Isolation of Carbon Black from Soils by Dispersion for Analysis: Quantitation and Characterization by Field Flow Fractionation Techniques.

In the present work, a procedure based on a dispersive medium for carbon black (CB) isolation from soil samples for analysis was proposed for the first time. Polymeric and biological dispersants and a sequential use of both dispersants were assayed. Asymmetrical flow field flow fractionation with dynamic light scattering detector (AF4-DLS) and sedimentation field flow fractionation with multi-angle light scattering detector (SdF3-MALS) were used for CB quantitation and characterization in the achieved dispersions. Soil samples contaminated with CB were processed, and CB isolation depended on the solid size distribution and composition and dispersant nature. More quantitative isolations were achieved for the four soils treated by the biological dispersant. As the organic matter percentage is higher in soil, the CB isolation was better, varying between 75 and 99% with standard deviation (s) ⩽ 2% for all soils. A soil contaminated with a CB-based pigment paste was analyzed, achieving (99 ± 2)% expressed as expanded uncertainty (K = 2) of dispersive isolation by the biological dispersant, and the sampling was scaled to 250 g of soil with positive results. The procedure was completed by CB recovery to obtain a solid residue able to be reused if necessary. For the filter-aided recovery step, different membranes (fiberglass, nylon, and Teflon) with a pore size between 0.1 and 5 µm were tested. The quantitation of the CB retained in the filter was measured by diffuse reflectance spectroscopy. Teflon (0.10 µm) provided better results for CB recovery, and its re-dispersion was also studied with suitable results. Determination of CB from the filters by diffuse reflectance spectrometry provided the same results than AF4 for CB dispersions.

Determination of antioxidant activity by in situ synthesis of AgNPs using in-tube SPME coupled on-line to capillary liquid chromatography.

A chromatographic system based on in-tube SPME coupled to capillary LC-DAD has been used to study the synthesis of silver nanoparticles using polyphenols in different scenarios: excess of the reducing agent or of the silver salt, addition of the cationic surfactants, and thermal synthesis. The optimized synthesis conditions allowed to quantify the polyphenols used as reducing agents, such as Trolox and chlorogenic acid. Two chromatographic peaks with different absorption spectrum were monitored during the syntheses. Depending on the molar relationship, a linear relation between the area of the chromatographic peaks and the concentration of the silver or polyphenol was established. For stabilization of silver nanoparticles, different cationic surfactants were used allowing to evaluate the role of anion (chloride and bromide) and of the alkyl chain. The proposed methodology can be used to determine chlorogenic acid up to 3 mM with a detection limit of 34 µM at λ= 400 nm. Chlorogenic acid was determined in dietary products with successful results. Precision (RSD=10%) and recovery (97-100%) were also satisfactory.

On-Site Multisample Determination of Chlorogenic Acid in Green Coffee by Chemiluminiscent Imaging.

The potential of antioxidants in preventing several diseases has attracted great attention in recent years. Indeed, these products are part of a multi-billion industry. However, there is a lack of scientific information about safety, quality, doses, and changes over time. In the present work, a simple multisample methodology based on chemiluminiscent imaging to determine chlorogenic acid (CHLA) in green coffee samples has been proposed. The multi-chemiluminiscent response was obtained after a luminol-persulfate reaction at pH 10.8 in a multiplate followed by image capture with a charge-coupled device (CCD) camera as a readout system. The chemiluminiscent image was used as an analytical response by measuring the luminescent intensity at 0 °C with the CCD camera. Under the optimal conditions, the detection limit was 20 µM and precision was also adequate with RSD < 12%. The accuracy of the proposed system was evaluated by studying the matrix effect, using a standard addition method. Recoveries of chlorogenic acid ranged from 93-94%. The use of the CCD camera demonstrated advantages such as analysis by image inspection, portability, and easy-handling which is of particular relevance in the application for quality control in industries. Furthermore, multisample analysis was allowed by one single image saving time, energy, and cost. The proposed methodology is a promising sustainable analytical tool for quality control to ensure green coffee safety through dosage control and proper labelling preventing potential frauds.

