Influence of the storage conditions on the concentration of clenbuterol in cattle urine samples

A study of the stability of clenbuterol in cattle urine samples under different time and temperature storing conditions is reported. At the farm, urine samples were spiked with several amounts of this compound. Then, they were immediately transported to the laboratory and stored at room temperature, between 4 and 8 °C and frozen. Clenbuterol was quantified by using high performance liquid chromatography with diode-array detection (HPLC-PDA) on days 1, 7 and 42 after sample collection. The drug concentration in frozen urine samples was apparently stable during the whole studied period. However, there was a notable decrease in the concentration of this analyte when samples were stored at room temperature and between 4 and 8 °C, specially during the first week. A complementary study showed that the decrease in clenbuterol concentration was particularly significant from 1st to 4th day after sample collection and when urine specimens were kept at room temperature. Based on the results of this study, it was concluded that sample freezing as soon as possible after collection is the most adequate way to guarantee that the reliable concentration of clenbuterol in urine specimens remains unchanging until sample analysis.     

The influence of temperature and different storage conditions on the stability of supersulphated cement

The stability of Supersulphated Cement (SSC) is investigated at 95°C when subjected to relative humidities of 100, 53 and 11% of water vapour. Previously [1] investigations at 25, 50, 75°C under the same conditions of humidity reported the stability of ettringite, one of the initial hydration products. At 95°C, decomposition of ettringite, is found at all humidities and is rapid at 100% relative humidity. The hydration products of cement pastes at a water cement ratio of 0.27 were determined by thermogravimetry (TG) and X-ray diffraction (XRD). The formation of the hydragarnet, plazolite is recorded during the decomposition/dehydration process enhanced by possible carbonation. Rehydration studies on the products after storage for up to 9 months were carried out using distilled water and the samples tested for ettringite content. It is concluded that ettringite in SSC is inherently unstable at 95°C.     

The influence of temperature and different storage conditions on the stability of supersulphated cement

The stability of supersulphated cement (SSC) is investigated. The hydration products of cement pastes prepared at a water cement ratio of 0.27 were determined by thermogravimetry (TG) and X-ray diffraction (XRD). Ettringite, one of the initial hydration products, is shown to be stable under conditions of storage at 25, 50 and 75°C and when subject to relative humidities of 100, 53 and 11% of water vapour in each case. The effect of drying on ettringite stability at the higher temperatures is discussed in relation to the relative humidity. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Influence of the storage on the thermo-oxidative stability of methyl and ethyl esters by PDSC

Biodiesel oxidation is a complex process widely influenced by the chemical composition of the biofuel and storage conditions. Several oxidation products can be formed from these processes, depending on type and amount of the unsaturated fatty acid esters. In this work, fatty acid methyl and ethyl esters were obtained by base-catalyzed transesterification of soybean oil and physicochemically characterized according to standards from ASTM, EN, and ABNT. The thermal and oxidative stabilities of biodiesel samples were investigated during the storage process by pressure differential scanning calorimetry (PDSC) and by viscosity measurements. Absolute viscosities of biodiesels after accelerated aging were also determined. The viscosity increased as the aging temperature and time were raised. The results showed that oxidation induction can occur during storage, decreasing the biodiesel stability. PDSC analysis showed that during storage under climate simulation the values of high-pressure oxidative induction times (HPOIT) were reduced for both FAEE and FAME.     

Influence of salt and acetonitrile on the capillary zone electrophoresis analysis of imatinib in plasma samples

A simple, sensitive, specific, and cost‐effective analytical methodology was developed for the analysis of human plasma samples spiked with imatinib by CZE with on‐line UV detection in the context of Therapeutic Drug Monitoring. Several analytical conditions such as the ionic strength (I) and the pH of the BGE composed of citric acid and ε‐amino caproic acid were studied in regards of the presence of sodium chloride (NaCl) in plasma samples (1% m/v). Computer simulations (Simul software) were used to confirm the experimental results and to understand imatinib electrophoretic behavior in the presence of NaCl. Furthermore, the advantages of adding ACN to the sample containing NaCl to combine efficient protein precipitation and on‐line CZE stacking of imatinib were demonstrated. LOD and LOQ values of 48 and 191 ng/mL were obtained from plasma sample supernatant after protein precipitation with ACN, which is much lower than mean imatinib plasma level observed for patients treated by imatinib mesylate (about 1000 ng/mL). Good linearity was obtained in the concentration range 191–5000 ng/mL (R² > 0.997). RSD of less than 1.68% and 2.60% (n = 6) for migration times and corrected peak areas, respectively, were observed at the LOQ.     

