Separation of short and medium-chain fatty acids using capillary electrophoresis with indirect photometric detection: Part I: Identification of fatty acids in rat feces

Short and medium-chain fatty acids (SMCFAs) are known as essential metabolites found in gut microbiota that function as modulators in the development and progression of many inflammatory conditions as well as in the regulation of cell metabolism. Currently, there are few simple and low-cost analytical methods available for the determination of SMCFA. This report focuses on SMCFA analysis utilizing CE with indirect photometric detection (CE-IPD). A ribonucleotide electrolyte, 5’-adenosine mono-phosphate (5’-AMP), is investigated as an IPD reagent due to its high molar absorptivity and dynamic reserve compatible with separation and detection of SMCFA. The operating parameters like the composition of organic solvent, millimolar concentrations of the complexing agent (alpha-cyclodextrin), 5’-AMP and non-absorbing electrolyte (boric acid), as well as the applied voltage, are optimized for resolution, efficiency, and signal-to-noise ratio. A baseline resolution of all nine SMCFAs is achieved in less than 15 min. Additionally, the developed CE-IPD method shows promising potential to identifying SMCFA in rat fecal supernatant. The presented analytical assay is simple, economical, and has considerably good repeatability. The intraday and interday RSD of less than 1 and 2% for relative migration time, as well as less than 14 and 15% for peak area, respectively, were obtained for SMCFA in fecal solution.     

Numerical simulation of nanofluid turbulent flow in a double-pipe heat exchanger equipped with circular fins

Journal of Thermal Analysis and Calorimetry - In this study, the thermal and flow characteristics of a nanofluid were evaluated numerically in a circular finned double-pipe heat exchanger. A 3D CFD...     

Spectral,morphological, and antibacterial studies of conducting copolymers,Ppy‐MA,and their nanocomposites,Ag@Ppy‐MA

Pyrrole and methyl anthranilate were copolymerized in different molar ratios in the presence of, H₂O₂, and FeSO₄ at ambient temperature and pressure to obtain efficient conducting copolymers, Ppy‐MA. These conducting copolymers, Ppy‐MA, were in situ reacted with silver nanoparticles to generate nanocomposites, Ag@Ppy‐MA, which exhibit enhanced electrical conductivity. The spectra and morphology of different copolymers, Ppy‐MA, and their nanocomposites, Ag@Ppy‐MA, were analyzed using Fourier transform infrared, SEM, tunneling electron microscopy, X‐ray diffraction, thermogravimetric analysis, and differential thermal analysis. These studies have shown that the nanocomposites, Ag@Ppy‐MA, are thermally more stable and good electrical conductors as compared with their copolymers, Ppy‐MA. The antibacterial activity of the copolymers, Ppy‐MA, prepared from different monomer ratios and their nanocomposites, Ag@Ppy‐MA, has been carried out using disk diffusion method. The copolymers, Ppy‐MA, and its nanocomposites, Ag@Ppy‐MA, were screened against the standard drug Ciprofloxacin. The results clearly suggest that the nanocomposites, Ag@Ppy‐MA, are better antibacterial agent as compared with their copolymers, Ppy‐MA. Copyright © 2016 John Wiley & Sons, Ltd.     

A new approach to extraction and preconcentration of Ce(III) from aqueous solutions using magnetic reduced graphene oxide decorated with thioglycolic-acid-capped CdTe QDs

