Comparison of liquid chromatography with fluorescence detection to liquid chromatography-mass spectrometry for amino acid analysis with derivatisation by 6-aminoquinolyl-N-hydroxysuccinimidyl-carbamate: Applications for analysis of amino acids in skin

The analysis of nineteen amino acids found in collagen was optimised using 6-aminoquinolyl-N-hydroxysuccinimidyl-carbamate (AQC) as a derivatisation reagent. The analysis and detection of nineteen AQC-amino acids using fluorescence and mass spectrometry were compared at different mobile phase pH’s and column temperatures. The pH range of the mobile phase was set between 2.7 and 6.0 and column temperatures, 15–60 °C. The majority of amino acids produced a mono-derivatised product with AQC, except cystine, lysine and hydroxylysine which were di-derivatised. Hydroxylysine’s retention time was affected most by changes in the pH, whilst hydroxyproline’s retention time was more affected by column temperature. Hydroxylysine was detected as two diastereomers which were completely resolved. The relative standard deviation of the retention times of AQC-amino acids was less than 1% and the limit of detection (LOD) and limit of quantitation (LOQ) were ranged from (0.05–0.23) µM and (0.07–0.76) µM on fluorescence and (0.02–0.10) µM and (0.06–0.33) µM on mass spectrometry respectively. This method was successfully applied for the quantitation of amino acids in different animal skins.     

药物释放环境对层状复合氢氧化物载体的影响

以层状复合氢氧化物(LDH)为载体用离子交换法制取乙酰苯甲酸(ASP)的插层复合物LDH-ASP, 通过体外释放实验和固相XRD、FT-IR、TEM、TG-DSC及BET-N2比表面积表征, 研究了药物释放环境对载体结构的影响. 结果表明释放环境pH为4.30-6.89时, 载体的层状特征减弱但晶体类型不变; pH为2.48-4.30时, H2PO-4对LDH的嫁接反应引起层状化合物向复杂磷酸盐转化; 随环境pH由6.89降低至2.48, 载体纯度下降, 晶态性征减弱,微孔吸附活性降低.     

Sonochemical oxidation of phenol and three of its intermediate products in aqueous media: Catechol,hydroquinone, and benzoquinone. Kinetic and mechanistic aspects

The sonochemical oxidation of phenol has been examined in airequilibrated aqueous media at various pH’s and at various insonation powers. Its disappearance follows zero-order kinetics at [phenol]_initial ~ 30 to 70 μM Three principal intermediate species formed at pH 3: catechol (CC), hydroquinone (HQ), and p-benzoquinone (BQ); at natural pH (5.4–5.7) only catechol and hydroquinone formed. No intermediate species were detected at pH 12 under the conditions used. The sonochemical fate of CC, HQ, and BQ was also examined at pH 3 and at natural pH’s. At pH 3, BQ is the major species formed during insonation of HQ, while HQ is produced during insonation of BQ. In both cases, an additional intermediate formed in trace quantities that is identified as hydroxy-p-benzoquinone. These same intermediate species have been identified in the heterogeneous photocatalyzed oxidation of phenol in irradiated titania suspensions. The present results confirm the important role of ’OH radicals in degradation processes. Although CO₂ is the ultimate product in heterogenous photocatalysis, irradiation of a phenolic aqueous solution by ultrasounds showed no loss of total organic carbon (TOC) after several hours, even though the aromatic substrate and the intermediates had degraded. A simple kinetic model/scheme is described to account for the events in the conversion of the substrates to products. It is concluded that the hydrophobic benzoquinone reacts with ¹OH and H¹ radicals at the hydrophobic gas bubble/liquid interface, while the hydrophilic species (phenol, CC, and HQ) react, to a large extent, with the ¹ OH radicals in the solution bulk.     

