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The paper proposes a simple approach for the preconcentration of carboxylated single-walled carbon nanotubes and their determination in river water samples. The method is based on a microliquid–liquid extraction into an ionic liquid (bmim PF6) in the presence of a cationic surfactant (CTAC). 10 μL of the ionic liquid phase are microfiltrated by using a home-made filtration device having a small diameter. The membrane was of cellulose with a pore size of 5 μm. Finally, the carbon nanotubes retained in the membrane are directly analyzed by Raman spectroscopy, which allows their direct characterization and quantification. The limit of detection was 0.050 mg L−1. The precision, for a 1.4 mg L−1 concentration of carbon nanotubes, is 3.2%.

For the first time a soft material formed from coiled carbon nanotubes and 1-hexyl-3-methylimidazolium hexafluorophosphate has been used as sorbent material. The soft material has high stability as well as a high capacity to adsorb analytes. In this work we propose using a natural cotton fiber impregnated with the soft material to miniaturize the system. The system was tested for the analysis of polycyclic aromatic hydrocarbons in spiked river water samples. The absolute recovery ranged between 97.5 and 105.5 %, demonstrating the usefulness of the soft material. The limit of detection ranged from 2.5 to 6.1 μg/L and the precision expressed as the relative standard deviation for the analysis of five consecutive analyses ranged between 2.5 and 5.8 %.

Here, we propose the use of ionic liquid-modified QDs for the combination of ionic liquid-based headspace single drop microextraction technique (IL-HS-SDME) and QD-based fluorimetric detection. In that way, we exploit the advantages of ILs as extractant solvent and the use of QDs as fluorescence detection probe. After in situ generation of volatile trimethylamine (TMA) from fish samples, the analyte was extracted and preconcentrated directly onto a (QD)IL microdrop by HS-SDME. Then, TMA was quantified through the enhancing effect produced on the initial fluorescence of the (QD)IL dispersion. The working conditions for the (QD)IL-HS-SDME procedure were: 20 μL microdrop of (QD)IL exposed for 2 min to the headspace of a 5 mL aqueous sample (0.2 g of fish in 10 M NaOH) placed in a 10 mL vial with stirring and thermostatted at 50-60 °C. For the detection, the microdrop was transferred to a microcuvette with 300 μL of acetonitrile and the fluorescence was recorded (λ(em) = 570 nm, λ(exc) = 400 nm). Under the selected conditions, the analytical response was linear over the range from 0.05 to 0.25 mg L(-1) (R(2) = 0.997) with a detection limit of 0.014 mg L(-1) (0.35 μg TMA per gram of fish) and the relative standard deviation was 3.5% (n = 5). The proposed method was applied to the determination of TMA in hake fish samples with satisfactory results.

Characterization of nanomaterials is an issue of increasing interest. Electrophoresis—in its different formats (e.g. capillary zone electrophoresis, gel electrophoresis, isotachophoresis)—as well as dielectrophoresis has shown great potential use in this field. They have been used not only for the size- or shape-based separation of nanoparticles of different nature (and its bioderivatives) but also to manipulate them in order to develop new nanotechnological devices. This chapter reviews the main progress in this field.

We have developed a new SERS substrate based on the reduction of silver nitrate in the presence of ZnS-capped CdSe quantum dots. This substrate showed higher sensitivities as compared to a hydroxylamine-reduced silver sol. On the basis of this new substrate, at-line SERS detection was coupled with capillary liquid chromatography (cap-LC) for the separation and selective determination of pyrimidine and purine bases. For this purpose, wells of a dedicated microtiter plate were loaded with 20 μL of the SERS substrate and placed on an automated x,y translation stage. A flow-through microdispenser capable of ejecting 50 pL droplets, at a frequency 100 Hz, was used as the interface to connect the cap-LC system to the wells loaded with SERS substrate. A detailed study of the dependence of both the separation and the surface-enhanced Raman spectra of each base on the pH was performed to optimize the system for maximum sensitivity and selectivity. Highly satisfactory analytical figures of merit were obtained for the six investigated bases (cytosine, xanthine, hypoxanthine, guanine, thymine, and adenine) with detection limits ranging between 0.2 and 0.3 ng injected on the capillary LC column, and the precisions were in the range of 3.0-6.3%.

