Simultaneous on-line pre-concentration and determination of trace metals in environmental samples by flow injection combined with inductively coupled plasma mass spectrometry using silica gel modified with niobium(V) oxide

This work presents the development of an on-line pre-concentration system for simultaneous determination of Cd, Cu, Ni, V, Zn, Co and Pb in aqueous environmental samples and detection by inductively coupled plasma mass spectrometry. The system is based on cationic retention of the analytes onto a mini-column filled with silica gel modified with niobium(V) oxide. The effects of chemicals and flow variables have been investigated. The optimized operating conditions, selected as a compromise between sensitivity and analytical frequency were: sample pH 7.0, sample flow rate of 6.0mL min(-1), eluent flow rate of 2.0mL min(-1), and eluent (HNO(3)) concentration of 2.5mol L(-1). The relative standard deviation (n=7), enrichment factor and linear working range were 0.8-4.5%, 23.3-37.2 and 0.05-25.0microg L(-1), respectively. Limits of detection were between 0.01 and 0.03microg L(-1). The accuracy of the proposed method was checked with certified materials (NASS-4, NASS-5, CASS-4 and SRM 1643e). Values obtained were in accordance with those reported for the certified materials. Recovery was found to be in the range of 90-110% for a suit of water samples with variable matrices (seawater, tap water and ground water) collected in Florianopolis, Brazil.     

Adsorption studies of Cd(II) onto Al2O3/Nb2O5 mixed oxide dispersed on silica matrix and its on-line preconcentration and determination by flame atomic absorption spectrometry

The present study describes the adsorption characteristic of Cd(II) onto Nb₂O₅/Al₂O₃ mixed oxide dispersed on silica matrix. The characterization of the adsorbent has been carried out by infrared spectroscopy (IR), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), energy dispersive X-ray fluorescence analysis (EDXRF) and specific surface area (S_BET). From batch experiments, adsorption kinetic of Cd(II) was described by a pseudo-second-order kinetic model. The Langmuir linear isotherm fitted to the experimental adsorption isotherm very well, and the maximum adsorption capacity was found to be 17.88 mg g⁻¹. Using the effective material, a method for Cd(II) preconcentration at trace level was developed. The method was based on on-line adsorption of Cd(II) onto SiO₂/Al₂O₃/Nb₂O₅ at pH 8.64, in which the quantitative desorption occurs with 1.0 mol L⁻¹ hydrochloric acid towards FAAS detector. The experimental parameters related to the system were studied by means of multivariate analysis, using 2⁴ full factorial design and Doehlert matrix. The effect of SO₄²⁻, Cu²⁺, Zn²⁺ and Ni²⁺ foreign ions showed no interference at 1:100 analyte:interferent proportion. Under the most favorable experimental conditions, the preconcentration system provided a preconcentration factor of 18.4 times, consumption index of 1.08 mL, sample throughput of 14 h⁻¹, concentration efficiency of 4.35 min⁻¹, linear range from 5.0 up to 35.0 μg L⁻¹ and limits of detection and quantification of 0.19 and 0.65 μg L⁻¹ respectively. The feasibility of the proposed method for Cd(II) determination was assessed by analysis of water samples, cigarette sample and certified reference materials TORT-2 (Lobster hepatopancreas) and DOLT-4 (Dogfish liver).     

Valorization of Bio-Residues from the Processing of Main Portuguese Fruit Crops: From Discarded Waste to Health Promoting Compounds

Food processing generates a large amount of bio-residues, which have become the focus of different studies aimed at valorizing this low-cost source of bioactive compounds. High fruit consumption is associated with beneficial health effects and, therefore, bio-waste and its constituents arouse therapeutic interest. The present work focuses on the main Portuguese fruit crops and revises (i) the chemical constituents of apple, orange, and pear pomace as potential sources of functional/bioactive compounds; (ii) the bioactive evidence and potential therapeutic use of bio-waste generated in the processing of the main Portuguese fruit crops; and (iii) potential applications in the food, nutraceutical, pharmaceutical, and cosmetics industries. The current evidence of the effect of these bio-residues as antioxidant, anti-inflammatory, and antimicrobial agents is also summarized. Conclusions of the revised data are that these bio-wastes hold great potential to be employed in specific nutritional and pharmaceutical applications.     