Comparative adsorption of methylene blue by magnetic baker’s yeast and EDTAD-modified magnetic baker’s yeast: Equilibrium and kinetic study

Magnetic baker’s yeast (MB) was prepared using glutaraldehyde cross-linking method and chemical modification with ethylenediaminetetraacetic dianhydride (EDTAD). The fabricated EDTAD-modified magnetic baker’s yeast (EMB) was then employed to remove methylene blue. Comparative adsorption of methylene blue by EMB and MB was systematically investigated with respect to pH, contact time, initial concentration and reaction temperature. The mechanism of methylene blue adsorption by EMB and MB was investigated by SEM, FTIR and Special surface area using methylene blue method. The results revealed that Fe₃O₄ nanoparticles were steadily cross-linked/incorporated with baker’s yeast biomass and the EDTA was modified on the surface of the magnetic baker’s yeast. The equilibrium adsorption data were fitted better by Langmuir isotherm, and the specific surface areas were 42.953–226.07 m²/g for MB and 94.972–499.85 m²/g for EMB, respectively. Kinetic studies suggested that the pseudo-second-order model was suitable to describe the adsorption process. Thermodynamic studies indicated that the adsorption was feasible, spontaneous and endothermic. The recovery efficiencies were above 80% by using 0.1 M HCl.     

Fouling during the cross-flow ultrafiltration of proteins: a mass-transfer model

A model was designed to predict the effect of pH and ionic strength on fouling in the cross-flow ultrafiltration (UF)of protein solutions. Ilias and Govind’s numerical approach for concentration polarisation was combined with the Stokes–Einstein generalised equation and Bowen and Jenner’s osmotic pressure model. Coagulation was predicted when the mass-transport equation diverged to concentrations higher than that of the maximum osmotic pressure. This occurred at concentrations exceeding that of the maximum diffusivity, when diffusion became too weak to resist drag forces. In this case, one or more monolayers of protein deposited. The model was experimentally tested with 1 g/l BSA and Amicon H1P30-20 modules, for a range of pressures, ionic strengths and pH.     

Dynamic Release of Riboflavin from Ethyl Cellulose Coated Barium Alginate Beads for Gastrointestinal Drug Delivery: An in vitro Study

The present work describes the dynamic release of model drug riboflavin form uncoated and ethyl cellulose coated barium alginate beads in the media of continuous varying pH at the physiological temperature 37°C. The drug release behavior has been studied in the simulating gastric fluid (SGF, pH 1.2) for 0–2 h and then in the simulating intestinal fluid (SIF pH 6.8) for 2–48 h. In addition to the traditional dissolution test (TDT, the dynamic release has also been studied by a newly developed method, called ‘flow through diffusion cell’ (FTDC). The release profiles, obtained by using these two methods have been found to differ appreciably from each other. Moreover, the nature of the solid mass surrounding the beads in the FTDC method also influences the release behavior of beads. The uncoated beads demonstrated faster drug release of drug in the medium of lower pH (i.e., 1.2) as compared to that in the medium of pH 6.8 and the release process was found to be diffusion controlled.     

动态pH联接-扫集毛细管电泳法测定化妆品中迷迭香酸的含量

采用动态pH联接-扫集毛细管电泳法对化妆品中的迷迭香酸进行检测。用重力进样的方式,进样高度为15 cm的情况下,研究了硼砂浓度、pH、十二烷基硫酸钠(SDS)浓度、甲醇浓度、样品基体、进样时间、分离电压对富集与分离的影响。优化后的实验条件:15 mmol/L硼砂-45 mmol/L SDS(pH8.8)-15%甲醇为缓冲液,进样时间60s,分离电压16kV,样品中磷酸盐浓度10 mmol/L,样品基质pH 4.7。在上述条件下,迷迭香酸(RA)的线性回归方程式为y=539200ρ+53588(r=0.9985),线性范围为0.144～3.6μg/mL,检出限0.036μg/mL,迷迭香酸的回收率为92.5%～103%,相对标准偏差为2.5%。     

Spectroscopic studies on the formation of charge transfer complexes of l-phenylalanine with 2,3,5-trichloro-6-alkoxy-1,4-benzoquinones in aqueous medium