Influence of substrate temperature on the stability of glasses prepared by vapor deposition

Physical vapor deposition of indomethacin (IMC) was used to prepare glasses with unusual thermodynamic and kinetic stability. By varying the substrate temperature during the deposition from 190 K to the glass transition temperature (Tg=315 K), it was determined that depositions near 0.85Tg (265 K) resulted in the most stable IMC glasses regardless of substrate. Differential scanning calorimetry of samples deposited at 265 K indicated that the enthalpy was 8 J/g less than the ordinary glass prepared by cooling the liquid, corresponding to a 20 K reduction in the fictive temperature. Deposition at 265 K also resulted in the greatest kinetic stability, as indicated by the highest onset temperature. The most stable vapor-deposited IMC glasses had thermodynamic stabilities equivalent to ordinary glasses aged at 295 K for 7 months. We attribute the creation of stable IMC glasses via vapor deposition to enhanced surface mobility. At substrate temperatures near 0.6Tg, this mobility is diminished or absent, resulting in low stability, vapor-deposited glasses.     

An effective and economical method for the storage of plasma samples using a novel freeze-drying device

Biological samples, especially plasma samples, are conventionally stored under freezing conditions to maintain sample integrity prior to the detections of analytes. However, the storage of samples in a low-temperature environment is electric energy consuming, and the preparation of samples prior to analytes detection may be complicated. In this work, an effective and economical method was proposed to freeze-dry the samples using a novel device to allow subsequent storage of samples at ambient temperature. The sample preparations integrated in the new method are simple and easy to follow. Analytes were directly extracted with the extraction agent before sample injections. This new method was validated with quality control (QC) samples of levetiracetam and mycophenolic acid (MPA), and it was also applied to the pharmacokinetic (PK) studies of both drugs in healthy volunteers. When QC samples were stored and prepared with the new method, the detections of analytes were accurate and repeatable, and the analytes maintained stability for a long time. The PK studies of levetiracetam and MPA in healthy volunteers showed that the PK parameters of analytes stored with the new method were consistent with those stored with the conventional method. In conclusion, this effective and economical method is a practical option in reality and can play a big role in clinical and scientific drug researches.     

Influence of sample temperature on the expansion dynamics and the optical emission of laser-induced plasma

We investigate the influence of sample temperature on the dynamics and optical emission of laser induced plasma for various solid materials. Bulk aluminum alloy, silicon wafer, and metallurgical slag samples are heated to temperature T_S ≤ 500 °C and ablated in air by Nd:YAG laser pulses (wavelength 1064 nm, pulse duration approx. 7 ns). The plasma dynamics is investigated by fast time-resolved photography. For laser-induced breakdown spectroscopy (LIBS) the optical emission of plasma is measured by Echelle spectrometers in combination with intensified CCD cameras. For all sample materials the temporal evolution of plume size and broadband plasma emission vary systematically with T_S. The size and brightness of expanding plumes increase at higher T_S while the mean intensity remains independent of temperature. The intensity of emission lines increases with temperature for all samples. Plasma temperature and electron number density do not vary with T_S. We apply the calibration-free LIBS method to determine the concentration of major oxides in slag and find good agreement to reference data up to T_S = 450 °C. The LIBS analysis of multi-component materials at high temperature is of interest for technical applications, e.g. in industrial production processes.     

Simultaneous determination of epinephrine and norepinephrine in human blood plasma and urine samples using nanotubes modified edge plane pyrolytic graphite electrode

The simultaneous determination of catecholamines - epinephrine and norepinephrine by square wave voltammetry (SWV) at physiological pH 7.2 is reported using multi-walled carbon nanotubes modified edge plane pyrolytic graphite electrode (MWNT/EPPGE). A broad bump at ∼250 mV is appeared for the oxidation of epinephrine (EP) and norepinephrine (NE) at bare EPPGE whereas at MWNT/EPPGE two well-separated peaks at ∼150 and ∼215 mV are appeared for the oxidation of EP and NE, respectively. The oxidation peak current of both the neurotransmitters also increased significantly along with the negative shift of peak potentials using MWNT/EPPGE. The oxidation of both compounds occurred in a pH dependent, 2e and 2H⁺ process and the electrode reaction followed diffusion controlled pathway. Linear calibration curves were obtained for epinephrine and norepinephrine in the range 0.5-100 nM with limits of detection 0.15 × 10⁻⁹ and 0.90 × 10⁻¹⁰ M, respectively. The developed protocol is implemented for the simultaneous determination of epinephrine and norepinephrine in blood plasma and urine samples of smokers as well as in athletes.     

