Relationships of Acid and water content to proton transport in statistically sulfonated proton exchange membranes: variation of water content via control of relative humidity

An in-depth analysis for proton exchange membranes to examine the effects of acid concentration and effective proton mobility upon proton conductivity as well as their relationship to water content was carried out on two main-chain, statistically sulfonated polymers at 25 degrees C. These polymer systems consisted of poly(ethylenetetrafluoroethylene-graft-polystyrenesulfonic acid) (1) and sulfonated trifluorostyrene (BAM) membrane (2). Nafion (3) was used for comparison. Water content (as represented by Xv, the water volume fraction, where Xv = volume of water in hydrated PEM / volume of hydrated PEM), for each sample was varied by adjusting the relative humidity (RH) of the membrane environment from 50% to 98%. It was found that, at low RH (RH < 70%), the major factor determining proton conductivity is proton mobility. In order to remove the differences in acid strength for the membranes, proton mobility values at infinite dilution (Xv = 1.0) and 25 degrees C were calculated and found to be 2.6 +/- 0.2 x 10-3 (average of 1a-c), 1.6 +/- 0.3 x 10-3 (average of 2a-e), and 2.32 +/- 0.01 x 10-3 cm2 s-1 V-1 (3). These were then compared to the theoretical value for the mobility of a free proton at infinite dilution and to previously reported data. Possible differences in tortuosity and the juxtaposition of acid groups are proposed in order to account for the significant deviations of all samples from the theoretical value.     

Absolute humidity measurement utilizing alpha-ray absorption

Changes in air density due to humidity were measured by a scintillation detector with alpha-particles. The distance between the scintillator and an alpha-ray source of 241 Am, 3.7 MBq (100 microCi), was fixed at 25 mm which was a little shorter than the range of alpha-particles from the source. The measured absolute humidities were in a range of 7.9 g/m3 to 52.2 g/m3 at temperatures of 35 degrees C and 45 degrees C and under atmospheric pressure. The counting rate of alpha-particles in an absolute humidity of 31.7 g/m3 (80% in relative humidity) at 35 degrees C increased 28% compared with that in dry air. From experimental results and theoretical calculation, the counting rate difference between humid air and dry air was shown to be almost proportional to the absolute humidity in air. The absolute humidity can be measured with an accuracy of +/- 3 g/m3, that is +/- 5% in relative humidity at 45 degrees C.     

Effects of moisture on glass transition and microstructure of glycerol-plasticized soy protein

The glass transition behavior of the glycerol-plasticized soy protein sheets (SL series) at various relative humidity (RH) was investigated by using differential scanning calorimetry with the aluminum pan and O-ring-sealed stainless steel capsule, and the microstructure of these sheets was detected on small-angle X-ray scattering. The results revealed that there were three glass transitions (Tg1, Tg2 and Tg3), corresponding to glycerol-rich, protein-rich and protein-water domains, in the protein-glycerol-water ternary system. The Tg1 values of the SL-series sheets at 75% RH decreased from -49.3 to -83.8 degrees C with an increase of glycerol content from 10 to 50 wt.-%, whereas Tg2 and Tg3 were almost invariable at about 60 degrees C and 3 degrees C, respectively. In addition, the Tg1, Tg2 and Tg3 values of the SL-25 containing 25 wt.-% glycerol at 0%, 35%, 58%, 75% and 98% RH were in the range of -12.7 - -83.2 degrees C, 65.8 - 53.1 degrees C and 3.5 - 1.9 degrees C, respectively. The result from small-angle X-ray scattering indicated that the radii of gyration (Rg) of protein-rich domain were in the range of 60-63 nm; this suggested the existence of protein macromolecules as aggregates in the stable protein-rich and protein-water domains. With an increase of RH, the tensile strength and Tg values of the SL-series sheets decreased, but the elongation at break increased. In view of the results above, the moisture in ambient environment significantly influenced the Tg values and microstructures of the glycerol-plasticized soy protein sheets, leading to the changes of the mechanical and thermal properties.     

