Raman spectroscopic characterization of single walled carbon nanotubes: influence of the sample aggregation state.

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.

Qualitative detection and quantitative determination of single-walled carbon nanotubes in mixtures of carbon nanotubes with a portable Raman spectrometer.

The main aim of this work is to develop a one-step method for the characterization of mixtures of single- and multi-walled carbon nanotubes using a simple and inexpensive tool, a portable Raman spectrometer. In order to overcome the problem of heat dissipation in solid samples, the suitability of three surfactants-SDS, Triton X-100 and CTAB-to disperse nanotubes has been evaluated. A systematic study of the wavelength and relative intensity of the D and G bands has been carried out with six samples of multiwalled carbon nanotubes (MWNTs) and one of single-walled carbon nanotubes (SWNTs) dispersed in these surfactants, and this has been compared with solid samples. Finally, the possibility has been demonstrated to identify and (semi)quantify the presence of SWNTs in a mixture containing MWNTs.

Solid phase extraction-capillary electrophoresis determination of sulphonamide residues in milk samples by use of C18-carbon nanotubes as hybrid sorbent materials.

The exceptional sorption capabilities of carbon nanotubes were used to preconcentrate trace sulphonamides from milk samples. To this end, single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) dispersed in the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate were retained on a C18 stationary phase to obtain a hybrid material in a simple manner. In this approach ionic liquids are an excellent alternative to improve the dispersion of CNTs, without chemical modification or the use of solid substances or organic solvents. MWNTs provided better results than SWNTs. Carbon nanotubes retained in the C18 sorbent matrix were found to confer aromatic character, increasing its preconcentration capacity as a result. The conventional C18 stationary phase played a two-fold role: as a support to retain carbon nanotubes in the cartridge and as a medium to prevent their aggregation. The modified MWNT/C18 and SWNT/C18 materials were used to preconcentrate residual sulphonamides (SAs) in milk samples for their determination at concentrations as low as 0.03-0.069 mg L(-1) by capillary electrophoresis. Analyte recoveries from spiked samples ranged from 103.2 to 98.8% and precision, as RSD, from 8.2 to 5.4%.

Rapid analysis of gold nanoparticles in liver and river water samples.

This paper describes a simple approach to determine gold nanoparticles in liver and river water samples. The method of purification of nanoparticles from the matrix is based on the stabilization of gold nanoparticles with a cationic surfactant followed by a microliquid-liquid extraction in ionic liquid. Finally, the extracted nanoparticles can be analysed by UV/Vis detection or Raman spectroscopy. The precision of the proposed method for the analysis of liver tissue and river water samples was 9.7% and 18% respectively for UV/Vis analysis. The sensitivity was 1.17 × 10(-12) M for the analysis of 3 mL of liver homogenate or river water sample.

Coiled carbon nanotubes combined with ionic liquid: a new soft material for SPE.

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%.

Analytical potential of hybrid nanoparticles.

The growing use of nanoparticles in the analytical process in recent years has set a new trend towards the simplification of analytical methods and improvement of their performance. Miniaturization and nanotechnology have allowed new analytical challenges to be met. Hybrid nanoparticles in particular possess exceptional properties enabling further improvement of analytical methods. Despite the continuous developments in their synthesis and characterization, hybrid nanomaterials have scarcely been used in analytical chemistry, however. This paper discusses the analytical potential of hybrid nanoparticles in terms of their special characteristics and properties, and describes their analytical applications.

The potential of carbon nanotube membranes for analytical separations.

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.

Characterisation of alkylamine ethoxylates (ANEOs) in commercial herbicide formulations using liquid chromatography/electrospray ionisation mass spectrometry.

A quantitative method is described for the characterization of alkylamine ethoxylate (ANEO) surfactants in commercial herbicide formulations using reversed-phase high-performance liquid chromatography with electrospray ionization mass spectrometric detection. The proposed protocol allows the simultaneous determination of a full range of oligomers which were monitored as [M-H](+) ions in positive ion mode. The instrumental detection limits (LODs) were 0.5 µg. The method developed was successfully applied to the determination of ANEOs in a number of glyphosate formulations. Both the total concentration of these surfactants and the oligomer distribution varied between the different commercial herbicides analysed. The precision of the determination of the oligomers in samples ranged from 0.5 to 15%.

Monitoring nanoparticles in the environment.

The presence of nanoparticles in the environment can have important implications for both environmental and human health. Nanoscience and nanotechnology are expected to change industrial production and the economy as we know them today. However, nanotechnologies can also be a source of risks. The increasing use of nanoparticles in industrial applications will inevitably lead to the release of such materials into the environment. Accurately assessing the environmental risks posed by nanoparticles requires using effective quantitative analytical methods to determine their mobility, reactivity, ecotoxicity and persistency, many of which have still to be developed. This overview describes some methodological aspects relating to the fields of nanoparticle analysis, nanometrology and analytical chemistry.

Determination of 2-ethylhexyl 4-(dimethylamino) benzoate using membrane-assisted liquid-liquid extraction and gas chromatography-mass spectrometric detection.

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.

Separation of single-walled carbon nanotubes by use of ionic liquid-aided capillary electrophoresis.

