Ionic-liquid-based microextraction method for the determination of silver nanoparticles in consumer products.

A simple method to determine hazardous silver nanoparticles (AgNPs) based on ionic liquid (IL) dispersive liquid-liquid microextraction and back-extraction is described. This approach involves AgNP stabilization using a cationic surfactant followed by extraction from the sample matrix by means of an IL as an extraction phase. Certain ILs have high affinity for metals, and preliminary experiments showed that those ILs consisting of imidazolium cation efficiently extracted AgNPs in the presence of a cationic surfactant and a chelating agent. Afterward, histamine was used as a dispersing agent to promote phase transfer of differently coated AgNPs from the IL in aqueous solution to be subsequently analyzed by UV-visible spectrometry. The analytical procedure allows AgNPs to be recovered from the sample matrix in an aqueous medium, the enrichment factor being up to 4, preserving both AgNP size and AgNP shape as demonstrated by transmission electron microscopy images and the localized surface plasmon resonance band characteristic of each AgNP. The present method exhibited a linear response for AgNPs in the range from 3 to 20 µg/mL, the limit of detection being 0.15 µg/mL. Method efficiency was assessed in spiked orange juice and face cream, yielding recoveries ranging from 75.7% to 96.6%. The method was evaluated in the presence of other nanointerferents (namely, gold nanoparticles). On the basis of diverse electrophoretic mobilities and surface plasmon resonance bands for metal nanoparticles, capillary electrophoresis was used to prove the lack of interaction of the target AgNPs with gold nanoparticles during the whole protocol; thus, interferents do not affect AgNP determination. As a consequence, the analytical approach described has great potential for the analysis of engineered nanosilver in consumer products. Graphical abstract Simple protocol for the determination of silver nanoparticles (AgNPs) based on dispersive liquid-liquid extraction with a specific short alkyl side chain ionic liquid and their quantitative detection with a UV-visible spectrometer. HMIM•PF6 1-hexyl-3-methylimidazolium hexafluorophosphate, NP nanoparticle, SPR surface plasmon resonance.

Cyclodextrin-modified nanodiamond for the sensitive fluorometric determination of doxorubicin in urine based on its differential affinity towards ß/γ-cyclodextrins.

The manuscript reports on the preparation of ß-cyclodextrin-modified nanodiamonds (ßCD-ND) for the extraction and preconcentration of the fluorescent anticancer drug doxorubicin (DOX) from biological samples. The inclusion of DOX into the cavities of ß- and γ-cyclodextrin (CD) confirms their utility for selective extraction and elution of the drug based on its good fit to the cyclodextrin cavity. Although both larger cyclodextrins (ßCD and γCD) accommodate DOX, DOX clearly prefers the bigger γCD cavities. Dispersive micro solid-phase extraction using ßCD-ND as sorbent enables the inclusion complexation of DOX. The elution of DOX from ßCD-ND cavities occurs with a basic solution of γCD containing 10% acetonitrile owing to the preferential affinity (i.e. optimal fit) of DOX into the larger γCD cavity. DOX is quantified by monitoring its intrinsic fluorescence (exc/em = 475/595 nm). The method can determine DOX in urine with a limit of detection of 18 ng·mL-1. Recoveries (93.2% and 94.0%) and precision (RSDs of 5.9% and 4.7%) at 100 and 400 ng·mL-1 DOX levels in urine are satisfactory. The matrix effect is negligible even when working with undiluted urine samples. Graphical abstract Nanodiamonds functionalized with ß-cyclodextrin (ßCD-ND) were used as sorbent for the determination of nanomolar levels of doxorubicin (DOX). It is based on host:guest interactions ruled by different stabilities of DOX within cyclodextrin (CD) cavity-size: ßCD/γCD.

Usefulness of Analytical Research: Rethinking Analytical R&D&T Strategies.

