High-performance liquid chromatographic determination of arbutin in skin-whitening creams and medicinal plant extracts

A high-performance liquid chromatographic method was developed for quantitative analysis of arbutin. The arbutin was separated on an ODS Hypersil^® C18 column with a mobile phase of water: methanol: 0.1 M hydrochloric acid (89:10:1, v/v/v). The level of arbutin was measured by means of UV detection at 222 nm. The optimum conditions for arbutin quantitative analysis were investigated. The calibration curve was found to be linear up to 1000 μg/ml^-1 of arbutin concentration, and the working calibration curve for arbutin determination over the range 0.5–30.0 μg/ml^-1 of arbutin ( r ² = 0.9999) was established. The relative standard deviations for intraday and interday were found to be 0.98% and 1.15%, respectively. A detection limit (3σ) and quantitation limit (10σ) of 0.02 μg/ml^-1 and 0.2 μg/ml^-1, respectively, and a mean percentage recovery of the spiked arbutin of 99.88 ± 1.12% were obtained. The proposed method has been applied to the determination of arbutin in commercial skin-whitening creams (Arbuwhite^® cream, Super Whitening^® cream, and Shiseido^® cream) with average contents of 7.60, 5.30, and 57.90 mg/g^-1, respectively. It was also applied to the determination of arbutin in medicinal plant extracts from Betula alnoides Buch. Ham., Clerodendrum petasites S. Moore, Curculigo latifolia Dryand. Var. latifolia, and Hesperethusa crenulata (Roxb.) Roem, levels of which were found to be 3.50, 1.50, 1.10, and 0.12 μg/g^-1, respectively (no article reported in the literature about arbutin analysis). The proposed HPLC method is rapid, simple, and selective for routine analysis.     

Microwave-assisted synthesis and characterization of zinc oxide/carbon nanotube composites

A composite material of zinc oxide and carbon nanotubes were successfully synthesized via a sol process using zinc acetate dihydrate and treated multi-wall carbon nanotubes under microwave irradiation. The morphology, microstructure and chemical bonding of as-obtained composites were well characterized using X-ray diffraction, scanning electron microscope, transmission electron microscope, and Fourier transform infrared spectroscopy. Zinc oxide nanoparticles were dispersively coated on the surface of carbon nanotube when the precursor was dried under microwave irradiation without post-annealing. X-ray diffraction results obviously showed the mixture of two phases of carbon nanotube and wurzite zinc oxide whose size is approximately 15 nm. The formation of zinc oxide nanoparticles on carbon nanotube surface in the composite prepared by microwave heating is much better than the composite heated by conventional annealing. Fourier transform infrared spectroscopic results suggest that carboxylic groups and uniform heating by microwave heating could play key roles on the nucleation of zinc oxide on carbon nanotube surface.     

Structural and magnetic properties of nanocrystalline zinc-doped metal ferrites (metal=Ni; Mn; Cu) prepared by sol–gel combustion method

In this work, nanocrystalline M–Zn ferrites (M=Ni; Mn; Cu) with compositions of M_1?xZn_xFe₂O₄ (x=0.0, 0.2 and 0.4) were synthesized from metal nitrate precursors by rapid the sol–gel combustion method using diethanolamine (DEA) as the fuel. As-synthesized powders were calcined at 1000 °C for 4 h. The crystal structures and morphologies of these compounds were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. The chemical interaction of ferrite powders was investigated by Fourier transform infrared spectroscopy (FTIR). The magnetic properties of after-calcined nanoparticles were measured at room temperature using a vibrating sample magnetometer (VSM). The single phase spinel cubic structure formation is confirmed by XRD and FTIR results. Meanwhile FE-SEM micrographs show the appearance of both undoped and Zn-doped ferrite ceramic samples. In addition, the VSM analyses indicate that the Zn content has a significant influence on the magnetic properties such as saturation magnetization (M_s) and coercivity (H_c).     

Physical properties of V-doped TiO2 nanoparticles synthesized by sonochemical-assisted process

V-doped TiO₂ nanoparticles were synthesized by sonochemical process using titanium isopropoxide as a titanium source, vanadyl acetylacetonate as a dopant source. Sonication was conducted using sonic horn operated at 20 kHz for 20 min until the completely precipitated product was reached. The as-synthesized precipitates with various vanadium dopant (1–5 mol %) were calcined at 500–1000 °C for 4 h. The relevant physical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). The anatase phase TiO₂ nanoparticles can be synthesized by sonochemical process. Post calcinations process results in the anatase-to-rutile phase transformation and the enhancement in crystallinity with increasing temperature. The results also indicate good incorporation of V ions in TiO₂ lattices and significant effect of V dopant on alternation of interplanar spacing of TiO₂.     

