Characterisation and identification of proteinaceous binding media (animal glues) from their amino acid profile by capillary zone electrophoresis

A capillary electrophoretic method for identifying different species of proteinaceous binders--collagen, egg white, and milk casein--is described. It allows characterisation of the proteins on the basis of the amino acid profiles obtained after their acidic hydrolysis. The profiles of the underivatised amino acids are recorded directly by capillary zone electrophoresis at pH 2.26 with the aid of a conductivity detector, thus eliminating the need for a derivatisation step. Identification is carried out by means of different relative peak areas of the amino acids. A scheme is given for identification, which is based on the main markers, hydroxyproline, proline, glycine, glutamic acid, and serine and valine.     

Solid phase microextraction-comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry for the analysis of honey volatiles

Head-space solid phase microextration (SPME), followed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GCxGC-TOFMS), has been implemented for the analysis of honey volatiles, with emphasis on the optimal selection of SPME fibre and the first- and second-dimension GC capillaries. From seven SPME fibres investigated, a divinylbenzene/Carboxen/polydimethylsiloxane (DVB/CAR/PDMS) 50/30 microm fibre provided the best sorption capacity and the broadest range of volatiles extracted from the headspace of a mixed honey sample. A combination of DB-5ms x SUPELCOWAX 10 columns enabled the best resolution of sample components compared to the other two tested column configurations. Employing this powerful analytical strategy led to the identification of 164 volatile compounds present in a honey mixture during a 19-min GC run. Combination of this simple and inexpensive SPME-based sampling/concentration technique with the advanced separation/identification approach represented by GCxGC-TOFMS allows a rapid and comprehensive examination of the honey volatiles profile. In this way, the laboratory sample throughput can be increased significantly and, at the same time, the risk of erroneous identification, which cannot be avoided in one-dimensional GC separation, is minimised.     

Raman, IR and SERS spectra of methyl(2-methyl-4,6-dinitrophenylsulfanyl)ethanoate

Methyl(2-methyl-4,6-dinitrophenylsulfanyl)ethanoate was prepared by nucleophilic substitution. FT-IR and FT-Raman spectra of methyl(2-methyl-4,6-dinitrophenylsulfanyl)ethanoate were recorded and analyzed. Surface-enhanced Raman scattering (SERS) spectrum was recorded on a silver colloid. The vibrationl wavenumbers were computed by density functional theoretical (DFT) computations at the B3LYP/6-31G* level and they were found to be in good agreement with the experimental values. The molecule is adsorbed on the silver surface with the benzene ring in a 'tilted orientation'.     

Analysis of Amaryllidaceae alkaloids from Chlidanthus fragrans by GC-MS and their cholinesterase activity

The underivatized alkaloid mixture extracted from the bulbs of Chlidanthus fragrans Herb. was investigated by capillary GC/MS for the first time. Fifteen known Amaryllidaceae alkaloids of five structure types were identified. The main alkaloids were tazzetine (9, tazettine-type), chlidanthine (2, galanthamine-type), belladine (8, belladine-type) and lycorine (12, lycorine-type). The alkaloid extract from the bulbs showed promising human blood acetylcholinesterase (IC50 = 20.1 +/- 2.9 microg/mL) and human plasma butyrylcholinesterase (IC50 = 136.8 +/- 6.9 microg/mL) inhibitory activity.     

Network diversity and supramolecular isomerism in copper(II)/1,2-bis(4-pyridyl)ethane coordination polymers

Reactions of copper(II) sources with 1,2-bis(4-pyridyl)ethane (bpe) yielded metal-organic networks with diverse topologies and dimensionalities. Compounds [Cu(bpe)₂(dmf)₂]_n(ClO₄)_2n·2ndmf (1·2ndmf), [Cu(bpe)₂(dmf)₂]_n(ClO₄)_2n·3.5ndmf (2·3.5ndmf), [Cu(bpe)₂(NO₃)₂]_n·2nH₂O (4·2nH₂O) and [Cu₂(bpe)(O₂CMe)₄]_n·0.7nH₂O (5·0.7nH₂O) have been isolated by altering the copper(II) source, the reaction solvent and the crystallization process. Compounds 1·2ndmf and 2·3.5ndmf consist of cationic [Cu(bpe)₂(dmf)₂]²⁺ repeating units assembled to 1D and 2D (4,4) networks, respectively, and represent supramolecular isomers due to the conformational isomerism of the bridging bpe molecules. Compound 4·2nH₂O consists of neutral mononuclear [Cu(dpe)₂(NO₃)₂] repeating units assembled to inclined interpenetrating (4,4) sheets describing an overall entanglement that is 3D in nature, and compound 5·0.7nH₂O consists of neutral dinuclear repeating units assembled to cross-linked 1D chains.     