UV–Vis, FT-IR, LC–MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of l-phenylalanine with new π-acceptors, 6-alkoxy-2,3,5-trichloro-1,4-benzoquinones. The interaction of these quinones with l-phenylalanine (LPA) yielding radical ion pair was found to proceed through the formation of donor–acceptor complex. The stoichiometry of the complexes was determined by Job’s continuous variation method and was found to be 1:1 in all the cases. Kinetic and thermodynamic properties of the complexes were determined in aqueous medium at physiological conditions (pH = 7). Fluorescence quenching studies indicated that the interaction between the donors and the acceptor is spontaneous. Correlation of association constants of the CT complexes with Taft’s polar and steric constants indicated that the electronic effects of the substitutions play a significant role in governing the reactivity of the quinones when compared to steric factors.     

Selective Interactions of Cyclodextrins with Isomeric 1,2,4-Thiadiazole Derivatives Displaying Pharmacological Activity: Spectroscopy Study

Complex formation of α-, β- and γ-cyclodextrins with 1,2,4-thiadiazole derivatives, which are structural isomers displaying an activity in the treatment of Alzheimer’s disease, was examined by the use of ¹H NMR and UV-spectroscopy. Stability constants of the complexes formed between cyclodextrins and thiadiazoles in two different buffers (pH 1.2 and 7.4) were calculated and analyzed. The temperature dependences of the stability constants were used to evaluate the enthalpy and entropy changes of complex formation. It was demonstrated that selectivity of the interactions between cyclodextrins and isometric 1,2,4-thiadiazole derivatives is determined by the size of macrocyclic cavity and relative position of the side groups in the benzene ring of the guest molecules. Higher stability of the complexes in the acidic medium (pH 1.2) in comparison with the slightly alkaline solution (pH 7.4) is caused by the important role of surface interactions.     

Activated Copper Cathodes as Sensors for Nitrite Analysis

The increased surface area of copper electrodes upon applying a suitable potential protocol was characterized by atomic force microscopy images. Scanning electrochemical microscopy was used to demonstrate the enhanced reactivity of the generated surface. The modified electrode showed excellent catalytic activity towards nitrite reduction in acidic medium (pH 2). This new platform was used in the development of a fast and simple voltammetric method for nitrite determination. Commercial and rainwater spiked samples were analyzed and the data showed an excellent agreement with those obtained with a reference spectrophotometric method (Griess reaction) at a confidence level of 95 % (Student’s t‐test).     

复合改性膨胀石墨的制备及对酸性艳蓝染料的吸附

采用相同反离子协同磷酸活化法, 以十六烷基三甲基溴化铵(CTAB)-KBr为复合改性剂, 制备了一种高效吸附剂复合改性膨胀石墨(M-EG), 通过扫描电子显微镜(SEM)、 傅里叶变换红外光谱(FTIR)及X射线电子能谱(XPS)等对膨胀石墨(EG)和改性膨胀石墨(M-EG)的形貌结构、 组成和价态进行了表征, 考察了EG和M-EG对酸性艳蓝染料废水的处理效果. 结果表明, 复合改性后的膨胀石墨孔隙度变大, 表面含氮和溴官能团增多. 吸附剂M-EG对酸性艳蓝染料废水具有较高的吸附性能, 在pH=1.0及30 ℃条件下对染料的去除率达到94.13%; EG符合二级动力学吸附模型, 用Langmuir等温线方程拟合效果较好; M-EG符合二级吸附动力学方程, 同时符合Langmuir和Freundlich等温吸附模型; M-EG的吸附动力学常数大于EG吸附动力学常数.     