N-doped MgZnO alloy thin film prepared by sol-gel method

In this work, nitrogen-doped MgZnO thin films were deposited on glass substrate by spin-coating technique and thermal annealing treatment. The X-ray diffraction (XRD), scanning electron microscope (SEM) and optical transmission measurement were carried out to investigate the effect of growth temperature and nitrogen doping on the physical and optical properties of the films. XRD and SEM results revealed that the crystallinity and preferred c-axis orientation was enhanced with increasing annealing temperature and certain concentration of N-doping. In addition, the films incorporated with nitrogen doping exhibit significant blue shift in optical band gap and improvement in its transparency.     

Microwave-assisted synthesis of ZnO/MWCNT hybrid nanocomposites and their alcohol-sensing properties

Zinc oxide and multi-walled carbon nanotube (ZnO/MWCNT) hybrid nanocomposites were synthesised by microwave-assisted method using the mixed solution of zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O) and treated MWCNTs. The syntheses were carried out at various microwave irradiation powers. The characterisation of the as-synthesised nanocomposites was conducted by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results revealed that the composites were composed of two phases of MWCNTs and hexagonal wurzite ZnO. The SEM results showed that the ZnO nanoparticles were well decorated on the surface of MWCNTs. The amount of ZnO nanoparticles and their size increased with increasing irradiation power. Thick-film sensors were fabricated onto interdigitated conducting electrodes using as-synthesised hybrid composites as sensing materials. The alcohol-sensing behaviour of the hybrid composite films was investigated. The results indicated that the irradiation power had significant influence on the sensing response of the sensors toward alcohol. The sensor fabricated from the composite synthesised at higher irradiation power exhibited an enhanced alcohol-sensing performance.     

Simple hydrothermal preparation of nanofibers from a natural ilmenite mineral

Titanate nanofibers were synthesized by a simple hydrothermal method using a natural ilmenite mineral as the starting material. The chemical composition, crystalline structure, shape, size, and specific surface area of the prepared samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the Brunauer–Emmett–Teller analysis (BET). The crystalline structure of the as-synthesized nanofibers demonstrated a layered titanate form, H₂Ti_xO_2x+1. The length of the prepared nanofibers ranged from 2 to 7 μm with diameters ranging from 20 to 90 nm. The as-synthesized nanofibers were solids with BET surface areas of approximately 50 m²/g. This synthetic method provides a simple route for the fabrication of one-dimensional (1-D) nanostructured materials from a low-cost natural mineral.     

Flow injection analysis of total curcuminoids in turmeric and total antioxidant capacity using 2,2′-diphenyl-1-picrylhydrazyl assay

A simple flow injection analysis procedure is proposed for the determination of curcuminoids content in turmeric extracts. The method is based on the formation of a coloured complex between 4-aminoantipyrine and curcuminoids, in the presence of an oxidising reagent such as potassium hexacyanoferrate (III) in alkaline media. Conditions selected as a result of these trials were implemented in a flow injection analytical system in which the influence of injection volume, flow rate, reagent concentration and mixing coil length, was evaluated. Under the optimum conditions the total amount of curcuminoids could be determined within a concentration range of 5–50 μg mL⁻¹ which can be expressed by the regression equation y = 0.003x − 0.0053 (r² = 0.9997). The limits of detection and quantitation were found to be 0.6 μg mL⁻¹ and 1.8 μg mL⁻¹, respectively. The reproducibility of analytical readings was indicative of standard deviations <2%. The sample was extracted and analysed by using the proposed method. The percentage recoveries were found to be 94.3–108.0. The proposed system was applied to the determination of curcuminoids content in turmeric. The total curcuminoid contents in turmeric extract were found to be 0.9–4.3% (w/w). The development method is simple, economic, rapid and especially suitable for quality control in pharmaceutical plants.     

Characterization and ozone-induced coloration of ZnxNi1 − xO thin films prepared by sol-gel method

Zn_xNi_1 − xO thin films were prepared by sol-gel spin coating method onto glass substrates in combination with annealing process. Effect of zinc content on the structural, optical and ozone-induced coloration properties of as-prepared films was investigated by X-ray diffraction, field emission-scanning electron microscope, atomic force microscopy and UV-VIS spectrophotometer, respectively. X-ray diffraction results reveal that the structures of all films are still cubic NiO structure. Average grain size of Zn_xNi_1 − xO film increases with increasing annealing temperature and its crystallization is strongly affected by Zn content. Coloration of the films was obtained after UV/ozone exposure due to a presence of ozone-induced hydroxyl groups. Significant enhancement of coloration efficiency of the films is achieved as content of Zn increases.