This Perspective is intended to help foster true innovation in Research & Development & Transfer (R&D&T) in Analytical Chemistry in the form of advances that are primarily useful for analytical purposes rather than solely for publishing. Devising effective means to strengthen the crucial contribution of Analytical Chemistry to progress in Chemistry, Science & Technology, and Society requires carefully examining the present status of our discipline and also identifying internal and external driving forces with a potential adverse impact on its development. The diagnostic process should be followed by administration of an effective therapy and supported by adoption of a theragnostic strategy if Analytical Chemistry is to enjoy a better future.

One-Step Synthesis and Characterization of N-Doped Carbon Nanodots for Sensing in Organic Media.

Photoluminescent nitrogen-doped carbon nanodots (N-doped CNDs) soluble in organic media are synthesized in a one-step synthesis from a single-source precursor (an amphiphilic polymer), which exhibits a very high quantum yield (QY = 78%), excitation wavelength-dependent emission, and upconversion emission properties. The evolution of N-doped CND formation is studied via ultraviolet-visible and photoluminescence spectroscopy. Their analytical application as an effective sensor for the direct determination of nitroaromatic explosives and byproducts is shown based on their selective response via a fluorescence quenching mechanism. The proposed method is validated in soil samples by directly using the sensor in organic media without any further treatment or additional functionalization, which is an interesting aspect for practical applications.

ß-Cyclodextrin functionalized carbon quantum dots as sensors for determination of water-soluble C60 fullerenes in water.

A selective photoluminescence method based on Carbon Quantum Dots (CQDs) functionalized with carboxymethyl-ß-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-ß-cyclodextrin cavitands was achieved and the obtained fluorescent ß-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".

Quo vadis, analytical chemistry?

This paper presents an open, personal, fresh approach to the future of Analytical Chemistry in the context of the deep changes Science and Technology are anticipated to experience. Its main aim is to challenge young analytical chemists because the future of our scientific discipline is in their hands. A description of not completely accurate overall conceptions of our discipline, both past and present, to be avoided is followed by a flexible, integral definition of Analytical Chemistry and its cornerstones (viz., aims and objectives, quality trade-offs, the third basic analytical reference, the information hierarchy, social responsibility, independent research, transfer of knowledge and technology, interfaces to other scientific-technical disciplines, and well-oriented education). Obsolete paradigms, and more accurate general and specific that can be expected to provide the framework for our discipline in the coming years are described. Finally, the three possible responses of analytical chemists to the proposed changes in our discipline are discussed.

ß-Cyclodextrin decorated nanocellulose: a smart approach towards the selective fluorimetric determination of danofloxacin in milk samples.

An innovative and versatile strategy of Solid Phase Microextraction (SPME) is shown by using a new type of ß-cyclodextrin-modified nanocellulose (CD-NC) as a sorbent material. ß-cyclodextrin (used as an inclusion-type selector) was covalently bonded to amine-modified nanocellulose by an amidation reaction. Such novel nanocavities were successfully applied to the selective recognition of danofloxacin (DAN), an antibiotic used to treat animal diseases, via supramolecular host-guest interactions. The SPME methodology, using a platform based on ß-cyclodextrin-"decorated" nanocellulose as a sorbent material, showed a wide linear fluorimetric response against DAN from 8 to 800 µg L(-1) and a detection limit of 2.5 µg L(-1). The specific recognition of DAN has been proven to be highly selective and efficient against this metabolite and other fluoroquinolones. The reusability and the high efficiency in the extraction and preconcentration of DAN in milk samples allow recoveries of 94%.

Determination of Tuta absoluta pheromones in water and tomato samples by headspace-gas chromatography-mass spectrometry.

