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1.
Phys Chem Chem Phys ; 21(35): 19209-19215, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31441478

RESUMO

Pure-shift NMR experiments provide highly resolved spectra, which could be perfect for precise monitoring of chemical shift variations under different conditions, such as temperature or concentration. However, their sensitivity is relatively low and signal sampling is time-consuming, which leads to long experimental times, making such serial acquisition problematic. In this paper we present a new method of NMR spectroscopy which improves the speed and sensitivity of serial pseudo-two-dimensional pure-shift experiments. The example of variable-temperature study of atorvastatin reveals the potential of the method in verifying the theoretical predictions of solvent-dependent spectral effects.


Assuntos
Atorvastatina/química , Técnicas de Química Analítica/métodos , Espectroscopia de Ressonância Magnética , Solventes/química , Temperatura Ambiente , Técnicas de Química Analítica/normas
2.
Phys Chem Chem Phys ; 21(35): 19288-19297, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31451821

RESUMO

This paper reports a facile, fast, and cost-effective method for the synthesis of three-dimensional (3D) porous AgNPs/Cu composites as SERS substrates for the super-sensitive and quantitative detection of food organic contaminations. Due to the 3D porous hotspot architecture and the strong plasmonic coupling between Ag and Cu, the porous AgNPs/Cu substrate achieves ultrasensitive detection of multiple analytes as low as 10-11 M (crystal violet, CV), 10-9 M (malachite green, MG), 10-11 M (acephate), and 10-9 M (thiram) even with a portable Raman device. Moreover, this 3D solid substrate has good signal uniformity (RSD < 11%) and superior stability (<14% signal loss), allowing for practical SERS detections. Importantly, by simply wiping the real sample surface using the substrate, it successfully detects CV and MG residues on crayfish, and the limit of detection (LOD) of CV and MG is determined to be 1.14 × 10-9 M and 0.94 × 10-7 M, respectively. Further, the substrate can also be applied to detect acephate on eggplant with a LOD of 1.41 × 10-9 M and thiram on an apple surface with a LOD of 1.04 × 10-7 M. Note that all these SERS detections on real samples have a broad dynamic concentration range and a good linear dependence. As a "proof of concept", multi-component detection on a real sample has also been demonstrated. This 3D solid substrate possesses excellent detection sensitivity, diversity, and accuracy, which allows rapid and reliable determination of toxic substances in foods.


Assuntos
Técnicas de Química Analítica/métodos , Análise de Alimentos/métodos , Contaminação de Alimentos/análise , Praguicidas/análise , Análise Espectral Raman , Animais , Técnicas de Química Analítica/economia , Cobre/química , Limite de Detecção , Nanopartículas Metálicas/química , Reprodutibilidade dos Testes , Prata/química
3.
Phys Chem Chem Phys ; 21(35): 18958-18969, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31453590

RESUMO

Enhanced sampling has been extensively used to capture the conformational transitions in protein folding, but it attracts much less attention in the studies of protein-protein recognition. In this study, we evaluated the impact of enhanced sampling methods and solute dielectric constants on the overall accuracy of the molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) and molecular mechanics/generalized Born surface area (MM/GBSA) approaches for the protein-protein binding free energy calculations. Here, two widely used enhanced sampling methods, including aMD and GaMD, and conventional molecular dynamics (cMD) simulations with two AMBER force fields (ff03 and ff14SB) were used to sample the conformations for 21 protein-protein complexes. The MM/PBSA and MM/GBSA calculation results illustrate that the standard MM/GBSA based on the cMD simulations yields the best Pearson correlation (rp = -0.523) between the predicted binding affinities and the experimental data, which is much higher than that given by MM/PBSA (rp = -0.212). Two enhanced sampling methods (aMD and GaMD) are indeed more efficient for conformational sampling, but they did not improve the binding affinity predictions for protein-protein systems, suggesting that the aMD or GaMD sampling (at least in short timescale simulations) may not be a good choice for the MM/PBSA and MM/GBSA predictions of protein-protein complexes. The solute dielectric constant of 1.0 is recommended to MM/GBSA, but a higher solute dielectric constant is recommended to MM/PBSA, especially for the systems with higher polarity on the protein-protein binding interfaces. Then, a preliminary assessment of the MM/GBSA calculations based on a variable dielectric generalized Born (VDGB) model was conducted. The results highlight the potential power of VDGB in the free energy predictions for protein-protein systems, but more thorough studies should be done in the future.