HPLC determination of andrographolide in rat whole blood: study on the pharmacokinetics of andrographolide incorporated in liposomes and tablets

A sensitive and simple high-performance liquid chromatographic method with UV detection was developed and validated for the determination of andrographolide in rat whole blood. Carbamazepine was employed as internal standard and the blood sample was extracted with chloroform. Chromatographic separations were achieved on a Chromasil ODS column (250 x 4.6 mm, 5 microm). The mobile phase was consisted of methanol-water (52:48, v/v) and delivered at 0.8 mL/min. The detection wavelength was set at 225 nm. The calibration curve had a good linearity in the range 0.053-530 microg/mL in rat whole blood with its correlation coefficient being 0.996. The extraction recovery of andrographolide was ranged from 65.7 to 72.6%. The intra-day and inter-days repeatabilities were below 4.2% in terms of the percentage of relative standard deviation (RSD). The method was used to provide data on the pharmacokinetics of the drug in rats. The data obtained was processed using the 3P87 pharmacokinetic program. The results showed that the disposition of andrographolide after intravenous administration of liposomal andrographolide conformed to a two-compartment open model with alpha = 4.75 x 10(-2) +/- 2.41 x 10(-3) min(-1), beta = 3.16 x 10(-3) +/- 1.58 x 10(-4) min(-1), V(c) = 174.67 +/- 13.97 mL, k(21) = 1.60 x 10(-2) +/- 8.12 x 10(-4) min(-1), k(10) = 9.38 x 10(-3) +/- 5.62 x 10(-4) min(-1), k(12) = 2.53 x 10(-2) +/- 1.27 x 10(-3) min(-1) and AUC(0-infinity) = 1525.47 +/- 92.35 microg min/mL. For the intragastric administration of andrographolide tablets, the disposition of andrographolide followed a one-compartment open model with k(e) = 6.78 x 10(-3) +/- 3.53 x 10(-4) min(-1), k(a) = 3.69 x 10(-2) +/- 4.68 x 10(-3) min(-1), T(max) = 59.69 +/- 3.61 min, C(max) = 1.62 +/- 0.11 microg/mL, V(c) = 1056.90 +/- 83.42 mL, AUC(0-infinity) = 348.75 +/- 24.41 microg min/mL.     

Growth and structure of water on SiO2 films on Si Investigated by Kelvin probe microscopy and in Situ X-ray spectroscopies

The growth of water on thin SiO2 films on Si wafers at vapor pressures between 1.5 and 4 Torr and temperatures between -10 and 21 degrees C has been studied in situ using Kelvin probe microscopy and X-ray photoemission and absorption spectroscopies. From 0 to 75% relative humidity (RH), water adsorbs forming a uniform film 4-5 layers thick. The surface potential increases in that RH range by about 400 mV and remains constant upon further increase of the RH. Above 75% RH, the water film grows rapidly, reaching 6-7 monolayers at around 90% RH and forming a macroscopic drop near 100%. The O K-edge near-edge X-ray absorption spectrum around 75% RH is similar to that of liquid water (imperfect H-bonding coordination) at temperatures above 0 degrees C and is ice-like below 0 degrees C.     

Kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD)

