Rosa Busquets

Driving forces of conformational changes in single-layer graphene oxide

The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance.

pH-driven physicochemical conformational changes of single-layer graphene oxide

Single-layer graphene oxides (SLGOs) undergo morphological changes depending on the pH of the system and may account for restricted chemical reactivity. Herein, SLGO may also capture nanoparticles through layering and enveloping when the pH is changed, demonstrating potential usefulness in drug delivery or waste material capture.

State-of-the-art in fast liquid chromatography–mass spectrometry for bio-analytical applications

There is an increasing need of new bio-analytical methodologies with enough sensitivity, robustness and resolution to cope with the analysis of a large number of analytes in complex matrices in short analysis time. For this purpose, all steps included in any bio-analytical method (sampling, extraction, clean-up, chromatographic analysis and detection) must be taken into account to achieve good and reliable results with cost-effective methodologies. The purpose of this review is to describe the state-of-the-art of the most employed technologies in the period 2009-2012 to achieve fast analysis with liquid chromatography coupled to mass spectrometry (LC-MS) methodologies for bio-analytical applications. Current trends in fast liquid chromatography involve the use of several column technologies and this review will focus on the two most frequently applied: sub-2μm particle size packed columns to achieve ultra high pressure liquid chromatography (UHPLC) separations and porous-shell particle packed columns to attain high efficiency separations with reduced column back-pressures. Additionally, recent automated sample extraction and clean-up methodologies to reduce sample manipulation, variability and total analysis time in bio-analytical applications such as on-line solid phase extraction coupled to HPLC or UHPLC methods, or the use of other approaches such as molecularly imprinted polymers, restricted access materials, and turbulent flow chromatography will also be addressed. The use of mass spectrometry and high or even ultra-high resolution mass spectrometry to reduce sample manipulation and to solve ion suppression or ion enhancement and matrix effects will also be presented. The advantages and drawbacks of all these methodologies for fast and sensitive analysis of biological samples are going to be discussed by means of relevant applications.

New method for the analysis of heterocyclic amines in meat extracts using pressurised liquid extraction and liquid chromatography-tandem mass spectrometry

Heterocyclic amines (HAs) were analysed in meat extract samples using a new method based on pressurised liquid extraction (PLE) and liquid chromatography-tandem mass spectrometry. This method combines the use of a pressurised fluid with a triple quadrupole MS/MS system, resulting in benefits from both systems: high extraction efficiency and sensitivity. The effects of solvent type and PLE operational parameters, such as temperature and extraction time, were studied to obtain maximum recovery of the analytes with minimum contamination. HA extraction was best achieved using dichloromethane/acetone (50/50, v/v) at 80 degrees C for 10 min. Recoveries ranged from 45% to 79% with good quality parameters: limit of detection values between 0.02 and 1 ng g(-1), linearity (r(2)>0.997), and run-to-run and day-to-day precisions with relative standard deviations lower than 13% achieved at both low (0.20 microg g(-1)) and medium (1.0 microg g(-1)) concentrations. This method reduces sample manipulation and total extraction time by nearly four-fold compared to conventional solid phase extraction. The optimised method was validated using laboratory reference material based on a meat extract, and was successfully applied to HA analysis in several cooked beef samples.

Method for the fast determination of bromate, nitrate and nitrite by ultra performance liquid chromatography-mass spectrometry and their monitoring in Saudi Arabian drinking water with chemometric data treatment.

