Preliminary Stability Tests Research Articles

Quasi-solid-state dye-sensitized solar cell fabricated with poly (β-hydroxyethyl methacrylate) based organogel electrolyte

A novel freestanding poly (β-hydroxyethyl methacrylate), PHEMA-based organogel electrolyte is developed simply by optimization of the solution polymerization in the same solvent as the organic electrolyte for dye-sensitized solar cells (DSCs). The room temperature ionic conductivity of the gel electrolyte is 4.54 × 10−3 S cm−1, and the conduction behavior can be well described by the free volume model. The quasi-solid-state dye-sensitized solar cell fabricated with this PHEMA-based polymer gel electrolyte can present high energy conversion efficiency up to 7.5%. Preliminary long-term stability test further reveals that this quasi-solid-state electrolyte exhibits good stability after 1000 h thermal test in comparison with the DSCs based on corresponding liquid electrolyte.

Development and preliminary testing of a unitized regenerative fuel cell based on PEM technology

Results related to the development and testing of a unitized regenerative fuel cell (URFC) based on proton-exchange membrane (PEM) technology are reported. A URFC is an electrochemical device which can operate either as an electrolyser for the production of hydrogen and oxygen (water electrolysis mode) or as a H2/O2 fuel cell for the production of electricity and heat (fuel cell mode). The URFC stack described in this paper is made of seven electrochemical cells (256 cм2 active area each). The nominal electric power consumption in electrolysis mode is of 1.5 kW and the nominal electric power production in fuel cell mode is 0.5 kW. A mean cell voltage of 1.74 V has been measured during water electrolysis at 0.5 A cm−2 (85% efficiency based on the thermoneutral voltage of the water splitting reaction) and a mean cell voltage of 0.55 V has been measured during fuel cell operation at the same current density (37% electric efficiency based on the thermoneutral voltage). Preliminary stability tests are satisfactory. Further tests are scheduled to assess the potentialities of the stack on the long term.

Physicochemical Characterization and Rheological Behavior Evaluation of the Liquid Crystalline Mesophases Developed with Different Silicones

This article presented physicochemical characterization and rheological behavior evaluation of the liquid crystalline mesophases developed with different silicones. There were prepared 5 ternary systems, which were carried out the determination of the relative density, the electric conductivity and polarized light microscopy analysis, being selected two systems to promote the Preliminary Stability Tests. The results showed that System 1 obtained the major liquid crystal formation and a higher stability. The temperature influences in the systems stability and phases structure. In hot oven, observed oneself the mixture of lamellar and hexagonal phase, for both systems.

Degradation of neonicotinoid insecticides by different advanced oxidation processes and studying the effect of ozone on TiO2 photocatalysis

Although some studies concerning the effect of pH and ozone dosage on TiO2 photocatalysis (O2/TiO2/UV) have already been published, no complete investigation and explanation of the effects of both parameters on photocatalytic ozonation (O3/TiO2/UV) have been carried out. Aqueous solutions of neonicotinoid insecticides (thiacloprid and imidacloprid) were chosen as a degradation medium, since they exhibit a high threat for aquatic systems and it is of great importance to find an effective method for their elimination from the environment. In preliminary stability tests, thiacloprid showed higher photo- and chemical stability compared to imidacloprid, therefore its degradation was studied in detail. To assess the suitability of various treatments for degradation and mineralization of thiacloprid in water at different pH values and ozone dosages, we applied ozonation (O3) and three different photochemical advanced oxidation processes, namely ozonation, coupled with UV radiation (O3/UV), O3/TiO2/UV and O2/TiO2/UV. Light source emitting mainly in UVA range was applied in all three processes. The photocatalytic ozonation (O3/TiO2/UV) was found to be the most efficient process irrespective of pH. The synergistic effect of ozone and TiO2 photocatalysis was noticed at acidic and neutral pH, but the synergism was lost at basic pH, probably due to faster self-decompositon of ozone under alkaline conditions. At acidic pH, also the oxidation of chloride anions to chlorate(V) was noticed in O3/TiO2/UV and in O3/UV processes. By plotting the disappearance rate constants of thiacloprid degradation in O3/TiO2/UV and O3/UV systems as a function of the flow rate of ozone, the synergistic effect of ozone was undoubtedly proven. The slope of the linear fit in case of O3/TiO2/UV process was considerably steeper than in case of O3/UV, which would not happen in absence of synergistic effect. The linearity in O3/TiO2/UV system was lost only at very high flow rates of ozone.