Tuta absoluta is a tomato pest which is originally from South America. This pest was detected in eastern Spain in 2006 and it rapidly invaded various European countries and spread throughout the Mediterranean basin. The usual detection of this pest is based on the physical evaluation of the crops and in the exhaustive count of potential insects in dedicated traps. The early detection of that pest on the basis of more objective or measurable indicators is desirable. In this case, the combination of headspace and gas chromatography with mass spectrometric detection is proposed for the identification of Tuta absoluta pest using two of its pheromone components as markers. These components, namely: (3E,8Z,11Z)-tetradecatrien-1-yl acetate and (3E,8Z)-tetradecadien-1-yl acetate, are characteristic of Tuta absoluta and they are not present in other insect pheromones. The developed combination allows the determination of both components in water and tomato samples with limits of detection in the range from 25-32 ng/L to 89-111 ng/kg, respectively. The precision, expressed as relative standard deviation, was better than 4.6% for water samples and better than 7.1% when tomato samples were analyzed. The relative recovery values varied in the interval 94-100 and 83-99% for water and tomato samples.

Use of switchable hydrophilicity solvents for the homogeneous liquid-liquid microextraction of triazine herbicides from environmental water samples.

A homogeneous liquid-liquid microextraction alternative, based on the use of switchable hydrophilicity solvents, is presented. The extraction technique makes use of 125 µL of a water-immiscible solvent (N,N-dimethylcyclohexylamine) that can be solubilized in the aqueous phase in 1:1 ratio using CO2 as a reagent. After the extraction, phase separation is induced by the addition of sodium hydroxide that produces a change on the ionization state of the amine, and centrifugation was not necessary. The extraction technique has been optimized and characterized using the determination of triazine herbicides by gas chromatography with mass spectrometry in water samples. The presence of metallic ions in environmental waters as interferents is easily avoided by the addition of ethylenediaminetetraacetic acid before the microextraction procedure. The proposed method allows the determination of the target analytes at the low microgram per liter range with good precision (relative standard deviation lower than 12.5%).

Graphene quantum dots sensor for the determination of graphene oxide in environmental water samples.

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.

Infrared attenuated total reflection spectroscopy for the characterization of gold nanoparticles in solution.

In situ synthesis of bare gold nanoparticles mediated by stainless steel as reducing agent was monitored via infrared attenuated total reflection (IR-ATR) spectroscopy. Gold nanoparticles were directly synthesized within the liquid cell of the ATR unit taking immediate advantage of the stainless steel walls of the ATR cell. As nanoparticles were formed, a layer of particles was deposited at the SiO2 ATR waveguide surface. Incidentally, the absorption bands of water increased resulting from surface-enhanced infrared absorption (SEIRA) effects arising from the presence of the gold nanoparticles within the evanescent field. Next to the influence of the Au(III) precursor concentration and the temperature, the suitability of IR-ATR spectroscopy as an innovative tool for investigating changes of nanoparticles in solution, including their aggregation promoted by an increase of the ionic strength or via a pH decrease, and for detailing the sedimentation process of gold nanoparticles was confirmed.

UV-polymerized butyl methacrylate monoliths with embedded carboxylic single-walled carbon nanotubes for CEC applications.

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.

Carbon nanotubes as SPE sorbents for the extraction of salicylic acid from river water.

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<8.2%). The combination of the specific chemical properties of analyte and the unique physicochemical features of carbon nanotubes sheds new light on the use of these nanoparticles as excellent sorbent materials of pharmaceutical compounds in environmental matrices.

Sequential preconcentration and on-membrane Raman determination of carboxylic single-walled carbon nanotubes in river water samples.

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.

Graphene nanoparticles as pseudostationary phase for the electrokinetic separation of nonsteroidal anti-inflammatory drugs.

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.

Solid-phase extraction of nitrophenols in water by using a combination of carbon nanotubes with an ionic liquid coupled in-line to CE.

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%.

Liquid-liquid extraction assisted by a carbon nanoparticles interface. Electrophoretic determination of atrazine in environmental samples.

A novel method for the determination of atrazine, using liquid-liquid extraction assisted by a nanoparticles film formed in situ and composed of organic solvent stabilized-carbon nanoparticles, is described. The presence of nanoparticles located at the liquid-liquid interface reinforced the extraction of analyte from matrix prior to capillary electrophoresis (CE) analysis. Some influential experimental variables were optimized in order to enhance the extraction efficiency. The developed procedure confirmed that carbon nanoparticles, especially multi-walled carbon nanotubes, are suitable to be used in sample treatment processes introducing new mechanisms of interaction with the analyte. The application of the proposed preconcentration method followed by CE detection enabled the determination of atrazine in spiked river water providing acceptable RSD values (11.6%) and good recoveries (about 87.0-92.0%). Additionally, a similar extraction scheme was tested in soil matrices with a view to further applications in real soil samples.

