Acid‐induced homogenous liquid‐phase microextraction: Application of medium‐chain carboxylic acid as extraction phase

In this research, a novel homogeneous liquid‐phase microextraction method was successfully developed based on applying octanoic acid as low‐density extraction solvent. The method was applied for extraction and determination of chlorophenols (CPs) as model compounds. Twelve milliliter of the sample solution was poured into a home‐designed glass vial. Sixty microliter of octanoic acid was solved in water sample by adjusting pH and ionic strength. By rapid addition of 75 μL of concentrated HCl (6 M), a cloudy solution was obtained. Phase separation occurred at 5000 rpm for 5 min. After that, 20 μL of the collected phase (approximately 26 μL) was injected into the HPLC‐UV instrument for analysis. The effect of some parameters such as the volume of concentrated HCl (phase separation reagent), ionic strength, extraction time, centrifugation time, and the volume of extracting phase on the extraction efficiency of the CPs were investigated and optimized. The preconcentration factors in a range of 159–218 were obtained under the optimal conditions. The linear range, detection limits (S/N = 3), and precision (n = 3) were 1– 200, 0.3–0.5 μg/L, and 4.6–5.1%, respectively. Tap water, seawater, and river water samples were successfully analyzed for the existence of CPs using the proposed method and satisfactory results were obtained.     

SMFs-supported Pd nanocatalysts in selective acetylene hydrogenation: Pore structure-dependent deactivation mechanism

In the present study, CNFs, ZnO and Al₂O₃ were deposited on the SMFs panels to investigate the deactivation mechanism of Pd-based catalysts in selective acetylene hydrogenation reaction. The examined supports were characterized by SEM, NH₃-TPD and N₂ adsorption-desorption isotherms to indicate their intrinsic characteristics. Furthermore, in order to understand the mechanism of deactivation, the resulted green oil was characterized using FTIR and SIM DIS. FTIR results confirmed the presence of more unsaturated constituents and then, more branched hydrocarbons formed upon the reaction over alumina-supported catalyst in comparison with the ones supported on CNFs and ZnO, which in turn, could block the pores mouths. Besides the limited hydrogen transfer, N₂ adsorption-desorption isotherms results supported that the lowest pore diameters of Al₂O₃/SMFs close to the surface led to fast deactivation, compared with the other catalysts, especially at higher temperatures.     

3D Printing in analytical sample preparation

In the last 5 years, additive manufacturing (three‐dimensional printing) has emerged as a highly valuable technology to advance the field of analytical sample preparation. Three‐dimensional printing enabled the cost‐effective and rapid fabrication of devices for sample preparation, especially in flow‐based mode, opening new possibilities for the development of automated analytical methods. Recent advances involve membrane‐based three‐dimensional printed separation devices fabricated by print‐pause‐print and multi‐material three‐dimensional printing, or improved three‐dimensional printed holders for solid‐phase extraction containing sorbent bead packings, extraction disks, fibers, and magnetic particles. Other recent developments rely on the direct three‐dimensional printing of extraction sorbents, the functionalization of commercial three‐dimensional printable resins, or the coating of three‐dimensional printed devices with functional micro/nanomaterials. In addition, improved devices for liquid–liquid extraction such as extraction chambers, or phase separators are opening new possibilities for analytical method development combined with high‐performance liquid chromatography. The present review outlines the current state‐of‐the‐art of three‐dimensional printing in analytical sample preparation.     

Dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-UV detection as a very simple,rapid and sensitive method for the determination of bisphenol A in water samples

Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied for the extraction and determination of bisphenol A (BPA) in water samples. An appropriate mixture of acetone (disperser solvent) and chloroform (extraction solvent) was injected rapidly into a water sample containing BPA. After extraction, sedimented phase was analyzed by HPLC-UV. Under the optimum conditions (extractant solvent: 142 μL of chloroform, disperser solvent: 2.0 mL of acetone, and without salt addition), the calibration graph was linear in the range of 0.5–100 μg L⁻¹ with the detection limit of 0.07 μg L⁻¹ for BPA. The relative standard deviation (RSD, n = 5) for the extraction and determination of 100 μg L⁻¹ of BPA in the aqueous samples was 6.0%. The results showed that DLLME is a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of BPA in water samples and suitable results were obtained.     

