Adsorption of CO2 as a method for the characterisation of the structure of alumina-pillared clay catalysts

The aim of this work was to study the effect of the metal loading on the structure of two series of cobalt and manganese pillared clay-supported catalysts. For this purpose, equilibrium data for CO₂ adsorption at 273 K were analysed using Freundlich, Langmuir and Toth isotherm models, in order to estimate the adsorption parameters and to relate them with the metal loading of the catalysts. The metal distributions on the porous structure of the catalysts were studied using the temperature programmed reduction results combined with information from the nitrogen physisorption data. Comparison of all results reveals that up to a certain metal loading, about 0.5 wt% of Co and 2 wt% of Mn, the metal oxide is well dispersed into the porous structure of the pillared clay. At higher metal loadings, bulk-metal oxide particles are formed on the external surface.     

Characterization of a titanium(IV)–porphyrin complex as a highly sensitive and selective reagent for the determination of hydrogen peroxide: a computational chemistry approach and a critical review

The Ti–TPyP reagent, i.e. an acidic aqueous solution of the oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato] titanium(IV) complex, TiO(tpyp), was developed as a highly sensitive and selective spectrophotometric reagent for determination of traces of hydrogen peroxide. Using this reagent, determination of hydrogen peroxide was performed by flow-injection analysis with a detection limit of 0.5 pmol per test. The method was actually applied to determination of several constituents of foods, human blood, and urine mediated by appropriate oxidase enzymes. The reaction specificity of the TiO(tpyp) complex for hydrogen peroxide was clarified from the viewpoint of the reaction mechanisms and molecular orbitals based on ab initio calculations. The results provided a well-grounded argument for determination of hydrogen peroxide using the Ti–TPyP reagent experimentally. This review deals with characterization of the high sensitivity and reaction specificity of the Ti–TPyP reagent for determination of hydrogen peroxide, to prove its reliability in analytical applications. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Polyaniline/graphene oxide nanocomposite as a sorbent for extraction and determination of nicotine using headspace solid-phase microextraction and gas chromatography–flame ionization detector

A solid-phase microextraction fiber was prepared by polyaniline/graphene oxide nanocomposite as sorbent on the surface of a platinized stainless steel wire using electrospinning technique. The nanocomposite structure was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The polyaniline/graphene oxide nanocomposite fiber was used for the determination of nicotine from tobacco samples using headspace solid-phase microextraction method and gas chromatography–flame ionization detection. Influential experimental variables on the extraction efficiency of nicotine, such as extraction time and temperature, humidity and desorption conditions, were evaluated and optimized. Under the optimal experimental conditions? the limit of detection, linear dynamic range, intraday and inter-days precisions were found to be 0.01 μg g^?1, 0.05–700 µg g^?1 (R²?=?0.996), 6.9 and 8.1%, respectively. Comparison of the polyaniline/graphene oxide nanocomposite sorbent with polyaniline and commercial fibers shows longer durability, larger capacity and higher extraction efficiency. The polyaniline/graphene oxide nanocomposite fiber was successfully applied for the determination of nicotine in tobacco samples.     

Hyphenation of reverse-phase HPLC and ICP-MS for metabolite profiling—application to a novel antituberculosis compound as a case study

In this study, a high-performance liquid chromatography (HPLC) inductively coupled plasma (ICP) mass spectrometry (MS) method was developed intended for use in metabolism studies of bromine-containing drugs, administered to test animals (or test persons). As a case study, the method was applied to a new antituberculosis compound, the bromine-containing diarylquinoline R207910. A method has been proposed to overcome the incompatibilities between the high organic solvent content (45%CH₃OH and 45% CH₃CN) used in the reverse-phase liquid chromatography (LC) separation on one hand and the limitations of the ICP on the other hand. Therefore, several instrument modifications had to be made. For the introduction of the column effluent, a combination of a perfluoroalkoxy LC nebulizer with a PC³ Peltier-cooled inlet system (operated at 2 °C) was used. Additionally, the standard injector tube (internal diameter 2 mm) was replaced by an injector tube with an internal diameter of 1 mm and to avoid carbon build-up on the interface cones and the torch, the nebulizer gas was admixed with 6% v/v of oxygen. After optimization of the method, HPLC-ICP-MS was applied for metabolite profiling of faeces samples after dosing of ¹⁴C-radiolabelled R207910 to dogs and rats. To evaluate the method developed, the HPLC-ICP-MS results were compared with those of HPLC with UV spectrophotometric and ¹⁴C radiochemical detection. As the HPLC-ICP-MS method gave rise to a higher selectivity than HPLC with UV detection and to a better detection limit (5 ng R207910) than the method with radiochemical detection (65 ng R207910), it can be concluded that ICP-MS can be used as a good alternative to the more traditional detection methods, even when a mobile phase with high organic solvent content has to be used in the LC separation.     