Assuntos
Técnicas de Química Analítica/métodos , Modelos Químicos , Proteínas/química , Técnicas de Química Analítica/normas , Simulação de Dinâmica Molecular , Ligação Proteica , Conformação Proteica , Reprodutibilidade dos Testes
4.
J Agric Food Chem ; 67(33): 9187-9202, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31259552

RESUMO

The rationale and scope of the main issues of antioxidant measurement are presented, with basic definitions and terms in antioxidant research (such as reactive species and related antioxidative defenses, oxidative stress, and antioxidant activity and capacity) in a historical background. An overview of technical problems and expectations is given in terms of interpretation of results, precision and comparability of methods, capability of simulating physical reality, and analytical performance (sensitivity, selectivity, etc.). Current analytical methods for measuring antioxidant and antiradical activity are classified from various viewpoints. Reaction kinetics and thermodynamics of current analytical methods are discussed, describing physicochemical aspects of antioxidant action and measurement. Controversies and limitations of the widely used antioxidant assays are elaborated in detail. Emerging techniques in antioxidant testing (e.g., nanotechnology, sensors, electrochemistry, chemometry, and hyphenated methods) are broadly introduced. Finally, hints for the selection of suitable assays (i.e., preferable for a specific purpose) and future prospects are given.


Assuntos
Antioxidantes/química , Técnicas de Química Analítica/métodos , Técnicas Eletroquímicas/métodos , Nanotecnologia/métodos , Espécies Reativas de Oxigênio/química , Oxirredução
5.
Phys Chem Chem Phys ; 21(29): 15917-15931, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31309206

RESUMO

X-ray nanochemistry studies how to use nanomaterials and particularly how to create new nanomaterials to increase the effects of X-rays such as chemical reactivity, damage to cells, tumor destruction, scintillation and more. The increase, also called enhancement, can be categorized into several groups, and the current categorization of enhancement follows a natural division of physical, chemical and biological enhancement based on how nanomaterials behave under X-ray irradiation. In physical enhancement, electrons released from atoms in the nanomaterials upon X-ray ionization interact with the nanomaterials and surrounding media to increase the effects. Scintillation also belongs to this category. Chemical enhancement results when reactive oxygen species (ROS) or reactive radical intermediates (RRI) produced in aqueous solutions under X-ray irradiation interact with the surface of catalytic nanomaterials to increase the effects. When the damage of cells is enhanced through biological pathways beyond the abovementioned physical or chemical enhancement due to the presence of nanomaterials under X-ray irradiation, the enhancement is called biological enhancement. Works supporting this systematic categorization, the reported values of these enhancements, and important aspects of the development of enhancement in the X-ray nanochemistry framework are given and discussed in this perspective.


Assuntos
Técnicas de Química Analítica/métodos , Nanoestruturas/química , Raios X , Células/química , Células/efeitos da radiação , Espécies Reativas de Oxigênio
6.
J Chromatogr A ; 1601: 365-374, 2019 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-31176483

RESUMO

Capillary electrophoresis (CE) coupled with contactless conductivity detector (C4D) was applied to characterize the migration of micellar segments under BGE/segment/BGE system, where a segment is a micellar phase surrounded by BGE. The transformation (non-ionic, ionic) → mixed micelles under the system was explained in terms of the features of the micellar phase discussed already in the literature. In the second part of the work, based on established phenomena for BGE/segment/BGE system, the BGE/segment/segment/BGE system was used to analyze the re-equilibration of two micellar phases (SDS│(TX-100/SDS)) during a run. This aspect was deeper analyzed with the conclusion that re-equilibration in the present system induces decomposition of the phase of mixed micelles by the phase of ionic micelles and this is a mechanism able to generate the boundary conditions. Established features for BGE/segment/segment/BGE system were further implemented towards preconcentration of nanoparticles and systematic studies show that the system in the configuration (SDS│(TX-100/SDS)) generates a trap state for nanoparticles. Due to this the preconcentration of nanoparticles, expressed in the terms of an enhancement factor (SEFheight), was found to reach level ca. 60.