A rapid, sensitive and precise method for the determination of bromate (BrO3(-)), nitrate (NO3(-)) and nitrite (NO2(-)) in drinking water was developed with Ultra performance Liquid Chromatography-Mass Spectrometry (UPLC-ESI/MS). The elution of BrO3(-), NO3(-) and NO2(-) was attained in less than two minutes in a reverse phase column. Quality parameters of the method were established; run-to-run and day-to-day precisions were <3% when analysing standards at 10 µg L(-1). The limit of detection was 0.04 µg NO2(-) L(-1) and 0.03 µg L(-1) for both NO3(-)and BrO3(-). The developed UPLC-ESI/MS method was used to quantify these anions in metropolitan water from Saudi Arabia (Jeddah, Dammam and Riyadh areas) and commercial bottled water (from well or unknown source) after mere filtration steps. The quantified levels of NO3(-) were not found to pose a risk. In contrast, BrO3(-) was found above the maximum contaminant level established by the US Environmental Protection Agency in 25% and 33% of the bottled and metropolitan waters, respectively. NO2(-) was found at higher concentrations than the aforementioned limits in 70% and 92% of the bottled and metropolitan water samples, respectively. Therefore, remediation measures or improvements in the disinfection treatments are required. The concentrations of BrO3(-), NO3(-) and NO2(-) were mapped with Principal Component analysis (PCA), which differentiated metropolitan water from bottled water through the concentrations of BrO3(-) and NO3(-) mainly. Furthermore, it was possible to discriminate between well water; blend of well water and desalinated water; and desalinated water. The point or source (region) was found to not be distinctive.

Quantification of heterocyclic amines from thermally processed meats selected from a small-scale population-based study

Heterocyclic amines (HAs) are potent mutagens that form at high temperatures in cooked, protein-rich food. Due to their frequent intake, these compounds are considered a risk factor for human cancer. Cooking conditions and eating habits strongly influence the level of HA exposure. Thus, it is difficult to assess the intake of HAs in a large population. Food-frequency questionnaires (FFQs), designed to provide data on parameters that affect HA formation, were used to survey a small population (459 persons) from Barcelona (NE Spain). Subsequently, the most-consumed food items named were cooked according to the preferences of the population surveyed and analyzed for HAs using SPE and LC-MS/MS. In the population studied, the estimated intake via consumption of 13 meat dishes was 285.6 ng of mutagenic HAs per capita and day. PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) was the HA to which the population was most exposed, mainly from fried chicken and griddled beef. When the co-mutagens norharman and harman are included, the mean daily intake of HAs rises to 475.6 ng per capita and day. A novel putative DMIP regioisomer was detected in the cooked meats, which was analyzed in the present study by multistage MS.

γ-Al2O3-based nanocomposite adsorbents for arsenic(V) removal: Assessing performance, toxicity and particle leakage.

The generation and development of effective adsorption materials for arsenic removal are urgently needed due to acute arsenic contamination of water sources in many regions around the world. In the search for these new adsorbents, the application of nanomaterials or nanocomposites, and especially the use of nanoparticles (NPs), has proven increasingly attractive. While the adsorptive performance of a range of nanocomposite and nanomaterial-based systems has been extensively reviewed in previously-published literature, the stability of these systems in terms of NP release, i.e. the ability of the nanomaterial or nanocomposite to retain incorporated NPs, is less well understood. Here we examine the performance of nanocomposites comprised of aluminium oxide nanoparticles (AluNPs) incorporated in macroporous polyacrylamide-based cryogels (n-Alu-cryo, where n indicates the percentage of AluNPs in the polymer material (n=0-6%, w/v)) for As(V) adsorption, and evaluate AluNP leakage before and after the use of these materials. A range of techniques is utilised and assessed (SEM, TEM, mass weight change, PIXE and in vitro toxicity studies). The 4-Alu-cryo nanocomposite was shown to be optimal for minimising AluNP losses while maximising As(V) removal. From the same nanocomposite we were further able to show that NP losses were not detectable at the AluNP concentrations used in the study. Toxicity tests revealed that no cytotoxic effects could be observed. The cryogel-AluNPs composites were not only effective in As(V) removal but also in immobilising the AluNPs. More challenging flow-through conditions for the evaluation of NP leakage could be included as a next step in a continued study assessing particle loss and subsequent toxicity.