Here, we report an optical sensor for fullerene C(60) in water using CdSe/ZnS quantum dots coated by p-tertbutylcalix[8]arene. This C(60)-nanosensor is based on the selective host-guest interaction between fullerene C(60) and p-tertbutylcalix[8]arene. The procedure for the synthesis of p-tertbutylcalix[8]arene-CdSe/ZnS complex is described, and its fluorescent characteristics are also reported. We found that the interaction between C(60) fullerene and p-tertbutylcalix[8]arene-CdSe/ZnS complex quenches the original fluorescence of calix-QDs according to the Stern-Volmer equation. The mechanism of interaction is discussed. Finally, the potential application of the proposed method using the designed nanosensor for determination of C(60) in spiked environmental river water samples is demonstrated. For the analysis of river samples, a liquid-liquid extraction multistep preconcentration procedure is proposed. The method, which is simple and rapid, allows the detection of 5 μg L(-1) of fullerene. This sensor could be a useful tool for environmental and toxicological studies.

This paper reports for the first time the use of microextraction by packed sorbents in combination with Capillary electrophoresis (CE) for carry out the preconcentration and determination of three characteristics cations of ionic liquids in river water. Before analysis a carbon nanotubes modified filter was used to remove potential organic interferences from the samples. The system was automated by connecting the syringe–microextraction by packed sorbents (MEPS) assembly to a syringe pump and interfacing it to a computer. After preconcentration, analytes were determined by NACE. The limits of quantification of analytes were of 0.02 mg L −1 from only 5 mL of sample with an RSD of less than 7%. The values of recovery range between 85 and 97%.

Assemblies of closed nanoparticles have focused interest because they exhibit new optical and chemical properties. The use of a 1D covalent strategy for quantum dots-assemblies has been proposed in this work as novelty. It was studied the effect of use different dithiols, including aromatic and aliphatic dithiol compounds, on the formation of QDs-assemblies in order to establish the influence of the linker's structure on the geometry of the assemblies, and hence on their properties. As a second part of the work, the changes on analytical response to analytes thanks to the formation of QDs-assemblies when dithiols are added were studied for firs time. For this study, some biogenic amines were selected as target analytes. We observed an improvement of 2.7–4 times in the sensitivity, expressed as slope of the calibration graph, when the dithiols were added to the system obtaining QDs-assemblies.

This paper presents a simple and rapid methodology to separate and characterize free CdSe quantum dots (QDs) in aqueous medium by capillary electrophoresis (CE). First, we describe a controlled derivatization procedure to obtain water-soluble QDs through noncovalent interactions. This derivatization methodology was based on the formation of a complex between the QDs and several types of surfactants to enhance the hydrophilicity and stability of the CdSe QDs. The surfactants used to achieve the surface functionalization were trioctylphosphine oxide/trioctylphosphine (TOPO/TOP) and sodium dodecyl sulfate (SDS). Different CdSe QDs core sizes were synthesized as function of the nanocrystals growing time and then subjected to controlled coating. These free QDs were separated by capillary zone electrophoresis (CZE) based on the differences in the charge-to-mass ratio of the QDs-TOPO/TOP-SDS complexes, and the detection was carried out with UV-vis and laser-induced fluorescence (LIF) techniques obtaining detection limits 5 times lower with CE-LIF. Under the optimal working conditions, four different-sized QDs were successfully separated whose average sizes were 3.1, 3.6, 4.3, and 4.9 nm, and the size distribution was less than 7% for all of them [calculated from the full width at half-maximum (fwhm) of the fluorescence spectra and confirmed by high-resolution transmission electron microscopy (HTEM)]. Therefore, we were able to separate QDs that differ in only 0.5 nm in diameter and 19 nm in fluorescence emission maximum. This corresponds to the better resolution achieved in the analysis of these kinds of nanoparticles. Finally, a correlation between the migration times plus or minus peak width and the core sizes plus or minus size distribution was established.