Assuntos
Técnicas de Química Analítica/métodos , Eletroforese Capilar , Micelas , Nanopartículas/química , Polietilenoglicóis/química
7.
J Chromatogr A ; 1602: 188-198, 2019 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-31147156

RESUMO

A liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS)-based dereplicative method was developed for identifying oplopane- and bisabolane-type sesquiterpenoids from buds of Tussilago farfara L. The analysis of these chemical analogues, sesquiterpene esters, is challenging by MS-based nontargeted metabolomic approaches because of their in-source fragmentation and structural diversity. To profile these sesquiterpenoids, four diagnostic ions (m/z 215.143, 217.158, 229.123, and 231.138) were suggested in the positive ion mode and the developed method utilized two sequential MS/MS scan modes to identify common skeletons and investigate the fragmentation patterns of their parent molecules. Precursor ion scan by triple quadrupole MS/MS provided the parent molecular ions from their diagnostic ions, and product ion scan by quadrupole time-of-flight MS/MS confirmed their fragmentation behaviors. Under the optimized UHPLC-MS/MS method, 74 sesquiterpenoids were characterized from the Farfarae Flos and 11 compounds were isolated for the method validation. Among those compounds, three sesquiterpenoids were newly separated from the Farfarae Flos. Furthermore, the diagnostic ions and the MS/MS fragment behaviors were applied to the accurate quantification of the 8 isolated sesquiterpenoids. Therefore, the developed LC-MS/MS-based method highlighted the chemical composition of the Farfarae Flos and could be extended to the screening and quantification of other sesquiterpene esters.


Assuntos
Técnicas de Química Analítica/métodos , Espectrometria de Massas , Sesquiterpenos/química , Tussilago/química , Cromatografia Líquida , Íons/química , Sesquiterpenos/isolamento & purificação
8.
Mar Drugs ; 17(5)2019 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-31130603

RESUMO

The replacement of synthetic compounds by natural products witnesses an increasing demand from the pharmaceutical, cosmetic, food and nutraceutical industries. Included in the set of natural raw materials that are poorly explored are the macroalgae. Despite the detailed characterization and identification of most relevant biomolecules that are present in the main macroalgae species, there remains a lack of efficient and economically viable processes available to meet the needs of the markets. In this work, an efficient and single-step process, based on aqueous solutions of Tween 20, to recover carotenoids from Sargassum muticum, an invasive brown macroalgae species present in the Portuguese coast, is proposed and optimized allowing an extraction yield of 2.78 ± 0.4 mgcarotenoids.gdried mass-1, which is shown to increase the extraction efficiency by 38% when compared with traditional methods.


Assuntos
Carotenoides/isolamento & purificação , Técnicas de Química Analítica/métodos , Extratos Vegetais/isolamento & purificação , Polissorbatos/química , Sargassum/química , Água/química , Produtos Biológicos/isolamento & purificação
9.
Fa Yi Xue Za Zhi ; 35(2): 216-223, 2019 Apr.
Artigo em Inglês, Chinês | MEDLINE | ID: mdl-31135118

RESUMO

Abstract: Objective To provide the reference for the identification of unknown fentanyl analogues by studying the characteristic ions and main fragmentation pathways of fentanyl analogues in the modes of collision induced dissociation (CID) and electron ionization (EI). Methods Nine fentanyl analogues (2, 2'-difluorofentanyl, acetyl fentanyl, fentanyl, butyl fentanyl, valeryl fentanyl, acryloyl fentanyl, furan fentanyl, 4-fluorine isobutyl fentanyl, carfentanyl) were selected and analyzed with ultra-high performance liquid chromatography-quadrupole time-of-flight-mass spectrometry (UHPLC-QTOF-MS) and gas chromatography-mass spectrometry (GC-MS). The mass spectrum obtained was analyzed. The CID and EI fragmentation routes of fentanyl analogues were speculated. Results The CID and EI fragmentation pathways were highly similar. In the CID mode, characteristic ions were formed by the carbon-nitrogen bond cleavage between the piperidine ring and the N-phenyl-amide moiety, within the piperidine ring, and between the phenethyl and piperidine ring. While in the EI mode, dissociation of the piperidine ring, as well as cleavage between the piperidine ring and the phenethyl were the main fragmentation pathways. Conclusion This study summarizes the main fragmentation pathways and characteristic ions of fentanyl analogues in the CID and EI modes, which is useful for forensic laboratories to identify and structural analyze fentanyl type new psychoactive substance in practical work.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia Líquida de Alta Pressão , Fentanila/análise , Cromatografia Gasosa-Espectrometria de Massas , Espectrometria de Massas , Fentanila/análogos & derivados , Humanos
10.
J Chromatogr A ; 1599: 231-238, 2019 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-31036364