Identification of seafood as an important dietary source of heterocyclic amines by chemometry and chromatography–mass spectrometry

Heterocyclic amines (HCAs), which are formed during the cooking of protein-rich foods, are potent mutagens and a risk factor for human cancers. Levels of HCAs have been extensively investigated in meat products but not in fish products. Here, we report levels of HCAs in fried salmon, tuna, hake, sardine, angler fish, cod, sole, swordfish, squid, and cuttlefish. The HCA levels of some of these foods have not been previously analyzed. We employed multivariate factor-analysis tools, including principal components analysis (PCA) and partial least-squares (PLS) regression, to study the effects of cooking weight loss and levels of creatine, glucose, and free amino acids on HCA levels. The highest concentrations of mutagenic HCAs, 159.3 ng·g(-1) total, where 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) accounted for 121 ng·g(-1), were found in fried swordfish (cooking loss of 51.8%). These levels are higher than those generally found in fried chicken, which is typically cited as the most contaminated food item. Thus, swordfish is among the richest known sources of HCAs. The other cooked seafood items contained from 0.4 to 35.4 ng·g(-1) HCAs, comparable to concentrations typically reported for meat. Chemometric analysis showed that the fish species is the most influential parameter on the formation of HCAs such as DMIP, PhIP, and norharman. Concentrations of histidine, lysine, creatine, and glucose, as well as weight loss, also influence the yield of HCAs. These results suggest that seafood is an important dietary source of HCAs. The formation of HCAs in fish is influenced by multiple factors, some of which remain unknown.

An ultra performance liquid chromatography-electrospray ionization-mass spectrometry method for the rapid analysis of nitrate in drinking water

Excess of nutrient load can cause water eutrophication and be harmful to humans. While nitrogen is an important nutrient for crops, its introduction into the soil with fertilizers containing nitrate (NO3−) has been a major source of water pollution and monitoring NO3− has become necessary. In the present work, an ultra performance liquid chromatography-mass spectrometry method has been developed for the rapid quantification of NO3− in drinking water with reversed phase chromatography using a Waters Acquity BEH C18 (50 mm × 2.1 mm i.d., 1.7 μm particle size) column and a triple quadrupole mass spectrometer operating in Single Ion Recording mode. The quality parameters of the developed method were established, obtaining a limit of detection of 0.02 μg L−1; linearity (r2 > 0.999) over a concentration range covering 3 orders of magnitude; high precision, with repeatability and reproducibility lower than 3% (n = 5) in terms of relative standard deviation when analyzing a standard (0.05 mg NO3− L−1) and unspiked drinking water samples with levels of NO3− of 1 μg L−1 (metropolitan water) and 3 mg L−1 (bottled water). These quality parameters show that the proposed method improves the performance of conventional analytical methods used for the analysis of NO3−. This method has been applied successfully for determination of NO3− in metropolitan and bottled water from the Kingdom of Saudi Arabia; a total of 25 samples have been analyzed where NO3− was found to be present from levels below the limit of detection to 6.49 mg L−1.

Preparation and characterisation of fried chicken as a laboratory reference material for the analysis of heterocyclic amines.

The preparation of a laboratory reference material (LRM) for the determination of naturally occurring heterocyclic amines (HAs) in processed foods is presented in this work. A LRM was prepared from raw chicken breast meat, which was fried under controlled cooking temperature and time. The cooked meat was ground, lyophilised, sieved, homogenised, bottled, and labelled. The HAs DMIP, PhIP, MeIQx, 4,8-DiMeIQx, Norharman and Harman were analysed in the LRM. Homogeneity and stability studies of the bulk LRM were carried out and no statistical differences were observed in the content of the studied HAs in between-bottle and within-bottle comparisons at different storage temperatures (-18, +4, +25 and +40 degrees C) and times (1, 3, 6 and 9 months) by means of HAs determination and analysis of the results. Consequently, the material can be considered homogeneous and stable and can be used in intercomparison exercises for the determination of HAs as well as for quality control purposes in the routine analysis of HAs in foodstuffs. This is the first LRM for the analysis of HAs where these analytes were naturally formed in the material.