Coupling of ultrasonic nebulization to flame furnace atomic absorption spectrometry—new possibilities for trace element determination

The use of ultrasonic nebulization (USN) with desolvation system for sample introduction in flame atomic absorption spectrometry (F AAS) and flame furnace atomic absorption spectrometry (FF AAS) with a nickel tube is described. Polytetrafluorethylene (PTFE) adaptors were built to replace the pneumatic nebulizer for USN-F AAS measurements. For USN-FF AAS analysis, an alumina injector allowed the direct introduction of the dry aerosol into the nickel tube. The analytical performance of both systems is shown for Ag, Bi, Cd, Cr, Cu, Mn, Pb, Sb, Se, Tl and Zn. The results demonstrate that a sensitivity gain of up to 39 times can be achieved using USN-FF AAS, mainly due to the increase in residence time and to the absence of dilution of the analyte by the flame gases, as the atomization takes place inside the nickel tube. However, elements that require higher atomization temperatures, such as Cr and Mn, are more efficiently determined using USN-F AAS. To evaluate the accuracy of the proposed methods for the determination of trace elements, five certified reference samples were analyzed, and good agreement was, in general, achieved between certified and determined values at a 95% confidence level. The relative standard deviation was frequently below 5%, demonstrating good precision, particularly for USN-FF AAS. In this sense, coupling of USN with F AAS and especially with FF AAS has proved to be simple, safe, with high precision and good accuracy, also maintaining some of the most important features of F AAS, such as the high analytical frequency and the low running cost.     

Determination of As, Ge, Hg, Pb, Sb, Se and Sn in coal slurries by CVG-ETV-ICP-MS using external or isotopic dilution calibration

A method for the multi-elemental determination of As, Ge, Hg, Pb, Sb, Se and Sn in coal reference materials by slurry sampling chemical vapor generation (CVG) using external calibration and isotopic dilution (ID) calibration and detection by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) is proposed. As, Ge, Sb, Se and Sn were determined using the external calibration, while, Hg, Pb, Se and Sn were determined by isotopic dilution. About 50–250 mg of sample was mixed with an acid solution, containing aqua regia and HCl, in an ultrasonic bath. For the isotopic dilution calibration, the enriched isotopes ²⁰¹Hg, ²⁰⁶Pb, ⁷⁷Se and ¹¹⁹Sn were added to the slurry in an adequate amount in order to produce an altered isotopic ratio close to 1. The vapor produced by the reaction of the sample slurry with the reducing agent was transported to the vaporizer and trapped in a Ir-treated graphite tube at 200 °C, before vaporization at 2100 °C and transportation of the vapor to the plasma. The accuracy of the method was assured by the analysis of four certified reference coal samples, using external calibration with aqueous solutions, prepared in the same medium and subjected to the same CVG and trapping procedure as the slurries and also by isotopic dilution calibration. The obtained concentrations were in agreement with the certified values, using the t-Student test for a confidence level of 95%. The detection limits (3 s; n = 5) of isotopic dilution, in ng g^− 1, were: 0.4 for Hg, 900 for Pb, 0.3 for Se and 0.2 for Sn. For external calibration, the detection limits, in ng g^− 1, were: 1.6 for As, 0.1 for Ge, 0.3 for Sb, 0.9 for Se and 7.5 for Sn. The relative standard deviations generally were lower than 14%, adequate for slurry analysis.     

Determination of Cd in biological samples by flame AAS following on-line preconcentration by complexation with O,O-diethyldithiophosphate and solid phase extraction with Amberlite XAD-4

A method for the on-line preconcentration of Cd based on its complex formation with the ammonium salt of O,O-diethylditiophosphate (DDTP) and using the Amberlite XAD-4 resin as a solid support in a column is proposed. Cadmium was detected by flame atomic absorption spectrometry. Different conditions, such as complexing agent concentration, preconcentration time, solutions flow rates and nature and concentration of the eluent were optimized. Different detection limits (LODs) could be established by using different preconcentration times, between 30 s and 5 min, with corresponding LODs from 5 to 1 μg L⁻¹, respectively. The method was validated by analyzing five biological certified samples. The relative standard deviation was usually around 3%, indicating a very good precision. The found concentrations values are in agreement with the certified ones, according to the t-test, for a confidence level of 95%. Enriched seawaters were also analyzed, and the recoveries were between 93 and 108%. The FI method is very simple and probably can be coupled to other measuring analytical techniques.     

Cellulose microfiber functionalized with N,N'-bis (2-aminoethyl)-1,2-ethanediamine as a solid sorbent for the fast preconcentration of Cd(II) in flow system analysis