The kinetics of thermal decomposition of 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD), an arenediazonium ion newly developed as a derivatizing reagent for drug analysis, are described. The arenediazonium ion, in an optimized concentrated sulfuric acid/orthophosphoric acid medium, was incubated for various time intervals at 30 degrees, 45 degrees, 55 degrees , 65 degrees , 75 degrees, and 85 degrees C. The amount of ion left after each time interval was quantified selectively by colorimetric assay at 490 nm, using mefenamic acid as a model diazo-coupling component. The rate constants for the decomposition were determined graphically. An Arrhenius plot was used to delineate the dependence of the rate constant on temperature and to predict the half-life at 25 degrees C and lower temperatures. The diazonium ion decomposed by first-order kinetics. The rate constants of decomposition, which increased progressively with temperature, were 3.18 +/- 0.41 x 10(-5), 1.19 +/- 0.07 x 10(-4), 4.87 +/- 0.15 x 10(-4), 12.88 +/- 0.73 x 10(-4), and 21.32 +/- 2.74 x 10(-4) (s(-1)) with corresponding half-lives of 363, 97.06, 23.72, 8.97, and 5.42 min at 30 degrees, 45 degrees, 55 degrees, 65 degrees, and 75 degrees C, respectively. CDNBD is highly stable in concentrated acid medium, with half-life values of about 10 h, 10 days, and 7.3 months at 25 degrees, 0 degrees, and -20 degrees C, respectively. The reagent stability profile shows that it could be readily adapted for routine applications in instrumental chemical analysis.     

气相色谱-质谱法分析橡苔浸膏中的挥发性化学成分

 用挥发油提取器提取橡苔浸膏中的挥发油,利用气相色谱-质谱法(GC-MS)分析了其中的化学成分,采用GC峰面积归一化法定量,鉴定出24种化合物,共占挥发油总量的83%以上     

反相高效液相法测定穿心莲药材及其制剂中的穿心莲内酯和脱水穿心莲内酯

 发展了穿心莲药材及其中成药中两种主要成分穿心莲内酯和脱水穿心莲内酯的反相高效液相测定方法。采用甲醇振荡提取法进行样品前处理 ,在以乙腈 水为流动相作梯度洗脱、ODS柱、检测波长为 2 2 5nm的条件下 ,穿心莲内酯和脱水穿心莲内酯在 1 5min内可达到基线分离。两种内酯在 1 0mg/L～ 1 0 0mg/L时其浓度与峰面积成良好的线性关系 ,加标回收率为 96 %～ 1 0 4 %。     

Effect of microwave dielectric heating on intraparticle diffusion in reversed-phase liquid chromatography

The influence of microwave (MW) irradiation on the mass transfer kinetics in reversed-phase liquid chromatography (RPLC) was studied by placing a column in a microwave oven and measuring the incremental change in the temperature of the column effluent stream at various microwave energies and mobile phase compositions. The microwave energy dissipated in the column was set between 15 and 200 W and the mobile phase composition used varied from 100 to 70, 50, and 10% methanol in water at 1.2 mL/min. At all the mobile phase compositions considered, the effluent temperature increased with increasing microwave energy. At 70% methanol, the mobile phase flow rate was set at 1.2, 2.0, and 2.8 mL/min. At 1.2 mL/min, the effluent temperatures at the lowest (15 W) and highest (200 W) microwave energy inputs were 25 +/- 1 degrees C and 41 +/- 1 degrees C for pure methanol, 25 +/- 1 degrees C and 48 +/- 1 degrees C for 70% methanol, 25 +/- 1 degrees C and 50 +/- 1 degrees C for 50% methanol, and, 25 +/- 1 degrees C and 52 +/- 1 degrees C for 10% methanol, respectively. With 70% methanol and microwave energy inputs of 15, 30, and 50 W, the effluent temperature did not change with increasing flow rate; a considerable change was observed at 100, 150, and 200 W between 1.2 and 2.0 mL/min and none between 2.0 and 2.8 mL/min. Chromatographic elution band profiles of propylbenzene were recorded under linear conditions, in 70% methanol solutions, for microwave energy inputs of 0, 15 and 30 W, at constant temperature. The intraparticle diffusion coefficient, De, under microwave irradiation was ca. 20% higher than without irradiation. These preliminary results suggest that microwave irradiation may have a considerable influence on intraparticle diffusion in RPLC.     

Properties of composite proton-conducting membranes prepared from three-dimensionally ordered macroporous polyimide matrix and polyelectrolyte

A new proton-conducting composite membrane has been prepared by use of a three-dimensionally ordered macroporous matrix of polyimide and a proton-conducting gel polymer; the resulting composite membrane exhibited very high conductivity of 1.7 x 10-1 S cm-1 at 60 degrees C under 90% relative humidity.     