A new liquid-phase microextraction method based on solidification of floating organic drop

In the present study, a new and versatile liquid-phase microextraction method is described. This method requires very simple and cheap apparatus and also a small amount of organic solvent. Eight microliters of 1-undecanol was delivered to the surface of solution containing analytes and solution was stirred for a desired time. Then sample vial was cooled by inserting it into an ice bath for 5 min. The solidified 1-undecanol was transferred into a suitable vial and immediately melted; then, 2 μL of it was injected into a gas chromatograph for analysis.Some polycyclic aromatic hydrocarbons (PAHs) were used as model compounds for developing and evaluating of the method performance. Analysis was carried out by gas chromatography/flame ionization detection (GC/FID).Several factors influencing the microextraction efficiency, such as the nature and volume of organic solvent, the temperature and volume of sample solution, stirring rate and extraction time were investigated and optimized. The applicability of the technique was evaluated by determination of trace amounts of PAHs in environmental samples. Under the optimized conditions, the detection limits (LOD) of the method were in the range of 0.07-1.67 μg L⁻¹ and relative standard deviations (R.S.D.) for 10 μg L⁻¹ PAHs were <7%. A good linearity (r² > 0.995) in a calibration range of 0.25-300.00 μg L⁻¹ was obtained. After 30 min extraction duration, enrichment factors were in the range of 594-1940. Finally, the proposed method was applied to the determination of trace amounts of PAHs in several real water samples, and satisfactory results were resulted. Since very simple devices were used, this new technique is affordable, efficient, and convenient for extraction and determination of low concentrations of PAHs in water samples.     

Oxidative coupling of methane over （Na2WO4＋Mn or Ce）/SiO2 catalysts： In situ measurement of electrical conductivity

The effects of manganese oxide or ceria promoters on the performance of Na2WO4/SiO2 catalysts for oxidative coupling of methane (OCM) are reported. The OCM reaction was performed in a continuous-flow microreactor at 800 ℃, atmospheric pressure and under GHSV = 13200 ml gC-1at h-1. Catalysts were characterized by in situ conductivity measurement, FT-IR spectroscopy, XRD, SEM and temperature programmed reduction analysis. Manganese oxide promoted Na2WO4/SiO2 is considered as one of the active and selective ca...     

Optimization of a novel method based on solidification of floating organic droplet by high-performance liquid chromatography for evaluation of antifungal drugs in biological samples

In this study, a simple, rapid, and highly efficient liquid-phase microextraction method based on solidification of floating organic droplet was coupled with high performance liquid chromatography-photo diode array detection (HPLC-PDA) for determination of ketoconazole, clotrimazole, and miconazole as antifungal drugs. Central composite design (CCD) was used for optimization of several factors affecting the extraction efficiency. The optimized conditions were established to be 550 rpm for stirring rate, 35 min for extraction time, 57 °C for extraction temperature, 8.5 for solution pH, 10 μl for organic solvent volume, and 7% (w/v) of NaCl for ionic strength. Limit of detections (LODs) of the extraction method ranged from 0.01 to 0.1 μg L⁻¹ and the linear dynamic ranges (LDRs) ranged from 0.1 to 300 μg L⁻¹ for the three antifungal drugs. Relative standard deviations (RSDs) of the proposed method were 5-11%. Preconcentration factors in the range of 306-1350 were obtained at extraction time of 35 min. Finally, performance of the proposed method was evaluated for the extraction and determination of the drugs’ levels in microgram per liter in samples and satisfactory results were obtained.     

