Ahmed Yacine Badjah-Hadj-Ahmed

Optical isomer separation of flavanones and flavanone glycosides by nano-liquid chromatography using a phenyl-carbamate-propyl-β-cyclodextrin chiral stationary phase.

In this paper a phenyl-carbamate-propyl-beta-cyclodextrin stationary phase was employed for the enantioseparation of several flavonoids, including flavanones and methoxyflavanones by using nano-liquid chromatography (nano-LC). The same stationary phase was also used for the diastereoisomeric separation of two flavanone glycosides. The compounds: flavanone, 2-hydroxyflavanone, 4-hydroxyflavanone, 6-hydroxyflavanone, 7-hydroxyflavanone, 4-methoxyflavanone, 6-methoxyflavanone, 7-methoxyflavanone, hesperetin, hesperidin, naringenin and naringin were studied using reversed, polar organic and normal elution modes. The effect of the nature and composition of the mobile phase (organic modifier type, buffer and water content in the reversed phase mode) on the enantioresolution (R(s)), retention factor (k) and enantioselectivity (alpha) were investigated. Baseline resolution of all studied flavonoids, with the exception of 2-hydroxyflavanone and naringin, was achieved in reversed phase mode using a mixture of MeOH/H(2)O at different ratios as mobile phase. Good results, in terms of peak efficiency and short analysis time, were obtained adding 1% triethylammonium acetate pH 4.5 buffer to MeOH/H(2)O mixture. The separation of the studied compounds was also performed in polar organic mode. By using 100% of MeOH as mobile phase, the resolution was achieved for the studied analytes, except for 7-hydroxyflavanone, 2-hydroxyflavanone, naringenin, hesperidin and naringin. Normal mode was tested employing a mixture of EtOH/hexane/TFA as mobile phase achieving the enantiomeric and diastereomeric separation of only hesperetin and hesperidin, respectively. The use of nano-LC technique for the resolution of flavanones optical isomers allowed to achieve good resolutions in shorter analysis time compared to the results reported in literature with conventional HPLC.

Analysis of hesperetin enantiomers in human urine after ingestion of blood orange juice by using nano-liquid chromatography

Hesperetin (HT) is a flavanone abundantly found in citrus fruits. It has been reported that HT possesses significant antioxidant, anticancer, anti-inflammatory and analgesic activities. This explains the necessity of developing new methods more powerful and sensitive for analyzing HT in biological fluids. Taking into account the chiral nature of HT, the study of the stereospecific kinetics of in vitro and in vivo metabolism and tissue distribution could be a useful tool for further understanding stereoselective biotransformations in human body. A simple nano-liquid chromatographic method for the determination of the enantiomeric composition of hesperetin in human urine was developed. Chiral separation was achieved using a 100 microm I.D. capillary, packed with phenyl-carbamate-propyl-beta-cyclodextrin stationary phase, employing a mobile phase composed by a mixture of triethylammonium acetate buffer (1%, v/v, pH 4.5) and water/methanol (30:70, v/v) at room temperature. The detection was done by using on-column UV detector at 205 nm. Calibration curves were linear in the studied concentration range from 0.25 to 25 microg/mL (r(2)>0.999). Precision assay was <4.5% and was within 3% at the limit of quantification (0.5 microg/mL). The recovery of 7-ethoxycoumarin (IS), R- and S-hesperetin was greater than 82.48%, utilizing a liquid-liquid extraction procedure. The developed method was successfully applied to the determination of hesperetin enantiomers in urine samples obtained from a male volunteer, after the ingestion of 1L of a commercial blood orange juice.

Fabrication of zeolitic imidazolate framework-8-methacrylate monolith composite capillary columns for fast gas chromatographic separation of small molecules

