Determination of steroid hormones in oral contraceptives by high-performance liquid chromatography

The aim of this research was to standardize a high-performance liquid chromatographic method for quantitative determination of steroid hormones, like ethinylestradiol (ETE), levonorgestrel (LEVO), and gestodene (GEST), in commercially available oral contraceptives (OCs). The combination ETE- LEVO was analyzed using a LiChrospher® 100 RP-8 column (5 μm, 125×4 mm) in LiChroCART®, with a mobile phase constituted of acetonitrile: water (60:40 v/v). Using the same column, ETE-GEST was analyzed with a mobile phase constituted of acetonitrile:water (50:50 v/v) at pH 7.5 adjusted with 0.02 M ammonium hydroxide. For both methods, a flow rate of 0.8 mL/min was utilized and detection was carried out at 215 nm. All analyses were performed at room temperature (24±2°C).

Calibration curves for ETE-LEVO were obtained using solutions with concentration ranges from 2.40 to 60.0 μg/mL (ETE), and from 12.0 to 300.0 μg/mL (LEVO). Calibration curves for ETE-GEST were obtained using solutions with concentration ranges from 2.40 to 60.0 μg/mL (ETE), and from 9.0 to 160.0 μg/mL (GEST). Correlation coefficients obtained were from 0.9999 to 0.9990. Coefficients of variation for samples containing ETE-LEVO were 0.47% and 0.38%, respectively. For samples with ETE-GEST they were 0.39% and 0.44%, respectively. The average recovery for samples with ETE-LEVO was 103.46% and 100.78%, respectively. For samples containing ETE-GEST it was 100.89% and 101.03%, respectively.     

Conductometric biosensor based on glucose oxidase and beta-galactosidase for specific lactose determination in milk

This paper investigates the development of a biosensor associating two distinct enzymatic activities, that of the beta-galactosidase and that of the glucose oxidase, in order to apply it for the quantitative detection of lactose in milk. To eliminate interferences with glucose, a differential mode of measurement was used. Results show a linear calibration curve for lactose concentration between 60 and 800 μM (0.03 to 0.3 g/L). Tests with real commercial milk samples were carried out to validate the conductometric biosensor.     

Elaboration of a new hydrogen peroxide biosensor using microperoxidase 8 (MP8) immobilized on a polypyrrole coated electrode

A novel strategy for elaborating a new biosensor for hydrogen peroxide has been developed by combining the known properties of microperoxidase 8 (MP8) as an oxidation catalyst, and the interesting properties of conducting polypyrrole as a supporting matrix to allow a good bioelectrochemical interface and a large dispersion of MP8 on the modified glassy carbon electrode.

MP8 was immobilized into the conducting polypyrrole by entrapment during the electrochemical polymerization, and the modified electrode was characterized both by electrochemical and FT-IR measurements. We demonstrated that MP8 could be immobilized into polypyrrole and could undergo an efficient electron transfer.

The obtained modified electrode showed a high catalytic activity toward H₂O₂ without the need for an electron mediator. A linear calibration curve was obtained by amperometric measurement at a potential of − 0.1 V/ECS for concentrations of H₂O₂ ranging from 1 to 10 μM. The detection limit obtained was 1 nM which constituted a real improvement, by about three orders of magnitude, when compared to the values reported for other systems using an electrochemical detection.     

A new approach for nitrite determination based on a HRP/catalase biosensor

In this paper, a new concept of enzyme inhibition-based biosensor involving a two enzyme system was developed. The latter displays a signal increase instead of a decrease in the presence of an inhibitor. HRP and catalase were thus separately entrapped into Layered Double Hydroxides (LDH), an anionic clay, as a host matrix. The inner layer was constituted of HRP electrically wired by [Zn₂CrABTS] LDH and the outer layer contained catalase immobilized in [Zn₃AlCl] LDH. Both enzymes catalyzed the decomposition of H₂O₂, HRP its reduction and catalase its breakdown into oxygen and water. Nitrite was selected as a specific inhibitor of catalase. In the presence of H₂O₂, the nitrite addition blocked the H₂O₂ consumption by catalase, inducing thus an increase in the amperometric signal of the H₂O₂ reduction at 0 V by the wired HRP. The optimum configuration of the bi-enzyme biosensor displayed in aerated aqueous solutions, a nitrite sensitivity of 102 μA M^− 1· cm^− 2 with a fast response time, the detective limit being 4 μM.     