基于三苯胺-罗丹明染料荧光探针对pH和Cu^2+的选择性识别

基于罗丹明B酰肼和三苯胺染料合成了pH和Cu^2+双识别分子探针(RTPA),并利用核磁氢谱、核磁碳谱和高分辨质谱表征了RTPA的分子结构。通过紫外-可见光谱法和荧光光谱法研究了该荧光分子探针在极性不同的有机溶剂中的光谱性能以及在THF/H2O(V:V=1:1)溶液中对Cu^2+和质子的选择性识别性能。结果表明:随着溶剂的极性增大,化合物RTPA的最大发射波长发生红移,从419 nm红移到500 nm。该探针在水溶液中可以实现高选择性识别Cu^2+离子,不受其他常见金属离子的竞争性干扰。通过Job’s plot曲线证明了探针RTPA识别Cu^2+的化学计量比是1:1,Cu^2+的检出限为0.635μmol/L。当pH在1.87~4.48区间内,探针的荧光强度与pH呈良好的线性关系,线性相关系数为0.9957,其pKa为3.13。探针RTPA也可用于极酸性条件下(pH<4)质子浓度的定量检测。     

Electrochemical reduction of selenium on a silver electrode and its determination in river water

A new, simple, and fast method is described for determining selenium based on a silver wire electrode flow-through voltammetric detector. A comparison was done between the sensitivity of disk silver, mercury-modified glassy carbon, and mercury-modified gold electrodes. The response of the flow-through voltammetric detector was evaluated with respect to each electrode’s operating potential and pH in direct current mode. The limit of detection (3s) for Se(IV) was below 0.01 mg/L. The flow-through system does not need deposition times and the organic matter does not need to be removed before determining selenium in river water.     

聚邻氨基苯酚接枝聚己内酯的合成与表征

以邻氨基苯酚为起始原料,合成了一新型接枝聚合物--聚邻氨基苯酚接枝聚己内酯(POAP-gPCL).利用核磁共振仪、红外光谱仪、X射线衍射仪、热重分析仪、电化学测试仪和紫外可见光谱仪等分析手段对聚邻氨基苯酚和聚己内酯接枝的聚邻氨基苯酚进行了结构和性能的表征.结果表明,与聚邻氨基苯酚相比,接枝聚合物表现出较好的热稳定性和电...     

Electrochemical studies on lawsone and its determination in henna (Lawsonia inermis) extract using glassy carbon electrode

The electrochemical behaviour of lawsone at glassy carbon electrode (GCE) was investigated by using cyclic and differential pulse anodic stripping voltammetric (DPASV) techniques. Cyclic voltammetry was used to study the influence of pH on the peak current and peak potential. The Mcllavnie’s buffer of pH 3.0 was selected as a suitable analytical medium in which lawsone exhibited sensitive diffusion controlled redox peaks (vs. Ag/AgCl). The peak current varied linearly with lawsone concentration in the range between 0.60 and 1.40 μM with a detection limit of 6 nM. The applicability of the proposed method was illustrated by the determination of lawsone present in real samples. A mean recovery of lawsone in the leaf of Lawsonia inermis was 99.5% with a relative standard deviation of 1.15%.     

Retention Behavior of Nucleic Acid Bases and Purine Derivatives on Titania

The retention of nucleic acid bases and purine derivatives on titania was studied using a 0.4 mM acetic acid–sodium acetate buffer (pH 6.0) and 70% aqueous methanol as mobile phases. We observed that the retention strength of tested analytes on titania was dependent on the structural differences between pyrimidine and purine skeletons and the variety and number of substituents. The retention order was purine derivatives with methyl groups, pyrimidine bases and purine derivatives with hydrophilic functional groups, which were retained most strongly on titania. We concluded that the retention of each analyte was caused by the analyte’s hydrophobicity in the case of purine derivatives with methyl groups and pyrimidine bases. In the case of purine and its derivatives with hydrophilic functional groups, it was considered that the retention was dependent on the analyte’s ability to form chelates, and the variety and number of functional groups on C6 and C2.     

