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A novel low-cost fluorimetric platform based on sulfur, nitrogen-codoped graphene quantum dots immersed into nanocellulosic hydrogels is designed and applied in detecting the laccase enzyme. Although most of methods for detecting laccase are based on their catalytic activity, which is strongly dependent on environmental parameters, we report a sensitive and selective method based on the fluorescence response of hydrogels containing graphene quantum dots (GQDs) acting as luminophore towards laccase. The easily-prepared gel matrix not only improves the fluorescence signal of GQDs by avoiding their self-quenching but also stabilizes their fluorescence signal and improves their sensitivity towards laccase. Noncovalent interactions between the sensor and the analyte are believed to be causing this significant quenching without peak-shifts of GQD fluorescence via energy transfer. The selective extraction of laccase was proved in different shampoos as complex matrices achieving a detection limit of 0.048 U mL−1 and recoveries of 86.2–94.1%. As the unusual properties of nanocellulose and GQDs, the fluorescent sensor is simple, eco-friendly and cost-efficient. This straightforward strategy is able to detect and stabilize laccase, being an added-value for storage and recycling enzymes.

In this paper, we report a simple, rapid and reproducible sensing approach for determination of fenoxycarb pesticide in river water based on the combined use of nitrogen-doped graphene quantum dots (N-GQDs) and acetylcholinesterase (AChE) enzyme as biorecognition element. Nanoparticles were used as fluorescent probes, while AChE was employed for inhibitor screening. The enzyme-generated products quenched the native fluorescence of N-GQDs. When fenoxycarb was introduced into the assay solution, the activity of AChE to convert substrate into products resulted to be reduced and consequently, N-GQD fluorescence was recovered gradually in an inhibitor concentration-dependent manner. Preliminary studies showed that nanoparticles were not directly sensitive to fenoxycarb, however, the inclusion of an enzymatic system in solution allowed for successful determination of pesticide in aqueous samples. Under optimized conditions, fenoxycarb concentrations ranging from 6 to 70 μM exhibited an excellent linear relationship with the inhibition efficiency percentage (R2 = 0.9941). The proposed biosensor has a limit of detection (LOD) of 3.15 μM, and excellent reproducibility values (RSD

In the run-up to Nanoscience and Nanotechnology (N&N), researchers have investigated and applied a wide variety of nanomaterials (e.g. from carbon nanotubes to graphene) with spectacular properties that overwhelmed the conventional materials. Far from most of nanoparticles (NPs) studied since the last decade like graphene, nanocellulose (NC) has been recently considered as one of the renewable materials that will revolutionize the future, as virtue of its powerful properties, biocompatibility, low toxicity and low production costs from natural resources. The main purpose of this paper is to compile the recent achievements of NC in analytical chemistry and other areas such as medicine. NC can play different roles in analytical processes. On the one hand, a first approximation consists of the consideration of NC as target analyte in real samples where it is added to improve some properties. On the other hand, a variety of methods in which NC acted as an efficient tool to improve the analytical processes is summarized, taking into account their use as sorbent, as separation media or as sensor. Within this thematic, some examples of great relevance related to sorbents and sensing platforms based on NC for the determination of other nanoobjects are thoroughly outlined, which belong to the new trending topic known as the Third way of Analytical Nanoscience and Nanotechnology (AN&N). Along this overview, emerging advances based on NC are further outlined for opening new research lines for such atypical eco-friendly functional nanoparticle.

A novel hybrid micro and meso porous silica monolith with embedded carbon nanoparticles (Si-CNPs monolith) was prepared inside a fused silica capillary (3cm in length) and used as a sorbent for solid-phase microextraction. The hybrid monolithic capillary was synthetized by hydrolysis and polycondensation of a mixture of tetraethoxysilane (TEOS), ethanol, and three different carbon nanoparticles such as carboxylated single-walled carbon nanotubes (c-SWCNTs), carboxylated multi-walled carbon nanotubes (c-MWCNTs), and oxidized single-walled carbon nanohorns (o-SWNHs) via a two-step catalytic sol-gel process. Compared with silica monolith without carbon nanoparticles, the developed monolithic capillary column exhibited a higher extraction efficiency towards the analytes which can be ascribed to the presence of the carbon nanoparticles. In this regard, the best performance was achieved for silica monolith with embedded c-MWCNTs. The resulted monolithic capillaries were also characterized by scanning electron microscopy (SEM), elemental analysis and nitrogen intrusion porosimetry. Variables affecting to the preparation of the sorbent phase including three different carbon nanoparticles and extraction parameters were studied in depth using polycyclic aromatic hydrocarbons (PAHs) as target analytes. Gas chromatography-mass spectrometry was selected as instrumental technique. Detection limits range from 0.1 to 0.3μgL-1, and the inter-extraction units precision (expressed as relative standard deviation) is between 5.9 and 14.4%.

Fluorescent nanodots have become increasingly prevalent in a wide variety of applications with special interest in analytical and biomedical fields. The present overview focuses on three main aspects: (i) a systematic description and reasonable classification of the most relevant types of fluorescent nanodots according to their nature, quantum confinement and crystalline structure is provided, starting with a clear distinction between semiconductor and carbon-based dots (graphene quantum dots, carbon quantum dots and carbon nanodots). A new set of abbreviations and definitions for them to avoid contradictions found in literature is also proposed; (ii) a rational classification allows the establishment of clear-cut differences and similarities among them. From a basic point of view, the origins of the photoluminescence of the different nanodots are also established, which is a relevant contribution of this overview. Additionally, the most outstanding similarities and differences in a great variety of criteria (i.e. year of discovery, synthesis, the physico-chemical characteristics like structure, nature, shape, size, quantum confinement, toxicity and solubility, the optical characteristics including the quantum yield and lifetime, limitations, applications as well as the evolution of publications) are thoroughly outlined; and (iii) finally, the promising future of fluorescent nanodots in both analytical and biomedical fields is discussed using selected examples of relevant applications.