A solid-phase microextraction GC/MS/MS method for rapid quantitative analysis of food and beverages for the presence of legally restricted biologically active flavorings

A method was developed using automated headspace solid-phase microextraction coupled with GC/MS/MS to simultaneously determine the presence of seven biologically active flavoring substances whose levels of use in processed foods is controlled by statutory limits. The method can be applied to identify and quantify the presence of 1,2-benzopyrone (coumarin), beta-asarone, 1-allyl-4-methoxybenzene (estragole), menthofuran, 4-allyl-1 ,2-dimethoxybenzene (methyl eugenol), pulegone, and thujone at levels ranging from 0.5 to 3000 mg/kg. The method has been optimized and validated for three different generic food types categorized on the basis of composition and anticipated use levels of flavorings and food ingredients. The food categories are alcoholic and nonalcoholic beverages; semisolid processed foods (e.g., soups, sauces, confectionary, etc.); and solid foods (muesli, bakery products, etc.). The method is simple, inexpensive, and rapid, and eliminates the use of flammable and toxic solvents. There is no sample preparation, and using MSIMS, unequivocal confirmation of identification is achieved even in highly complex matrixes containing many potential interfering volatiles. The method precision for spiked samples ranged from 2 to 21%, with the greatest variability associated with solid matrixes. The LOD and LOQ values were well below 0.1 and 0.5 mg/kg, respectively, in all cases for individual substances, fulfilling requirements for enforcement purposes. The robustness of the method was demonstrated in a small survey of retail samples of four spirits, five flavored milks, three energy drinks, five liqueurs, five soups, 10 sauces, five herbal teas, and three breakfast cereals.     

Adsorption of Polycation and Anionic Surfactant onto Iron Surfaces and the Inhibition of Carbon Dioxide Corrosion

The adsorption process of two polycations (pDADMAC and C‐PAM) with different charge densities has been investigated using the quartz crystal microbalance technique with dissipation monitoring (QCM‐D). The effect of the charge density of the polycation, the NaCl concentration, and the complexation with an anionic surfactant are addressed in this work. X‐ray photoelectron spectroscopy and atomic force microscopy were utilized to analyze the adsorbate with respect to the film coverage and film structure. The corrosion‐inhibiting performance of the films on high‐purity iron in a CO₂ saturated brine, at 25°C, 1 bar CO₂, and pH 4, was investigated by the linear polarization resistance technique. It was found that the polycations adsorbed onto the iron surface, but the corrosion rate of 1 mm yr^?1 was not lowered. However, the polycations formed a complex with an anionic surfactant, and such films showed excellent inhibition performance. Both films, of pDADMAC/SDS and of C‐PAM/SDS, lowered the corrosion rate of iron below 0.01 mm yr^?1. The SDS concentration was below the cmc. It is believed that the SDS adsorbed into the preadsorbed polycation film, forming a complex structure resulting in a hydrophobic and dense film.     