In the present study, a nanocomposite consisting of magnetic reduced graphene oxide decorated with thioglycolic-acid-capped CdTe quantum dots (TGA/CdTe QDs/Fe₃O₄/rGO) was synthesised using simple ‘hydrothermal method’ and applied as a nanosorbent for extraction and preconcentration of cerium (Ce)(III) from aqueous solutions prior to inductively coupled plasma-optical emission spectroscopy detection. Under the optimised extraction conditions, the calibration graph for Ce(III) was linear in a concentration range of 0.1–511.0 μg L^?1 with a correlation coefficient of 0.9986. A detection limit of 0.1 μg L^?1 Ce(III) with an enrichment factor of 125 was obtained. Precisions, expressed as relative standard deviation for single-sorbent repeatability and sorbent-to-sorbent reproducibility, were 3.6% and 9.1% (n = 5), respectively. Finally, spiked sea, mineral and tap waters were analysed to evaluate the performance of the proposed method. The high recoveries indicated that the suggested protocol was acceptable for determination of Ce(III) ions in the water samples. The use of QDs and study of their ability for preconcentration of metal ions is an important achievement towards designing novel adsorbents with high efficiency.     

Preconcentration and spectrophotometric determination of trace amount of formaldehyde using hollow fiber liquid-phase microextraction based on derivatization by Hantzsch reaction

Formaldehyde is known as a highly toxic compound to humans and identified as a carcinogenic substance. In this study, Hantzsch reaction was utilized for the derivatization of trace amounts of formaldehyde in aqueous samples with acetylacetone in the presence of ammonia to form an extractable colored product named 3,5-diacetyl 1,4-dihydrolutidine (DDL) and its further extraction using two-phase hollow fiber liquid-phase microextraction. The main experimental variables affecting the extraction performance were investigated and optimized. Under the optimum conditions (sample volume 12 mL; reaction temperature 70 °C; ammonium acetate buffer solution 4 mL 0.1 mol L^?1; acetylacetone 5 mL 0.15 mol L^?1; solvent octanol, salt concentration 20% (w/v) NaCl; pH of donor phase 7.0; stirring speed 400 rpm and extraction time 30 min), the linear dynamic range, limit of detection (LOD as 3S _b/m) and relative standard deviation (RSD %) of the proposed method were obtained as 5–250 μg L^?1 (r ² = 0.9979), 3.6 μg L^?1 and 2.5%, respectively. Finally, the applicability of the proposed method was examined, and very good results were obtained. The results confirmed the applicability of the proposed method as a versatile, low-cost and sensitive preconcentration method for determination of low concentrations of formaldehyde in aqueous solutions.     

The role of weak hydrogen-bonds on the formation of short-lived molecular associations

Weak molecular homo- and hetero-associations among some ethene derivatives and several common solvents are studied using (1)H NMR spectroscopy. In connection with the aromatic-solvent induced shifts which is a special case of molecular association between aromatic solvents and polar molecules a model for association was suggested that involves the interaction of the positive end of the solute dipole with the aromatic pi-electrons. This model met with certain difficulties. An alternative model for configuration of associated molecules that explains the literature results and the results obtained in this paper is presented. The model is based on interaction of protons of the acceptor molecules with the lone-pair electrons or pi-electrons of the donor molecules. The present model removes the difficulties met with the former model and extends the concept of aromatic-solvent induced shifts to include non-polar molecules besides polar ones. In all cases, the interaction of protons of acceptor molecules with lone-pair electrons of donor molecules gives rise to a deshielding effect, while interaction with aromatic pi-electrons leads to shielding.     

Polymeric alkenoxy amino acid surfactants: V. Comparison of carboxylate and sulfate head group polymeric surfactants for enantioseparation in MEKC