Thermal Optical Properties of Plasma-Sprayed Mullite Coatings for Space Launch Vehicles

Thermal optical properties, for example, solar absorptance a and thermal emittance e of thin plasma sprayed mullite coatings, were determined to assess the material's suitability for space application. The mullite coatings were developed in an attempt to find a new material for thermal protection systems as well as thermal barrier coatings for atmospheric reentry vehicles. All mullite coatings show the properties of a solar reflector and hence suggest a potential application as thermal control coating to protect space-bound structures from the effect of heating by solar radiation in the low Earth orbit. Preliminary space stability tests including atomic-oxygen resistance tests confirmed that the coatings show only negligible variations both in their mechanical and thermal optical properties under the conditions selected.

Enzyme/semiconductor nanoclusters combined systems for novel amperometric biosensors

In this work quantum-sized CdS nanocrystals were synthesized using a quaternary water-in-oil microemulsion and immobilized onto gold working electrode by self-assembled monolayers techniques. Formaldehyde dehydrogenase was covalently immobilized onto a protecting membrane, which was stratified on part of the semiconductor nanoparticles modified electrode. The covalent enzyme immobilization has been required to improve the stability of the catalytic oxidation of formaldehyde, which occurs after light stimulation of the semiconductor through the electron/hole recombination. A study about the best electrochemical oxidation potentials under different flow conditions was performed. Preliminary sensor stability and interferences tests were also carried out, for a sensitive and selective detection of formaldehyde. A detection limit of 41 ppb of formaldehyde was calculated and an operational stability of 6 h was achieved under flow conditions by means of this novel amperometric biosensor based on FDH-semiconductor hybrid systems, not requiring NAD +/NADH as charge transfer in the enzymatic reaction.

Lipophilic conjugates of idebenone with short and medium alkylamino acids: synthesis and antioxidant activity

Lipophilic conjugates of idebenone (IDE) were synthesized; they would be expected to possess a high degree of membrane-like character, thus facilitating the crossing of cell membranes. A carbodiimide-assisted (EDAC HCl) coupling reaction was used to link 2-alkylamino acids with increasing chain length (4 to 7 carbon atoms) to the primary hydroxyl group of IDE. A preliminary stability test was carried out to delineate the hydrolytic degradation of these conjugates into IDE, showing no sign of further degradation of the latter drug. The in vitro free-radical scavenging activity of IDE-conjugates was investigated, in particular the scavenger effect on superoxide anion test, their ability to bleach the stable DPPH radical, and the inhibition of lipid peroxidation in human plasma, as well as their capacity of inhibiting the xanthine oxidase activity. In all assays but the last one, compounds endowed with a short aminoacyl chain (C4 and C5) showed a strong dose-dependent antioxidant activity, close to or higher than IDE. This preliminary study indicated that the derivatization of IDE molecule did not suppress the biological antioxidant activity of the drug, and that the shorter-chain alkylamino acid esters showed higher activity as radical scavengers.