Reliable assessment of carbon black nanomaterial of a variety of cell culture media for in vitro toxicity assays by asymmetrical flow field-flow fractionation.

Carbon black nanomaterial (CB-NM), as an industrial product with a large number of applications, poses a high risk of exposure, and its impact on health needs to be assessed. The most common testing platform for engineered (E)NMs is in vitro toxicity assessment, which requires prior ENM dispersion, stabilization, and characterization in cell culture media. Here, asymmetric flow field-flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series was used for the study of CB dispersions in cell culture media, optimizing instrumental variables and working conditions. It was possible to disperse CB in a non-ionic surfactant aqueous solution due to the steric effect provided by surfactant molecules attached on the CB surface which prevented agglomeration. The protection provided by the surfactant or by culture media alone was insufficient to ensure good dispersion stability needed for carrying out in vitro toxicity studies. On the other hand, cell culture media in combination with the surfactant improved dispersion stability considerably, enabling the generation of shorter particles and a more favourable zeta potential magnitude, leading to greater stability due to electrostatic repulsion. It was demonstrated that the presence of amino acids in the culture media improved the monodisperse nature and stability of the CB dispersions, and resulted in a turn towards more negative zeta potential values when the pH was above the amino acid isoelectric point (IEP). Culture media used in real cell culture scenarios were also tested, and in vitro toxicity assays were developed optimizing the compatible amount of surfactant.

Improving Sustainability of the Griess Reaction by Reagent Stabilization on PDMS Membranes and ZnNPs as Reductor of Nitrates: Application to Different Water Samples.

A new approach based on the use of polydimethylsiloxane (PDMS) membranes doped with Griess reagents for in situ determination of NO2- and NO3-- in real samples is proposed. The influence of some doping compounds, on the properties of the PDMS membranes, such as tetraethyl orthosilicate (TEOS), or/and ionic liquids (OMIM PF6) has been studied. Membrane characterization was performed. To apply the procedure to NO3- determination, dispersed Zn nanoparticles (ZnNPs) were employed. The analytical responses were the absorbance or the RGB components from digital images. Good precision (RSD < 8%) and detection limit of 0.01 and 0.5 mgL-1 for NO2- and NO3-, respectively, were achieved. The approach was satisfactory when applied to the determination of NO2- and NO3- in drinking waters, irrigation and river waters, and waters from canned and fresh vegetables. The results obtained were statistically comparable with those by using nitrate ISE or UV measurement. This approach was transferred satisfactory to 96 wells for multianalysis. This study enables the improvement in the on-site determination of NO2- and NO3- in several matrices. It is a sustainable alternative over the reagent derivatizations in solution and presents several advantages such as being versatile, simplicity, low analysis time, cost, and energy efficiency. The response can be detected visually or by portable instruments such as smartphone.

Characterization and Quantitation of Carbon Black Nanomaterials in Polymeric and Biological Aqueous Dispersants by Asymmetrical Flow Field Flow Fractionation.

Characterization of carbon black (CB) nanomaterials is required in industrial and research areas. Hence, in this study, asymmetrical flow field flow fractionation coupled to UV-vis and DLS detectors in series (AF4-UV-vis-DLS) was studied to evaluate the CB dispersion behavior in polymeric and biological dispersants, given the relevance of these media in practical applications. Under the experimental conditions, the results indicated that polymeric and biological dispersions showed size distributions with hydrodynamic diameters of 404 and 175 nm, respectively, for a particle core diameter of 40 nm. The polymeric dispersant provided lower stability as a function of time than that achieved by the biological dispersant. AF4 allowed separation of different core-sized CB (40, 69, and 72 nm) according to their hydrodynamic size using cross-flow rates of 0.5 mL·min-1 and 1 mL·min-1 for polymeric and biological dispersants, respectively. The dilution of the polymeric dispersion with different real water matrices produced a dramatic loss of dispersion stability, this effect being negligible in the case of biological dispersions.

