity detection. Dissolved carbon and residual acidity in the final digests were used for the proposed method assessment. Phosphorus and sulfur values were compared with those obtained using conventional microwaveassisted wet digestion in closed vessels associated with inductively coupled plasma optical emission spectrometry and with those obtained using an official method (Association of Official Analytical Chemists International). Recovery tests and certified reference material analyses were performed. Animal feeds were analyzed using the proposed method.

Results:

Sample masses of 500 mg were efficiently digested using only 2 mol L-1 HNO3. The results obtained by the proposed method were not differing significantly (p > 0.05) from those obtained by conventional and by official methods. Suitable recoveries (from 94 to 99%), agreement with certified values (101 and 104%), and suitable relative standard deviations (< 8%) were achieved. Phosphorus and sulfur content in commercial products varied in a wide range (P: 5,873 to 28,387 mg kg-1 and S: 2,165 to 4,501 mg kg-1).

Conclusion:

The proposed method is a green, safe, accurate, precise and sensitive alternative for animal feed quality control.

A solid sampling approach for direct determination of Cl and S in flour by an elemental analyzer

Direct analysis of flour was proposed for the determination of Cl and S by an elemental analyzer for the first time. The main operational conditions of the direct solid sampling elemental analysis (DSS-EA) were optimized and calibrated by standard solutions, rather than by certified reference material (CRM). Accuracy was evaluated by the analysis of CRM of rice flour and by comparison with analyte determination by independent techniques, i.e., ion chromatography and inductively coupled plasma optical emission spectrometry; both were carried out after microwave-induced combustion. Sample mass from 0.5 to 260 mg was used and limits of quantification of 1.2 µg g^-1 for Cl and 0.2 µg g^-1 for S were achieved. Wheat, whole wheat, potato and corn flour were analyzed by DSS-EA. Concentrations of Cl and S ranged from 4.8 to 685 µg g^-1 and from 13 to 1328 µg g^-1, respectively.

Advances in the Understanding of Oxaliplatin-Induced Peripheral Neuropathy in Mice: 7-Chloro-4-(Phenylselanyl) Quinoline as a Promising Therapeutic Agent

In this study, the deposition of platinum in oxaliplatin (OXA)-exposed mice and the effects of the oxidative damage on the central nervous system were investigated. The relationship between the reactive species (RS) levels as well as the expression and activity of enzymes, such as catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD) and acetylcholinesterase (AChE), in the development of peripheral neuropathy after OXA exposure, was evidenced. The effects of 7-chloro-4-(phenylselanyl) quinoline (4-PSQ) on OXA-induced peripheral neuropathy was also investigated. Swiss mice received OXA (10 mg kg^-1) or vehicle by intraperitoneal route (days 0 and 2). Oral administration of 4-PSQ (1 mg kg^-1) or vehicle was performed on days 2 to 14. Behavioural tasks started on day 9, after the first OXA administration. It was observed that 4-PSQ reduced the mechanical and thermal hypersensitivity induced by OXA. 4-PSQ and OXA did not affect locomotor and exploratory activities. The results revealed, for the first time, a high concentration of platinum in the spinal cord of mice exposed to OXA. 4-PSQ reversed the increased levels of RS in the spinal cord, cerebral cortex and hippocampus of mice exposed to OXA. The alterations in the activity and expression of the GPx, SOD, CAT and AChE induced by OXA exposure were normalized by 4-PSQ. Therefore, the 4-PSQ might be a good prototype for the development of a more effective drug for the treatment of OXA-induced peripheral neuropathy. The results obtained by the present study expanded the knowledge about the mechanisms involved in the physiopathology of peripheral neuropathy. Graphical abstract.

Determination of trace elements in Sergio mirim: an evaluation of sample preparation methods and detection techniques

In this work, some trace elements (As, Cd, Cr, Cu, and Pb) were determined for the first time in the crustacean Sergio mirim (Decapoda: Thalassinidea: Callianassidae) from Southern Coast (Rio Grande, RS) of Brazil. The trace element determination was carried out by graphite furnace atomic absorption spectrometry (GF AAS) and inductively coupled plasma mass spectrometry (ICP-MS). Different microwave radiation-based sample digestion methods were evaluated. The analyte concentration ranged from 1.45 to 3.70 μg g^-1 for As, 0.615 to 0.942 μg g^-1 for Cd, 0.884 to 7.20 μg g^-1 for Cr, 122 to 275 μg g^-1 for Cu, and 0.390 to 0.916 μg g^-1 for Pb. The limits of quantification for As, Cd, Cr, Cu, and Pb were 0.12, 0.01, 0.16, 0.92, and 0.06 μg g^-1, respectively. The accuracy was evaluated by results comparison between GF AAS and ICP-MS techniques, as well as by analysis of certified reference materials of fish muscle and oyster tissue, with agreement from 92 to 108%. The feasibility of using Sergio mirim as a promising environmental bioindicator candidate was evaluated, since that it is an abundant organism in the studied area (South cost of Brazil) as well as in other places around the world.