A selective photoluminescence method based on Carbon Quantum Dots (CQDs) functionalized with carboxymethyl-β-cyclodextrin for the direct determination of water-soluble C60 fullerene has been developed. CQDs were synthesized using a top-down methodology from multiwall carbon nanotubes (MWCNTs) and further functionalized with N-Boc-ethylenediamine to confer monoprotected amine groups onto their surface. Once amine-functionalized CQDs were obtained after deprotection, an amidation reaction with carboxymethyl-β-cyclodextrin cavitands was achieved and the obtained fluorescent β-cyclodextrin functionalized Carbon Quantum Dots (cd-CQDs) were investigated for the inclusion complexation of water-soluble C60. Quenching of their fluorescence was observed owing to the non-covalent self-assembly of cd-CQDs and C60, making possible the quantification of C60. A method to determine water-soluble C60 is then proposed with detection and quantification limits of 0.525 and 1.751 μg mL(-1), respectively. The method was validated by determining soluble C60 fullerene in spiked river water. One added value of the paper is the fact that it can be ascribed to the "Third Way in Analytical Nanoscience and Nanotechnology".

The article describes a method for the determination of titanium oxide nanoparticles (TiO2NPs) in sunscreens using N-doped graphene quantum dots (N-GQDs). The TiO2-NPs are first extracted from the highly lipophilic sunscreen via liquid-liquid extraction. Subsequent fluorimetric analysis of the extracts is based on the quenching effect exerted by TiO2NPs on the fluorescence of N-GQDs. The effect is assumed to be due to an electrostatic interaction and/or hydrogen bonding between the particles. The limit of detection for TiO2NPs is 1.4 μg⋅g‾1. The precision at a 5 μg⋅g‾1 concentration of TiO2NPs is 6.95 %. The optimized procedure was successively applied to the determination of TiO2 NPs in sunscreens with different sun protection factors.

This article reports on the enhancement of the capacity of an acrylate-based monolithic solid sorbent by anchoring carboxylated multi-walled carbon nanotubes (c-MWCNTs) in its pores and on its surface. Monolithic poly(butyl acrylate-co-ethyleneglycol dimethacrylate) [poly(BA-co-EGDMA)] was synthetized inside a fused silica capillary via free-radical polymerization, and an ethanolic dispersion of c-MWCNTs was passed through the capillary. The resulting poly(BA-co-EGDMA-c-MWCNTs) monolith was characterized by scanning electron microscopy to confirm the presence of the c-MWCNTs. The effect of using three different kinds of carbon nanoparticles and the microextraction step were studied using triazine herbicides as model compunds. The use of c-MWCNTs resulted in best performance in terms of extraction enhancement (compared to carboxylated single-walled carbon nanotubes and oxidized single-walled carbon nanohorns). The use of these carbon nanoparticles improved the extraction of triazines in any case when compared to using a bare poly(BA-co-EGDMA) monolith. The triazines were then quantified by gas chromatography with mass spectrometric detection. Detection limits ranged from 0.03 to 0.1 μg·L−1 (except for simazine; 0.6 μg·L−1), and the precision (relative standard deviation) varied between 3.0 and 11.4 %. The reproducibility between units is

This work presents a simple, fast and sensitive method for the preconcentration and quantification of graphene quantum dots (GQDs) in aqueous samples. GQDs are considered an object of analysis (analyte) not an analytical tool which is the most frequent situation in Analytical Nanoscience and Nanotechnology. This approach is based on the preconcentration of graphene quantum dots on an anion exchange sorbent by solid phase extraction and their subsequent elution prior fluorimetric analysis of the solution containing graphene quantum dots. Parameters of the extraction procedure such as sample volume, type of solvent, sample pH, sample flow rate and elution conditions were investigated in order to achieve extraction efficiency. The limits of detection and quantification were 7.5 μg L(-1) and 25 μg L(-1), respectively. The precision for 200 μg L(-1), expressed as %RSD, was 2.8%. Recoveries percentages between 86.9 and 103.9% were obtained for two different concentration levels. Interferences from other nanoparticles were studied and no significant changes were observed at the concentration levels tested. Consequently, the optimized procedure has great potential to be applied to the determination of graphene quantum dots at trace levels in drinking and environmental waters.

Graphene quantum dots (GQDs) are small fluorescent nanoparticles with unique properties that make them attractive tools for research in various fields. We review their state of the art in analytical chemistry and summarize their analytical applications. Also, we deal with GQDs as target analytes, a scarcely explored aspect in analytical nanoscience and nanotechnology, and suggest potential future directions for GQD-based analytical research.

In this work we present the results from the use of ionic liquids (ILs) for the sample preparation of carbon nanotubes prior to their characterization by scanning electron microscopy (SEM). Their use implies some advantages such as no damage of the surface of CNTs, the aggregation of the nanoparticles decreases while the number of CNTs individually dispersed increases, therefore, the sample is more representive. The use of ILs avoids the gold sputtering of the sample prior to analysis owing to the conductivity of the ionic liquid medium while increasing the contrast and brightness of the image. A comparative study of the feasibility of three different solvents — namely methanol, surfactant Triton X-100 solution, and imidazolium-based ionic liquid – for the dispersion of MWNTs prior to SEM analysis was carried out. Complementarily, Raman spectroscopy was employed to follow the solubilization of carbon nanotubes within the ionic liquid medium, demonstrating the excellent features of ILs for their use as solvent of CNTs.