NQS-Doped PDMS Solid Sensor: From Water Matrix to Urine Enzymatic Application.

The development of in situ analytical devices has gained outstanding scientific interest. A solid sensing membrane composed of 1,2-naphthoquinone-4-sulfonate (NQS) derivatizing reagent embedded into a polymeric polydimethylsiloxane (PDMS) composite was proposed for in situ ammonium (NH4+) and urea (NH2CONH2) analysis in water and urine samples, respectively. Satisfactory strategies were also applied for urease-catalyzed hydrolysis of urea, either in solution or glass-supported urease immobilization. Using diffuse reflectance measurements combined with digital image processing of color intensity (RGB coordinates), qualitative and quantitative analyte detection was assessed after the colorimetric reaction took place inside the sensing membrane. A suitable linear relationship was found between the sensor response and analyte concentration, and the results were validated by a thymol-PDMS-based sensor based on the Berthelot reaction. The suggested sensing device offers advantages such as rapidity, versatility, portability, and employment of non-toxic reagents that facilitate in situ analysis in an energy-efficient manner.

Study of the Stability of Citrate Capped AgNPs in Several Environmental Water Matrices by Asymmetrical Flow Field Flow Fractionation.

Asymmetrical flow field-flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series, was tested for stability studies of dispersions of citrate-capped silver nanoparticles (AgNPs) in several water matrices. The main goal is to provide knowledge to understand their possible behavior in the environment for short times since mixturing (up to 180 min). Ultrapure (UPW), bottled (BW1, BW2), tap (TW), transitional (TrW) and sea water (SW) matrices were assayed. Observations were compatible with the aggregation of AgNPs, a change in the plasmon band and a size growth with time were done. Fractograms showed different evolution fingerprints in the function of the waters and batches. The aggregation rate order was BW2, SW, TrW, BW1 and TW, being BW2 the lowest and TW the highest. NP aggregation can be induced by increasing the salt concentration of the medium, however transitional and sea waters did not follow the rule. Both matrices presented a lower aggregation rate in comparison with other aqueous matrices with much lower ionic strength (BW1 and TW), which can be explained by the potential presence of dissolved organic matter and/or the high concentration of halides providing their stabilization and passivation, respectively. AF4 provides relevant information with respect to static DLS and UV-Vis Spectroscopy showing that at least two populations of aggregates with different sizes between them, depending on both, the mixture time for a given matrix and type of water matrix for the same time.

Aqueous Dilution of Noble NPs Bulk Dispersions: Modeling Instability due to Dissolution by AF4 and Stablishing Considerations for Plasmonic Assays.

Among different nanomaterials, gold and silver nanoparticles (AuNPs and AgNPs) have become useful tools for a wide variety of applications in general, and particularly for plasmonic assays. Particle size and stability analysis are key elements for their practical applications since the NPs properties depend on these parameters. Hence, in the present work, asymmetrical flow field flow fractionation (AF4) coupled to UV-Vis and dynamic light scattering (DLS) detectors in series, has been evaluated for stability studies of citrate-capped AuNPs and AgNPs aqueous dispersions. First, experimental parameters, such as mobile phase or cross-flow rate were optimized. Sodium azide to pH 7 for AuNPs and pH 9.2 for AgNPs were selected as the optimum mobile phase. The analytical response of bulk dispersions of AuNPs (20, 40, 60 and 80 nm) and AgNPs (20, 40 and 60 nm) and their dilutions have been studied. Fractograms showed a decrease on the absorbance signal in diluted dispersions as a function of time and particle size for the diluted dispersions that can be explained by dissolution in diluted dispersion since hydrodynamic diameter was constant. The results indicated that the dependence of the signal with time was more intense for AgNPs than for AuNPs, which can be correlated with its lower stability. These findings should be considered when plasmonic assays are realized. Here, assays involving non-oxidant acidic acids as use cases, were tested for several batches of NPs and considerations about their stability and operability stablished.