In this work, six amino acid derived (L-leucinol, L-leucine, L-isoleucinol, L-isoleucine, L-valinol, and L-valine) polymeric chiral surfactants with carboxylate and sulfate head groups that were recently synthesized in our laboratory [30, 33, 35] are compared for the simultaneous enantioseparation of several groups of structurally similar analytes under neutral and basic pH conditions. The physicochemical properties of the monomers and polymers of both classes of sulfated and carboxylated surfactants are compared. In addition, cryogenic high-resolution electron microscopy showed tubular structures with distinct order of the tubes of 50-100 nm width. A Plackett-Burmann experimental design is used to study the factors that influence the chiral resolution and analysis time of ten structurally related phenylethylamines (PEAs). It is observed that increasing the number of hydroxy groups on the benzene ring of the PEAs resulted in deterioration of enantioseparation using any of the six polymeric surfactants. For all three classes of PEAs, polysodium N-undecenoxycarbonyl-L-amino acidate (poly-L-SUCAA)-type surfactants provided enhanced resolution compared to that of polysodium N-undecenoxycarbonyl-L-amino acid sulfates (poly-L-SUCAASS). Several classes of basic and neutral chiral compounds (e.g., beta-blockers benzoin derivatives, PTH-amino acids, and benzodiazepines) also provided improved chiral separations with poly-L-SUCAA. Among the poly-L-SUCAAs, polysodium N-undecenoxycarbonyl-L-isoleucine sulfate (poly--SUCL) exhibited overall the best enantioseparation capability for the investigated basic and neutral compounds, while among the poly-L-SUCAASs, polysodium N-undecenoxycarbonyl-L-isoleucine sulfate (poly-L-SUCILS), and polysodium N-undecenoxycarbonyl-L-valine sulfate (poly-L-SUCVS) proved to be equally effective for enantioseparation. This work clearly demonstrates that variation in the head group of polymeric alkenoxy amino acid surfactants has a significant effect on chiral separations.     

Simultaneous chiral separation and determination of ephedrine alkaloids by MEKC-ESI-MS using polymeric surfactant I: method development

In this work, simultaneous separation of eight stereoisomers of ephedrine and related compounds ((+/-)-ephedrine, (+/-)-pseudoephedrine, (+/-)-norephedrine and (+/-)-N-methylephedrine) was accomplished using a polymeric chiral surfactant, i.e. polysodium N-undecenoxycarbonyl-L-leucinate (poly-L-SUCL) by chiral (C)MEKC-ESI-MS. The conditions of CMEKC were first investigated. The baseline separation of all eight stereoisomers of ephedrine and related compounds was achieved under optimum CMEKC conditions (35 mM poly-L-SUCL, 15 mM NH(4)OAc, pH 6.0, 30% v/v ACN, 30 kV and 20 degrees C) in less than 30 min. Next, a central composite design for response surface modeling has been described to evaluate the electrospray chamber parameters and the sheath liquid conditions. Optimum mass abundance of stereoisomers of ephedrine and related compounds was observed using the spray chamber parameters, namely 250 degrees C drying gas temperature and 8 L/min drying gas flow rate at a nebulizer pressure of 4 psi. Furthermore, the experimental design indicates that the optimum mass abundance of the stereoisomers of ephedrine and related compounds can be obtained using a sheath liquid containing 80:20 v/v methanol-water, 5 mM NH(4)OAc at pH 8.5 delivered at 5 microL/min. Finally, compared to MEKC-UV, the use of poly-L-SUCL in MEKC-MS provided significantly higher sensitivity for stereoisomers of ephedrine and related compounds.     

Synthesis and application of a nanoporous ion‐imprinted polymer for the separation and preconcentration of trace amounts of vanadium from food samples before determination by electrothermal atomic absorption spectrometry

A vanadium ion‐imprinted polymer was synthesized in the presence of V(V) and N‐benzoyl‐N‐phenyl hydroxyl amine using 4‐vinyl pyridine as the monomer, ethylene glycol dimethacrylate as the cross linker and 2,2’‐azobis(isobutyronitrile) as the initiator. The imprinted V(V) ions were completely removed by leaching the polymer with 5 mol/L nitric acid, and the polymer structure was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The ion‐imprinted polymer was used as the sorbent in the development of the solid‐phase extraction method for V(V) prior to its determination by electrothermal atomic absorption spectrometry. The maximum sorption capacity for V(V) ions was 26.7 mg/g at pH 4.0. Under the optimum conditions, for a sample volume of 150.0 mL, an enrichment factor of 289.0 and a detection limit of 6.4 ng/L were obtained. The developed method was successfully applied to the determination of vanadium in parsley, zucchini, black tea, rice, and water samples.