Comparison of portable devices for sub-ambient concentration measurements of methane (CH4) and nitrous oxide (N2O) in soil research

ABSTRACT

Production and consumption of methane (CH₄) and nitrous oxide (N₂O) in soils have a strong influence on global greenhouse gases (GHG) budgets. Therefore, it is crucial to precisely measure GHG fluxes at the soil–atmosphere interface. In upland soils, CH₄ and N₂O can be consumed by microbiological processes, and the respective concentrations can be lower than in the atmosphere, demanding highly sensitive gas analysing systems. Traditionally, soil air is sampled in vials and analysed in the laboratory by gas chromatography (GC). During the last decade, different technologies have been developed that allowed to build portable gas analysers that are able to measure sub-ambient gas concentration directly in the field. Here, we compared sub-ambient to ambient CH₄ and N₂O concentration values from four portable devices using different measurement technologies (a portable GHG analyser based on laser absorption spectroscopy [LAS], two portable Fourier transform infrared spectroscopy [FTIR] devices and a field gas analyser using photoacoustic spectroscopy [PAS]) to traditional GC analysis in the laboratory (a GC system equipped with a flame ionisation detector [GC-FID] and an electron capture detector [GC-ECD]). The accuracy and precision of photoacoustic spectroscopy measurements are strongly influenced by the water vapour content and non-target gases in the sampling air. We used an advanced set-up for a widely used PAS analyser enabling N₂O measurements at sub-ambient concentrations with similar precision and accuracy as the GC-ECD system. Measurements of CH₄ and N₂O by FTIR and LAS devices were in good agreement with the GC systems. We conclude that the portable devices are suitable for studies of GHG fluxes in the field. Thanks to their universal and portable character, LAS, PAS and FTIR devices represent useful alternatives to currently used technologies for field studies.     

Determination of phenolic compounds and hydroxymethylfurfural in meads using high performance liquid chromatography with coulometric-array and UV detection

The objective of this study was the determination of 25 phenolic compounds in different mead samples (honeywines) using high performance liquid chromatography (HPLC) with coulometric-array detection and in case of hydroxymethylfurfural with UV detection. Our method was optimized in respect to both the separation selectivity of individual phenolic compounds and the maximum sensitivity with the electrochemical detection. The method development included the optimization of mobile phase composition, the pH value, conditions of the gradient elution and the flow rate using a window-diagram approach. The developed method was used for the determination of limits of detection and limits of quantitation for individual compounds. The linearity of calibration curves, accuracy and precision (intra- and inter-day) at three concentration levels (low, middle and high concentration range) were verified. Mead samples were diluted with the mobile phase at 1:1 to 1:50 ratio depending on the concentration and filtered through a PTFE filter without any other sample pre-treatment. Phenolic compounds concentration was determined in 50 real samples of meads and correlated with meads composition and hydroxymethylfurfural concentration. The most frequently occurred compounds were protocatechuic acid and vanillic acid (both of them were present in 98% samples), the least occurred compounds were (+)-catechin (10% samples) and sinapic acid (12% samples). Vanillin and ethylvanillin, which are used as artificial additives for the taste improvement, were found in 60% and 42% samples, respectively. Hydroxymethylfurfural concentration, as an indicator of honey quality, was in the range from 2.47 to 158 mg/L. Our method is applicable for the determination of 25 phenolic compounds in mead, honey and related natural samples.     

Development of an SPME-GC-MS/MS procedure for the monitoring of 2-phenoxyethanol in anaesthetised fish

2-Phenoxyethanol (ethylene glycol monophenyl ether, C(8)H(10)O(2)) is a promising anaesthetic agent used in fisheries and aquaculture. The aim of this study was to develop a fast and easy method to determine 2-phenoxyethanol residue levels in fish tissue and blood plasma, and, subsequently, to use the method to monitor the dynamics of 2-phenoxyethanol residues in fish treated with anaesthetic. We developed a new procedure that employs solid phase microextraction (SPME) of the target analyte from the sample headspace followed by gas chromatography-mass spectrometry (GC-MS). Both sample handling, aimed at maximum transfer of 2-phenoxyethanol into the headspace, and SPME-GC-MS conditions were carefully optimised. Using a divinylbenzene/Carboxen/polydimethylsiloxane (PDMS/CAR/DVB) fiber for 60 min sampling at 30 degrees C and an ion trap detector operated in MS/MS mode, we obtained detection (LOD) and quantification (LOQ) limits of 0.03 and 0.1 mg kg(-1) of sample, respectively. The method was linear in a range of 0.1-250 mg kg(-1) and, depending on the sample matrix and spiking level, a repeatability (expressed as relative standard deviation, R.S.D.) of between 3% and 11% was obtained.