Magnetic solid-phase extraction (M-SPE) is a procedure based on the use of magnetic sorbents for the separation and preconcentration of different organic and inorganic analytes from large sample ...volumes. The magnetic sorbent is added to the sample solution and the target analyte is adsorbed onto the surface of the magnetic sorbent particles (M-SPs). Analyte-M-SPs are separated from the sample solution by applying an external magnetic field and, after elution with the appropriate solvent, the recovered analyte is analyzed. This approach has several advantages over traditional solid phase extraction as it avoids time-consuming and tedious on-column SPE procedures and it provides a rapid and simple analyte separation that avoids the need for centrifugation or filtration steps. As a consequence, in the past few years a great deal of research has been focused on M-SPE, including the development of new sorbents and novel automation strategies. In recent years, the use of magnetic carbon nanotubes (M-CNTs) as a sorption substrate in M-SPE has become an active area of research. These materials have exceptional mechanical, electrical, optical and magnetic properties and they also have an extremely large surface area and varied possibilities for functionalization. This review covers the synthesis of M-CNTs and the different approaches for the use of these compounds in M-SPE. The performance, general characteristics and applications of M-SPE based on magnetic carbon nanotubes for organic and inorganic analysis have been evaluated on the basis of more than 110 references. Finally, some important challenges with respect the use of magnetic carbon nanotubes in M-SPE are discussed.
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•Magnetic carbon nanotubes (M-CNTs) as a sorption substrate for SPE.•Synthesis of M-CNTs and approaches for their use in M-SPE.•M-CNTs as sample preparation substrates for organic and inorganic analysis.
•The use of solid phase extraction for speciation of inorganic Se is described.•Different SPE strategies and sorbents used for inorganic selenium speciation are discussed.•Analytical methods for ...speciation of inorganic Se in water samples are reviewed.
Selenium is an essential element for the normal cellular function of living organisms. However, selenium is toxic at concentrations of only three to five times higher than the essential concentration. The inorganic forms (mainly selenite and selenate) present in environmental water generally exhibit higher toxicity (up to 40 times) than organic forms. Therefore, the determination of low levels of different inorganic selenium species in water is an analytical challenge. Solid-phase extraction has been used as a separation and/or preconcentration technique prior to the determination of selenium species due to the need for accurate measurements for Se species in water at extremely low levels. The present paper provides a critical review of the published methods for inorganic selenium speciation in water samples using solid phase extraction as a preconcentration procedure. On the basis of more than 75 references, the different speciation strategies used for this task have been highlighted and classified. The solid-phase extraction sorbents and the performance and analytical characteristics of the developed methods for Se speciation are also discussed.
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► The use of CNTs as sorbent for metal species in solid phase extraction has been described. ► Physical and chemical strategies for functionalization of carbon nanotubes have been ...discussed. ► Published analytical methods concerning solid phase extraction and atomic spectrometric determination have been reviewed.
New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes – due to their high adsorption and desorption capacities – have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.
In the last decades, the extensive use of chromium in industrial activities has led to the discharge of different chromium species into the biosphere. The two stable chromium forms are Cr(III) and ...Cr(VI), which have dramatically different properties. While the first one is essential, the second is harmful and carcinogenic, even at very low concentration. Therefore, the appropriate analysis of chromium in environmental, biological, food and other kind of samples need a reliable separation and subsequent quantification of both Cr species. The present paper provides a critical review of chromium speciation methods in which solid phase extraction was employed as sample pretreatment using graphene and carbon nanotubes (and their diverse oxidized, functionalized and magnetic derivatives) as sorbents. The different published methods for the speciation of Cr(III), Cr(VI) or both species are described and classified on the basis of the separation strategy employed: (i) the selective retention of only one of the two species by the sorbent, (ii) the retention of a Cr-chelate formed by using a ligand selective for only one of the Cr-species, or (iii) the sorption of both Cr(III) and Cr(VI) species. In addition, the distinct applied SPE modes (on-column, dispersive or magnetic) and their automation possibilities, the analytical techniques utilized for measurement of the Cr-species after separation, as well as the analytical figures of merit of the methods developed up to date are evaluated. Finally, the expected future trends of solid phase extraction for Cr speciation based on carbon nanomaterials such as graphene, carbon nanotubes and their derivatives as sorbents are commented.
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•Carbon nanomaterials (graphene and CNTs) as sorbents in solid phase extraction.•Solid phase extraction strategies for Cr speciation with graphene and CNT as sorbents.•Last trends for Cr speciation with functionalized graphene and CNTs.
•Develop of an authentication system for honeys with protected geographical indication.•Authentication system based on NIR spectra processed by multivariate chemometric techniques.•SIMCA builds a ...classification model that will allow the detection of falsifications.
In this work, information contained in near infrared (NIR) spectra of honeys with protected geographical indication (PGI) “Mel de Galicia” was processed by means of different chemometric techniques to develop an authentication system for this high quality food product. Honey spectra were obtained in a fast and single way, and they were pretreated by means of standard normal variate transformation in order to remove the influence of particle size, scattering and other factors, and prior to their use as input data. As the first step in chemometric study, display techniques such as principal component analysis and cluster analysis were applied in order to demonstrate that the NIR data contained useful information to develop a pattern recognition classification system to authenticate honeys with PGI. The second step consisted in the application of different pattern recognition techniques (such as D-PLS: Discriminant partial least squares regression; SIMCA: Soft independent modelling of class analogy; KNN: K-nearest neighbours; and MLF-NN: Multilayer feedforward neural networks) to derive diverse models for PGI-honey class with the objective of detecting possible falsification of these high-quality honeys. Amongst all the classification chemometric procedures, SIMCA achieved to be the best PGI-model with 93.3% of sensitivity and 100% of specificity. Therefore, the combination of NIR information data with SIMCA developed a single and fast method in order to differentiate between genuine PGI-Galician honey samples and other commercial honey samples from other origins that, due to their lower price, could be used as substrates for falsification of genuine PGI ones.