Separation of polyethylene glycol oligomers using inverse temperature programming in packed capillary liquid chromatography

Inverse temperature programming in packed capillary liquid chromatography coupled to evaporative light-scattering detection has been used to resolve native polyethylene glycol (PEG) oligomers. The model compound, PEG 1000, was separated on a 300 mm x 0.32 mm I.D. capillary column packed with 3 microm Hypersil ODS particles with acetonitrile-water (30:70, v/v) as mobile phase. The retention of the PEG oligomers increased with increasing temperature, different from what is commonly observed in liquid chromatography. The retention times of the oligomers were approximately doubled for each 25 degrees C increment of the column temperature in the temperature range 30-80 degrees C. The oligomers were almost unretained and co-eluted at a column temperature of 30 degrees C. At 80 degrees C a baseline separation of more than 22 peaks was obtained, but the last eluting peaks were severely broadened and all oligomers did not elute. When a negatively sloped temperature ramp from 80 to 25 degrees C at -1.5 degrees C/min was applied, the peak shapes were improved, additional peaks were detected and the analysis time was reduced by 48%. In the temperature programming mode, the intra-day precision of the retention times ranged from 0.5 to 5.8% (n=5).     

Photosensitized heterogeneous chemistry of ozone on organic films

The interactions of ozone with benzophenone and phenol solid films have been investigated under simulated atmospheric conditions with respect to relative humidity, pressure, temperature, and O3 concentration using a coated flow tube reactor. The steady-state reactive uptake coefficients (gammass) of ozone on benzophenone films ranged from below 10(-6) in dark conditions to approximately 4 x 10(-6) under UV-A irradiation and decreased with increasing O3 concentration in the range 28-320 ppbv. A similar trend was observed for the initial uptake coefficient (gammai) which varied from ca. 1.5 x 10(-6) in the dark to approximately 7 x 10(-6) under UV-A irradiation. The uptake coefficients under irradiation were strongly dependent on the relative humidity (from 5 to 70%), with their lowest values at high humidity (70% RH). The ozone uptakes for multilayer coverage turned out to be independent of the deposited mass of the organic compound. The benzophenone-phenol mixture also showed photoenhanced uptake with a larger steady-state uptake under visible irradiation, approximately 2.9 x 10(-6). Contact angle measurements showed an increase of the organic film hydrophobicity for the benzophenone-phenol mixture upon combined exposure to light and ozone. A linear dependence of the kinetic values on the photon flux has been demonstrated and when extrapolated to the solar spectral irradiance would lead to uptake coefficients of approximately 10(-5). UV-vis analysis and contact angle measurements of the organic film after irradiation and ozone exposure showed relevant changes only in the mixture, with an increase in the hydrophobic character of the film and the appearance of a new absorption band up to 450 nm.     

Determination of 1-(2-methoxyphenyl)piperazine derivatives of isocyanates at low concentrations by temperature-programmed miniaturized liquid chromatography