In this paper, a simple, quick and reproducible SERS substrate combining the properties of multilayer graphene (≈ 4 layers) and gold nanoparticles has been developed. The Raman signal of metronidazole is enhanced at a factor of 124 when deposited on the hybrid substrate enabling its determination at low concentrations. The five most relevant added values of the paper as regards other similar proposed procedures are: i) better sensibility, ii) good reproducibility, iii) rapidity, iv) reusability and v) instrumental simplicity. The procedure presented is capable of detecting and quantifying small quantities of metronidazole without implying any preconcentration step, just using an affordable and portable Raman spectrometer. The LOD and LOQ achieved with this hybrid substrate were 1.1 and 3.68 mg L− 1 of the analyte. The use of graphene provides high reproducibility to the SERS active hybrid substrate. The RSD was 7.76% within a substrate and 10.92% between substrates. The developed SERS active hybrid substrate can be reused without loss in sensitivity.

The preparation of polymeric monoliths with embedded carboxy-modified single-walled carbon nanotubes (c-SWNTs) and their use for capillary electrochromatography (CEC) is described. Carbon nanotube composites were obtained by preparing a polymerization mixture in the presence of increasing c-SWNT concentrations, followed by UV initiation. The novel stationary phases were studied by optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Using short UV-polymerization times, the optimized porogenic solvent (a binary mixture of 1,4-butanediol and 2-propanol) gave rise to polymeric beds with homogenously dispersed embedded c-SWNTs. The CEC features of these monoliths were evaluated using polycyclic aromatic hydrocarbons (PAHs), non-steroidal anti-inflammatory drugs (NSAIDs) and chiral compounds. The monolith prepared in the presence of c-SWNTs showed enhanced resolution of the text mixtures, including a remarkable capability to separate enantiomers.

A new method for the determination of the phenol fraction of olive oil is reported. An optical nanosensor based on graphene quantum dots, obtained by pyrolysis of citric acid, was specifically developed for this purpose. The ensuing fluorescence sensing method, which is simple, and highly sensitive and reproducible, was used here to determine gallic acid and oleuropein as model analytes commonly found in olive oils, as well as the phenolic concentration of olive oil real samples. The detection limits were lower than 0.12 mg L −1 and the precision, expressed as relative standard deviation, lower than 1.7%.

The aim of this study was to assess the toxicological risks arising from the coexistence of polyethylene glycol coated single-walled carbon nanotubes (SWCNTs-PEG) and a known environmental contaminant: 4-nonylphenol (NP). To this end, in vitro toxicity assays involving the exposure of 3T3-L1 cells (mouse embryonic fibroblasts) to SWCNTs-PEG alone or in combination with NP for 24 or 48 h were performed. Experimental treatments were conducted in both presence (10%) and absence of serum in order to evaluate its influence on the toxicity of SWCNTs-PEG. Although the results provided no unambiguous evidences of synergistic toxicity between SWCNTs-PEG and NP, some specific treatments with mixtures (SWCNTs-PEG + NP) resulted in an unexpected combined toxicity in relation to the individual treatments. Only in those cases the interaction between SWCNTs-PEG and NP could have a synergistic effect on the resulting toxicity. The addition of 10% serum increased the stability of SWCNTs-PEG in the culture medium—possibly by steric repulsions—and reduced the toxicity of nanoparticles as a result. Overall, the serum had a “protective effect” on cells against all treatments: SWCNTs-PEG, NP or their mixtures (SWCNTs-PEG + NP). Raman spectroscopy allowed the intracellular distribution of SWCNTs-PEG to be elucidated.

We describe a method for the synthesis of gold nanoparticles in a stainless steel continuous flow tubular reactor using tetrachloroauric acid as a precursor but without using a classical reducing agent. Gold(III) ion is reduced by stainless steel to form gold nanoparticles which are collected at the end of the coil. A single-phase system is introduced that generates dispersed nanoparticles in the absence of reducing agents on their surface. By controlling flow rates and temperature, the size of the nanoparticles can be tuned in the range from 24 nm to 36 nm. The reproducibility of the preparation was investigated, relative standard deviation of both the wavelength of the peak and the intensity of the plasmonic absorption band were determined and found to vary by 0.15 % and 6.5 %, respectively. Flow synthesis is found to be an excellent alternative to chemical methods to produce stable gold nanoparticles of varying size in an efficiently way. The particles obtained also perform very well when used as a substrate in surface enhanced Raman scattering as shown by the characterization of carboxylated single walled carbon nanotubes.

This paper deals with the ability of different types of carbon nanotubes to adsorb salicylic acid in river water samples. The use of these nanoparticles as a sorbent in a SPE procedure prior to CE analysis is essential for improving the enrichment factor and the recovery values. Several experimental variables were optimized in order to maximize the extraction efficiency. The proposed analytical method is simple, fast, and entails low solvent consumption. Furthermore, salicylic acid could be extracted from river water providing good recovery values in the range from 76.2 to 102.0% (RSD

A piezoelectric quartz crystal microbalance (PQCM) was modified with multi-walled carbon nanotubes (MWCNTs) to develop a chemically based sensor for measurements other than the typical mass change in the quartz crystal. Slight conductivity changes in the carbon nanotubes are amplified to obtain a vibrational frequency signal in the crystal. A commercially available quartz crystal microbalance was modified by replacing its electrode with MWCNTs to obtain a sensor with high sensitivity, selectivity, robustness and stability over time. The modified microbalance was successfully used to determine various types of analytes including volatile organic compounds (VOCs), aldehydes and amines.