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•Analytical techniques for characterization of CNTs: classification, description and examples.•Determination methods for CNTs in biological and environmental samples.•Future trends ...and perspectives for characterization and determination of CNTs.
In the present paper, a critical overview of the most commonly used techniques for the characterization and the determination of carbon nanotubes (CNTs) is given on the basis of 170 references (2000–2014). The analytical techniques used for CNT characterization (including microscopic and diffraction, spectroscopic, thermal and separation techniques) are classified, described, and illustrated with applied examples. Furthermore, the performance of sampling procedures as well as the available methods for the determination of CNTs in real biological and environmental samples are reviewed and discussed according to their analytical characteristics. In addition, future trends and perspectives in this field of work are critically presented.
In humans the main route of exposure to toxic metals is through the diet, and there is therefore a clear need for this source of contamination to be minimized, particularly in food of animal origin. ...For this purpose, the various sources of toxic metals in livestock farming (which vary depending on the production system) must be taken into account. The objectives of the present study were to establish the profile of metal exposure in dairy cattle in Spain and to determine, by chemometric (multivariate statistical) analysis, any differences between organic and conventional systems. Blood samples from 522 cows (341 from organic farms and 181 from conventional farms) were analysed by inductively coupled plasma mass spectrometry to determine the concentrations of 14 elements: As, Cd, Co, Cr, Cu, Fe, Hg, I, Mn, Mo, Ni, Pb, Se and Zn. In conventional systems the generally high and balanced trace element concentrations in the mineral-supplemented concentrate feed strongly determined the metal status of the cattle. However, in organic systems, soil ingestion was an important contributing factor. Our results demonstrate that general information about the effects of mineral supplementation in conventional farming cannot be directly extrapolated to organic farming and special attention should be given to the contribution of ingestion of soil during grazing and/or ingestion of soil contaminated forage.
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•Chemometric analysis allow to establish a pattern of metals related to farming.•In organic farming, the soil ingestion is the main factor affecting metal status.•In conventional farming, metal profile is determined by the supplementation of feed.•Mineral supplementation in conventional may not be directly extrapolated to organic farming.
•We used chemometric analysis to differentiate between organic and conventional milk.•We designed mathematical models to predict type of milk based on metal content.•The prediction model is capable ...of identifying types of milk in almost 95% of cases.•The method is valuable for initial verification of organic products.
The objective of this study was to develop a method for authenticating organic milk samples in North Spain on the basis of its trace mineral composition. Fourteen elements in 98 samples were determined by inductively coupled plasma mass spectrometry. Although concentrations of Co, Cr, Cu, I, Se and Zn where statistically higher in conventional milk and As in organic, none of these elements by itself was able to discriminate between organic and conventional milk. The chemical data was examined by principal component analysis and cluster analysis, revealing a natural separation between organic and conventional milk. In a second step, several supervised pattern recognition techniques were used to construct mathematical models for predicting the type of milk (organic or conventional) based on the metal content. The results proved that the model constructed using the artificial neural network is capable of correctly identifying the type of milk in almost 95% of cases.
The present study aimed to evaluate trace mineral status of organic dairy herds in northern Spain and the sources of minerals in different types of feed. Blood samples from organic and conventional ...dairy cattle and feed samples from the respective farms were analysed by inductively coupled plasma mass spectrometry to determine the concentrations of the essential trace elements (cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), iodine (I), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se) and zinc (Zn)) and toxic trace elements (arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb)). Overall, no differences between organic and conventional farms were detected in serum concentrations of essential and toxic trace elements (except for higher concentrations of Cd on the organic farms), although a high level of inter-farm variation was detected in the organic systems, indicating that organic production greatly depends on the specific local conditions. The dietary concentrations of the essential trace elements I, Cu, Se and Zn were significantly higher in the conventional than in the organic systems, which can be attributed to the high concentration of these minerals in the concentrate feed. No differences in the concentrations of trace minerals were found in the other types of feed. Multivariate chemometric analysis was conducted to determine the contribution of different feed sources to the trace element status of the cattle. Concentrate samples were mainly associated with Co, Cu, I, Se and Zn (i.e. with the elements supplemented in this type of feed). However, pasture and grass silage were associated with soil-derived elements (As, Cr, Fe and Pb) which cattle may thus ingest during grazing.
Honeybees interact strongly with vegetables, air, soil, and water in the vicinity of the hive and, as a consequence, pollutants from these sources are translated to the honeybees and to the hive ...products. Therefore, over the last decades of the past century, honeybees and honey have been proposed as possible bioindicators for the study of the environmental status of the area surrounding the hive. This work is a critical review on the use of the hive as a passive sampling device and on the use of honeybees and honey as environmental bioindicator substrates for metals and radionuclides. The design of sampling networks, sampling procedures, sample pretreatments, analytical techniques, data analysis, and other influencing factors in this area are also reviewed.
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