Microextraction by packed sorbents combined with surface-enhanced Raman spectroscopy for determination of musk ketone in river water.

Microextraction by packed sorbents (MEPS) combined with Surface-enhanced Raman spectroscopy (SERS) was investigated, and applied to the determination of musk ketone (MK) in river water samples. The full MEPS-SERS method includes analyte enrichment by MEPS preconcentration with C18 sorbent followed by SERS detection supported by silver nanoparticles. An eluent drop containing the analyte is deposited directly from the MEPS syringe on a CaF2 glass plate. When the drop has dried, a specific volume of silver nanoparticles solution is added on it before each SERS measurement. Several experimental variables were studied in depth; under the optimum experimental conditions MK can be extracted from a 500 µL sample with recoveries in the range 47-63 %. The limit of detection was 0.02 mg L(-1) and the relative standard deviation 15.2 % (n = 4). Although not investigated in this work, the proposed method might be suitable for in-situ monitoring, because of the portability of the Raman spectrometer used.

Effervescence-assisted carbon nanotubes dispersion for the micro-solid-phase extraction of triazine herbicides from environmental waters.

Extraction techniques are surface-dependent processes since their kinetic directly depends on the contact area between the sample and the extractant phase. The dispersion of the extractant (liquid or solid) increases this area improving the extraction efficiency. In this article, the dispersion of a nanostructured sorbent at the very low milligram level is achieved by effervescence thanks to the in situ generation of carbon dioxide. For this purpose, a special tablet containing the effervescence precursors (sodium carbonate as carbon dioxide source and sodium dihydrogen phosphate as proton donor) and the sorbent [multiwalled carbon nanotubes (MWCNTs)] is prepared. All the microextraction steps take place in a glass beaker containing 100 mL of the sample. After the extraction, the MWCNTs, enriched with the extracted analytes, are recovered by vacuum filtration. Methanol was selected to elute the retained analytes. The extraction mode is optimized and characterized using the determination of nine herbicides in water samples as model analytical problem. The absolute recoveries of the analytes were in the range 48-76 %, while relative recoveries were close to 100 % in all cases. These values permit the determination of these analytes at the low microgram per liter range with good precision (relative standard deviations lower than 9.3 %) using ultra performance liquid chromatography (UPLC) combined with ultraviolet detection (UV).

Oxidized single-walled carbon nanohorns as sorbent for porous hollow fiber direct immersion solid-phase microextraction for the determination of triazines in waters.

This paper evaluates the potential of oxidized single-walled carbon nanohorns (o-SWNHs) immobilized on the pores of a hollow fiber (HF) for the direct immersion solid-phase microextraction of triazines from waters. The fabrication of the device requires the oxidation of the nanoparticles by means of microwave irradiation in order to obtain a homogeneous dispersion in methanol. Then, a porous hollow fiber is immersed in the methanolic dispersion of the o-SWNHs under ultrasound stirring. This procedure permits the immobilization of the o-SWNHs in the pores of the hollow fiber. For the extraction, a stainless steel wire was introduced inside the fiber to allow the vertical immersion of the o-SWNHs-HF in the aqueous standard/water sample. The triazines were preconcentrated on the immobilized o-SWNHs and further eluted using 150 µL of methanol. The solvent was evaporated and the residue reconstituted in 10 µL of methanol for sensitivity enhancement. Gas chromatography-mass spectrometry was selected as instrumental technique. The limits of detection were between 0.05 and 0.1 µg L(-1) with an excellent precision (expressed as relative standard deviation) between runs (below 10.2 %) and between fibers (below 12.8 %). Finally, the method was applied to the determination of the triazines in fortified waters, an average recovery value of 90 % being obtained.