Soft materials resulting from the combination of carbon nanotubes with ionic liquids have aroused analytical interest; thank to their peculiar characteristics. This paper compares the sorption capacity of eight different soft materials obtained from the combination of 1-hexyl 3-methylimidazolium hexafluorophosphate (ionic liquid) with different types of carbon nanotubes. The main characteristics of carbon nanotubes were established by Raman spectroscopy. The results obtained pointed out the critical role of the carbon nanotube types on the stability as well as the sorption capacity of the soft material. By using the adequate carbon nanotube it is possible to improve the LOD 4 times when they are used as sorbent materials for SPE. Working in the recommended conditions the LOD for the analysis of 5 mL of water sample was 5 μg/L of fluoranthene and the precision 5.9%.

The combination of ionic liquids with carbon nanotubes has opened a new possibility of ionic liquids as modifiers for carbon nanotubes. Upon being ground into ionic liquids, carbon nanotube bundles are untangled, and the resultant fine bundles form a network structure. This is due to the possible specific interaction between the imidazolium ion component and the p-electronic nanotube surface. The resultant soft material has a high capacity to adsorb/absorb analytes from samples. In this work, the soft material was prepared by mixing 15 mg of carbon nanotubes with 300 μL of IL. The soft material was immobilized on cotton fibers to perform the preconcentration of aromatic compounds such as PAHs from river water samples. The most important fact is the synergic effect between the ionic liquid and the carbon nanotubes which results in a high capacity to preconcentrate analytes. In fact, the sorption capacity of 15 mg of the soft material containing 0.55 mg of MWNT and 11 μl of IL is two times higher than the capacity of 15 mg of MWNT and 3.7 times higher than that of 100 μl IL.

This work presents a novel fluorescent sensor for the determination of tacrine by combining the magnificent fluorescence properties of nitrogen-doped graphene quantum dots (N-GQDs) with the high potential of acetylcholinesterase (AChE) enzyme for screening its inhibitors. Tacrine was the first drug approved for Alzheimer's disease and it is currently being used in several therapeutic treatments given its activity as a reversible inhibitor of AChE. The principle of the developed biosensor relies on the fact that the native fluorescence of the synthesized N-GQDs is quenched by interaction with enzymatic reaction products, and the inclusion of tacrine in assay solution results in the gradual recovery of the original fluorescence in an inhibitor concentration-dependent manner. While N-GQD fluorescence was not directly affected by tacrine, the inclusion of an AChE based-enzymatic system allowed for its determination with a detection limit (S/N = 3) of 1.22 μM. This biosensor was demonstrated to be simple, rapid and reproducible (%RSD 4.87, n = 7) for analysis of tacrine in aqueous solutions.

Fluorescent nanodots have become increasingly prevalent in a wide variety of applications with special interest in analytical and biomedical fields. The present overview focuses on three main aspects: (i) a systematic description and reasonable classification of the most relevant types of fluorescent nanodots according to their nature, quantum confinement and crystalline structure is provided, starting with a clear distinction between semiconductor and carbon-based dots (graphene quantum dots, carbon quantum dots and carbon nanodots). A new set of abbreviations and definitions for them to avoid contradictions found in literature is also proposed; (ii) a rational classification allows the establishment of clear-cut differences and similarities among them. From a basic point of view, the origins of the photoluminescence of the different nanodots are also established, which is a relevant contribution of this overview. Additionally, the most outstanding similarities and differences in a great variety of criteria (i.e. year of discovery, synthesis, the physico-chemical characteristics like structure, nature, shape, size, quantum confinement, toxicity and solubility, the optical characteristics including the quantum yield and lifetime, limitations, applications as well as the evolution of publications) are thoroughly outlined; and (iii) finally, the promising future of fluorescent nanodots in both analytical and biomedical fields is discussed using selected examples of relevant applications.

This paper describes the combined use of carbon nanotubes and an ionic liquid directly coupled in-line to commercial CE equipment for sample treatment. The extraction unit operates as a spin column to preconcentrate the analytes. The extraction unit is inserted into the sample vial. The elution is performed in-line, placing the vial on the carrousel of the CE equipment. The joint use of carbon nanotubes and ionic liquids as sorbent is based on the high adsorption capacity of these materials, which makes them highly suitable for microextraction purposes. The LOQ of analytes were within the range of 0.65-0.83 μg/L with a RSD of less than 7%. The values of recovery range between 90 and 112%. The absolute recovery obtained from samples containing 1 μg/L of analytes was 38%.

A new dispersive micro solid-phase extraction method which uses single-walled carbon nanohorns (SWNHs) as sorbent is proposed. The procedure combines the excellent sorbent properties of the nanoparticles with the efficiency of the dispersion of the material in the sample matrix. Under these conditions, the interaction with the analytes is maximized. The determination of polycyclic aromatic hydrocarbons was selected as model analytical problem. Two dispersion strategies were evaluated, being the functionalization via microwave irradiation better than the use of a surfactant. The extraction was accomplished by adding 1 mL of oxidized SWHNs (o-SWNHs) dispersion to 10 mL of water sample. After extraction, the mixture was passed through a disposable Nylon filter were the nanoparticles enriched with the PAHs were retained. The elution was carried out with 100 μL of hexane. The limits of detection achieved were between 30 and 60ngL(-1) with a precision (as repeatability) better than 12.5%. The recoveries obtained for the analytes in three different water samples were acceptable in all instances. The performance of o-SWNHs was favourably compared with that provided by carboxylated single-walled carbon nanotubes and thermally treated carbon nanocones.