Peptide Metal-Organic Frameworks for Enantioselective Separation of Chiral Drugs.

We report the use of a chiral Cu(II) 3D metal-organic framework (MOF) based on the tripeptide Gly-l-His-Gly (GHG) for the enantioselective separation of metamphetamine and ephedrine. Monte Carlo simulations suggest that chiral recognition is linked to preferential binding of one of the enantiomers as a result of either stronger or additional H-bonds with the framework that lead to energetically more stable diastereomeric adducts. Solid-phase extraction of a racemic mixture by using Cu(GHG) as the extractive phase permits isolating >50% of the (+)-ephedrine enantiomer as target compound in only 4 min. To our knowledge, this represents the first example of a MOF capable of separating chiral polar drugs.

Disinfection by-products effect on swimmers oxidative stress and respiratory damage.

Disinfection by-products (DBPs) are generated through the reaction of chlorine with organic and inorganic matter in indoor swimming pools. Different DBPs are present in indoor swimming pools. This study evaluated the effects of different chlorinated formations in oxidative stress and lung damage in 20 swimmers after 40 min of aerobic swimming in 3 indoor pools with different characteristics. Biological samples were collected to measure lung damage (serum-surfactant-associated proteins A and B), oxidative stress parameters (plasma protein carbonylation and malondialdehyde, and whole-blood glutathione oxidation), and swimming exertion values (blood lactate) before and after exercise. Free chlorine and combined chlorine in water, and chlorine in air samples were determined in all the swimming pools. Chlorination as disinfection treatment led to the formation of chloramines in water samples, mainly mono- and dichloramine. However, free chlorine was the predominate species in ultraviolet-treated swimming pool. Levels of total chlorine increased as a function of the swimming activity in chlorinated swimming pools. The lower quality of the installation resulted in a higher content of total chlorine, especially in air samples, and therefore a higher exposure of the swimmer to DBPs. However, the concentration level of chlorinated DBPs did not result in significant variation in serum-surfactant-associated proteins A and oxidative stress parameters in swimmers. In conclusion, the quality of the installation affected the DBPs concentration; however, it did not lead to lung epithelial damage and oxidative stress parameters in swimmers.

New Tools for Characterizing Metallic Nanoparticles: AgNPs, A Case Study.

Currently, transmission electron microscopy (TEM) is the main technique for estimating the sizes of spherical nanoparticles (NPs) and through them, their concentrations. This paper demonstrates for the first time that C18 reversed-phase capillary liquid chromatography (Cap-LC) coupled to diode array detection (DAD) has the potential to estimate mean concentrations of silver nanoparticles (AgNPs) and thereby determine their average size. Direct injection of the sample without previous extraction or separation steps is carried out. Only a unique standard with a known AgNP size is needed for the calibration. In a first approach, the new method has been tested over silver nanoparticles, produced using different methods of synthesis, and their water dilutions. Good results were achieved: relative errors ranged up to 5% compared with TEM. Also stability and functionality-related NP properties, as well as nonspherical AgNPs, can be studied using this method. Moreover, by coupling online in-tube solid-phase microextraction (IT-SPME) to Cap-LC-DAD, the effect of the dilution can be studied as particles distribute by polarity in two groups, a distribution that responds to average particle size of not only AgNPs, but also gold nanoparticles (AuNPs). In such a distribution, the average particle size is correlated with the peak area ratio. Additionally, besides higher sensitivity and concentration-dependent signals, IT-SPME-Cap-LC responds to changes in the particle's hydrodynamic diameter allowing, for instance, the detection of cationic surfactants. Size-exclusion and hydrophobic effects are the mechanisms involved to explain this behavior.

Microextraction with phases containing nanoparticles.