HIGH PERFORMANCE LIQUID CHROMATOGRAPHIC ASSAY FOR THE DETERMINATION OF QUERCETIN IN PLASMA

A sensitive, reproducible, simple, and accurate high performance liquid chromatographic (HPLC) method for the quantitative determination of quercetin in plasma has been developed and validated. Sample preparation involves simultaneous precipitation of plasma proteins and extraction of quercetin and kaempferol (the internal standard) from 0.1 mL plasma. The separation was performed in a stainless steel Ultrasphere-ODS column with a mobile phase consisted of a mixture of 30% acetonitrile and 70% of 5% acetic acid in HPLC water. The mobile phase was pumped at a flow rate of 1.5 mL/min and the effluent was monitored at 375 nm. The retention times for the drug and the internal standard were found to be 3.5 and 6.2 minutes, respectively. Peak-area ratios of the drug to the internal standard were used for quantitation of quercetin in plasma samples. The limit of detection of drug in plasma was found to be 0.06 μg/mL. The intra-day coefficient of variation (CV) ranged from 4.35% to 9.47%, and the inter-day CV ranged from 1.77% to 6.38% at three different concentrations. Mean absolute recoveries ranged from 96.52% to 101.19% and the relative recoveries ranged from 92.64% to 111.03% at three different concentrations. Preliminary stability tests showed that quercetin is stable for at least 8 weeks in plasma after freezing at -20°C. The method was applied for the determination of the pharmacokinetic parameters of quercetin after intravenous administration to three rats.

Stability constant determinations of alitame with H(I) and Cu(II) under physiological conditions using potentiometric measurements

Stability constant determinations of the new artificial sweetener alitame ( l-α-aspartyl- N-(2,2,4,4-tetramethyl-3-thietanyl)- d-alaninamide), an HL type ligand (L −=the deprotonated form of the ligand), was carried out with H(I) and Cu(II) under physiological conditions ( I=0.15(NaCl) in water, 37°C) using potentiometric titration. The molar concentration stability constants of H(I) and Cu(II) complexes with alitame, together with a distribution diagram of the Cu(II)-alitame complex species as a function of pH, are obtained. Cu(II) is able to form binary complex species (CuL +, CuL 2) with alitame in solution. Those species are further deprotonated to form the corresponding CuLH −1, CuLH −2 − and CuL 2H −1 − species. The neutral Cu(II)-alitame complex, CuL 2, is the major species between pH=6.5 and 7.5 followed by CuLH −1. A comparison with the less-stable artificial sweetener, aspartame ( N- l-α-aspartyl- l-phenylalanine 1-methyl ester), is considered. Preliminary stability tests for alitame and Cu(II)-alitame solutions, using pH and stability constant methods, are reported.

A Simple High-performance Liquid Chromatographic Assay for Loracarbef in Human Plasma

Abstract A simple, rapid and reproducible high-performance liquid chromatographic (HPLC) method for the determination of loracarbef in human plasma has been developed and evaluated. Plasma protein was precipitated with ammonium sulfate. The drug and the internal standard (Cefetamet) were eluted from a μ-bondapak C-18 column with a mobile phase consisting of acetonitrile:methanol:water:glacial acetic acid (2.5:17.5:79.2:0.8%, v/v). The column eluent was monitored at 265 nm. Quantification was achieved by the measurement of the peak-height ratio of the analyte to the internal standard and the limit of quantification for loracarbef in plasma is 0.5 ug/ml. The within-day coefficient of variation (CV) ranged from 2.28% to 3.67%, and between-day CV from 2.38% to 5.59% at three different concentrations. The absolute recoveries ranged from 91.1% to 93.88%, and the relative recoveries from 93.4% to 108% at three different concentrations. Preliminary stability tests showed that loracarbef is stable for at least 5-w...

A Simple High-performance Liquid Chromatographic Assay for Sparfloxacin in Human Plasma

Abstract A simple, rapid and selective high-performance liquid chromatographic (HPLC) method for the determination of sparfloxacin in human plasma has been developed and evaluated. Plasma protein was precipitated with acetonitrile. The drug and the internal standard (furosemide) were eluted from a Nova Pak C18 cartridge column at 50°C with a mobile phase consisting of 5% acetic acid:acetonitrile:methanol (70:15:15% v/v). The column eluent was monitored at 364 nm. Each analysis required no longer than 5 min. Quantification was achieved by the measurement of the peak-area ratio of the analyte to the internal standard and the limit of quantification for sparfloxacin in plasma is 25 ng/ml. The intraday coefficient of variation (CV) ranged from 1.71% to 6.1%, and interday CV from 2.60% to 4.28% at four different concentrations. The absolute recoveries ranged from 98.6% to 104%, and the relative recoveries from 93.6% to 116.4% at four different concentrations. Preliminary stability tests showed that sparfloxaci...

