Development and Application of Porous Membrane-Protected Carbon Nanotube Micro-Solid-Phase Extraction Combined with Gas Chromatography/Mass Spectrometry

HPLC-MS/MS combined with membrane-protected molecularly imprinted polymer micro-solid-phase extraction for synthetic cathinones monitoring in urine

Synthetic cathinones are a type of drug belonging to group of new psychoactive substances (NPSs). The illicit market for these substances is characterized by the continuous introduction to the market of new analogs to evade legislation and to avoid detection. New screening and confirmation assays are therefore needed, mainly in forensic/clinical samples. In the current development, a porous membrane-protected, micro-solid-phase extraction (μ-SPE) has been developed for the assessment of several cathinones in urine. The μ-SPE device consisted of a cone-shaped polypropylene (PP) porous membrane containing the adsorbent (molecularly imprinted polymers, MIPs, synthesized for the first time for this class of drugs). MIPs were prepared using ethylone and 3-methylmethcathinone (3-MMC) as templates, ethylene glycol dimethacrylate (EGDMA) as a functional monomer, divinylbenzene (DVB) as a cross-linker, and 2,2´-azobisisobutyronitrile (AIBN) as an initiator. The prepared ethylone-based MIP and 3-MMC-based MIP have been fully characterized and evaluated as new selective adsorbents for μ-SPE. Cathinones separation/determination was performed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Optimum loading conditions (pH 5.0, loading for 4.0 minutes under orbital-horizontal shaking at 200 rpm) and elution conditions [2.0 mL of 75:20:5 heptane/2-propanol/ammonium hydroxide and ultrasounds assistance (37 kHz, 325 W) for 4.0 minutes] were found for ethylone-based MIP. Validation (intra-day and inter-day precision and analytical recovery) showed RSD values lower than 9 and 10% for intra-day and inter-day precision, and within the 88%-101% range for intra-day and inter-day analytical recovery.

Development of Dispersive Liquid-Liquid Microextraction method combined with UV spectrophotometry for the Determination of Malathion Pesticide

A simple and novel method was developed by combination of dispersive liquid-liquid microex-traction with UV spectrophotometry for the preconcentartion and determination of trace amount of malathion. The presented method is based on using a small volume of ethylenechloride as the extraction solvent was dissolved in ethanol as the dispersive solvent, then the binary solution was rapidly injected by a syringe into the water sample containing malathion. The important parame-ters, such the type and volume of extraction solvent and disperser solvent, the effect of extraction time and rate, the effect of salt addition and reaction conditions were studied. At the optimum conditions, the calibration graph was linear in the range of 2-100 ng mL-1 of malathion with a limit of detection of 0.8 ng L-1. In addition, the enrichment factor was 30. The developed method was successfully applied for the determination of malathion pesticide in water samples

Recovery of Anthocyanins Using Membrane Technologies: A Review

Anthocyanins are naturally occurring polyphenolic compounds and give many flowers, fruits and vegetable their orange, red, purple and blue colors. Besides their color attributes, anthocyanins have received much attention in recent years due to the growing evidence of their antioxidant capacity and health benefits on humans. However, these compounds usually occur in low concentrations in mixtures of complex matrices, and therefore large-scale harvesting is needed to obtain sufficient amounts for their practical usage. Effective fractionation or separation technologies are therefore essential for the screening and production of these bioactive compounds. In this context, membrane technologies have become popular due to their operational simplicity, the capacity to achieve good simultaneous separation/pre-concentration and matrix reduction with lower temperature and lower operating cost in comparison to other sample preparation methods. Membrane fractionation is based on the molecular or particle sizes (pressure-driven processes), on their charge (electrically driven processes) or are dependent on both size and charge. Other non-pressure-driven membrane processes (osmotic pressure and vapor pressure-driven) have been developed in recent years and employed as alternatives for the separation or fractionation of bioactive compounds at ambient conditions without product deterioration. These technologies are applied either individually or in combination as an integrated membrane system to meet the different requirements for the separation of bioactive compounds. The first section of this review examines the basic principles of membrane processes, including the different types of membranes, their structure, morphology and geometry. The most frequently used techniques are also discussed. Last, the specific application of these technologies for the separation, purification and concentration of phenolic compounds, with special emphasis on anthocyanins, are also provided.

