Self-organizing map applied to the choice of internal standards for the determination of Cd, Pb, Sn, and platinum group elements by inductively coupled plasma mass spectrometry.

The behaviors of internal standards, according to different flow rates of the cell collision gas (He), were studied for the determination of Cd, Pb, Pd, Pt, Rh, and Sn in samples of fish and mollusks by inductively coupled plasma mass spectrometry (ICP-MS). The elements Bi, Ge, In, Sc, and Y were selected as internal standards, considering their masses and first ionization energies. Addition and recovery experiments were carried out at three concentration levels to evaluate the accuracy of the method applied for the analysis of two samples with different matrices. The results were evaluated using a self-organizing map (SOM). The best analyte/IS pairs were as follows: 114Cd+/74Ge+, 195Pt+/74Ge+, and 208Pb+/74Ge+. For 103Rh+, 106Pd+, and 120Sn+, greater accuracy was achieved without use of an internal standard. Helium gas (2.8 mL min-1) was used in the collision cell for the analytes, except for Sn, and recoveries ranged from 98 to 101% under optimal conditions. The use of SOM as an exploratory analysis tool was an effective approach for selection of the most appropriate internal standards.

Synthesis of natural deep eutectic solvents using a mixture design for extraction of animal and plant samples prior to ICP-MS analysis.

Solvents with both low density and viscosity have the advantage of higher extraction efficiency due to lower diffusivity and consequently higher mass transfer. In this study, a mixture design was performed for the synthesis of three different natural deep eutectic solvents (NADES) using citric acid, malic acid, and xylitol. The optimized proportion for each of the three solvents synthesized was selected based on density and viscosity values. The NADES were characterized by infrared spectroscopy analysis, that showed characteristic bands of the initial reagents and the presence of hydrogen bonds confirming the formation of each deep eutectic solvent. Then, the NADES were used as solvents in ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) of biological tissue and plant material samples for the determination of As, Cd, Hg, Pb, Se, and V by inductively coupled plasma mass spectrometry (ICP-MS). The results for the proposed methods were compared to microwave-assisted acid digestion (MW-AD). The extraction recoveries ranged from 80 to 120% for most of the elements determined. The use of NADES as carbon sources improved the sensitivity of the As and Cd analyses, due to charge transfer reactions between the analyte and C+ and/or other carbon species. In addition, the Analytical Eco-Scale was used to assess the greenness of the proposed analytical procedures (UAE and MAE). It showed that the UAE and MAE methods provided excellent green analyses, while the MW-AD method was rated as an acceptable green procedure.

Natural deep eutectic solvents for sample preparation prior to elemental analysis by plasma-based techniques.

Natural deep eutectic solvents (NADES) based on xylitol, citric acid, and malic acid were synthesized and were then characterized using infrared spectroscopy, thermogravimetry (TG), differential scanning calorimetry (DSC), also density and viscosity were measurements. The deep eutectic solvents were used as solvent in ultrasound-assisted extraction (DES-UAE) of plant samples prior to elemental analysis. Inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP OES) were employed for the determination of As, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, and Zn in the extracts. The infrared analyses of the NADES revealed bands characteristic of the initial reagents, with the presence of hydrogen bonds, which confirmed the formation of a NADES. The thermal analyses showed decomposition temperatures of around 170 °C and endothermic events related to degradation of the NADES. The viscosity and density parameters were found to be related to the presence of hydrogen bonds. The extraction recoveries ranged from 80% to 120%, with some analytes presenting poor recoveries. There were no significant differences between the NADES, in terms of the concentrations of the analytes found in the extracts. However, there were differences between the analyte concentrations obtained using the NADES extraction method and the concentrations obtained using microwave-assisted acid digestion (MW-AD), possibly due to the different types of interactions between the solvents and the analytes. Plant tissues are complex matrices containing substantial amounts of silica, so some elements may be tightly bound and consequently difficult to release. The results indicated that UAE using NADES is a promising technique for the elemental extraction of plant samples.

Bioaccumulation and acute toxicity of As(III) and As(V) in Nile tilapia (Oreochromis niloticus).