Study of the GC-MS determination of the palmitic-stearic acid ratio for the characterisation of drying oil in painting: La Encarnación by Alonso Cano as a case study

The correct identification of drying oils plays an essential role in providing an understanding of the conservation and deterioration of artistic materials in works of art. To this end, this work proposes the use of peak area ratios from fatty acids after ensuring that the linear responses of the detector are tested. A GC-MS method, previously reported in the literature, was revisited to its developed and validated in order to identify and quantify of eight fatty acids that are widely used as markers for drying oils in paintings, namely myristic acid (C(14:0)), palmitic acid (C(16:0)), stearic acid (C(18:0)), oleic acid (C(18:1)), linoleic acid (C(18:2)), suberic acid (2C(8)), azelaic acid, (2C(9)) and sebacic acid (2C(10)). The quaternary ammonium reagent m-(trifluoromethyl)phenyltrimethylammonium hydroxide (TMTFAH) was used for derivatization prior to GC-MS analysis of the oils. MS spectra were obtained for each methyl ester derivative of the fatty acids and the characteristic fragments were identified. The method was validated in terms of calibration functions, detection and quantification limits and reproducibility using the signal recorded in SIR mode, since two of the methyl derivatives were not totally separated in the chromatographic run. The proposed method was successfully applied to identify and characterise the most widely used drying oils (linseed oil, poppy seed oil and walnut oil) in the painting La Encarnación. This 17th century easel painting is located in the main chapel of the cathedral in Granada (Spain) and was painted by the well-known artist of the Spanish Golden Age, Alonso Cano (1601-1667).     

Chiroptical properties of 12,15-dichloro[3.0]orthometacyclophane—correlations between molecular structure and circular dichroism spectra of a biphenylophane

The valence excited electronic states and the circular dichroism (CD) spectra of the recently synthesized 12,15-dichloro[3.0]orthometacyclophane 1 are discussed by means of quantum chemical calculations which combine density functional theory with the single-excitation configuration interaction approach (DFT/SCI). The X-ray structure of this highly strained biphenylophane is presented. In order to investigate the influence of the cyclophane-type distortions on the CD spectrum of 1, the CD spectra of three model geometries (2a–2c) are also calculated. It appears that the CD spectrum of the biphenylophane 1 differs substantially from that of the corresponding unstrained biphenyl 2c. Furthermore, it is found that the pyramidalization of the bridging atoms of the cyclophane ring is an important factor for the red shift of the first band with respect to that of an unstrained benzene chromophore.     

The coordination chemistry of divalent cobalt,nickel and copper—IX: The crystal structure and characterisation of a cationic 5-coordinate Cu(II) complex

The preparation, properties and X-ray crystal structure of [Cu(ttda)(tmen)](ClO₄)₂, a complex of divalent copper perchlorate with the ligands N,N,N′,N′-tetramethyl-1,2-diaminoethane (tmen) and bis-(N,N′-dimethyl-acetamido)thioether(ttda) are reported. The crystals are monoclinic with a = 15.35(1), b = 15.04(1), c = 10.91(1) A, β = 98.74(2)°, four formula units per unit cell and space group P2₁/n. The complex cation is shown to be penta-coordinate with a distorted square pyramidal geometry. Comparison is made with the properties and structure of the previously reported CuCl₂·ttda.     