Recent applications of metal-organic frameworks in sample pretreatment

Metal-organic frameworks are promising materials in diverse analytical applications especially in sample pretreatment by virtue of their diverse structure topology, tunable pore size, permanent nanoscale porosity, high surface area, and good thermostability. According to hydrostability, metal-organic frameworks are divided into moisture-sensitive and water-stable types. In the actual applications, both kinds of metal-organic frameworks are usually engineered into hybrid composites containing magnetite, silicon dioxide, graphene, or directly carbonized to metal-organic frameworks derived carbon. These metal-organic frameworks based materials show good extraction performance to environmental pollutants. This review provides a critical overview of the applications of metal-organic frameworks and their composites in sample pretreatment modes, that is, solid-phase extraction, magnetic solid-phase extraction, micro-solid-phase extraction, solid-phase microextraction, and stir bar solid extraction.

Porous membrane protected micro-solid-phase extraction: A review of features, advancements and applications

Membrane protected micro-solid-phase extraction (μ-SPE) was introduced in 2006 as an alternative to multistep SPE. μ-SPE is based on packing of very small amount of sorbent inside the porous membrane sheet whose edges are heat sealed to fabricate a μ-SPE device. This device performs clean up, extraction, and pre-concentration in a single step. It suits best for extraction of complex samples as sorbent is effectively protected inside the membrane and extraneous matter cannot adsorb over it. This review summarizes most important aspects of μ-SPE including basic principles, extraction procedure, different formats, sorbents employed and affecting parameters. The article also provides a brief account on modified μ-SPE procedures where μ-SPE was either combined with other techniques or some major changes were introduced in original procedure. Finally, the applications of μ-SPE in environmental, food and biological analysis are described. At the end, advantages and pitfalls of μ-SPE are critically appraised.

Nanomaterials for sample pretreatment prior to capillary electrophoretic analysis

Nanomaterials are, in analytical science, used for a broad range of purposes, covering the area of sample pretreatment as well as separation, detection and identification of target molecules.

Solid-phase microextraction of ultra-trace amounts of tramadol from human urine by using a carbon nanotube/flower-shaped zinc oxide hollow fiber

A new method is successfully developed for the separation and determination of a very low amount of tramadol in urine using functionalized multiwalled carbon nanotubes/flower-shaped zinc oxide before solid-phase microextraction combined with gas chromatography. Under ultrasonic agitation, a sol of multiwalled carbon nanotubes and flower-shaped zinc oxide were forced into and trapped within the pore structure of the polypropylene and the sol solution immobilized into the hollow fiber. Flower-shaped zinc oxide was synthesized and characterized by Fourier transform infrared spectroscopy. The morphology of the fabricated solid-phase microextraction surface was investigated by scanning electron microscopy and X-ray diffraction. The parameters affecting the extraction efficiencies were investigated and optimized. Under the optimized conditions, the method shows linearity in a wide range of 0.12-7680 ng/mL, and a low detection limit (S/N = 3) of 0.03 ng/mL. The precision of the method was determined and a relative standard deviation of 3.87% was obtained. This method was successfully applied for the separation and determination of tramadol in urine samples. The relative recovery percentage obtained for the spiked urine sample at 1000 ng/mL was 94.2%.

Electrochemical sensing of bisphenol using a multilayer graphene nanobelt modified photolithography patterned platinum electrode

An electrochemical sensor has been developed for the detection of Bisphenol-A (BPA) using photolithographically patterned platinum electrodes modified with multilayer graphene nanobelts (GNB). Compared to bare electrodes, the GNB modified electrode exhibited enhanced BPA oxidation current, due to the high effective surface area and high adsorption capacity of the GNB. The sensor showed a linear response over the concentration range from 0.5 μM-9 μM with a very low limit of detection = 37.33 nM. In addition, the sensor showed very good stability and reproducibility with good specificity, demonstrating that GNB is potentially a new material for the development of a practical BPA electrochemical sensor with application in both industrial and plastic industries.