Intensely fluorescent, colistin-functionalised CdSe/ZnS QDs (Colis-QDs) nanoparticles, are synthesized and used as sensitive probes for the detection of Escherichia coli, a Gram-negative bacteria. Colistin molecules are attached to the terminal carboxyl of the mercaptoacetic acid-capped QDs in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) as amide bond promoters. The TEM analysis of bacteria treated with Colis-QDs conjugates showed the accumulation of Colis-QDs in the cell wall of E. coli. Under the recommended working conditions, the method provides a detection limit as few as 28 E. coli cells per mL, which is competitive which more elaborate detection systems. The simplicity of the method together with short analysis time (< 15 min, without including preparation and photoactivation of the Colis-QDs conjugate) make the proposed approach useful as quick bacteria screening system.

CdSe/ZnS QDs have demonstrated capacity to act as reducing agent in organic media such as acetonitrile and ethanol. By using fluorescence and Raman spectroscopy, it has been demonstrated that QDs reduce diquat herbicide to its monocation radical. The reaction is characterized to present a high reaction rate making possible to perform the reaction by simple filtration of the solution containing the herbicide through a QDs modified filter. The monocation radical presents a high fluorescence emission spectrum which was selected as the analytical signal to quantify the diquat herbicide. The method described here for the analysis of diquat herbicide in oat grains is simple and fast allowing the analysis of trace level of herbicide in only 6 min. The excellent sensitivity and reproducibility of the methods indicate that the reaction is favoured from both thermodynamic and kinetic point of view. The results presented open up the possibility to use QDs as redox agent. The sensitivity of the method expressed as detection limit was only of 0.01 mg kg(-1).The lineal range was between 0.05 and 0.5 mg kg(-1). The time of analysis per sample, including extraction, reaction and fluorescent measurement was only of 6 min.

Studies in vitro have permitted the identification of enteric neural progenitor cells. Now the question arises as to where these progenitor cells are located in vivo. The purpose of this paper is to identify possible candidate cells by means of transmission electron microscopy (TEM). We have located three interstitial cellular types around the rat duodenum myenteric plexus. Type I cells have been identified as Interstitial Cells of Cajal (ICCs). These cells present well defined ultrastructural characteristics, including the triple connexion IC-nervous trunk-blood vessels. Type II cells show characteristics of immature cells, emphasizing the presence of a single cilium with the structure (9+0). To analyse this nanostructure, we have elaborated a reconstruction on ultrathin sections. The two previously described cellular types could be considered to be different functional states of the same cell. Type III cells present ultrastructural characteristics of fibroblast-like cells. This study suggests that Type II cells could be a source of neural progenitor cells.

La presente Memoria, dividida en cuatro capítulos, describe la síntesis de ligandos heteroditópicos que puedan presentar un comportamiento hemilábil, la preparación y caracterización de complejos de rodio(I) con dichos ligandos y la evaluación de estos compuestos como catalizadores en reacciones catalíticas homogéneas de hidroaminación de alquenos y polimerización e hidrosililación de alquinos. Los resultados descritos en este trabajo demuestran el potencial que éste tipo de ligandos hemilábiles tienen en el campo de la catálisis homogénea ya que no solo ofrecen la posibilidad de protección reversible de una o varias posiciones de coordinación sino que también permiten la activación y transformación de los sustratos.

The paper presents a general overview of the use of nanoparticles to perform sample preparation. In this way the main uses of nanoparticles to carry out solid phase extraction, solid phase microextraction, liquid–liquid extraction and filtration techniques are described for a wide range of nanoparticles including carbon nanoparticles, metallic, silica and molecular imprinted polymer nanoparticles.

Advances in nanotechnology have enabled the development of nanoporous membranes based on carbon nanotubes, which, by virtue of their exceptional properties, constitute excellent supports for analytical processes, including the selective separation of some molecules.

SCOPUS: er.j, info:eu-repo/semantics/published

Amplification of fluorescence is a nanoscale phenomenon which is particularly pronounced in close proximity to metal nanostructures. We have demonstrated for first time that fluorescence amplification can also be produced by single-walled carbon nanotube-quantum dot nanocomposites (SWCNT-QDs). Concretely we exploit the adsorption capabilities of SWCNTs to facilitate the interaction of analytes with the nanoparticle. The fluorescence amplification mechanism is discussed in the paper. The analytical potential of these nanocomposites has been demonstrated for the detection of trace levels of polycyclic aromatic compounds (PAHs) in river water samples. Compared with QDs nanoparticles, the fluorescence enhancement achieved with the SWCNT-QDs nanocomposites was 3.6-5.5 times higher.