Combined use of β-cyclodextrin and ionic liquid as electrolyte additives in EKC for separation and determination of carob's phenolics—A study of the synergistic effect

In this work, a simple, reliable, and fast capillary electrophoretic method was developed and validated for the simultaneous determination of 12 polyphenolic compounds, the most frequently found in carob's pulp and seeds. The present work deals with the development of a novel dual electrophoretic system based on the combined use of β-CD and ionic liquid (IL) as buffer additives. A baseline separation of the target analytes was achieved in less than 10 min by using a BGE consisting of 35 mM borate along with 15 mM β-CD and 3 mM l -alanine tert butyl ester lactate (l -AlaC₄Lac) IL as buffer additives at pH 9.5, a temperature of 25°C, and an applied voltage of 30 kV. The application of the developed electrophoretic method to real samples enabled the identification and quantification of the main phenolic constituents of both ripe and unripe carob pulp extracts. The results revealed the predominance of gallic acid in both ripe (183.92 μg/g carob pulp) and unripe (205.10 μg/g carob pulp) carob pulp and highlighted the great influence of the ripening stage on carobs polyphenolic composition, with unripe pods being more enriched in polyphenols (total phenolics detected: 912.58 and 283.13 μg/g unripe and ripe carob pulp).     

Development of a fast and selective method for the sensitive determination of anatoxin-a in lake waters using liquid chromatography–tandem mass spectrometry and phenylalanine-d 5 as internal standard

Anatoxin-a is a potent alkaloid neurotoxin produced by a number of cyanobacterial species and released in freshwaters during cyanobacterial blooms. Its high toxicity is responsible for several incidents of lethal intoxications of birds and mammals around the world; therefore anatoxin-a has to be regarded as a health risk and its concentration in lakes and water reservoirs should be monitored. Phenylalanine is a natural amino acid, also present in freshwaters, isobaric to anatoxin-a, with a very similar fragmentation pattern and LC retention. Since misidentification of phenylalanine as anatoxin-a has been reported in forensic investigations, special care must be taken in order to selectively determine traces of anatoxin-a in the presence of naturally occurring phenylalanine. A fast LC tandem MS method was developed by using a 1.8 μm 50 × 2.1 mm C18 column for the separation of anatoxin-a and phenylalanine, achieving a 3-min analysis time. Isotopically labelled phenylalanine-d ₅ was employed as internal standard to compensate for electrospray ion suppression and sample preconcentration losses. Both compounds were preconcentrated 1,000-fold on a porous graphitic carbon solid-phase extraction (SPE) cartridge after adjustment of sample pH to 10.5. The method was validated by using lake water spiked at four different levels from 0.01 to 1 μg L⁻¹. Anatoxin-a recovery ranged from 73 to 97%, intra-day precision (RSD%) ranged from 4.2 to 5.9, while inter-day precision (RSD%) ranged from 4.2 to 9.1%. Limits of detection and quantification were 0.65 and 1.96 ng L⁻¹ respectively. The method was successfully applied for the detection of anatoxin-a in Greek lakes at concentrations ranging from less than 0.6 to 9.1 ng L⁻¹.     

SPE HG-AAS method for the determination of inorganic arsenic in rice—results from method validation studies and a survey on rice products

The present paper describes the development, validation and application of a method for inorganic arsenic (iAs) determination in rice samples. The separation of iAs from organoarsenic compounds was done by off-line solid-phase extraction (SPE) followed by hydride generation atomic absorption spectrometry (HG-AAS) detection. This approach was earlier developed for seafood samples (Rasmussen et al., Anal Bioanal Chem 403:2825–2834, 2012) and has in the present work been tailored for rice products and further optimised for a higher sample throughput and a lower detection limit. Water bath heating (90 °C, 60 min) of samples with dilute HNO₃ and H₂O₂ solubilised and oxidised all iAs to arsenate (As^V). Loading of buffered sample extracts (pH 6?±?1) followed by selective elution of arsenate from a strong anion exchange SPE cartridge enabled the selective iAs quantification by HG-AAS, measuring total arsenic (As) in the SPE eluate. The in-house validation gave mean recoveries of 101–106 % for spiked rice samples and in two reference samples. The limit of detection was 0.02 mg kg^?1, and repeatability and intra-laboratory reproducibility were less than 6 and 9 %, respectively. The SPE HG-AAS method produced similar results compared to parallel high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS) analysis. The SPE separation step was tested collaboratively, where the laboratories (N?=?10) used either HG-AAS or ICP-MS for iAs determination in a wholemeal rice powder. The trial gave satisfactory results (HorRat value of 1.6) and did not reveal significant difference (t test, p?>?0.05) between HG-AAS and ICP-MS quantification. The iAs concentration in 36 rice samples purchased on the Danish retail market varied (0.03–0.60 mg kg^?1), with the highest concentration found in a red rice sample.      