Determination of halogens and sulfur in honey: a green analytical method using a single analysis

The halogen determination is important in view of their biological and environmental roles, but their determination has still been considered a challenge, especially at low concentrations. Therefore, a method for honey decomposition using microwave-induced combustion (MIC) combined with ion chromatography and conductimetric detection (for Cl, F, and S determination) or mass detection (for Br and I determination) (IC-CD-MS) is proposed. Trueness was evaluated by adding reference materials (RMs) or a standard solution in the sample. By using 50 mmol L^-1 NH₄OH as the absorbing solution, recoveries for all analytes were between 94 and 103%, in both tests. Moreover, no statistical difference (t test, confidence level of 95%) was observed for the results obtained by IC in comparison with those obtained by inductively coupled plasma optical emission spectroscopy (Cl and S) and by inductively coupled plasma mass spectrometry (Br and I). Finally, the proposed method was applied to 19 honey samples from different origins. The concentrations ranged from < 0.45 to 2.39 mg kg^-1 (Br), 21.8 to 671 mg kg^-1 (Cl), and 11 to 154 mg kg^-1 (S), while the F and I concentrations were below that their quantification limits (LOQs) in all analyzed samples. The LOQs for Br, Cl, F, I, and S were 0.45, 21, 3.7, 0.077, and 8.7 mg kg^-1, respectively. The MIC method provided a compatible solution to IC for the halogen and S determination in honey by a single analysis. Graphical abstract.

Evaluation of sample preparation methods for cereal digestion for subsequent As, Cd, Hg and Pb determination by AAS-based techniques

Sample preparation methodsforcereal digestion were evaluated for the first time for subsequent As, Cd, Hg, and Pb determination by atomic absorption spectroscopy techniques. Microwave-assisted digestion (MW-AD) under high and medium pressure and microwave-induced combustion (MIC) were evaluated. The use of MIC made it possible to digest 700 mg of samples, and agreements of 97, 96, 100 and 92% were obtained for As, Cd, Hg and Pb, respectively, when 7 mol L^-1 HNO₃ was used as the absorbing solution. It was not necessary to dilute the digests obtained to avoid interferences in the quantification of As, Cd, Hg, and Pb. Although high pressure MW-AD was efficient for cereal digestion, interferences were observed on analyte determination. Limits of quantification obtained by MIC were 0.034 (As), 0.015 (Cd), 0.021 (Hg) and 0.105 (Pb) μg g^-1, which are suitable to attain the maximum levels recommended by international agencies in cereal samples.

Intensification of ultrasonic-assisted crude oil demulsification based on acoustic field distribution data

Water removal is an essential step during crude oil production due to several problems such as increased transportation costs and high corrosion rate due to dissolved salts. Indirect low frequency ultrasonic energy (US), using baths, has been recently proposed as an effective alternative for crude oil demulsification. However, the reactor position during sonication and its influence on the demulsification efficiency for crude oil has not been evaluated. In this sense, the aim of this study was to develop an automated system based on an open source hardware for mapping the acoustic field distribution in an US bath operating at 35kHz using a hydrophone. Data acquired with this system provided information to evaluate the demulsification efficiency in the different positions of the US bath and correlate it with the acoustic intensity distribution. The automated 3D-mapping system revealed a higher acoustic intensity in the regions immediately above the transducers (ca. 0.6Wcm^-2), while the other regions presented a relatively lower intensity (ca. 0.1Wcm^-2). Experimental data demonstrated that reactors positioned in the most intense acoustic regions provided a much higher efficiency of demulsification in comparison with the ones positioned in the less intense acoustic field regions. Demulsification efficiency up to 93% was obtained with 15min of sonication (100% amplitude) using few amount of chemical demulsifier. Hence, this work demonstrated that the information acquired with the developed mapping system could be used for inducing a higher efficiency of demulsification only by finding the more suitable position of reactor in the US bath, which certainly will help development of appropriate reactors design when looking for such approach.