RESUMO

Specifying effective analytical techniques and methods can be very challenging when a large number of sample streams need to be analyzed with high frequency. Combining those requirements with the need to monitor multiple components over a wide range of concentrations makes at-line analytical approaches preferred by many analytical scientists. Traditionally, at-line analytical support requires sample preparation and operator time. Recently developed technologies enabled automated sample preparation tools coupled with gas chromatography; thus, eliminating sample preparation steps and increasing productivity. Recently a commercial micro-reactor was introduced that can be combined with a flame ionization detector, providing the ability to quantify components without the need to perform a standard calibration, which saves significant time and materials. In this manuscript, we describe a unique analytical capability that combines automated sample preparation and gas chromatography with flame ionization detection and universal carbon response to provide high flexibility and accuracy when there is minimal information about the unknowns or reference materials are not available. Some of the challenges and performance monitoring techniques for this technology are also discussed in this manuscript.


Assuntos
Carbono/química , Técnicas de Química Analítica/métodos , Cromatografia Gasosa , Automação , Calibragem , Ionização de Chama
11.
J Chromatogr A ; 1599: 203-214, 2019 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-31047657

RESUMO

Colloidal iron(III) oxyhydroxides (FeOx) are important reactive adsorbents in nature. This study was set up to determine the size of environmentally relevant FeOx colloids with new methods, i.e. Flow Field Flow Fractionation (FlFFF-UV-ICP-MS) and single-particle ICP-MS/MS (sp-ICP-MS) and to compare these with standard approaches, i.e. dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), microscopy (TEM), membrane filtration, centrifugation and dialysis. Seven synthetic nano- and submicron FeOx with different mineralogy and coating were prepared and two soil solutions were included. The FlFFF was optimized for Fe recovery, yielding 70-90%. The FlFFF determines particle size with high resolution in a 1 mM NH4HCO3 (pH 8.3) background and can detect Fe-NOM complexes <5 nm and organo-mineral FeOx particles ranging 5-300 nm. The sp-ICP-MS method had a size detection limit for FeOx of about 32-47 nm. The distribution of hydrodynamic diameters of goethite particles detected with FlFFF, NTA and DLS were similar but the values were twice as large as the Fe cores of particles detected with sp-ICP-MS and TEM. Conventional fractionation by centrifugation and dialysis generally yielded similar fractions as FlFFF but membrane filtration overestimated the large size fractions. Particles formed from Fe(II) oxidation in the presence of NOM showed strikingly smaller organo-mineral Fe-Ox colloids as the NOM/Fe ratio increased. The soil solution obtained with centrifugation of an acid peat was dominated by small (<30 nm) Fe-OM complexes and organo-mineral FeOx colloids whereas that of a mineral pH neutral soil mainly contains larger (30-200 nm) Fe-rich particles. The FlFFF-UV-ICP-MS is recommended for environmental studies of colloidal FeOx since it has a wide size detection range, it fractionates in an environmentally relevant background (1 mM NH4HCO3) and it has acceptable element recoveries.


Assuntos
Técnicas de Química Analítica/métodos , Coloides/análise , Compostos Férricos/análise , Fracionamento por Campo e Fluxo , Minerais/análise , Espectrometria de Massas em Tandem , Técnicas de Química Analítica/normas , Coloides/química , Difusão Dinâmica da Luz , Compostos de Ferro/análise , Compostos de Ferro/química , Minerais/química , Nanopartículas/análise , Tamanho da Partícula , Solo/química , Análise Espectral
12.
J Chromatogr A ; 1600: 158-166, 2019 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-31040030

RESUMO

This study is concerned with a chromatography-based approach (Immobilized Metal Ion Affinity Chromatography) for the recovery of gallium binding peptide sequences from a recombinant phage display library. The here described methods apply the fundamental knowledge and methods of separation science and meet thereby the key requirement of the phage display technique of precise separation of target-binding bacteriophage clones from non-interacting bacteriophage during the biopanning. During the chromatopanning called process, a total of 101 bacteriophage clones were identified of which in subsequent binding experiments, phage clones expressing the peptide sequences TMHHAAIAHPPH, SQALSTSRQDLR and HTQHIQSDDHLA were characterized to bind >10 fold better to a target that presents immobilized gallium ions than control phage, displaying no peptide sequence. The performance of biopanning experiments in chromatographic systems is particularly suitable for demanding targets such as trivalent metal ions. We found, that the selection process benefits immensely from the stable immobilization of the target metal ions during the entire biopanning process as well as the complete recovery of well interacting bacteriophage clones. Among others, this was possible due to an enhanced monitoring of process conditions and fractionation of eluates.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia de Afinidade , Gálio/química , Peptídeos/química , Sequência de Aminoácidos , Biblioteca de Peptídeos , Peptídeos/isolamento & purificação
13.
J Chromatogr A ; 1600: 80-86, 2019 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-31047663