Novel sucrose three-enzyme conductometric biosensor

For the first time a conductometric biosensor for sucrose determination has been developed using a complex three-enzyme (invertase, mutarotase, and glucose oxidase) containing membrane as a sensitive element immobilized on the conductometric interdigitated planar electrodes. The time of measurement of sucrose concentration in the solution was about 1–2 min. The dynamic range of biosensor depends on buffer capacity, being 2 μM–5 mM of sucrose in 5 mM phosphate buffer. The conductometric biosensor developed demonstrates high selectivity, operational stability and reproducibility. The dependence of sensor response on pH and ionic strength of tested solution has been studied in this work. Storage conditions have also been under investigation. The sensor appeared to be eligible towards application in practice.     

基于花状MoS2微米材料的葡萄糖生物传感器的制备及其性能研究

本研究采用水热法制备了花状MoS₂微米材料, 将其作为电极构建葡萄糖生物传感器, 并研究了相关性能。结果表明: 水热法制备的MoS₂呈花状, 具有较好的结晶质量, 尺寸约为3.6 μm, 比表面积约为9.646 m²/g; MoS₂电极具有优良的电催化活性, 且电阻抗较小, 使得传感器对葡萄糖具有较好的响应。葡萄糖检测结果表明, 该传感器在0~20 mmol/L范围内, 氧化峰电流与葡萄糖浓度呈良好的线性关系, 相关系数(R)为0.9653, 灵敏度为262 μA•L/mmol。     

A novel low-cost approach of implementing electrochemiluminescence detection for microfluidic analytical systems

This paper presents an inexpensive approach of implementing electrochemiluminescence (ECL) detection for microfluidic analytical systems. It consists in using printed circuit board (PCB) technology to design electrodes and sealing the epoxy substrate with a transparent microfluidic structure in polymer for ECL detection and system integration. A pair of PCB electrodes (10 mm²) and an ECL microfluidic device are designed and fabricated. They are tested via luminol ECL detection to quantify H₂O₂. Characterization of the PCB electrodes is performed via the determination of the optimum potential (0.7 V vs. Ag/AgCl) to trigger luminol oxidation. Electrode potential is square-wave modulated from 0 to 0.7 V at a minimum period of 17 s. Measurements of on/off modulated ECL signals for different H₂O₂ concentrations are carried out to establish their relationship. The obtained results show a 50-nM detection limit at a signal-to-noise ratio (SNR) equal to 3 and a linear range extending up to 0.1 mM in batch or in microfluidic conditions. The detection volumes for these two systems are 2 ml and 4 μl, respectively.     

Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

A new method of immobilization of proteins on activated ester terminated alkanethiol monolayers towards the label free impedancemetric detection