Development of a dispersive liquid–liquid microextraction (DLLME) method coupled with GC/MS as a simple and valid method for simultaneous determination of phthalate metabolites in plasma

Phthalates are ubiquitous environmental contaminants, and frequent biological monitoring of their metabolites (as toxic species of phthalates in human body) is highly recommended. A novel dispersive liquid–liquid microextraction (DLLME) coupled with Gas Chromatography–Mass Spectrometry (GC-MS) has been developed for the determination of seven phthalate metabolites in human plasma for the first time. Plasma proteins were efficiently precipitated by adding of 0.2mg dry trichloroacetic acid to 10 mL plasma samples, incubation and centrifuging. For DLLME, a mixture of extraction solvent (chlorobenzene, 10 µL) and dispersive solvent (acetonitrile, 750 µL) were rapidly injected into 5.0 mL aqueous sample for the formation of cloudy solution, the analytes in the sample were extracted into the fine droplets of chlorobenzene. After extraction, phase separation was performed by centrifugation and the enriched analytes in the sedimented phase were subjected to GC-MS analysis. All important parameters affecting DLLME performance were investigated and optimised. Under the optimum extraction condition, the method yields a linear calibration curve for all target analytes in the concentration range from 5 to 5000 ng mL^?1. The limits of detection and relative standard deviations for all phthalate metabolites were between 1.21–2.09 ng mL^?1 and 4.8–6.8%, respectively. This is a very simple, rapid and reproducible method, which requires low volume of sample and toxic solvents.     

Physical properties and structure of fine core–shell particles used as packing materials for chromatography: Relationships between particle characteristics and column performance

The recent development of new brands of packing materials made of fine porous-shell particles, e.g., Halo and Kinetex, has brought great improvements in potential column efficiency, demanding considerable progress in the design of chromatographic instruments. Columns packed with Halo and Kinetex particles provide minimum values of their reduced plate heights of nearly 1.5 and 1.2, respectively. These packing materials have physical properties that set them apart from conventional porous particles. The kinetic performance of 4.6 mm I.D. columns packed with these two new materials is analyzed based on the results of a series of nine independent and complementary experiments: low-temperature nitrogen adsorption (LTNA), scanning electron microscopy (SEM), inverse size-exclusion chromatography (ISEC), Coulter counter particle size distributions, pycnometry, height equivalent to a theoretical plate (HETP), peak parking method (PP), total pore blocking method (TPB), and local electrochemical detection across the column exit section (LED). The results of this work establish links between the physical properties of these superficially porous particles and the excellent kinetic performance of columns packed with them. It clarifies the fundamental origin of the difference in the chromatographic performances of the Halo and the Kinetex columns.     

Synthesis of a “memory tripeptide” (Arg—Glu—Arg,RER) and the Kabachnik—Fields reaction with di- and tripeptides as a method for the synthesis of phosphorus-containing peptide analogs

Methods for the synthesis of potential “twin-drugs” containing fragments of the glutamate receptor antagonist and cognitive function enhancing oligopeptides were developed. The “memory tripeptide” Arg—Glu—Arg (RER) containing the tripeptide sequence of a protein APP_328–330, a gB-amyloid precursor, was synthesized. A method for the synthesis of gA-aminophosphonates with oligopeptides as the amine component of the one-pot three-component Kabachnik—Fields reaction was developed. A method for the synthesis of phosphonopeptides by the introduction of gA-aminophosphonates into the peptide chain was proposed.     

Evaluation of tungsten–rhodium coating on an integrated platform as a permanent chemical modifier for cadmium,lead, and selenium determination by electrothermal atomic absorption spectrometry

A tungsten–rhodium coating on the integrated platform of a transversely heated graphite atomizer is proposed as a permanent chemical modifier for the determination of Cd, Pb, and Se by electrothermal atomic absorption spectrometry. It was demonstrated that coating with 250 μg W+200 μg Rh is as efficient as the conventional Mg(NO₃)₂+NH₄H₂PO₄ or Pd+Mg(NO₃)₂ modifiers for avoiding most serious interferences. The permanent W–Rh modifier remains stable for 300–350 firings of the furnace, and increases tube lifetime by 50%–100% when compared to pyrolytic carbon integrated platforms. Also, there is less degradation of sensitivity during the atomizer lifetime when compared with the conventional modifiers, resulting in a decreased need of re-calibration during routine analysis. The characteristic masses and detection limits achieved using the permanent modifier were respectively: Cd 1.1±0.4 pg and 0.020 μgL⁻¹; Pb 30±3 pg and 0.58 μgL⁻¹ and Se 42±5 pg and 0.64μgL⁻¹. Results from the determination of these elements in water reference materials were in agreement with the certified values, since no statistical differences were found by the paired t-test at the 95% level.     