RESUMO

Lysozyme is widely used in medical, food and industrial fields due to its bacteriolytic effect and thus it is significant to design and develop a specific adsorbent with high adsorption capacity and selectivity for lysozyme. Inspired by the high uptake capacity of tetrafluoroterephthalonitrile-crosslinked porous ß-cyclodextrin polymers (P-CDPs) and the noncovalent interaction between lysozyme and carboxyl groups, the carboxyl-functionalized P-CDPs (P-CDP-COO-) were synthesized by base-catalysed hydrolysis of nitrile group in P-CDPs to carboxyl. Porous structure, large extent of carboxylic functional groups, cyclodextrin's preventing aggregation, and negatively charged make P-CDP-COO- possess an outstanding adsorption capability for lysozyme. The maximum saturated adsorption capacity reaches 1520 mg g-1, which is much better than the parent polymer and other reported materials. The as-prepared material was successfully utilized for the selective extraction of lysozyme from egg white.


Assuntos
Técnicas de Química Analítica/métodos , Clara de Ovo/química , Muramidase/isolamento & purificação , beta-Ciclodextrinas/química , Adsorção , Ácidos Carboxílicos/química , Ciclodextrinas/química , Muramidase/química , Porosidade
14.
J Chromatogr A ; 1600: 183-196, 2019 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-31053351

RESUMO

A semi-quantitative method was developed to monitor the misuse of 15 SARM compounds belonging to nine different families, in urine matrices from a range of species (equine, canine, human, bovine and murine). SARM residues were extracted from urine (200 µL) with tert-butyl methyl ether (TBME) without further clean-up and analysed by ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). A 12 min gradient separation was carried out on a Luna Omega Polar C18 column, employing water and methanol, both containing 0.1% acetic acid (v/v), as mobile phases. The mass spectrometer was operated both in positive and negative electrospray ionisation modes (ESI±), with acquisition in selected reaction monitoring (SRM) mode. Validation was performed according to the EU Commission Decision 2002/657/EC criteria and European Union Reference Laboratories for Residues (EU-RLs) guidelines with CCß values determined at 1 ng mL-1, excluding andarine (2 ng mL-1) and BMS-564929 (5 ng mL-1), in all species. This rapid, simple and cost effective assay was employed for screening of bovine, equine, canine and human urine to determine the potential level of SARMs abuse in stock farming, competition animals as well as amateur and elite athletes, ensuring consumer safety and fair play in animal and human performance sports.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia Líquida de Alta Pressão/normas , Espectrometria de Massas em Tandem/normas , Urinálise/métodos , Antagonistas de Receptores de Andrógenos , Animais , Bovinos , Cães , Cavalos , Humanos , Metanol/química , Camundongos , Receptores Androgênicos/metabolismo , Reprodutibilidade dos Testes , Urinálise/normas
15.
J Chromatogr A ; 1598: 223-231, 2019 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-31053352

RESUMO

The characterization of hydrosoluble oligomers in latexes is an important topic in emulsion polymerization since oligomers are suspected to be responsible for latex destabilization. In this work, the hydrosoluble fraction of poly(vinylidene chloride) latexes synthesized by emulsion polymerization of three monomers (acrylic acid, methyl acrylate, vinylidene chloride) was characterized by capillary electrophoresis (CE). CE using direct UV detection permitted to estimate residual monomers and surfactants concentrations contained in the latexes serums. Water soluble oligomers, polymerization initiator (persulfate) and other inorganic anions were detected by indirect UV detection. The oligomers content in the dry extract of serum was estimated to be about 6% (% m/m) represented mainly by 9 different compounds belonging to 3 different families. Using a semi-empirical electrophoretic mobility modeling, the charge number of these oligomers was estimated to be -2 and the molar masses were estimated in the range of ∼300-550 g.mol-1. Oligomer samples obtained by surfactant-free polymerization, with different initial monomers proportions, provided qualitatively 14 different oligomers, including the 9 oligomers previously detected in the serums. Finally, the latex was characterized (electrophoretic mobility and zeta potential) using its serum as a background electrolyte. This approach could be very useful to study the behavior of the latexes, and possibly destabilization effect, in analytical conditions very close to its real environment / applications.