This paper investigates a new immobilization procedure for biological molecules that is based on the formation of reactive ω-functionalized-self-assembled thiol monolayers onto a gold electrode. The homogeneous self-assembled monolayer was characterized by X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The SAM modified gold electrode showed a clear peak corresponding to S_2p that characterized the Au-thiolate bond, while cyclic voltammetry and electrochemical impedance spectroscopy measurements, in 10 mM phosphate buffer pH 7, in the presence of Fe(CN)₆^{− 3/− 4} as redox probe, showed that these monolayers were densely packed and prevented electron transfer towards the gold surface. These homogeneous SAMs were used to immobilize biotin hydrazide by covalent attachment, after the nucleophilic attack of the amino group of biotin hydrazide on the ω-activated ester function of thiols. The biotin–avidin interaction was then examined as a model for an affinity biosensor with electrochemical impedance spectroscopy. A Randles equivalent circuit was used for the interpretation of impedance data and the change in the interfacial properties at the modified-electrode/electrolyte interface were monitored through charge-transfer resistance variation. The proposed affinity biosensor showed a detection range that was linear between 200 and 800 ng/ml for avidin. In order to improve the sensitivity the technique of mixed self-assembled monolayers was adopted. Mixed SAMs were elaborated by co-adsorption of two differently substituted thiols, one was substituted by a reactive group that was used to react with the amino group of biotin hydrazide, whereas the other was substituted by an hydroxyl group that was chosen to mimic protein resistance. In this study, we started with a 1:3 activated ester:hydroxyl-terminated alkanethiol ratio. The results obtained with the mixed SAMs appeared to be better than those obtained with the homogeneous SAMs, and the corresponding affinity biosensor presented two detection ranges that were linear between 20 and 100 ng/ml and between 100 and 1200 ng/ml, respectively, with two different slopes.     

Deposition of HfO2 thin films on ZnS substrates

HfO₂ thin films with columnar microstructure were deposited directly on ZnS substrates by electron beam evaporation process. SiO₂ thin films, deposited by reactive magnetron sputtering, were used as buffer layers, HfO₂ thin films of granular microstructure were obtained on SiO₂ interlayer by this process. X-ray diffraction patterns demonstrate that the as-deposited HfO₂ films are in an amorphous-like state with small amount of crystalline phase while the HfO₂ films annealed at 450 °C in O₂ for 30 min and in Ar for 150 min underwent a phase transformation from amorphous-like to monoclinic phase. Antireflection effect in certain infrared wave band, such as 3–6 μm, 4–12 μm, 4–8 μm and 3–10 μm, can be observed, which was dependent on the thickness of thin films. The cross-sectional images of HfO₂ films, obtained by field emission scanning electron microscopy, revealed that there was no distinct morphological change upon annealing.     

Amperometric biosensor for lactate analysis in wine and must during fermentation

A lactate oxidase-based amperometric biosensor is designed for lactate determination. Two methods of lactate oxidase immobilization on the surface of commercial SensLab platinum printing electrodes are compared. The sensor with lactate oxidase immobilized by physical adsorption in Resydrol polymer is shown to have both narrower dynamic range (0.004–0.5 mМ lactate) and higher sensitivity (320 nA/mM) as compared with that immobilized in poly(3,4-ethylenedioxythiophene) by electrochemical polymerization (0.05–1.6 mM and 60 nA/mM respectively). The operational stability of the biosensors developed is studied; the immobilization method is shown to be of no influence. The lactate content in wine and in wine material during fermentation is analyzed. The data obtained by amperometric lactate biosensor correlated with those of standard chromatography. The biosensor developed can be used in food industry for control and optimization of process of wine fermentation as well as for control of wine quality.     

EFFECT OF PARTICLE SIZE DISTRIBUTION ON TRANSFER EFFICIENCY AND APPEARANCE IN POWDER COATINGS

Three powder samples of identical chemistry were taken from the same lot under different conditions: (1) relatively wide size distribution (Sample A) d₅₀ = 18.1μm, (2) narrow size distribution, d₅₀ = 22.4μm (Sample B), and (3) wide size distribution with more fines than Sample A, d₅₀ = 15.1μm (Sample C). Within this relatively minor variation of Particle Size Distribution (PSD) with respect to d₅₀, the appearance of the powder with minimum d₅₀ (15.1μm) was best. The results show two trends: (1) PSD with d₅₀ about 15μm can result in excellent appearance (GM Tension in the range of 18 to 19 on a scale of 0 to 20), and (2) the width of the distribution need not be narrow when d₉₀ is less than 40μm.