This paper describes for the first time the use of single-walled carbon nanohorns (SWNHs) as pseudostationary and stationary phases for EKC and CEC, respectively, taking advantage of their characteristic features, such as conical-end termination, formation of spherical assemblies dahlia-flower like superstructure and easy functionalization. The use of SWNHs as pseudostationary phase for EKC required the study of their dispersion in different surfactants as well as their compatibility with the electrophoretic system. The carboxylation and subsequent immobilization of carboxylated SWNHs in fused-silica capillary to obtain useful, reproducible and stable stationary phases for CEC has also been investigated, with promising results. The electrophoretic separations obtained for water-soluble vitamins in both modalities (EKC and CEC) have been systematically compared with those obtained with single-walled carbon nanotubes.

Magnetic nanoparticles (MNPs) were deposited onto multiwalled carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of the magnetic precursor [iron(III)] and MWCNTs, in ethylene glycol. This one-step synthetic method was applied to commercially available carbon nanotubes (CNTs). Scanning electron micrographs of the resulting products revealed that MNPs decorated the surface of the MWCNTs. The hybrid nanoparticles thus obtained were used for sampling and cleanup in the determination of eight fluoroquinolones (FQs) and two quinolones (Qs) at trace levels by ultra performance liquid chromatography (UPLC). A systematic study of analyte adsorption and desorption was conducted with MNPs and MWCNTs separately. Although both solid phases adsorbed the analytes to some extent, the much higher recoveries were obtained by using the MNP-MWCNT composite which was thus selected to treat plasma samples containing FQs and Qs. Lower accuracies were determined at spiked plasma compared to the standard solution caused by the complexation affinity of the analytes with proteins because high recoveries were observed when deproteinization was performed before treating the sample with the magnetic MWCNTs. The performance characteristics of the optimized method were determined, and the method was applied to the analysis of plasma samples from antibiotic-treated patients. On the basis of the results, the use of an in situ synthesized MWCNT-MNP composite allows the simple, expeditious sampling and treatment of such complex biological samples for the subsequent determination of FQs and Qs present at free form.

This article presents a novel application of the surfactant-coated carbon nanotubes for the joint extraction of phthalates, xylene isomers and styrene from virgin olive oils. For this purpose, two carbon nanotubes, multi-walled and single-walled carbon nanotubes, were evaluated, the former providing the better results. The target migrants were liquid-liquid extracted from the virgin olive oil samples by means of the carbon nanotube pseudophase, and the aqueous extracts were analysed by headspace-gas chromatography-mass spectrometry. Sodium chloride was added to favour the release of the analytes to the gaseous phase of the vial. The comparison of the chromatograms obtained with the direct analysis reveals a sensitivity enhancement with the use of the surfactant-coated carbon nanotubes, especially for the phthalates, which can be ascribed to the pi-pi interaction between the aromatic ring and the nanotube surface. Limits of detection were between 6 and 30 microg L(-1) for 1 mL of sample. The precision of the method was better than 7.6% and the recoveries higher than 92%. Finally, the influence of the package material and the storage conditions on the concentration of the analytes was accomplished, and it was found that the concentration of phthalates increases with time in all the packages studied, while the more volatile compounds were found to decrease under the same conditions.

This paper provides an overview of the use of carbon nanoparticles (CNPs) as pseudo-stationary phases (PSPs) in EKC. Specifically, it describes the characteristics and properties of the major types of CNPs used as PSPs in EKC separations, namely C(60) fullerenes, carbon nanotubes and covalently modified carbon nanotubes. Based on such properties, a plausible mechanism for the interactions governing EKC separation with these materials is proposed. Also, the most salient uses of CNPs as PSPs are outlined. Finally, CNPs are compared in terms of performance with other well-established types of nanostructures used to enhance selectivity in EKC over the past decade.

The use of carbon nanostructures in different modalities is a topic of growing interest. This article provides a systematic comparison of surfactant-coated single-wall carbon nanotubes, multi-wall carbon nanotubes and C 60 fullerenes as pseudostationary phases (PSPs) in electrokinetic chromatography. The differences on the electrophoretic behaviour as a function of the pseudostationary phase for phenolic compounds, triazines and nitroimidazole derivatives have been explored. Phenolic compounds, triazines and nitroimidazole derivatives has been selected as model compounds of aromatic compounds, π-exceeding heteroaromatic compounds and π-deficient heteroaromatic compounds, respectively. Resolution was also evaluated on the basis of the differences in the electrophoretic behaviour and in this sense the best PSP for each group of compounds can be proposed.

Over time, new materials have been used and incorporated in a wide variety of analytical processes. This century, technology has produced novel nanomaterials with unique properties whose use has increased in analytical sciences. Carbon nanostructures are among these new nanomaterials. This overview reports on the use of carbon nanomaterials, mainly fullerenes and carbon nanotubes, as sorbents in the analytical process. After a brief description of their main characteristics, we present their use in the development of selective membranes. Next, we describe their role as sorbent materials and stationary phases in chromatography and provide relevant examples. We also comment on the presence of carbon nanoparticles as components of electrophoretic buffers to improve both resolution and sensitivity of separations. Finally, we briefly describe other applications in which the sorption capabilities of carbon nanostructures play a role.

In the present paper, surfactant coated fullerenes C60 (SC-C60) have been proposed as a novedous pseudostationary phase to improve separation of different aromatic compounds. The target analytes were β-lactams antibiotics, non-steroidal anti-inflammatory drugs and amphenicols. In all cases, the analytes interacted with the pseudostationary phase producing an important enhancement on resolution. The results were compared with those obtained with surfactant coated carbon nanotubes (single-walled and multi-walled nanotubes), showing that in the proposed conditions, fullerenes C60 were advantageous as interactions between the analytes and the pseudostationary phase were more effective. Finally, the procedure was applied to pharmaceuticals and urine samples, with satisfactory results.