Application of ionic liquid-based ultrasonic-assisted microextraction coupled with HPLC for determination of citalopram and nortriptyline in human plasma

In this paper, an effective and environmentally friendly method of ultrasound-assisted ionic liquid-based dispersive liquid–liquid microextraction (UA-IL-DLLME) combined with high-performance liquid chromatography (HPLC)–photodiode array detector was applied for extraction and determination of two antidepressant drugs citalopram hydrobromide and nortriptyline hydrochloride from human plasma samples. Several important parameters affect the steps and efficiency of extraction, some of which are sample solution’s pH, type and volume of ionic liquid, ultrasonic time, centrifuging time and rate, and the ionic strength of solution. Optimum conditions were obtained at pH?=?11, 1-octyl-3-methyl imidazolium hexafluorophosphate for ionic liquid, 55?µL for ionic liquid volume, 4?min for ultrasonic time, 5?min and 3,500?rpm for centrifuging time and rotation’s speed, due to ionic strength by the addition of NaCl 1%. Under optimized conditions, the linearity was obtained in the range of 0.02–2,000?µg/L, with correlation coefficients higher than 0.995. The limits of detection were 10?µg/L for citalopram and 6?µg/L for nortriptyline. Preconcentration factors were 920 for citalopram and 800 for nortriptyline. The present method of UA-IL-DLLME combined with HPLC was successfully used for the determination of citalopram and nortriptyline drugs in real samples of human plasma.     

Sorption of strontium ions from aqueous solutions by oxidized multiwall carbon nanotubes

Multiwall carbon nanotubes (MWCNTs) oxidized by nitric acid solution were used to investigate the adsorption behavior of strontium from aqueous solutions similar to the nuclear waste media. The physical properties of both as produced and oxidized MWCNTs were studied by Boehm’s titration method and nitrogen adsorption/desorption. The results showed that the surface properties of MWCNTs such as specific surface area, functional groups and the total number of acid sites were improved after oxidation. Furthermore, the effect of solution conditions such as initial concentration of strontium(II), pH, ionic strength, MWCNT concentration and contact time were studied at room temperature. The results of this study showed that the adsorption of strontium(II) was significantly influenced by the pH value and the solution ionic strength. According to the Langmuir model, the maximum adsorption capacities of strontium(II) onto the as produced and oxidized MWCNTs were obtained as 1.62 and 6.62 mg g^?1, respectively. The contact time to reach equilibrium was 100 min. The good adsorption of strontium(II) on oxidized MWCNTs at the lower ionic strength, the relatively high pH and the short equilibrium time indicate that the oxidized MWCNTs have great potential applications in the field of the environmental protection.     

Magnetic chitosan grafted with polymerized thiourea for remazol brilliant blue R recovery: Effects of uptake conditions

Magnetic chitosan was prepared by co-precipitation with polymeric Schiff’s base resulting from the reaction of thiourea with glutaraldehyde. This material has great potential as high-effective sorbent for Remazol Brilliant Blue R (RBBR): maximum sorption capacity reached 0.441?mmol?g^?1 at pH 1.6 and at 25°C. Kinetic plots, pH dependence, isotherm data, and influences of ionic strength were reported. The data from equilibrium sorption experiments are well fitted to the Langmuir isotherm and the pseudo-second-order sorption kinetics indicates that chemisorption controls the process. The distribution coefficient was calculated at different temperatures and the thermodynamic parameters have been calculated: the sorption reaction is endothermic, spontaneous, and increases the entropy of the system. Alkaline solution (0.5?M NaOH) was used for desorbing RBBR from loaded sorbent. The sorbent exhibited good regenerability over several repeated adsorption/desorption cycles.     

用热分析技术测定碳化硅粉体对聚乙二醇的吸附量

用热分析技术TG-DTA(thermal gravimetric and differential thermal analysis)测定浆料中碳化硅粉体对分散剂聚乙二醇PEG(polyethylene glycol)的吸附量. 结果显示PEG在Ar气氛中411.5 ℃时完全分解; 碳化硅表面分散剂PEG的吸附量随着pH的增大而下降, 在较高pH下大多数分散剂仍存在于溶液中; 分散剂PEG的吸附量通过公式(1)进行计算. 该方法简单方便, 可以应用于测量氧化物或非氧化物吸附紫外-可见分光光度法不能测定的一些有机聚合物分子.