Assuntos
Técnicas de Química Analítica/métodos , Dicloroetilenos/química , Eletroforese Capilar , Modelos Químicos , Acrilatos/química , Eletrólitos , Ensaio de Desvio de Mobilidade Eletroforética , Emulsões , Látex/química , Polimerização , Tensoativos/análise
16.
J Chromatogr A ; 1602: 199-205, 2019 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-31109745

RESUMO

A hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) method was developed for qualitative and quantitative analysis of ethanolamines (EAs), which are nitrogen mustard degradation products. With this method, the retention times of the highly hydrophilic EAs on the HILIC column were sufficient (retention times: methyl diethanolamine, 12.2 min; ethyl diethanolamine, 11.2 min; and triethanolamine, 9.5 min) and the EAs were analyzed more efficiently than with reported HILIC-MS/MS methods. The detection limits of methyl diethanolamine and ethyl diethanolamine in serum and urine using this approach were 15-20 ng/mL. The suitability of the method for real samples was evaluated via recovery tests involving urine and serum, and the method was validated. The MS/MS fragmentation of EAs was discussed based on density functional theory calculations.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia Líquida , Espectrometria de Massas em Tandem , Etanolaminas/análise , Interações Hidrofóbicas e Hidrofílicas , Limite de Detecção , Mecloretamina/análise , Mecloretamina/metabolismo
17.
J Chromatogr A ; 1602: 228-236, 2019 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-31126590

RESUMO

The separation of enantiomers of some chiral weak acids was studied in HPLC with chiral HPLC columns prepared by coating or covalent immobilization of the same chiral selector, namely amylose tris(3-chloro-5-methylphenylcarbamate) onto silica. After screening some representatives of arylpropionic acid derivatives, coumarins and barbiturates in hydrocarbon-alcohol type mobile phases, we studied the temperature dependence of separation parameters for ketoprofen and naproxen. Instances of reversal of the enantiomer elution order were observed function of column temperature, nature of polar modifier and its content in the mobile phase, as well as between the coated and covalently immobilized versions of the columns made with more-or-less the same chiral selector. Thermodynamic parameters such as Gibb's free energy, the standard molar entropy and the standard molar enthalpy of analyte transfer from the mobile to the stationary phase were calculated in some cases in order to explain the differences observed in the enantiomer separation ability and pattern of coated and covalently immobilized columns.


Assuntos
Ácidos/isolamento & purificação , Carbamatos/química , Técnicas de Química Analítica/métodos , Cromatografia Líquida de Alta Pressão , Dióxido de Silício/química , Entropia , Estereoisomerismo , Temperatura Ambiente , Termodinâmica
18.
J Chromatogr A ; 1602: 206-216, 2019 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-31133423

RESUMO

Adsorptive membrane-based chromatography can provide the high separation efficiency common to column chromatography but at a lower working pressure. Herein, a novel membrane chromatography system for lithium isotope adsorptive separation is reported. It uses polysulfone-graft-4'-aminobenzo-15-crown-5-ether (PSf-g-AB15C5) porous membranes (0.52 mmol/g of immobilization crown ether, average pore size of 62.7 nm, porosity of 80.4%) as a stationary phase packed in a chromatography column (Ø 25 × 100 mm). Furthermore, a four-stage tandem membrane chromatography system was designed to enhance lithium isotope separation performance. The partial eluate from the former column was used as the feed solution for the next stage. Results show that the flow rate of the eluent could reach 18 mL/h owing to the lower internal diffusion resistance of membranes. Meanwhile, adsorption isotherms and adsorption kinetics show that Li+ adsorption was an exothermic and spontaneous process. The surface diffusion, multilayer adsorption and ion-pore electrostatic interaction between Li+ and the crown ether groups on the membranes played a key role in the separation of 7Li+ and 6Li+ by membrane chromatography. The separation factor obtained from the single-stage membrane chromatography was up to 1.0232. The abundances of 7Li+ and 6Li+ gradually increased with an increase in the elution stages. The relative abundances of 7Li+ and 6Li+ obtained from the four-stage tandem membrane chromatography increased by 0.26% (from 92.40 to 92.66%) and 0.2% (from 7.60 to 7.80%), respectively. In conclusion, our current research opens a new avenue for the simultaneous enrichment of 7Li+ and 6Li+ during lithium isotope adsorptive separation.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia , Éteres/química , Isótopos/isolamento & purificação , Lítio/isolamento & purificação , Adsorção , Difusão , Isótopos/química , Cinética , Lítio/química , Membranas Artificiais , Porosidade
19.
J Chromatogr A ; 1602: 217-227, 2019 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-31133424

