Ahmad Aqel

Metal-organic frameworks in chromatography

Metal-organic frameworks (MOFs) emerged approximately two decades ago and are the youngest class of porous materials. Despite their short existence, MOFs are finding applications in a variety of fields because of their outstanding chemical and physical properties. This review article focuses on the applications of MOFs in chromatography, including high-performance liquid chromatography (HPLC), gas chromatography (GC), and other chromatographic techniques. The use of MOFs in chromatography has already had a significant impact; however, the utilisation of MOFs in chromatography is still less common than other applications, and the number of MOF materials explored in chromatography applications is limited.

Effect of multi-walled carbon nanotubes incorporation into benzyl methacrylate monolithic columns in capillary liquid chromatography

This work describes the preparation of polymer based monolithic materials and their use as stationary phases in capillary liquid chromatography. Multi-walled carbon nanotubes (MWCNT) were incorporated into a mixture containing benzyl methacrylate (BMA) and ethylene dimethacrylate (EDMA) as co-monomers. The optimized porogenic mixture was a ternary solution composed of cyclohexanol, 1,4-butandiol and butanol which resulted in a stable and homogeneous suspension. Six capillary columns with increasing amounts of MWCNT, from 0 to 0.4 mg mL(-1), were prepared by thermal polymerization in 0.32 mm (i.d.) and 150 mm length fused silica tubing. The chromatographic evaluation showed that the synthesized monolithic beds were mechanically stable while their porosity and permeability increased with the MWCNT content. The prepared capillary columns were tested for the separation of mixtures of ketones and phenols at an optimum flow rate of 2 μL min(-1). The results showed that incorporation of MWCNT slightly affected the retention while it enhanced the column efficiency by increasing the column efficiency by a factor of up to 9. This effect corresponded also to an improved resolution and full separation of the solutes.

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.

Determination of free fatty acids in olive oils by UPHLC-MS.

A simple, fast, highly efficient and direct method using ultra-performance liquid chromatography coupled to mass spectrometry has been established for the simultaneous separation, identification and quantitation of a few saturated and unsaturated fatty acids in olive oils from various countries. No sample pretreatment techniques were employed such as extraction or derivatization for the analysis of target acids from oil samples, as the oil samples were just diluted, filtered and then directly injected to the instrument. The chromatographic separations of all target fatty acids were achieved on a Hypersil Gold C18 column of particle size 1.9μm, 50×2.1mm I.D, while the gradient elution using a binary mobile phase mixture of acetonitrile and water at a flow rate of 1.5ml/min was adopted for achieving optimum separations. The identification and quantitation of target compounds was accomplished using selected ion reaction monitoring mode. The recoveries of the fatty acids were obtained higher than 89% with good validation parameters; linearity (r(2)>0.992), detection limit between 0.09 and 0.24μg/ml, run to run and day to day precisions with percent relative standard deviation lower than 2.4% at both low (1μg/ml) and medium (10μg/ml) concentration levels. The total content of fatty acids in each individual oils was found in the range of 472.63-7751.20μg/ml of olive oil, while oleic acid was found to be the major fatty acid among all analyzed oils with the amount 3785.94μg/ml (maximum) in Syrian olive oil. The obtained validation parameters confirm that the proposed analytical method is rapid, sensitive, reproducible and simple and it could be applied for the successful evaluation of fatty acids in various oils and other matrices. All the fatty acids were efficiently eluted in a time of less than 8min with well resolved peaks by employing the proposed method.

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 evaluation of benzyl methacrylate monoliths for capillary chromatography.