Polymer powders in this size range do not fluidize well without agitation, but when vibration was applied, all three samples had R values (fluidity) 200 or above, which is adequate for fluidization and transport. The maximum R value was obtained for Sample A, which had the widest size distribution. Thus, the fluidity tests agreed with the expected results.     

A simple tool for quality evaluation of the microcrystalline silicon prepared at high growth rate

Silicon thin films were grown by plasma enhanced chemical vapor deposition at high-pressure (700 Pa), high-power (4– W/cm²) depletion regime using multi-hole cathode. Series of samples were deposited by varying hydrogen/silane ratio or plasma power to study evolution of film structure and transport properties near a-Si:H/μc-Si:H transition. We suggest a simple “μc-Si:H layer quality factor” based on the ratio of subgap optical absorption (1.4 eV)/ (1 eV) measured by constant photocurrent method. This ratio correlates well with the values of ambipolar diffusion lengths measured by surface photovoltage method perpendicularly to the substrate, i.e., in the direction of the collection of the photogenerated carriers in solar cells.     

Plasmon mediated Brillouin scattering of surface acoustic waves (in different directions to polymer line structures on a silver coated glass substrate)

In this paper measurement on the propagation of Rayleigh waves on the surface of polymer line structures on top of a silver layer were examined by using plasmon mediated Brillouin scattering. The line structures grating constants were 8, 4 and 1 μm. Spectra were recorded with different scattering angles and propagation directions with respect to the line direction. Three Rayleigh modes have been observed in samples with grating constants 8 and 4 μm. In the parallel direction, one mode is unshifted relative to a pure silver surface. In the perpendicular direction there is one unshifted and one shifted mode. The observed shift of 6 μm^− 1 is independent of the grating constant. The 1 μm sample shows a somewhat contrasting behavior. Two different scattering mechanisms, involving surface plasmons at each interface, are proposed to explain the observed effects.     

Effect of the microwave oven on structural, morphological and electrical properties of SrBi4Ti4O15 thin films grown on Pt/Ti/SiO2/Si substrates by a soft chemical method

Thin films of SrBi₄Ti₄O₁₅ (SBTi), a prototype of the Bi-layered-ferroelectric oxide family, were obtained by a soft chemical method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional method at 700 °C for 2 h. Structural and morphological characterization of the SBTi thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates, the ferroelectric properties of the films were determined. Remanent polarization P_r and a coercive field E_c values of 5.1 μC/cm² and 135 kV/cm for the film thermally treated in the microwave oven and 5.4 μC/cm² and 85 kV/cm for the film thermally treated in conventional furnace were found. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10¹⁰ switching cycles indicating that SBTi thin films are a promising material for use in non-volatile memories.     

Electrochemical study of human olfactory receptor OR 17–40 stimulation by odorants in solution

The human olfactory receptor OR 17–40 co-expressed with -subunit of G_olf protein in yeast was attempted as a bio recognition part of impedimetric biosensor. The receptor in its natural membrane environment was anchored to a gold-coated glass substrate modified with thiol-based multilayer. Step-by-step building-up of the OR 17–40 based biofilm was monitored using surface plasmon resonance technique. Stimulation of the OR 17–40 with its cognate odorant helional in phosphate-buffered saline was probed by means of electrochemical impedance spectroscopy under various conditions. Activation of OR 17–40 in the presence of GTP-γ-S at 4 °C was found to improve the sensitivity of the developed label-free biosensor, probably via the enhancement of the specific biochemical signal.     