Influence of temperature on the colloidal stability of the F-DPPC and DPPC liposomes induced by lanthanum ions

The influence of La(3+) on the colloidal stability of liposomes made up by two zwitterionic phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-[16-fluoropalmitoyl-phosphatidylcholine (F-DPPC), in aqueous media has been investigated by dynamic light scattering and electrophoretic mobility. The critical aggregation concentration (c.a.c.) of La(3+) for F-DPPC and DPPC liposomes were experimentally obtained, and the results were compared with theoretical predictions using the Derjaguin-Landau-Verwey-Overbeek theory. In order to evaluate the influence of the state of the bilayer on the stability of liposomes, all experiments were performed at temperatures below and above the chain-melting phase-transition temperature of lipids (transition temperature of lipids). Changes in the size of both types of liposomes and high values of polydispersity in the presence of La(3+) showed that these ions induce aggregation of liposomes at 25 °C and at 60 °C. At 25 °C, when the bilayer of F-DPPC liposomes is interdigited, DPPC liposomes are more resistant to aggregation than the liposomes formed with F-DPPC. However, this difference disappears at 60 °C, when both bilayers have the same conformation. The experimental results also indicate that the c.a.c. is higher at 60 °C than at 25 °C for both types of liposomes. In fact, it has been observed by dynamic light scattering measurements that aggregation of liposomes at 25 °C can be prevented by increasing the solution temperature for La(3+) concentrations near to the c.a.c. Moreover, the behavior of these liposomes in the presence of the ion was studied at temperatures above and below the transition temperature of the phospholipids.     

Influence of velocity and surface temperature of alumina particles on the properties of plasma sprayed coatings

In this paper are described the main characteristics of the plasma spraying process of alumina deposits, i.e., the temperature and flow field of the plasma jets obtained with the classical spraying torches, the injection of the particles into the plasma jet, the particle surface temperature and velocities in the plasma (measured for calibrated alumina particles), and the coating generation. The measurements on the alumina particles are compared with the predictions of a mathematical model. The experimental and computed particle velocities are in rather good agreement. However, this is not the case for the particle surface temperature. Possible reasons for the discrepancy are proposed (influence of the carrier gas, thermophoretic forces, and poor penetration of the particles into the plasma core even for an injection velocity twice that of the optimal calculated one, as shown by recent measurements). Finally the correlations between the particle velocities and surface temperature, and the properties of the alumina coating (porosity, crystal structure, mechanical properties) are studied.     

Studies on the stability of acrylamide in food during storage

Acrylamide levels in a variety of food samples were analyzed before and after 3 months of storage at 10 degrees-12 degrees C. The analysis was performed by liquid chromatography tandem mass spectrometry (LC/MS/MS) using deuterium-labeled acrylamide as internal standard. Acrylamide was stable in most matrixes (cookies, cornflakes, crispbread, raw sugar, potato crisps, peanuts) over time. However, slight decreases were determined for dietary biscuits (83-89%) and for licorice confection (82%). For coffee and cacao powder, a significant decrease occurred during storage for 3 or 6 months, respectively. Acrylamide concentrations dropped from 305 to 210 microg/kg in coffee and from 265 to 180 microg/kg in cacao powder. On the contrary, acrylamide remained stable in soluble coffee as well as in coffee substitutes. Reactions of acrylamide with SH group-containing substances were assumed as the cause for acrylamide degradation in coffee and cacao. Spiking experiments with acrylamide revealed that acrylamide concentrations remained stable in baby food, cola, and beer; however, recovery levels dropped in milk powder (71%), sulfurized apricot (53%), and cacao powder (17%). These observations suggest that variations in the acrylamide content of food, especially in coffee and cacao, can vary depending on the storage time because special food constituents and/or reaction products can affect the levels.     