A procedure allowing hydrolysis reactions to be conducted in a dynamic supercritical-CO2 medium was developed for quantifying total safranal (viz. free safranal present in the sample + safranal resulting from picrocrocin hydrolysis), which are the main component of the essential oil and responsible for the characteristic aroma of saffron. The proposed method allows total safranal amounts over the ranges 0.05–1.5 mg mL−1 to be determined. The standard deviation achieved was 2%. This method was applied to the determination of safranal in natural saffron samples. The results obtained were compared with the “safranal value” total index, which is widely used as a quality measure of saffron products. The comparison revealed that the proposed method provides useful information not contained in the safranal value, based on the fact that, some samples with a high “safranal index” contain low concentrations of safranal. The proposed method is very useful for quality control in commercial saffron samples.

A method for the determination of three tetracyclines (viz. tetracycline, oxytetracycline and doxycycline) is proposed. The method uses a flow manifold coupled on-line to a capillary electrophoresis (CE) system. The tetracyclines are preconcentrated on a STRATA-X solid-phase minicolumn inserted in the manifold. This provides an average recovery of tetracyclines of 92% from spiked water samples. The proposed method allows the resolution of mixtures of tetracyclines at concentrations ranging from 7 to 45 g l −1 and has a limit of detection of 2 g l −1 . Under optimal conditions, recoveries range from 99 to 106% and the precision is better than 7.5%. Based on the results, the method is a highly efficient choice for the separation and determination of tetracyclines in surface water samples.

The usefulness of lyophilisation for the direct screening of biological fluids for bile acids was investigated. Human serum and urine were lyophilised without losses of the target compounds and further extracted with n-hexane in acidic medium under magnetic stirring. An integrated flow injection-liquid chromatographic system coupled to an evaporative light scattering detector (ELSD) was used for automated screening/confirmation. The continuous module allows sequential filtration of the organic phase, solvent changeover and solid-phase extraction for clean-up and preconcentration purposes. Retained bile acids were eluted with an acetonitrile-methanol (65:35, v/v) stream. For screening purposes, the effluent was directly introduced in the ELSD detector and the total bile acid content of the sample determined. For confirmatory analysis, another aliquot of the sample was processed in the screening module but the effluent was directed to the chromatographic columns, which provided the free bile acid profile of the sample. Fasting serum and urine samples obtained from healthy individuals were lyophilised and processed. Good agreement was obtained in the analysis of the two matrices assayed following the screening and confirmatory methods.

The paper proposes a simple and sensitive approach for the preconcentration and determination of graphene oxide (GO) in environmental samples by using fluorescent graphene quantum dots (GQDs). The method is based on the preconcentration of GO on a cellulose membrane and their subsequent elution prior to fluorescence analysis of the quenching effect produced on the GQD solution due to the hydrophobic interactions between GO and GQDs. The limit of detection was 35 μg·L(-1). The precision, for a 200 μg·L(-1) concentration of GO, is 5.16%. The optimized procedure has been successively applied to the determination of traces of GO in river water samples.

In this paper, flame atomic absorption spectrometry was used for the determination of silver in various materials. The proposed preconcentration method is based on the continuous precipitation of silver as p -dimethylaminobenzilidene–rhodanine (PDBR) complex and dissolution of the precipitate with potassium cyanide. EDTA was added to the sample solution to mask large concentrations of Fe(III), Ni(II), Cu(II), Zn(II), Pb(II), Co(II) and Al(III). An enhancement factor of 20 was obtained for a preconcentration time of 3 min, resulting in a sampling frequency of 16 h −1 . The detection limit (3 σ ) in the sample solution was 5 ng ml −1 . The relative standard deviation at 30 ng ml −1 level was 4.7%. Analytical results obtained for alloy, biological reference material and ore samples analyzed were in good agreement with the certified values and comparable to those obtained with other techniques.

A slurry electrothermal atomic absorption spectrometric technique was used to determine Ni and Cr in wheat flour and its by-products. Slurries (3%, w/v) were prepared in a mixture of 15% HNO3–10% H2O2 as suspended medium. Differences in Ni and Cr contents due to origin and texture of the wheat and to the effects of the milling process were studied. Ni and Cr levels were more markedly influenced by the geographical origin of the wheat than by its texture. Both metals were related to the amount of bran present in each milled fraction and varied over the ranges of 212–298 ng/g (Ni) and 34–85 ng/g (Cr) in flours (with minimal bran contents); 297–460 ng/g (Ni) and 67–118 ng/g (Cr) in shorts; and 424–723 ng/g (Ni) and 106–165 ng/g (Cr) in brans. The Ni and Cr contents were not significantly affected by the technological processes typically performed in a flour-producing factory.

A simple and novel screening method for lead compounds in environmental waters is proposed. The analytes, in an acetic medium, are sorbed on a C 60 fullerene column as diethyldithiocarbamate complexes and subsequently eluted with isobutyl methyl ketone (IBMK), the lead being determined by flame atomic absorption spectrometry. The screening method acts as filter and indicates whether the target analytes are present above or below the detection limit of the method (0.5 ng/mL), giving no false positives. Positive samples were speciated by GC/MS, using a flow system similar to that of the screening method. Lead(II) and ionic di- and trialkyllead are derivatized with a Grignard reagent. Both methods use similar chemical and flow variables except for the eluent, IBMK in the screening method and n-hexane in the speciation method. The GC/ MS speciation method is very sensitive; it exhibits a linear range of 0.02-5 ng/mL, and detection limits of 1-4 ng/L are achieved. Also, its repeatibility, as RSD, is less than 6%. The method was applied to the speciation of Pb 2+ and di- and trialkyllead in positive prescreened rainwater samples from three different urban areas.