A temperature-programmed packed capillary LC method with large-volume injection on-column focusing has been developed for screening and determination of 1-(2-methoxyphenyl)piperazine derivatives of airborne toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, hexamethylenediisocyanate and methylenebisphenyl-4,4-diisocyanate, based on sampling methods described in MDHS 25/3. Injection volumes up to 100 microl were successfully loaded onto the 250x0.32 mm I.D. capillary column packed with 3 microm Hypersil ODS particles. The isocyanate derivatives were loaded at 10 degrees C and eluted by a three-step temperature program starting at 10 degrees C for 10 min, followed by a temperature ramp of 2.5 degrees C min(-1) to 45 degrees C and then 9.9 degrees C min(-1) to 90 degrees C. The mobile phase consisted of acetonitrile-acetate buffer (3% triethylamine, pH 4.5) (45:55, v/v). The isocyanate derivatives were dissolved in acetonitrile-acetate buffer (3% triethylamine, pH 4.5) (30:70, v/v) to achieve sufficient focusing. The concentration limit of detection of the individual derivatives utilizing an "U" shaped flow cell with a 8.0 mm light path and an injection volume of 100 microl was 44, 87, 43 and 210 pg ml(-1) for toluene-2,6-diisocyanate, hexamethylenediisocyanate, toluene-2,4-diisocyanate and methylenebisphenyl-4,4-diisocyanate, respectively. Within the investigated concentration range, 10-500 ng ml(-1), the linear calibration curves gave correlation coefficients ranging from 0.994 to 0.998. The repeatability of the method with regard to retention time and peak height ranged from 0.3 to 1.1% and 1.1 to 2.3% (n=9) relative standard deviation, respectively. The average recovery of the method, with regard to toluene-2,4-diisocyanate, was 97.7+/-1.6% (n=9).     

毛细管电泳扫描伏安电化学法分离检测肾上腺素、氯丙嗪和异丙嗪

采用自制的高效毛细管电泳扫描伏安电化学检测装置,在磷酸盐缓冲溶液中进行了肾上腺素、异丙嗪和氯丙嗪的分离检测,在优化的条件下获得了较好的检测重现性和低的检出限。结果表明,采用扫描伏安电化学方法不但能够减少电极的污染,而且可以在电泳过程中获得被测物质的伏安特性及检测体系的动态伏安图,更有利于被测物质的识别。     

Micellar electrokinetic chromatography method for the determination of sulfamethoxazole, trimethoprim and their main metabolites in human serum

A complete analytical procedure, including sample clean-up and a micellar electrokinetic chromatographic method, is presented for the determination of sulfamethoxazole, trimethoprim, and their main metabolites by using 20 mmol L(-1) borate buffer (pH 9.3), 25 mmol L(-1) sodium dodecylsulfate, and 5% v/v acetonitrile as electrolyte. The separation was carried out at 30 kV and 20 degrees C in a fused silica capillary (60.2 cm x 75 microm inner diameter) fitted with a window in the capillary cartridge of 100 x 800 microm. The detector response was linear from the limit of quantification to 3 mg L(-1) for the individual components. The limits of quantification ranged from 0.13 up to 0.24 mg L(-1). The method was applied to human serum, previously spiked at different concentrations of all the analytes, and recoveries between 95% and 108% were obtained.     

Water sorption isotherms on aminopropyltriethoxysilane coated surface acoustic wave sensors

Water sorption isotherms were obtained on surface acoustic wave sensors (SAWS) coated with aminopropyltriethyoxysilane (APTES), and on uncoated SAWS of which the substrate material was polished ST-quartz. The isotherms were obtained at 25 degrees , 30 degrees and 40 degrees over the range 1-80% relative humidity (RH). The isotherms exhibit BDDT type III characteristics typical of weak gas-solid interaction. The isotherms showed good fit to quadratic equations relating frequency change on exposure to humid air with relative humidity. There was no significant hysteresis in the isotherms when the SAWS was taken through a cycle of relative humidity at any of the three temperatures employed. These results are similar to those obtained in earlier work on FPOL and polyvinylpyrollidone coated SAWS. They demonstrate that a correction algorithm based on a quadratic equation should be possible to overcome water vapour response of coated SAWS.     