The present paper describes the synthesis of a new chemically modified cellulose microfiber through oxidation with sodium periodate and functionalization with N,N′-bis (2-aminoethyl)-1,2-ethanediamine for the fast and selective preconcentration of Cd(II) ions in flow system analysis. The new sorbentsorbent was characterized by FTIR, SEM, and surface area values. The uptake behavior of Cd(II) ions onto this sorbent was evaluated from kinetic data, pseudo-first-order and pseudo-second-order models, as well as from Langmuir, Freundlich and Langmuir-Freundlich adsorption isotherms. The maximum sorption capacity of 4.59 mg g⁻¹ was estimated by the Langmuir-Freundlich model with fast kinetics for the sorption of Cd(II) described by the pseudo-second-order kinetic model. After characterization, the sorbent was packed in a mini-column, and a fast flow injection preconcentration system for Cd(II) determination by FAAS was developed. The best Cd(II) preconcentration condition, obtained by means of factorial design and response surface methodology, was achieved at pH 9.36 and a flow rate of 10 mL min⁻¹ followed by elution with 1.0 mol L⁻¹ nitric acid. By using 78 s preconcentration time, fast and highly sensitive determination of Cd(II) ions could be achieved with a limit of quantification of 0.20 μg L⁻¹, preconcentration factor of 26, consumption index of 0.5 mL, concentration efficiency of 20 min⁻¹, and sample throughput of 39 h⁻¹. The repeatability for 10 replicate determinations was found to be 7.8 and 2.5% for Cd(II) ion concentrations of 5.0 and 100.0 μg L⁻¹, respectively. The new sorbent efficiency for the interference-free preconcentration of Cd(II) ions was assessed by analysis of tap, mineral and lake waters, as well as synthetic seawater and normal saline waters. Furthermore, complex samples, such as biological samples, could be analysed by the proposed method in accordance with the accuracy attested by analysis of certified reference materials, TORT-2 (lobster hepatopancreas), and DOLT-4 (dogfish liver).     

Association of 3-O-methylquercetin with β-cyclodextrin: complex preparation, characterization and ex vivo skin permeation studies

3-O-Methylquercetin (3-MQ) is a poorly soluble flavonoid not commercially available that presents antiviral activity. In this work, 3-MQ was isolated from Achyrocline satureioides and an inclusion complex of the flavonoid with β-cyclodextrin (βCD) was prepared. The complex was characterized by means of IR, ¹H NMR and molecular mechanics calculation, which suggested the insertion of the B ring of 3-MQ into the βCD cavity. In addition, the skin permeation of 3-MQ and its associations with βCD from hydroxypropyl methylcellulose (HPMC) hydrogels was investigated using Franz diffusion cells. For 3-MQ assay in pig ear skin, a LC method was developed and validated in the range 0.05–1.5 μg/mL. The hydrogels presented similar behavior, although in the absence of polymeric matrix, the complexation of 3-MQ with βCD seems to enhance its availability on skin surface, demonstrating the influence of the inclusion phenomena on 3-MQ diffusion through the gel and partition toward the stratum corneum.     

Determination of bismuth in metallurgical materials using a quartz tube atomizer with tungsten coil and flow injection-hydride-generation atomic absorption spectrometry

A method for the determination of bismuth in metallurgical materials using hydride generation coupled with a merging zones flow system and atomic absorption spectrometry using a quartz tube atomizer with tungsten coil is proposed. The parameters related to the bismuthine generation, the flow injection system and the use of a tungsten coil were studied and the optimized system shows a wide calibration range and good stability over time, without losses in sensitivity. The analytical curve is linear from 10 to 750 μg l⁻¹ of Bi with R0.999. A detection limit of 1.9 ng Bi and an analytical frequency of 60 determinations per hour were obtained. Five metallurgical reference materials were analyzed with the proposed method after their acid dissolution. The results obtained were in good agreement with certified or recommended values, and the relative standard deviations were lower than 5%.     

Slurry sampling of sediments and coals for the determination of Sn by HG-GF AAS with retention in the graphite tube treated with Th or W as permanent modifiers

A method for the determination of Sn in slurry samples of sediment and coal by hydride generation graphite furnace electrothermal atomic absorption spectrometry (HG-GF AAS) is proposed. The slurries were prepared by mixing the ground sample (particle size 50 m) with 2.0 mol L^–1 HCl for the sediment samples or with 2.0 mol L^–1 HCl+1.0% v/v HF in a saturated boric acid medium for the coal samples. The slurry was placed in an ultrasonic bath for 30 min, before and after standing for 24 h, with occasional manual stirring. The graphite tube was treated with 0.5 mg of Th or W as a permanent modifier. Sn determination was carried out by electrothermal atomic absorption spectrometry at the optimized retention temperatures of 450 and 300°C for Th and W treatment, respectively. With this coupling, kinetic interference in the formation of the hydrides is avoided, and excellent detection limits can be obtained by using peak height. For the chemical vapor generation device, an optimized volume of 2 mL of sample slurry and an optimized NaBH₄ concentration of 5% m/v were employed. The vapor produced was transported and retained on the graphite tube surface, which was further heated for Sn atomization. The accuracy of the method was verified by analyzing five certified sediments and three coals. By using the external calibration against aqueous standard solutions, the results obtained were in agreement with the certified values only for the sediment samples. For the coal samples, an addition calibration curve, obtained for one certified coal, was necessary to achieve accurate results. The obtained limits of detection were 0.03 g g^–1 for sediment and 0.09 g g^–1 for coal with Th as permanent modifier. The relative standard deviations were lower than 15%, demonstrating an adequate precision for slurry analysis. Sediment and coal samples from Santa Catarina, Brazil, were also analyzed.