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.

Analytical nanoscience and nanotechnology today and tomorrow.

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.

Determination of non-steroidal anti-inflammatory drugs in urine by combining an immobilized carboxylated carbon nanotubes minicolumn for solid-phase extraction with capillary electrophoresis-mass spectrometry.

Last years, the usefulness of the use of carbon nanotubes (CNTs) as sorbent material have been demonstrated for a wide variety of compounds. In this work, it has been demonstrated for first time that immobilized carboxylated single-walled carbon nanotubes (c-SWNTs) offer clear advantages over the use of CNTs. The higher adsorption capacity has been attributed to the special orientation of c-SWNTs molecules on the glass surface. The potential of this new sorbent was evaluated for the preconcentration of non-steroidal anti-inflammatory drugs (NSAIDs) from urine samples. Purified samples were analysed by capillary electrophoresis-mass spectrometry detection allowing the determination of 1.6 to 2.6 microg/L of NSAIDs with only 5 mL of sample. The precision of the method for the determination of real spiked urine samples ranged from 5.4 to 7.4% and the recoveries from 98.6 to 102.2%.

Principles of qualitative analysis in the chromatographic context.

This article presents the state of the art of qualitative analysis in the framework of the chromatographic analysis. After establishing the differences between two main classes of qualitative analysis (analyte identification and sample classification/qualification) the particularities of instrumental qualitative analysis are commented on. Qualitative chromatographic analysis for sample classification/qualification through the so-called chromatographic fingerprint (for complex samples) or the volatiles profile (through the direct coupling headspace-mass spectrometry using the chromatograph as interface) is discussed. Next, more technical exposition of the qualitative chromatographic information is presented supported by a variety of representative examples.

Solid-phase extraction-capillary electrophoresis-mass spectrometry for the determination of tetracyclines residues in surface water by using carbon nanotubes as sorbent material.

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 microg/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.

Vial position in the determination of chlorophenols in water by solid phase microextraction.

The extraction of chlorophenol from water by headspace solid phase microextraction (HS-SPME) in vials located both vertically and horizontally is compared. The results obtained show that kinetic parameters are clearly affected by how the vial is placed in the analysis of semivolatile compounds. Extraction time for reach the equilibrium was three times lower in the horizontal configuration. An on-line extraction unit coupled to a continuous flow system is used to analyse unmodified ground water samples. In order to increase the high throughput, the analysis time is reduced and the sensitivity increased by making the extraction simultaneously with two fibres. The proposed method is applied to the analysis of spiked river water samples. The precision expressed as relative standard deviation ranges from 3.5 to 4.8%, and the recoveries from 94 to 105%.

Alternatives for coupling sequential injection systems to commercial capillary electrophoresis-mass spectrometry equipment.

On-line coupling of an automated flow system with a commercially available capillary electrophoresis (CE) system with an electrospray interface (ESI) for mass spectroscopic (MS) detection is described. The peculiarities of CE-ESI-MS interfaces, in which a high electrical field must be applied to the capillary end where the sample is provided by the flow system, introduce significant difficulties for the appropriate work of the entire arrangement. Experimental strategies are proposed for achieving stable conditions for on-line sample pre-treatment, conditioning of the separation capillary, sample injection, as the proper separation. The versatility and robustness of the proposed arrangement is discussed, taken as example the separation of a variety of amines. Connection of the CE system's pressure to the automated flow system enables hydrodynamic introduction of sample with high precision. The developed hyphenated system is of practical relevance as it opens an avenue for the simplification and automation of the whole analytical process required when using powerful CE-ESI-MS equipments.

Use of non-aqueous capillary electrophoresis for the quality control of commercial saffron samples.

A non-aqueous capillary electrophoresis (NACE) method for quantifying the seven crocin metabolites that are the major biologically active ingredients of saffron was developed. Separation is done by using a fused silica capillary filled with a 12.5 mM H3BO3/37.5 mM sodium tetraborate methanolic solution as background electrolyte. The results obtained were compared with the total index "safranal value", widely used as a quality measure of saffron products. The comparison revealed that the proposed NACE method provides useful information not obtained in the safranal value. Infact, samples with a similar safranal value can contain crocin metabolites in different concentrations and relative proportions. This new method is very useful for quality control in commercial saffron samples.

Determination of pyrophosphate in renal calculi and urine by means of an enzymatic method.

An enzymatic method for the determination of pyrophosphate which has been applied to renal calculi is described. The method involves the preconcentration of pyrophosphate using anionic exchange resin and development of the enzymatic reactions with the pyrophosphate retained on the resin. The study of calculi treatment according to calculi composition is also reported. The pyrophosphate content was dependent on the calculi composition. The highest amount of pyrophosphate was found in hydroxyapatite calculi (of the order of 10 microg/g), struvite and oxalate calculi showed a lower amount (the order was 2.5 and 4.5 microg/g, respectively) and was not detected in uric acid and cystine stones. The method was also successfully applied to the determination of pyrophosphate in human urine. For urinary pyrophosphate determination, a modification based on a clean-up of urine using activated carbon has been proposed. Pyrophosphate in human urine was of the order of 4 mg l(-1).