A Rapid and Sensitive High-Performance Liquid Chromatographic Method for the Determination of Metoclopramide in Plasma and Its Use In Pharmacokinetic Studies

Abstract A rapid and sensitive high-performance liquid chromatographic (HPLC) assay has been developed for the determination of metoclopramide in plasma. The assay is performed after single extraction of metoclopramide and diazepam (internal standard) from alkalinized plasma into ether and eluted from a Nova Pak C18-column with a mobile phase composed of acetonitrile:water (55:45%, v/v) adjusted to pH 3. The column eluent was monitored at 273 nm. Measurement was achieved by taking the peak-height ratios of the drug to the internal standard. The detection limit for metoclopramide in plasma is 5 ng/ml. Within-day coefficients of variation (CVs) ranged from 3.05 to 4.43% and between-day (CVs) from 4.1 to 5.7% at three different concentrations. Preliminary stability tests showed that metoclopramide is stable for at least 3 weeks in plasma after freezing. The method is applied for the determination of the pharmacokinetic parameters of metoclopramide after administration of two tablet formulations, to 4 healthy...

A simple high-performance liquid chromatographic assay for ciprofloxacin in human serum.

A simple and selective high-performance liquid chromatographic (HPLC) method for the determination of ciprofloxacin in serum has been developed and evaluated. Serum protein was precipitated with acetonitrile. The drug and the internal standard (quinine) were evaluated from a 10 microns U-Bondapack C-18 cartridge at ambient temperature with a mobile phase consisting of acetonitrile: 0.1 M sodium dihydrogen phosphate (20:80%, v/v) adjusted to pH 3.9 with phosphoric acid, and at a flow rate of 2.5 ml/min. The effluent was monitored on a fluorescence detector using an excitation and emission wavelength of 280 and 455 nm, respectively. Each analysis required no longer than 6 min. Quantification was achieved by the measurement of the peak-height ratio and the limit of quantification for ciprofloxacin in serum is 25 ng/ml. The intraday coefficient of variation (CV) ranged from 0.4 to 5.8%, and interday CV from 4.6 to 8.8% at three different concentrations. Relative recovery ranged from 98 to 100.2% at three different concentrations. Preliminary stability tests show that ciprofloxacin is stable for at least 3 weeks in serum after freezing.

A SENSITIVE HIGH-PERFORMANCE LIQUID CHROMATOGRAPHIC ANALYSIS OF PROPRANOLOL IN SERUM

A rapid and sensitive high-performance liquid chromatographic (HPLC) assay was developed for quantitative determination of propranolol in serum. The assay is performed after single extraction of propranolol and indenolol [internal standard (IS)] from alkalinized serum into ether and eluted from C-18 U Bondapak column with a mobile phase composed of methanol: 0.01 M phosphate buffer pH 3.4 (40:60%, v/v). The column eluant was monitored on a fluorescence detector. Measurement was achieved by taking the peak height ratio of propranolol and comparing it to that of the IS. The detection limit for propranolol in serum is 2.5 ng/ml. Intraday coefficients of variation (CV) ranged from 2.84 to 4.0% and interday (CVs) from 5.8 to 8.4% at three different concentrations. The relative and absolute recoveries varied from 93.8 to 102.3%. Preliminary stability tests showed that propranolol is stable for at least 3 weeks in serum after freezing. The method is applied for the determination of the pharmacokinetic parameters of propranolol after intravenous administration (1 mg/kg) to rabbits.