Bromine and Iodine Contents in Raw and Cooked Shrimp and Its Parts

The concentration of bromine and iodine was determined in shrimp and its parts (tissue and shells), and changes in the analyte concentration were evaluated after the cooking procedure. Bromine and iodine concentrations were determined by a method recently developed by our research group based on microwave-induced combustion for sample preparation and inductively coupled plasma mass spectrometry for analyte determination. The accuracy was evaluated using a reference material (NIST 8414) that was digested using the proposed method. No statistical difference was observed between certified and determined values (Student's t test, 95% confidence level). Suitable limits of detection (Br, 0.02 μg g(-1) and I, 0.01 μg g(-1)) were obtained for both analytes. Higher concentrations of both analytes were observed in shrimp shells in comparison to shrimp tissue for raw and cooked samples. Moreover, losses of Br and I (between 24 and 43%) were observed after cooking.

Feasibility of ultra-trace determination of bromine and iodine in honey by ICP-MS using high sample mass in microwave-induced combustion

This work demonstrates the feasibility of ultra-trace determination of halogens in biological samples by inductively coupled plasma mass spectrometry (ICP-MS) after decomposition by microwave-induced combustion (MIC). The conventional MIC method was improved to allow the combustion of samples with mass higher than that used in previous works in order to achieve better limits of detection (LODs). The applicability of the proposed method for ultra-trace determination of bromine and iodine in organic samples was demonstrated here using honey. It was possible to decompose up to 1000 mg of honey using microcrystalline cellulose as a combustion aid and polyethylene film for sample wrapping. After combustion, analytes were absorbed using 50 mmol L(-1) NH4OH and recoveries for Br and I were between 99 and 104 %, and relative standard deviations were lower than 5 %. Microwave-assisted alkaline dissolution (MA-AD) was also evaluated for honey sample preparation using NH4OH or tetramethylammonium hydroxide solutions. However, the LODs for the MA-AD method were unsuitable because the high carbon content in digests required a dilution step prior to the analysis by ICP-MS. The LODs obtained by MIC were improved from 1143 to 34 ng g(-1) for Br and from 571 to 6.0 ng g(-1) for I, when compared to the MA-AD method. Furthermore, it was possible to decompose up to eight samples simultaneously in 30 min (including the cooling step) with very low reagent consumption and consequently lower generation of effluents, making MIC method well suited for routine ultra-trace determination of Br and I in honey. Graphical Abstract A high mass of honey was efficiently digested by MIC for subsequent Br and I determination by ICP-MS.

Evaluation of nitrates as igniters for microwave-induced combustion: understanding the mechanism of ignition

Recent studies have reported the use of microwave-induced combustion (MIC) for digestion of several kinds of matrices.

Focused microwave-induced combustion for digestion of botanical samples and metals determination by ICP OES and ICP-MS

The advantages and shortcomings of focused microwave-induced combustion (FMIC) for digestion of plant samples were studied. The effects of sample mass, absorbing solution, oxygen gas flow-rate, and time of reflux step on recoveries of major, minor and trace metals were systematically evaluated. Afterwards, Al, Ba, Ca, Co, Cr, Cu, Mg, Mn, Ni, Sr, V, and Zn were determined by inductively coupled plasma optical emission spectrometry (ICP OES) and by inductively coupled plasma mass spectrometry (ICP-MS). The main advantages of FMIC when compared to microwave-assisted wet digestion (MAWD) and focused-microwave-assisted wet digestion (FMAWD) are the possibility to digest larger masses of samples (up to 3g) using shorter heating times and diluted nitric acid solution for absorbing all analytes. Using the selected experimental conditions for FMIC, residual carbon content was lower than 0.7% for all samples and relative standard deviation (RSD) varied from 1.5 to 14.1%. Certified reference materials (NIST 1515 apple leaves and NIST 1547 peach leaves) were used for checking accuracy and determined values for all metals were in agreement with certified values at a 95% confidence level. No statistical difference (ANOVA, 95% of confidence level) was observed for results obtained by FMIC, FMAWD, and MAWD. Limits of detection were lower when using FMIC in the range of 0.02-0.15 μg g(-1) for ICP OES and 0.001-0.01 μg g(-1) for ICP-MS, which were about 3 and 6 times lower than the values obtained by FMAWD and MAWD, respectively. It is important to point out that FMIC was a suitable sample preparation method for major, minor and trace metals by both determination techniques (ICP OES and ICP-MS). Additionally, since it allows lower LODs (because up to 3g of sample can be digested) and diluted acid solutions are used (without any further dilution), the use of ICP-MS is not mandatory.