A simple flow injection system for the on-line preconcentration of metal dithiocarbamates (fungicides) by sorption on a C60 fullerene column was developed. Neither the acid hydrolysis needed by the conventional method to release CS2 nor derivatization is required as the fungicides are directly retained on the sorbent column and subsequently eluted from it with dilute HNO3. The eluted fraction is directly fed into a flame atomic absorption spectrometer. Group speciation can be done according to the metals present in the dithiocarbamate (viz., dithiocarbamates of Zn2+, Mn2+, or Fe3+) but no within-group discrimination is possible (ziram, zineb and propineb provide a global response). The analytical figures of merit of the proposed method are as follows: limits of detection (3ς) from 1 to 5 ng ml−1; precision (RSD) ca. 2.5%; and preconcentration factor 45 (using 10 ml of sample). No interference from metals such as Zn, Mn or Fe, as inorganic salts, was observed. The method was applied to the resolution of synthetic mixtures as well as to the speciation/determination of ziram, maneb and ferbam in spiked grain samples, all with acceptable recoveries.

A new method for the speciation of inorganic lead and trialkyllead compounds involving the selective separation of the analytes in a continuous system and their subsequent introduction into a flame atomic absorption spectrometer was developed. The proposed flow system consists of two units. In the first unit, total inorganic lead at concentrations from 8 to 200 ng ml−1 is continuously precipitated as lead chromate and the filtrate, containing trialkyllead cations, is collected in a vessel, the precipitate then being dissolved in diluted acid and driven to the instrument. In the second unit, trimethyllead (TML+) and triethyllead (TEL+) cations at ng ml−1 levels are complexed with sodium diethyldithiocarbamate and retained on a C60 pre-conditioned fullerene column; the mixture of both species was resolved by conditioning the sorbent column with n-hexane or isobutyl methyl ketone solvents. Detection limits of 1–2 ng ml−1 can be achieved by using a sample volume of 50 ml. Special attention was given to the reliability and robustness of the global flow injection method in assessing its applicability to both types of organolead compounds and inorganic lead present in different proportions. Trimethyllead provides the poorest results as consequence of its low adsorption constant on C60; however, the three different types of species (Pb2+/TML+/TEL+) can be effectively determined in proportions from 1:1:1 to 30:12:1 with relative errors less than 10%.

The slurry technique was applied to the determination of Ni, Cr and Co in wheat flour by electrothermal atomic absorption spectrometry (ETAAS). The influence of the graphite furnace temperature programme was optimized. Optimum sensitivity was obtained by using a mixture of 15% HNO(3)-10% H(2)O(2) as suspended medium for a 3% w/v slurry in the determination of Ni; lower concentrations of HNO(3) were necessary for the determination of Co and Cr (viz. 5 and 10%). The precision of direct analyses of the slurries was improved by using mechanical agitation between measurements; thus, the RSD of the measurements was ca. 5% for repeatability. The direct slurry sampling (SS) technique is suitable for the determination of Ni and Cr in wheat flour samples at levels of 150-450 and 30-72 ng g(-1), respectively, as it provides results similar to those obtained by ashing the sample. However, the typically low level of Co in these samples precluded its determination by the proposed method (the study was made in an SRM spiked wholemeal flour), at least in those samples that were contaminated with elevated concentrations of the metal (viz. more than 90 ng of Co per g of flour). The method provides a relative standard deviation of 6, 8, and 4% for Ni, Cr, and Co, respectively.

A flow injection system for the on-line preconcentration of ultratrace levels of cobalt by sorption with ammonium pyrrolidinedithiocarbamate on a C 60 fullerene column was developed. The eluate volume is reduced and dispersion minimized by using a nitrogen (or air) stream to carry the eluent (IBMK) for elution of the adsorbed chelate, which is collected in a 500 µl PTFE autosampler cup. The analytical figures of merit for the determination of cobalt are as follows: limit of detection (3σ), 8 ng l –1 ; precision (RSD), 4% for 0.2 ng ml –1 ; preconcentration factor, 40 (using 25 ml of sample and 500 µl of IBMK). Similar experiments involving C 18 -bonded silica as sorbent revealed ethanol to be the most suitable eluent under these conditions. The results obtained in the determination of cobalt in wheat flour testify to the usefulness of the proposed method.

A flow system was coupled to a tungsten coil electrothermal atomizer (150 W) for on-line separation and preconcentration of cadmium, lead and nickel based on the formation of DDC complexes and sorption into a minicolumn packed with fullerene C60. Three way solenoid valves used for sample and reagents management as well as the tungsten coil power supply were controlled by a computer running a programme written in Visual Basic, which was employed in synchronism with the original software of the atomic absorption spectrometer. The fullerene column (5 mm length, 2 mm i.d.) was inserted into the tip of the autosampler arm, and elution was performed by sampling 35 μl of methanol from the autosampler cup. With 3.0 ml of sample (loading time of 60 s) enrichment factors ranging from 100 to 150 were achieved. The detection limits for cadmium, lead and nickel were 2.2, 23 and 75 ng l−1, respectively. No interference effects were observed on cadmium, lead and nickel preconcentration in the presence of up to 106 fold concentrations of sodium, potassium, calcium or magnesium. Application of t-test to the results obtained by the proposed method and the certified values of cadmium, lead and nickel in five water reference materials did not reveal significant differences at the 5% probability level.