Evaluation of synthetic procedures for the chemical modification of alumina for HPLC

Several reactions are tested for the chemical modification of alumina. These include the following: chlorination of the surface hydroxyls followed by reaction with an organolithium compound; chlorination of the surface hydroxyls followed by reaction with a Grignard reagent; chlorination of the surface hydroxyls followed by reaction with an amine; chlorination of the surface hydroxyls followed by reaction with an alcohol; direct reaction of the alumina with an organochloroalane and direct reaction of the alumina with an alcohol. Only the first reaction gave a product which contained enough bonded organic material to be easily detected by FTIR. Preliminary stability tests show that the product of the first reaction retains the bonded organic material when exposed to nonpolar and polar organic solvents as well as aqueous solutions of pH 1.0, 7.0 and 12.0. Chromatographic testing establishes reversed-phase behavior for alkylarylketones as solutes and the bonded phase displays good biocompatibility for a series of protein standards.

Acetylation phenotyping of isoniazid using a simple and accurate high-performance liquid chromatography.

A simple, specific, accurate and reproducible method for the analysis of isoniazid and its major metabolite, N-acetylisoniazid in urine using high-performance liquid chromatography (HPLC) is described. The assay is performed after extraction of isoniazid, N-acetylisoniazid and 5-(4-methylphenyl)-5-phenylhydantoin (internal standard) from urine using a mixture of chloroform:isopropanol (70:30, v/v) and eluted from a 5 microns C-18 reversed phase column at ambient temperature with a mobile phase consisting of 10 mM sodium acetate:methanol:acetonitrile (40:40:20, v/v) containing 10 mM dioctylsulphosuccinate sodium and adjusted to pH 2.9 with sulphuric acid (less than 1 ml), at a flow rate of 1 ml/min with u.v. detection at 266 nm. Quantification was achieved by the measurement of the peak height ratio, and the absolute recoveries ranged from 94 to 99%. Within-day coefficients of variation ranged from 2.81 to 4.54% for isoniazid and from 2.37 to 3.75% for N-acetylisoniazid. Between-day CVs varied from 3.27 to 5.62% and from 2.5 to 4.91% for isoniazid and N-acetylisoniazid, respectively. Preliminary stability tests using a urine sample from a subject showed an increase in mean isoniazid concentration of about 25% after 1 month storage at -20 degrees C. The method was used for acetylation phenotyping of five individuals.

Preparation of new perfluoro ether fluids exhibiting excellent thermal-oxidative stabilities

A series of low molecular weight perfluoroalkylethers (PFAE) were synthesized by direct fluorination. Viscosity-temperature properties and oxidation stabilities were determined. Viscosity-temperature correlations indicated that increases in branching and increases in the size of the branching substituent caused a deterioration in viscometric properties (i.e., an increase in ASTM slope). In addition, increasing the ratio of carbon to oxygen in these compounds also increased the ASTM slope. Preliminary oxidation stability tests indicated that highly branched PFAE fluids. (i.e., those containing quaternary carbons) may be less stable than either those containing a single trifluoromethyl pendant group or those containing no branching at all.

Determination of two Fenamates in Plasma by High-performance Liquid Chromatography

A high-performance liquid chromatographic determination of two fenamates in human plasma is described. Plasma samples, 1.0 ml, to which 4 μg of internal standard had been added, were extracted with carbon tetrachloride under acidic conditions. Portions of the organic layer were transferred and evaporated to dryness under nitrogen. Residues were dissolved in methanol, and an aliquot was injected into the liquid chromatograph. An intermediate polarity, bonded cyanopropylsilane column was used with a mobile phase of water-acetonitrile-acetic acid (60:30:10 v/v/v). The flow rate was 1 ml/min, and the effluent was monitored at 254nm. Flufenamic acid and mefenamic acid had retention times of 10.4 and 9.2 min, respectively. In the 1-10-μg range, the mean flufenamic acid recovery from control plasma was 100.7 ± 3.4% (n = 18). A typical calibration curve had a regression equation of y = 0.132x − 0.04 with γ2 = 0.99. Preliminary stability tests showed that flufenamic acid is stable for at least 2weeks in plasma after freezing.