Designing a simple semi-automated system for preconcentration and determination of nickel in some food samples using dispersive liquid–liquid microextraction based upon orange peel oil as extraction solvent

A simple semi-automated dispersive liquid–liquid microextraction system was designed and used for off-line preconcentration and determination of nickel (II) ion in some food samples. The methodology submitted in the present work is based upon the microextraction of [Ni(C₃₈H₂₈O₂N)₂] complex employing an orange peel oil (OPO) as an extractant without a dispersing solvent and the estimation of nickel (II) ion in sediment by electrothermal atomic absorption spectrometry (ETAAS). 3 mL of sample solution, 0.5 mL of acetate buffer (pH 6), and 300 µL of the complexing agent (1-[4-[(2-hydroxynaphthalen-1-yl)methylideneamino] phenyl]ethanone) (HNE) dissolved in OPO were automatically transferred to separation tube and the cloudy solution was obtained by dispersing OPO as droplets throughout the aqueous phase using nitrogen gas. Under the optimized conditions, the analytical methodology used in this study provided a good efficiency in term of sensitivity and selectivity where the calibration plot was linear in the range of 5–150 ngL^–1, while, the enhancement factor (EF) and the detection limit were 300 and 0.87 ngL^–1, respectively for a sample volume of 3 mL. On the other hand, the method was completely free of most potential interferences. Certified reference wheat sample (NCS ZC11018) and some food samples were used to evaluate the developed method and results were compared using ICP–MS. Moreover, the new [Ni(C₃₈H₂₈O₂N)₂] complex was synthesized and characterized using diverse characterization techniques.     

Dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-UV detection as a very simple,rapid and sensitive method for the determination of bisphenol A in water samples

Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied for the extraction and determination of bisphenol A (BPA) in water samples. An appropriate mixture of acetone (disperser solvent) and chloroform (extraction solvent) was injected rapidly into a water sample containing BPA. After extraction, sedimented phase was analyzed by HPLC-UV. Under the optimum conditions (extractant solvent: 142 μL of chloroform, disperser solvent: 2.0 mL of acetone, and without salt addition), the calibration graph was linear in the range of 0.5–100 μg L⁻¹ with the detection limit of 0.07 μg L⁻¹ for BPA. The relative standard deviation (RSD, n = 5) for the extraction and determination of 100 μg L⁻¹ of BPA in the aqueous samples was 6.0%. The results showed that DLLME is a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of BPA in water samples and suitable results were obtained.     

Pulse time interval analysis (TIA) combined with liquid scintillation counting for the determination of environmental α-nuclides: Preparation and utilization of225Ra as a yield tracer

Time interval analysis (TIA), which has been verified to be suitable for the selective extraction of correlated successive α-decay events within a liquid scintillator, was further developed by combining pulse shape discrimination technique and simple chemical analysis. A β-emitter nuclide,²²⁵Ra, which is suitable for the use as a yield tracer belonging to Np-decay series, was also found to be detectable by the TIA-method after a certain standing period when the radium-extractant (RADAEX) was added small amounts of HDEHP [di (2-ethylhexyl) phosphoric acid], which was proved to keep the equilibrium state between Ra and its descendants. The present counting system (TIA analysis incorporated α-LSC/PSD) has been verified to be applicable to the simultaneous determination of three (including Th, Ac, and Np) decay series, if the chemical purification of radium fraction was applied to the environmental samples using an extractive scintillator in addition to utilization of an α-peak itself at lowest energy for the determination of²²⁶Ra in uranium decay series. This radioanalytical method was practically applied to the determination of natural radionuclides belonging to three decay series in environmental samples and compared to the alpha-spectrometric results using a Si-surface barrier detector (SSB).