Nanostructured polypyrrole for automated and electrochemically controlled in-tube solid-phase microextraction of cationic nitrogen compounds

The authors describe an efficient method for microextraction and preconcentration of trace quantities of cationic nitrogen compounds, specifically of anilines. It relies on a combination of electrochemically controlled solid-phase microextraction and on-line in-tube solid-phase microextraction (SPME) using polypyrrole-coated capillaries. Nanostructured polypyrrole was electrically deposited on the inner surface of a stainless steel tube and used as the extraction phase. It also acts as a polypyrrole electrode that was used as a cation exchanger, and a platinum electrode that was used as the anode. The solution to be extracted is passed over the inner surface of the polypyrrole electrode, upon which cations are extracted by applying a negative potential under flow conditions. This method represents an ideal technique for SPME of protonated anilines because it is fast, easily automated, solvent-free, and inexpensive. Under optimal conditions, the limits of detection are in the 0.10–0.30 μg L‾¹ range. The method works in the 0.10 to 300 μg L‾¹ concentration range. The inter- and intra-assay precisions (RSD%; for n = 3) range from 5.1 to 7.5 % and from 4.7 to 6.0 % at the concentration levels of 2, 10 and 20 μg L‾¹, respectively. The EC-in-tube SPME method was successfully applied to the analysis of methyl-, 4-chloro-, 3-chloro and 3,4-dichloroanilines in (spiked) water samples.

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A new effective on chip electromembrane extraction coupled with high performance liquid chromatography for enhancement of extraction efficiency

In the present research, an effective on chip electromembrane extraction (CEME) coupled with high performance liquid chromatography was presented for analysis of nortriptyline (NOR) and amitriptyline (AMI) as basic model analytes from urine samples. The chip consists of two polymethyl methacrylate (PMMA) parts with two craved microfluidic channels in each part. These channels were used as flow path for the sample solution and a thin compartment for the acceptor phase. A porous polypropylene sheet membrane impregnated with an organic solvent was placed between two parts of chip device to separate the channels. Two platinum electrodes were mounted at the bottom of these channels that were connected to a power supply providing the electrical driving force for migration of ionized analytes from sample solution through the porous sheet membrane into the acceptor phase. This new setup provides effective and reproducible extractions with low volume of sample solution. Efficient parameters on CEME of the model analytes were optimized using one variable at a time method. Under the optimized conditions, the calibration curve was linear in the range of 10.0–500 μg L⁻¹ with coefficient of determination (r²) more than 0.9902. The relative standard deviations (RSDs %) for extraction and determination of the analytes were less than 6.8% based on six replicate measurements. LODs less than 4.0 μg L⁻¹ were obtained for both of the model analytes. The preconcentration factors higher than 17.0-fold were obtained. The results demonstrated that CEME would be used efficiently for extraction and determination of AMI and NOR from urine samples.     

Homogeneous Liquid–Liquid Microextraction for Determination of Organochlorine Pesticides in Water and Fruit Samples

A fast and effective preconcentration method for extraction of organochlorine pesticides (OCPs) was developed using a homogeneous liquid–liquid extraction based on phase separation phenomenon in a ternary solvent (water/methanol/chloroform) system. The phase separation phenomenon occurred by salt addition. After centrifugation, the extraction solvent was sedimented in the bottom of the conical test tube. The OCPs were transferred into the sedimented phase during the phase separation step. The extracted OCPs were determined using gas chromatography–electron capture detector. Several factors influencing the extraction efficiency were investigated and optimized. Optimal results were obtained at the following conditions: volume of the consolute solvent (methanol), 1.0 mL; volume of the extraction solvent (chloroform), 55 μL; volume of the sample, 5 mL; and concentration of NaCl, 5 % (w/v). Under optimal conditions, the preconcentration factors in the range of 486–1,090, the dynamic linear range of 0.01–100 μg L^?1, and the limits of detection of 0.001–0.03 μg L^?1 were obtained for the OCPs. Using internal standard, the relative standard deviations for 1 μg L^?1 of the OCPs in the water samples were obtained in the range of 4.9–8.6 % (n = 5). Finally, the proposed method was successfully applied for extraction and determination of the OCPs in water and fruit samples.