A composite zeolitic imidazolate framework-8 (ZIF-8) with a butyl methacrylate-co-ethylene dimethacrylate (BuMA-co-EDMA) monolithic capillary column (33.5cm long×250μm i.d.) was fabricated to enhance the separation efficiency of methacrylate monoliths toward small molecules using conventional low-pressure gas chromatography in comparison with a neat butyl methacrylate-co-ethylene dimethacrylate (BuMA-co-EDMA) monolithic capillary column (33.5cm long×250μm i.d.). The addition of 10mgmL(-1) ZIF-8 micro-particles increased the BET surface area of BuMA-co-EDMA by 3.4-fold. A fast separation of five linear alkanes in 36s with high resolution (Rs≥1.3) was performed using temperature program. Isothermal separation of the same sample also showed a high efficiency (3315platesm(-1) for octane) at 0.89min. Moreover, the column was able to separate skeletal isomers, such as iso-octane/octane and 2-methyl octane/nonane. In addition, an iso-butane/iso-butylene gas mixture was separated at ambient temperature. Comparison with an open tubular TR-5MS column (30m long×250μm i.d.) revealed the superiority of the composite column in separating the five-membered linear alkane mixture with 4-5 times increase in efficiency and a total separation time of 0.89min instead of 4.67min. A paint thinner sample was fully separated using the composite column in 2.43min with a good resolution (Rs≥0.89). The perfect combination between the polymeric monolith, with its high permeability, and ZIF-8, with its high surface area and flexible 0.34nm pore openings, led to the fast separation of small molecules with high efficiency and opened a new horizon in GC applications.

Monolithic metal-organic framework MIL-53(Al)-polymethacrylate composite column for the reversed-phase capillary liquid chromatography separation of small aromatics.

A monolithic capillary column containing a composite of metal-organic framework MIL-53(Al) incorporated into hexyl methacrylate-co-ethylene dimethacrylate was prepared to enhance the separation of mixtures of small aromatic compounds by using capillary liquid chromatography. The addition of 10 mg/mL MIL-53(Al) microparticles increased the micropore content in the monolithic matrix and increased the Brunauer-Emmett-Teller surface area from 26.92 to 85.12 m(2) /g. The presence of 1,4-benzenedicarboxylate moieties within the structure of MIL-53(Al) as an organic linker greatly influenced the separation of aromatic mixtures through π-π interactions. High-resolution separation was obtained for a series of alkylbenzenes (with resolution factors in the range 0.96-1.75) in less than 8 min, with 14xa0710 plates/m efficiency for propylbenzene, using a binary polar mobile phase of water/acetonitrile in isocratic mode. A reversed-phase separation mechanism was indicated by the increased retention factor and resolution as the water percentage in the mobile phase increased. A stability study on the composite column showed excellent mechanical stability under various conditions. The higher resolution and faster separation observed at increased temperature indicated an exothermic separation, whereas the negative values for the free energy change of transfer indicated a spontaneous process.

Preparation and characterization of alkyl methacrylate-based monolithic columns for capillary gas chromatography applications

Gas chromatography (GC) is considered the least common application of both polymer and silica-based monolithic columns. This study describes the fabrication of alkyl methacrylate monolithic materials for use as stationary phases in capillary gas chromatography. Following the deactivation of the capillary surface with 3-(trimethoxysilyl)propyl methacrylate (TMSM), the monoliths were formed by the co-polymerization of either hexyl methacrylate (HMA) or lauryl methacrylate (LMA) with different percentage of ethylene glycol dimethacrylate (EDMA) in presence of an initiator (azobisisobutyronitrile, AIBN) and a mixture of porogens include 1-propanol, 1,4-butanediol and water. The monoliths were prepared in 500mm length capillaries possessing inner diameters of 250μm. The efficiencies of the monolithic columns for low molecular weight compounds significantly improved as the percentage of crosslinker was increased, because of the greater proportion of pores less than 50nm. The columns containing lower percentages of crosslinker were able to rapidly separate a series of 8 alkane members in 0.7min, but the separation was less efficient for the light alkanes. Columns prepared with the lauryl methacrylate monomer yielded a different morphology for the monolith-interconnected channels. The channels were more branched, which increased the separation time, and unlike the other columns, allowed for temperature programming.

Preparation and enantioseparation characteristics of three chiral stationary phases based on modified β-cyclodextrin for liquid chromatography

AbstractIn order to study the effect of the nature and the length of the spacer, three mixed 10-undecenoate/phenylcarbamate derivatives of β-cyclodextrin have been prepared and linked to allylsilica gel by means of a radical reaction. The chiral recognition ability of the resulting materials, when used as liquid chromatography chiral stationary phases (CSPs), was evaluated using heptane and either 2-propanol or chloroform as organic mobile-phase modifiers. A large variety of racemic compounds have been separated successfully on these CSPs (mainly pharmaceuticals and herbicides). Optimization of these separations was discussed in terms of mobile-phase composition and structural patterns of the injected analytes. The efficiencies of the three prepared materials were compared to those of previously described perphenylated-β-cyclodextrin column and to analogous cellulose derivative-based CSPs.n Schematic illustration of the b-cyclodextrin/mandelic acid inclusion complex

Zeolitic imidazolate framework-methacrylate composite monolith characterization by inverse gas chromatography