In this article, the state of the art of microextraction techniques that involve nanoparticles or nanomaterials (NPs) is reviewed, with special emphasis on the applications described in the biomedical field. The uses and advantages of the different types of NPs such as carbon nanotubes (either single- and multi-walled) and other carbon-based materials, metallic NPs, including gold, silver and magnetic NPs, and silica NPs are summarized. The main strategies used to modify the selectivity, extractive capacity and/or the stability of NPs through a chemical reaction are also reviewed. The potential advantages of NPs in different forms of off-line and on-line microextraction are discussed, and illustrative examples of application in the biomedical field are shown.

Analysis of polar triazines and degradation products in waters by in-tube solid-phase microextraction and capillary chromatography: an environmentally friendly method.

This paper describes a new method for the determination of polar triazines, including some degradation products, which combines online in-tube solid-phase microextraction (IT-SPME) and capillary liquid chromatography with UV-diode array detection (DAD). Different extractive coatings have been evaluated for IT-SPME, a capillary column with a polydimethylsiloxane (PDMS) coating, and the same coating modified with carboxylated single-wall carbon nanotubes (c-SWCNTs) and carboxylated multiwall carbon nanotubes (c-MWCNTs). On the basis of the results obtained, a new method is presented for the identification and determination of triazines in water samples. A careful selection of the eluent composition provides the required selectivity and sensitivity for the quantification of the target analytes, even those highly polar (log K ow ≤ 2.3). The proposed conditions have been successfully used for the quantitation of the analytes in the 0.25-50.0 µg L(-1) range. The limits of detection (LODs) are in the 0.02-0.1 µg L(-1) range, and the intraday and interday relative standard deviation (RSD) coefficients are ≤9 and ≤17 %, respectively. The reliability of the described method has been tested by analyzing several real water samples. The proposed method can be considered an environmentally friendly and cost-effective alternative for routine monitoring of triazines and their degradation products in waters.

Capillary electrophoresis method for the characterization and separation of CdSe quantum dots.

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

Preconcentration of emerging contaminants in environmental water samples by using silica supported Fe3O4 magnetic nanoparticles for improving mass detection in capillary liquid chromatography.

A magnetic material based on Fe(3)O(4) magnetic nanoparticles incorporated in a silica matrix by using a sol-gel procedure has been used to extract and preconcentrate emerging contaminants such as acetylsalicylic acid, acetaminophen, diclofenac and ibuprofen from environmental water samples prior to the analysis with Capillary LC-MS. The use of the proposed silica supported Fe(3)O(4) magnetic nanoparticles enables surfactant free extracts for the analysis with MS detection without interferences in the ionisation step. Under the optimum conditions, we demonstrated the reusability of the magnetic sorbent material during 20 uses without loss in the extraction efficiency. In addition, no cleanup was necessary. The preconcentration factor was 100 and the detection limits were between 50 and 150 ng/L. The proposed procedure has been applied to the analysis of water samples obtaining recoveries between 80 and 110% and RSD values lower than 12%. Concentrations of the target analytes over the range 1.7 and 0.1 µg/L have been found in different water samples.

Evaluation of the performance of single-walled carbon nanohorns in capillary electrophoresis.

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.

Recent developments in capillary EKC based on carbon nanoparticles.

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.

Carboxylic multi-walled carbon nanotubes as immobilized stationary phase in capillary electrochromatography.

Carboxylic multi-walled carbon nanotubes (c-MWNT) have been immobilized into a fused-silica capillary for capillary electrochromatography. The c-MWNT were successfully incorporated after the silanization and coupling with glutaraldehyde on the inner surface of the capillary. The electrochromatographic features of the c-MWNT immobilized stationary phase have been evaluated for the analysis of different compounds of pharmaceutical interest. The results indicated high electrochromatographic resolution, good capillary efficiency and retention factors. In addition, highly reproducible results between runs, days and capillaries were obtained.

Monitoring of carboxylic carbon nanotubes in surface water by using multiwalled carbon nanotube-modified filter as preconcentration unit.

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