A validated stability indicating LC method for Nateglinide

A simple, isocratic, rapid and accurate reverse phase high-performance liquid chromatography (RP-HPLC) method was developed for the quantitative determination of Nateglinide. The developed method is also applicable for determination of related substance in bulk drugs. The chromatographic separation was achieved on a Hypersil C18 (250 × 4.6 mm 5 μm) column using aqueous mixture of 0.025 M potassium hydrogen phosphate and 0.1% triethyl amine, v/v (pH 3.0 with dilute phosphoric acid)—methanol (25:75, v/v) as a mobile phase. Solution concentrations were measured on a weight basis to avoid the use of an internal standard. The chromatographic resolutions between Nateglinide and its potential impurities A and B were found to be greater than four. Forced degradation studies were performed for Nateglinide using acid (0.5 N hydrochloric acid), base (0.5 N sodium hydroxide), oxidation (3% hydrogen peroxide) heat (60°C) and UV light (254 nm). The limit of detection and limit of quantification of Nateglinide, impurities A and B were found to be 0.05 and 0.15 μg /mL, respectively for 20 μL injection volume. The percentage recovery of Nateglinide was ranged from 98.4 to 100.9. The percentage recovery of impurities in Nateglinide sample was ranged from 96.8 to 103.5. The developed RP-HPLC method was validated with respect to linearity, accuracy, precision, robustness, and forced degradation studies prove the stability indicating power of the method.     

Indium Tin Oxide Thin-Film Sensor for Detection of Volatile Organic Compounds (VOCs)

Indium tin oxide (ITO) (In₂O₃ + 17% SnO₂) thin films were grown on glass substrate by direct evaporation method. Two thick gold pads were deposited to take out contacts. The response of these films at different operating temperatures, when exposed to various volatile organic compounds (VOCs) such as methanol, ethanol, butanol, and acetone in the concentration range 200-2500 ppm was evaluated. Additionally, the effect of film thickness on the response charateristics of methanol and acetone was studied. The linearity and sensitivity of the sensors were measured. The ITO thin-film sensors showed a sensitivity of 0.256 ohms/ppm to acetone vapors, which was almost linear in the range 200-2500 ppm. In order to improve sensitivity and selectivity, a thin layer of various metal and metal oxides such as Cu and PbO was deposited on the sensor surface to work as catalytic layer and the effect on the performance of the sensor was studied. The response and recovery times of the sensor were determined for acetone vapors and were found to be 155 sec and 110 sec, respectively.     

Average bioequivalence of clarithromycin immediate released tablet formulations in healthy male volunteers

The objective of this study was to assess average bioequivalence of two immediate released tablet formulations of 500-mg clarithromycin tablets in 24 healthy Thai male volunteers. In a randomized, single dose, fasting state, two-period, crossover study design with a 1-week washout period, each subject received a 500-mg clarithromycin tablet. Plasma samples were collected over a 24-hour period after oral administration and were analyzed by using a validated method using high performance liquid chromatography with electrochemical detection. Pharmacokinetic parameters were determined by using noncompartmental analysis. The time to reach the maximal concentration (t_max, h), the peak concentration (C_max, ng/mL), and the area under the curve (AUC_{0 - ∞}, ng.h/mL) of the Reference and Test formulations were 2.0 ± 0.8 vs. 2.2 ± 0.9, 2793 ± 1338 vs. 2642 ± 1344, and 17912 ± 7360 vs. 17660 ± 7992, respectively. Relative bioavailability was 0.99. The 90% confidence interval of C_max and AUC_{0 - ∞} were 82.6-112.1% and 84.7-112.0%. Bioequivalence between the Test and Reference formulation can be concluded.     

Optical gain calculation of mid-infrared InAsN/GaSb quantum-well laser for tunable absorption spectroscopy applications

We report on optical gain calculations of a dilute-nitride mid-infrared laser structure designed to be grown on InAs substrate. The active region is composed of several strain-compensated type-II “W”-like InAsN/GaSb/InAsN quantum wells adapted to operate near 3.3 μm at room temperature. For typical injected carrier density σ = 1.1012 cm^− 2, the theoretical laser structure performances reveal a gain value at around 1000 cm^− 1 at 300 K, inducing a modal gain value equal to 50 cm^− 1. Low radiative current densities lower than 100 A/cm² are predicted, indicating that this dilute-nitride structure could operate at 300 K with small threshold current density.