Characterisation of different inulin samples by DSC: Influence of polymerisation degree on melting temperature

Melting behaviour of powder inulin has been studied by differential scanning calorimetry. DSC curves show two endothermic peaks, relative to water elimination and to inulin melting, respectively. The second peak is dependent on inulin type and a shift to a higher temperature is observed with increasing average polymerisation degree (DP) of the sample. For similar crystallinity index, linear relations have been underlined and so predicting inulin mean DP can be done by DSC analysis. The study shows that a relatively high heating rate (25°C min^–1) can be used and brings a supplementary interest by an important reduction of analysis time.This revised version was published online in November 2005 with corrections to the Cover Date.     

Influence of temperature on the preparation of CoFe2O4 by the sol-gel method and its application in electrochemical energy storage

Journal of Solid State Electrochemistry - CoFe2O4 particles were successfully synthesized by a sol-gel proteic route in three different temperatures, and their structural and morphological...     

Investigation on stability and preservation of antimonite in iron rich water samples

The stability of antimonite in iron rich water samples is rather poor. The aim of the study was to find a simple procedure by using preservation agents to keep the speciation information from sampling till analysis. Species analysis of antimony traces (lower μg L⁻¹ range) was done by HPLC–ICP-MS. Phosphoric acid, tartrate, and EDTA were tested as preservation agents in comparison to no addition. The use of EDTA as the preservation agent provided the best results. The suggested procedure is to add 20 mM EDTA as final concentration immediately during sampling and store them at dark and cool (6 °C) as usual. Using this procedure, the stability of Sb(III) as well as of Sb(V) was proven for at least 7 days, even for high iron concentrations.     

生物油储存稳定性实验研究

对松木和玉米芯快速热解制取的生物油进行储存稳定性实验,经过储存老化后的生物油黏度增大,水分含量和固体颗粒物含量增加,pH值、热值、密度无明显变化。通过GC-MS对储存前后生物油中主要组分进行定量分析表明,生物油经过储存后,羟基丙酮、乙酸、糠醛等主要组分的含量明显下降,而2-甲氧基苯酚、4-甲基-2-甲氧基-苯酚、4-甲基-苯酚的含量有所上升。核磁共振的碳谱分析表明,经过储存后生物油中甲氧基碳和双氧-烷基碳的含量降低,而芳基碳和不饱和碳的含量增大,生物油的芳香度有所提高。     

Characterization and storage stability analysis of bio-oil

对松木和玉米芯快速热解制取的生物油进行储存稳定性实验,经过储存老化后的生物油黏度增大,水分含量和固体颗粒物含量增加,pH值、热值、密度无明显变化.通过GC-MS对储存前后生物油中主要组分进行定量分析表明,生物油经过储存后,羟基丙酮、乙酸、糠醛等主要组分的含量明显下降,而2-甲氧基苯酚、4-甲基-2-甲氧基-苯酚、4-甲基-苯酚的含量有所上升.核磁共振的碳谱分析表明,经过储存后生物油中甲氧基碳和双氧-烷基碳的含量降低,而芳基碳和不饱和碳的含量增大,生物油的芳香度有所提高.     

Thermal degradation and stability of epoxy nanocomposites: Influence of montmorillonite content and cure temperature

The thermal behaviour and stability of epoxy nanocomposites were studied by thermogravimetric analysis (TGA). The nanocomposites consisted of a trifunctional epoxy resin, a hardener containing reactive primary amine groups and clay nanoparticles (i.e. montmorillonite), previously treated with octadecyl ammonium. Three levels of nanoclay content (0, 5 and 10%) and three temperature levels (120, 150 and 200 °C) were used. The exfoliation of nanoparticles within the material was analyzed by X-ray diffraction (XRD). The cure conversion was determined by Fourier transform infrared (FTIR) spectroscopy by selecting the suitable band for epoxide functional groups. The study demonstrated that the nanoclay greatly accelerates the cure, at the different cure temperatures studied. Finally, the thermal stability of the various nanocomposites was established by calculating various characteristic temperatures from thermograms as well as conversion and conversion derivative at maximum decomposition rate. The collisions between resin molecules, which are trapped within the nanoclay galleries, were less effective because they were protected against thermal degradation by the galleries. However, once the collision was effective, the thermal activation occurred more readily.