The distribution of arsenic in the different tissues of tilapia fish is determined by the exposure time and the depuration rate. The mechanisms of toxicity/carcinogenicity depend on the arsenic species involved in the biotransformation processes. After a 7-day exposure period, the accumulation of inorganic arsenic (iAs) in the tilapia tissues studied was in the order: liver > stomach > gills > muscles. In bioaccumulation assays, the values of the organ uptake constant (ka) ranged from 0.06 to 0.51 mL g-1 d-1, while the depuration rate constant (kd) values were in the range 0.03-1.15 d-1. Higher iAs bioaccumulation factor (BCF) values were observed for the stomach (3.1 mL g-1) and the liver (1.6 mL g-1), reflecting their high capacity to accumulate iAs species. These organs act as long-term storage sites for iAs, following chronic exposure. The LC50 values were determined considering the average iAs concentration and the cumulative fish mortality. For As(III), the LC50 values indicated fish mortality at concentrations above 30 mg L-1. The fish showed greater tolerance to exposure to As(V), compared to As(III), with fish mortality after the second day of exposure requiring an As(V) concentration 7-fold higher than As(III).

In situ digestion for the determination of Ca in beverages by tungsten coil atomic emission spectrometry.

Tungsten coil atomic emission spectrometry (WCAES) is employed for the determination of calcium in juice, mineral and coconut water samples. A sample aliquot of 20 µL is placed directly on the coil and a constant-voltage power source is used to dry and atomize the sample, as well as to promote Ca atomic emission. Analytical signals are resolved and detected using a Czerny-Turner spectrometer and a charge coupled device detector. Some experimental parameters such as coil position related to the spectrometer entrance slit and integration time are critically evaluated. A heating program with relatively constant drying temperatures is used in all measurements. An in situ digestion procedure is used to partially decompose organic matrices and improve WCAES precision and accuracy. By adding an oxidizing mixture to the sample and including a digestion step in the heating cycle, no statistical difference was observed between WCAES and ICP OES results for Ca in juice and coconut water samples. Mineral water samples were simply diluted with 1% vv(-1) HNO(3) before analysis and no significant interference was observed for concomitants such as Na and K. Despite severe positive interference caused by Mg, good agreement was obtained between WCAES and ICP OES results for Ca in several mineral water samples. Limits of detection and quantification obtained were 0.02 and 0.07 mg L(-1), respectively. The method precision, calculated as the relative standard deviation for 10 consecutive measurements of a 2.5 mg L(-1) Ca solution, is 3.8%.

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 matrices containing amino acids, proteins and lipids in their composition produced nitrobenzoic acid isomers and other organic compounds after cleavage of chemical bonds.

Coconut coir as biosorbent for Cr(VI) removal from laboratory wastewater.

A high cost-effective treatment of sulphochromic waste is proposed employing a raw coconut coir as biosorbent for Cr(VI) removal. The ideal pH and sorption kinetic, sorption capacities, and sorption sites were the studied biosorbent parameters. After testing five different isotherm models with standard solutions, Redlich-Peterson and Toth best fitted the experimental data, obtaining a theoretical Cr(VI) sorption capacity (SC) of 6.3 mg g(-1). Acid-base potentiometric titration indicated around of 73% of sorption sites were from phenolic compounds, probably lignin. Differences between sorption sites in the coconut coir before and after Cr adsorption identified from Fourier transform infrared spectra suggested a modification of sorption sites after sulphochromic waste treatment, indicating that the sorption mechanism involves organic matter oxidation and chromium uptake. For sulphocromic waste treatment, the SC was improved to 26.8+/-0.2 mg g(-1), and no adsorbed Cr(VI) was reduced, remaining only Cr(III) in the final solution. The adsorbed material was calcinated to obtain Cr(2)O(3,) with a reduction of more than 60% of the original mass.

Microwave-assisted Acid decomposition of animal- and plant-derived samples for element analysis.

A single microwave-assisted acid-decomposition procedure is proposed for sample preparation of plant- and bovine-derived materials prior to multielement determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). The procedure involved sample grinding in a cryogenic mill to reduce particle sizes and increase the surface area for acid attack, followed by decomposition under high pressure and temperature. A single heating program was employed and efficiently destroyed most of the organic matrix by using small volumes of nitric acid and hydrogen peroxide. Accuracy of the elemental analysis was indicated by the good agreement between certified and found values of elements in plant and animal samples at 95% confidence level. The sample preparation procedure was fast and reproducible, and proved to be efficient for elemental analysis in agricultural and food-related samples by a sensitive multielement technique such as ICP-OES.