Thermostability testing and degradation profiles of doxycycline in bulk, tablets, and capsules by HPLC

A high-performance liquid chromatography (HPLC) method for the quantitation of doxycycline in bulk, tablets, and capsules after storage at -20, 5, 25, 40, 50, 60, and 70 degrees C, has been developed and validated. The samples are eluted from a micro-Bondapak C8 column (4.6x150-mm, i.d., 5-microm particle size) at 27 degrees C, with a mobile phase of acetonitrile-water-THF (29.5:70:0.5, v/v/v), adjusted to pH 2.5 with 1.0M HCl. The flow rate is 1.0 mL/min and detection by UV is at 350 nm. The stability of doxycycline in bulk and in pharmaceuticals is checked over 90 days. Doxycycline shows thermo-degradation after exposure to high temperature; tablets are more stable than capsules. The shelf lives (t90%) are determined to be 1.00, 2.84, and 5.26 years in bulk, capsules, and tablets, respectively, at 25 degrees C. Metacycline and 6-epidoxycyline are identified as degradation products at high temperatures. Amounts of doxycycline, metacycline, and 6-epidoxycycline in all samples are determined by HPLC, and the results compare with those from micellar electrokinetic capillary chromatography. After 90 days, metacycline and 6-epidoxycyline are almost equal in test samples from standard bulk form, tablets, and capsules. It is 27.8+/-0.3%, 13.7+/-0.1%, and 18.8+/-0.2%, respectively.     

Bulky aluminum alkyl scavengers in olefin polymerization with group 4 catalysts

The binding of H2O to MeAl(OAr)2 (1: Ar = 2,6-di-tert-butyl-4-methylphenyl) in THF-d8 at -40 degrees C provides aquo complex 2, the structure of which was determined by X-ray crystallography. Complex 2 is unstable above 0 degrees C in THF-d8 and decomposes to form ArOH (major), CH4 (minor), and a methyl aluminoxane of undetermined structure. Decomposition of 2 follows first-order kinetics with k = 3.0 x 10-4 s-1 at 5 degrees C. The hindered phenol ArOH slowly reacts with [Cp2ZrMe][MeB(C6F5)3] (4) in bromobenzene-d5 solution at 25 degrees C to furnish CH4 and [Cp2ZrOAr][MeB(C6F5)3] (5), the structure of which was confirmed by X-ray crystallography. This reaction follows second-order kinetics for [ArOH] = [4] = 0.045 M and with k = 2.8 x 10-3 M-1 s-1 at 25 degrees C. This corresponds to a rate that is >107 x slower than the apparent rate of ethylene insertion for 4 at 25 degrees C at typical concentrations encountered in olefin polymerization. The kinetic data, as well as control experiments involving the addition of ArOH to active catalyst producing poly(ethylene), demonstrate that ArOH has essentially no effect on polymerization kinetics involving 4.     

丹参药材水溶性成分的高效液相色谱指纹图谱研究

采用高效液相色谱法(HPLC)对贵州铜仁丹参基地的丹参药材进行了指纹图谱研究。实验采用Zorbax SB-C18色谱柱 (5 μm, 4.6 mm i.d.×250 mm),以乙腈-0.4%(体积分数)冰醋酸水溶液为流动相,乙腈的体积分数在70 min内由0线性 增加到40%;流速1.0 mL/min;柱温25 ℃;检测波长254 nm。以19个主要共有峰为评价指标,采用国家药品监督管理局推荐 的“计算机辅助中药指纹图谱相似度计算软件”计算处理,建立了铜仁地区丹参药材的HPLC共有指纹图谱。该法操作简单 ,精密度、稳定性和重现性良好,有助于加强丹参药材的质量控制。     

Analysis of amides in the air by sampling with SPME and detection by GC-FID

This paper proposes a solid-phase microextraction (SPME) method for the passive sampling and determination of N,N-dimethylacetamide (DMA) and N,N-dimethylformamide (DMF) in air by capillary GC with flame ionization detection. The optimized conditions for SPME method were grab sampling, polydimethylsiloxane/divinylbenzene fiber, extraction for 90 min at 25 +/- 2 degrees C, desorption for 3 min at 220 degrees C, and relative humidity 45 +/- 2%. Under these conditions, the method presented good linearity (R = 0.996), repeatability (%RSD 2.79 and 9.85 for DMF and DMA, respectively), and detection limit (0.021 and 0.024 mg/m3 for DMF and DMA, respectively).