A flow-cell for micro-porous membrane liquid-liquid extraction with a sheet membrane was used to extract 2-ethylhexyl 4-(dimethylamino) benzoate (EDB) from urine of solar-cream users and spiked wine samples. The cell enabled the target analyte to be extracted from 7.9 mL of donor solution into 200 microL of acceptor solution (decane). After extraction, the acceptor solution was transferred to a micro-vial for GC-MS analysis without derivation. In this work, variables affecting the enrichment factor were also studied, such as organic solvent, extraction time, recirculation flow of the donor solution through the donor chamber, presence of potassium chloride and ethanol in the donor solution and pH. The method has been evaluated in terms of linearity, sensitivity, precision, limits of detection and quantification and extraction efficiency. Limits of quantification were 1 and 3 microg L(-1) EDB for urine and wine, respectively. Quantitative analysis has been carried out by applying the method of standard additions. Within- and between-day relative standard deviations were lower than 12% and 20%, respectively. EDB was found in the urine of users of cream containing EDB in the concentration interval 1.2-7.2 microg L(-1). Therefore, this provides evidence of EDB dermal absorption and subsequent excretion through the urinary tract. EDB was not found in the analysed wine samples.

In this paper, for the first time, the possibility of preconcentrating and determining carboxylic single-walled carbon nanotubes (c-SWNTs) from environmental water samples is demonstrated. The method is based on the preconcentration of c-SWNTs and their further electrophoretic analysis. The preconcentration of c-SWNTs has been successfully performed on a filter modified with multiwalled carbon nanotubes (MWNTs), which allows the use of high preconcentration rates. MWNT-modified filters were fabricated in the laboratory from a surfactant dispersion of MWNTs. The main variables affecting the preconcentration of analytes are studied and discussed in the paper. Electrophoretic separation of carboxylic SWNTs was accomplished by using a 50 mM ammonium acetate solution at pH 7.5 as a background electrolyte and a potential of 15 kV. Under these conditions, separation was completed within only 5 min. Recoveries for the analysis of spiked samples ranged from 70 to 85% and the precision from 6.4 to 7.3%.

Microorganisms can be considered a bio-colloid. That is, they have a characteristic outer surface that carries, or can carry, a charge. Precisely, differences in the surface can be exploited for separation by capillary electrophoresis (CE). In fact, methods based on CE seem to be very promising because they should produce rapid and high-efficiency separations. Although CE can be used to separate microbial (i.e., bacteria, virus, fungi, and whole cells) and subcellular particles (i.e., mitochondria and nuclei), this chapter is focused mainly on the determination of bacteria and virus for their interest. At difference to the separation off molecules, microorganisms are characterized as living. This makes their analysis more difficult because several aspects such as possible lysis, aggregation, evolution, growing etc. must be taken into count.

This paper presents a simple, highly efficient method for analyzing single-walled carbon nanotube (SWNT) bundles based on (1) ultrasound-assisted solubilization/dispersion of SWNTs in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, (2) encapsulation of the nanotubes in sodium dodecyl sulfate micelles, and (3) analysis by capillary electrophoresis. The process by which SWNTs disperse in the ionic liquid was studied by Raman spectroscopy. No degradation of SWNTs was observed under mild sonication conditions. The shape and position changes observed in the Raman spectral bands for the nanotubes are ascribed to debundling and interaction with the ionic liquid. Separation of solubilized SWNTs was accomplished by using a 50 mM formic acid solution at pH 2.0 as background electrolyte and a potential of -10 kV. Under these conditions, separation was completed within only 4 min. Eighteen peaks for SWNTs were identified in the analysis of commercial SWNT bundles. The two types of bundles studied exhibited distinct, highly characteristic electrophoretic profiles which could be used to control SWNTs purity.