RESUMO

The aim of this paper is to develop and validate a methodology with potential for routine analysis that allows a fast and easy quantification of 19 primary aromatic amines (PAAs) in acid simulant (3% (w/v) acetic acid aqueous) in food contact materials (FCM). The main reason for studying these amines was the fact that some of them have a carcinogenic factor according to toxicological studies. To validate the method, the parameters linearity, limit of detection (LOD) and limit of quantification (LOQ), precision and accuracy using an UPLC-MS/MS were evaluated. This study also analyzed 36 samples of kitchenware obtained from retail markets: 16 were made of polyamide (PA), one was made of polypropylene (PP) and 19 were made of silicone. The origins of samples were Brazil, China and Turkey. Eleven samples had levels of 4,4´-diaminodiphenylmethane higher than permitted by legislation and five samples showed values of aniline above the limit. Considering the Mood test for polyamides, there were significant differences between the samples from Brazil and China, as well as between the colors in the silicone samples. Regarding the polyamides, the Chinese samples showed higher amounts of PAAs than the Brazilian ones, being above that allowed by legislation. Three Chinese silicone samples presented values above the legislation limit. These were all from the same importer.


Assuntos
Aminas/análise , Técnicas de Química Analítica/métodos , Cromatografia Líquida , Utensílios de Alimentação e Culinária/normas , Contaminação de Alimentos/análise , Espectrometria de Massas em Tandem , Compostos de Anilina/análise , Brasil , Carcinógenos/análise , China , Contaminação de Alimentos/prevenção & controle , Limite de Detecção , Nylons/química , Polipropilenos/química
20.
J Chromatogr A ; 1600: 23-32, 2019 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-31040032

RESUMO

Sunscreens are used to protect skin against ultraviolet radiation, avoiding the damages that can be caused by it. However, in vitro and in vivo studies report that some organic substances employed as sunscreens can alter the biological effects of several hormones. Therefore, a methodology for passive sampling using a semipermeable membrane device (SPMD) was developed for the extraction and preconcentration of some organic compounds employed in sunscreen formulations, such as benzophenone (BZP), 2-hydroxy-4-methoxybenzophenone (BZP-3), 3-(4-methylbenzylidene)-camphor (4-MBC), 2-ethylhexyl-4-methoxycinnamate (4-MCN), 2-ethylhexyl salicylate (EHS), and homomethyl salicylate (HMS), from swimming pool waters where exposure to these substances is unintended. The determination of these analytes in the acceptor phase was performed using high performance liquid chromatography with diode array detection (HPLC-DAD). The optimization of the methodology included the evaluation of several variables, such as type and volume of acceptor phase, dimensions and time of exposure of the SPMD, sample pH, and volume. The optimum conditions for the collection of the solar filters were achieved with an 8-cm device filled with 3.0 mL of acetonitrile and without adjustment of the sample pH, which was approximately 5.8. The collection time was 24 h. Afterwards, some parameters of merit of the developed method were determined. The working range for BZP, BZP-3, 4-MBC, 4-MCN, EHS, and HMS was established as 25-500 µg L-1. The methodological limits of detection and quantification for these analytes were 0.2-1.0 µg L-1 and 0.7-3.1 µg L-1, respectively. Quantification of the analytes was performed on four samples collected from different swimming pools. Recovery tests were performed with the samples spiked with 100 µg L-1 of each substance, and recovery percentages in the range of 75-116% were obtained. The performance of the SPMD was also verified through the determination of BZP-3, EHS, and HMS in a swimming pool water sample intentionally contaminated with a commercial sunscreen.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia Líquida de Alta Pressão , Protetores Solares/análise , Piscinas , Poluentes Químicos da Água/análise , Água/química
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