UNLABELLEDnThermodynamic characterization of butyl methacrylate-co-ethylene dimethacrylate neat monolith and zeolitic imidazolate framework-8 incorporated with butyl methacrylate-co-ethylene dimethacrylate composite monolith were studied using inverse gas chromatography at infinite dilution under 1MPa column pressure and various column temperatures. The free energy of adsorption (ΔGA), enthalpy of adsorption (ΔHA) and entropy of adsorption (ΔSA) were determined using a series of n-alkanes. The dispersive component of surface energy (γS(D)) was estimated by Dorris-Gray and Schultz et al.nnnMETHODSnThe composite monolith showed a more energetic surface than the neat monolith. The acidic, KA, and basic, KD, parameters for both materials were estimated using a group of polar probes. A basic character was concluded with more basic behavior for the neat monolith. Flory-Huggins parameter, χ, was taken as a measure of miscibility between the probes with the low molecular weight and the high molecular weight monolith. Inverse gas chromatography provides a better understanding of the role of incorporated zeolitic imidazolate framework (ZIF-8) into the polymer matrix in its monolithic form.

Effect of sporopollenin microparticle incorporation into the hexyl methacrylate-based monolithic columns for capillary liquid chromatography

ABSTRACT Sporopollenin microparticles have been prepared form Lycopodium clavatum spores, defatted and incorporated into a porous methacrylate polymer monolith to enhance liquid chromatographic performance of different sets of small neutral molecules. A stable suspension between sporopollenin microparticles and porogenic solvents composed of 1-propanol and 1,4-butandiol has proved before preparation, and seven compositions with increasing sporopollenin microparticles were prepared inside fused silica tubing. After optimizing of the preparation conditions, the structure of the stationary phase was characterized by scanning electron microscopy, surface area analysis, thermodynamic study, short- and long-term precision, and hydrodynamic properties including mechanical stability, porosity, and permeability. The columns were successfully applied to improve the separation efficiency of different mixtures using capillary liquid chromatography. Addition of very small amount of sporopollenin microparticles to the methacrylate mixture enhanced the column efficiency from 3 to 5 times for ketonic and phenolic compounds and reduced the retention with the corresponding better resolution and peak shapes for all studied compounds. GRAPHICAL ABSTRACT

Level of Polychlorinated Biphenyls in Marine Environment of Algiers Bay, Algeria

Polychlorinated Biphenyls (PCBs) are persistent organic pollutants with significant bioaccumulation in the global environment. Owing to their high toxicity and lipophilic property, PCBs are potential threat to the human and ecological system. The objective of this work was to investigate the polychlorinated biphenyls in seawater and blue mussels Mytilus galloprovincialis collected in the eastern coastal side of the Algiers bay. Surface and bottom water samples were collected at six different periods from July to October 2002 in the port of Tamentfoust and four locations around the port. Mussel samples were collected from Tamentfoust port and Surcouf beach. After extraction, the PCBs levels were determined in marine water and biological samples by gas chromatography with electron capture detector. Total polychlorinated biphenyls concentrations varied from 4.0 to 18.8 ng · L−1 in surface and from 4.4 to 16.6 ng · L−1 in bottom seawater and were relatively high in August (30th and 45th days). In mussels that concentrate the organochlorinated compounds in their tissues, the sum of ICES 7 PCBs concentrations was relatively high. It ranged from 64.2 to 185.8 ng · g−1 dw (average 125.8 ng · g−1 dw) in samples collected from Surcouf. The level of contamination in Tamentfoust port mussels was about twice higher (225.2 ng · g−1 dw). The observed PCBs distribution was close to that of common commercial mixture and suggests an industrial origin of this pollution emitted from a continental source in addition to the port activities. Although the use of target compounds has been banned for more than three decades, they are still persistent in Algiers Bay.

Analysis of the Mechanism of Retention on a Modified β‐Cyclodextrin/Silica Chiral Stationary Phase using a Computational Chemical Method

Abstract Quantitative analysis of the retention of various optically active solutes on a modified β‐cyclodextrin/silica chiral stationary phase was achieved using a molecular mechanics calculation of the CAChe program. Using computational chemical calculations, the various interactions between each enantiomer and the modified β‐cyclodextrin chiral selector were calculated as energy contributions. These interaction energy values were then compared to the experimental values measured in normal phase liquid chromatography. Among the obtained predicted values, the best correlation was observed between the molecular interaction energy and the selectivity factor, α, calculated for the studied racemates.