Microorganisms can be considered a bio-colloid. That is, they have a characteristic outer surface that carries, or can carry, a charge. Precisely, differences in the surface can be exploited for separation by capillary electrophoresis (CE). In fact, methods based on CE seem to be very promising because they should produce rapid and high-efficiency separations. Although CE can be used to separate microbial (i.e., bacteria, virus, fungi, and whole cells) and subcellular particles (i.e., mitochondria and nuclei), this chapter is focused mainly on the determination of bacteria and virus for their interest. At difference to the separation off molecules, microorganisms are characterized as living. This makes their analysis more difficult because several aspects such as possible lysis, aggregation, evolution, growing etc. must be taken into count.

This article discusses the mutual impact of nanotechnology and analytical science and illustrates how this technical trend can be expected to strengthen the role of analytical chemists. To this end, it defines the limits of actual nanotechnological approaches and uses selected examples to illustrate the three major relationships between nanotechnology and analytical science, namely: the design and use of nanodevices; the use of nanoparticles (and nanostructures) in analytical processes; and the extraction of accurate chemical information from the nanoworld. Finally, the future of analytical nanotechnology in the short and medium term is briefly addressed.

14 páginas, 12 figuras, 6 tablas., [ES] En el presente trabajo se estudian, mediante el análisis XPS (espectroscopia fotoelectrónica de rayos-X), los recubrimientos de anodizado, sellados y sin sellar, obtenidos sobre Al-puro y aleaciones de Al-Cu, Al-Mg-Si y Al-Mg. En general, se observa un aumento significativo en las relaciones O/Al en el recubrimiento como resultado del proceso de sellado. En el caso de las aleaciones de Al-Cu y Al-Mg, se ha observado también un significativo aumento de la relación O/Al respecto al Al-puro y la aleación Al-Mg-Si, que puede estar asociado a una mayor porosidad de los recubrimientos obtenidos sobre las primeras. Se ha intentado así mismo establecer posibles relaciones entre las características de las capas anódicas y las heterogeneidades superficiales que también han actuado en la fase previa al anodizado. Según los resultados de este trabajo, estas mismas heterogeneidades afectan el grado de disolución del substrato metálico durante la operación de anodizado., [EN] In the present work, X-ray photoelectron spectroscopy (XPS) is used to study sealed and unsealed anodic coatings obtained on pure-Al and on Al-Cu, Al-Mg-Si and Al-Mg alloys. In general, the sealing process is seen to produce a significant increase in the O/Al ratio in the anodic coatings. This increase is more considerable with the Al-Cu and Al-Mg alloys than with the pure Al and the Al-Mg-Si alloy, perhaps due to the greater porosity of the coatings obtained on the former. An attempt is made to establish possible relationships between anodic film characteristics and surface heterogeneities, which also act in the phase prior to anodising. According to the results of this work, these heterogeneities affect the degree of dissolution of the metallic substrate during the anodising operation., Esta investigación ha sido financiada por la Comisión Interministerial de Ciencia y Tecnología (CICYT) de España, en el marco del Proyecto MAT 2003- 02217.

Analytical science has gone through several turning points, one of the most decisive of which was signaled by the development and massive use of instruments for analytical purposes. One other pivotal turning point was the inception of computer science, which not only enabled the automatic control of analytical systems but also facilitated the acquisition of vast amounts of data and their processing with the aid of chemometrics. Following the growing significance of automation and miniaturization in recent times, the early 21st century is witnessing the rise of nanotechnology as a new, increasingly important, revolutionary trend in science in general and analytical science in particular. The ability to exploit molecular interactions between analytes and nanoparticles has opened up new, challenging prospects in this area. Good proof of the interest aroused by nanoparticles is the large number of papers on their use in quantum dots, fullerene, aurum nanoparticles, or carbon nanotubes published in recent years.

On many occasions, sample treatment is a critical step in electrophoretic analysis. As an alternative to batch procedures, in this work, a new strategy is presented with a view to develop an on-capillary sample cleanup method. This strategy is based on the partial filling of the capillary with carboxylated single-walled carbon nanotube (c-SWNT). The nanoparticles retain interferences from the matrix allowing the determination and quantification of carbohydrates (viz glucose, maltose and fructose). The precision of the method for the analysis of real samples ranged from 5.3 to 6.4%. The proposed method was compared with a method based on a batch filtration of the juice sample through diatomaceous earth and further electrophoretic determination. This method was also validated in this work. The RSD for this other method ranged from 5.1 to 6%. The results obtained by both methods were statistically comparable demonstrating the accuracy of the proposed methods and their effectiveness. Electrophoretic separation of carbohydrates was achieved using 200 mM borate solution as a buffer at pH 9.5 and applying 15 kV. During separation, the capillary temperature was kept constant at 40 degrees C. For the on-capillary cleanup method, a solution containing 50 mg/L of c-SWNTs prepared in 300 mM borate solution at pH 9.5 was introduced for 60 s into the capillary just before sample introduction. For the electrophoretic analysis of samples cleaned in batch with diatomaceous earth, it is also recommended to introduce into the capillary, just before the sample, a 300 mM borate solution as it enhances the sensitivity and electrophoretic resolution.