An integrated continuous flow-capillary electrophoresis for the determination of soluble anions in soil samples is presented. A filtration probe coupled with the flow system, which is located before the capillary electrophoresis instrument, was designed to simplify sample pretreatment and to perform clean-up of aqueous soil suspensions. Only the manual weighing of the samples is needed. The extraction process for soil samples was optimized. The clear filtrate containing the soluble anions from soil was then passed to the capillary electrophoresis equipment by a home-made programmable arm. Chloride, sulfate, nitrite and nitrate were determined in soil samples at μg g–1 level and the results compared to manual reference methods. The precision expressed as relative standard deviation was in the range of ± 1.6 to ± 2.5% for the set of analytes determined. The procedure is up to 4 times faster than the competitive manual methods.

A simple, rapid continuous-flow method with gas chromatographic detection for the simultaneous determination of natural and synthetic antioxidants (α-tocopherol, α-tocopheryl acetate, 2,6-di-tert-butyl-p-hydroxytoluene, tert-butyl-4-hydroxyanisole and tert-butylhydroquinone) is proposed. A solid-phase extractor is coupled to the flow system to isolate antioxidants from the sample matrix. During extraction, analytes are released from ca. 70% of the triglycerides present in fats and oils by using XAD-7 sorbent; after selective elution with 400 μl of 2-propanol, only ca. 0.7–0.8% of total triglycerides originally present in the sample remain in the final extract. XAD-7 adsorbs 70–95% of the antioxidants except BHT of which only ca. 30% is adsorbed. The proposed method is considered an effective alternative to earlier procedures.

Three methods for the determination of Cr, Co and Ni in vegetables were tested with a view to the evaluation of various sample preparation procedures involving dry ashing, the direct slurry technique and continuous flow microwave-assisted digestion. NIST SRM 1572 Citrus Leaves was used for this purpose. For the determination of the analytes by AAS, the temperature programmes of the graphite furnace were optimized and the use of some chemical modifiers was studied. Direct slurry analyses of vegetables (in samples prepared at a 2% m/v concentration in 1% HNO 3 containing 10% H 2 O 2 ) were generally accurate and precise for Co and Ni, but gave low recoveries (about 85%) for Cr. Continuous digestion of the samples in a microwave oven was necessary for the reliable determination of Cr (about 100% recovery) by use of 5% HNO 3 as the digesting reagent. The best method for each application was used for the determination of Cr, Co and Ni in a variety of vegetables, using direct calibration with aqueous standards.

Raman spectroscopy has been employed in analytical sciences for purity determination of carbon nanotube samples based on the consideration of G-/D-band intensity ratios. This work demonstrates the role of aggregation in these feature bands, which, in the case of single walled carbon nanotubes (SWNTs), has proved to be crucial for G-/D-band intensity ratio measurements. We have found variation in the relative intensities of G- and D-bands across a sample of SWNTs without any other treatment, discarding the possible influence of the laser beam or sample focusing. In the case of multiwalled carbon nanotubes (MWNTs), this effect is less notorious. Thus, to achieve a good representativeness of Raman measurements, it is important to consider the sample preparation procedure in order to avoid aggregation, which has an effect over the signals, making difficult the subsequent interpretation of results.

This article proposes a simple and sensitive approach for the preconcentration and determination of carboxylated single-walled carbon nanotubes (c-SWNTs) in environmental samples using membranes modified with multiwalled carbon nanotubes (MWNTs). The method is based on the preconcentration of c-SWNTs and their direct on-filter Raman spectroscopic analysis. The preconcentration of c-SWNTs is performed by microfiltrating the sample through a cellulose membrane modified with MWNTs fabricated from a surfactant dispersion of the same. The analytes are retained in the membrane through π-π interactions with MWNTs forming the membrane. The G-/D-band ratio of the carbon nanotubes has been used as an analytical parameter to quantify the presence of c-SWNTs, which mainly contribute to the intensity of the G band. The limit of detection was found to be 1 μg·L(-1), and the precision, for a 10 μg·L(-1) concentration of c-SWNTs, was 4.74% intramembrane and 6.3% intermembrane. The optimized procedure was successfully applied to the determination of traces of c-SWNTs in river water samples.

A simple, environmentally friendly, one-pot method to synthesize highly stable bare gold nanoparticles (AuNPs) has been developed. AuNPs have been synthesized from tetrachloroauric acid solution using steel or stainless steel as solid reducing agent, which can be reused. The proposed method yields bare gold nanoparticles at atmospheric pressure and room temperature for potentially producing large quantities. The obtained AuNPs have been characterized by SEM, TEM and AFM finding an average diameter of around 20 nm, polygonal yet nearly spherical shape and a narrow size distribution. The mechanism of reaction has been investigated by UV–vis spectroscopy, ICP-OES and EDX analysis. The obtained dispersed gold nanoparticles proved to be stable if stored a 4 °C for over four months without the addition of a stabilizing agent. Their analytical potential as SERS substrate has been demonstrated and their performance compared with that showed by citrate-coated gold nanoparticles. Thanks to their unique properties, their use as analytical tools provides analytical processes with enhanced selectivity and precision.

The exceptional properties of graphene (G) were exploited here to facilitate capillary electrokinetic separations. Two types of commercially available G consisting of nanoparticles containing-one to three and-four to six G sheets, respectively, were compared for this purpose. Both proved effective in separating the arylpropyl derivatives of nonsteroidal anti-inflammatory drugs. The highest resolution and shortest migration times were obtained with G containing high amount of single and double G nanosheets. G affords higher resolution than other types of nanoparticles; stable suspensions can be easily prepared and used as BGE without the need of adding an additional surfactant. This results in a high reproducibility in migration times and stability in background noise. The LOD and LOQ obtained by using G nanoparticles as pseudostationary phases spanned the range 0.29-1.18 mg/L and 0.95-3.95 mg/L, respectively, and the RSD was less than 4.7% in all instances.