This paper describes the comprehensive fabrication of monolithic materials for use as stationary phases in capillary liquid chromatography. Several columns were synthesized in the confines of 320 µm i.d. fused-silica capillaries by single-step in situ copolymerization of benzyl methacrylate and ethylene dimethacrylate (EDMA). The polymerization procedure was optimized by varying the reaction time within the range of 0.5-20 h, and by changing the composition contents of the polymeric mixture. The EDMA content showed a predominant influence on the characteristics of the columns and hence, on their chromatographic properties. The optimum value of the thermal initiator corresponded to 5 mg/mL. Changes of the porous, hydrodynamic properties and morphology of the prepared columns were thoroughly investigated and characterized. Different solvents were used as the mobile phase to demonstrate that the resulting monoliths exhibited good permeability and mechanical stability, whereas swelling and shrinking behaviors were observed and discussed. The efficiency and performance toward different sets of analytes were obtained; mixtures of aromatic hydrocarbons and phenolic compounds were successfully separated and evaluated, and adding tetrahydrofuran to the mobile phase showed improvement in both resolution and peak shapes. The characteristics of the columns were also checked in terms of repeatability and reproducibility.

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

UNLABELLED Thermodynamic 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. METHODS The 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.

Carbon nanotube-based benzyl polymethacrylate composite monolith as a solid phase extraction adsorbent and a stationary phase material for simultaneous extraction and analysis of polycyclic aromatic hydrocarbon in water

A composite of multi-walled carbon nanotubes incorporated into a benzyl methacrylate-co-ethylene dimethacrylate porous monolith was prepared, characterized and used as solid phase adsorbent and as stationary phase for simultaneous extraction and separation of ten polycyclic aromatic hydrocarbons, followed by nano-liquid chromatography analysis. The extraction and chromatographic parameters were optimized with regard to the extraction efficiency and the quality of chromatographic analytes separation. Under the optimized conditions, all PAHs were separated in 13 min with suitable resolution values (Rs = 1.74-3.98). Addition of a small amount of carbon nanotubes (0.1% with respect to monomers) to the polymerization mixture increased the efficiency for the separation column to over 41,700 plates m-1 for chrysene at flow rate of 0.5 μL min-1. The method showed a wide linear range (1-500 μg L-1 with R2 more than 0.9938), acceptable extraction repeatability (RSDs < 6.4%, n = 3) and reproducibility (RSDs < 12.6%, five parallel-made solid phase extraction cartridges) and satisfactory detection limits (0.02-0.22 μg L-1). Finally, the proposed method was successfully applied to the detection of polycyclic aromatic hydrocarbons in environmental water samples. After a simple extraction procedure with preconcentration factor equal to 100, the average recovery values in ultra-pure, tap and sea water samples were found to be in the range 81.3-95.4% with %RSD less than 6.4. Again, the presence of carbon nanotubes (0.3% relatively to monomers) in native polymer enhanced the extraction performance for the solid phase adsorbent up to 78.4%. The application of the monoliths modified with CNTs in extraction and nano-scale liquid chromatography for analysis of environmental samples offered several advantages; it demonstrated an acceptable precision, low detection limits, good reproducibility, satisfying recoveries and wide dynamic linear ranges.

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

Analysis of Quercetin and Kaempferol in an Alcoholic Extract of Convolvulus pilosellifolius using HPLC

A simple, rapid, and sensitive high-performance liquid chromatography (HPLC) method was developed and validated for identification and determination of flavonoids in Convolvulus pilosellifolius. The chromatographic separation was achieved in less than 6 min using C18 column (150 × 4.6 mm, 3 μm) with isocratic mixture of methanol and water containing 0.1 percent v/v formic acid in the ration of 80:20 at 258 nm with a flow rate of 0.4 mL/min. The method was validated in the linear calibration curve ranged between 1 and 300 μg/mL with detection limits of 0.39 and 0.26 μg/mL and quantification limits of 1.20 and 0.79 μg/mL for quercetin and kaempferol, respectively. Good repeatability of the method were achieved at percent relative standard deviation (RSD < 2.18 percent) with respect to inter- and intraday repeatability. Recovery values were found to be in the range of 98.2–100.2 percent, indicating high accuracy of the method. The maximum flavonoid contents were 1.07 and 1.54 percent for quercetin and kaempferol, respectively.