A simple methodology for converting a commercial CE-MS instrument into an integrated 2-D CE system has been developed. The first-dimensional capillary operates as a typical CE instrument with UV/visible detection. Fractions leaving the first dimension are automatically collected and introduced into the second dimension, performed on a CE-MS apparatus, for analysis. The integrated system allows fractions in the second dimension to be analyzed using various electrophoretic modes. As an example, in this work we performed the separation of two families of antibiotics (nitroimidazoles and tetracyclines) in the first dimension and the subsequent resolution of the antibiotics in each family (nitroimidazoles were resolved by MEKC and tetracyclines by CZE) in the second dimension. The proposed system, which operates in an highly automatic manner, is flexible and allows various combination of electrophoretic modes to be implemented. In addition, the use of a mass spectrometer detector in the second dimension further increases the analytical potential of the system as a result of the high selectivity and wealth of structural information provided by the MS detector.

We developed a new interface for the on-line coupling of a fiber for solid-phase microextraction (SPME) with a CE system with an electrospray interface for MS detection. The on-line interface was a modification of a split-flow interface typically used for coupling flow systems to CE. The modification consists of an additional channel closed with a septum that permits the introduction of the fiber in the interface, right at the inlet region of the separation capillary. The interface was designed to be used with commercial fibers. Although commercial fibers can be used directly, we recommend cutting the stationary phase and using fibers with a 2-mm stationary phase. The system was tested for the analysis of tetracycline antibiotic residues, viz., tetracycline, oxytetracycline and doxycycline in soils. The overall accuracy was assessed by regression analysis of spiked samples, showing successful results at a 95% confidence level. The reproducibility, expressed as RSD, was 5.3% and the LOD of tetracycline antibiotics in soil ranged from 2.9 to 3.2 microg/kg.

Last years chemical properties of carbon nanotubes (CNTs) have attracted high interest. One of the most important issues is the capability of CNTs to adsorb analytes on its surface. In this work, such property has been used to preconcentrate trace tetracyclines from environmental water samples at the trace level. Multi-walled carbon nanotubes (MWNTs) have showed higher capacity than other two single-walled carbon nanotubes (SWNTs). Preconcentration of the samples was performed in a flow system at-line coupled to the CE-MS equipment. The preconcentration of tetracyclines on MWNTs followed by capillary electrophoresis-mass spectrometry allows the detection of 0.30–0.69 μg/L of tetracyclines for the analysis of 10 mL of samples. Recoveries for the analysis of spiked samples ranged from 98.6 to 103.2% and the precision from 5.4 to 8.2%. Separation of tetracylines in the electrophoretic system was achieved using 50 mM formic acid at pH 2.0 as a background electrolyte. Atmospheric pressure electrospray ionization mass spectrometry detection was accomplished using 50:50 (v/v) methanol/water containing 0.5% (v/v) formic acid as a sheath liquid.

A new hexane-in-water microemulsion was investigated as buffer in microemulsion EKC (MEEKC). At difference with other microemulsions, the addition of cosurfactant was not necessary to stabilize the microemulsion. The proposed microemulsion was successfully used to achieve electrophoretic separation of seven antibiotics including nitroimidazoles, cephapirin and tetracyclines. Selectivity and separation efficiency achieved in MEEKC were compared with MEKC. MEEKC technique proved to be more efficient than MEKC for performing the separation of the analytes and the presence of microemulsions was found to be critical to achieve the separation of tetracyclines. The proposed microemulsion also points out that solvents with high volatility, such as hexane, can be stabilized and used as a microemulsion of SDS.