Evaluation of non-specific binding suppression schemes for neutravidin and alkaline phosphatase at the surface of reticulated vitreous carbon electrodes

Non-specific binding (NSB) of high-molecular-weight proteins onto electrode surfaces can complicate the application of electroanalytical techniques to clinical and environmental research, particularly in biosensor applications. We present herein various strategies to modify the surface of reticulated vitreous carbon (RVC) electrodes to suppress non-specific binding of biomolecules onto its surface. Non-specific binding and specific binding (SB) of two enzyme conjugates, neutravidin-alkaline phosphatase (NA-ALP) and biotinylated alkaline phosphatase (B-ALP), and also neutravidin itself, were studied using hydroquinone diphosphate (HQDP) as an enzyme substrate for ALP inside the pores of RVC electrodes that had been subjected to various modification schemes. The extent of NSB and SB of these biomolecules inside RVC pores was assessed by measuring the initial rate of generation of an electroactive product, hydroquinone (HQ), of the enzyme-catalyzed reaction, using linear scan voltammetry (LSV) for HQ detection. Electrodes functionalized with phenylacetic acid and poly(ethylene glycol) (PEG) showed low NSB and high SB (when biotin capture ligands were included in the modification scheme) in comparison with unmodified electrodes and RVC electrodes modified in other ways. A simple sandwich bioassay for neutravidin was performed on the RVC electrode with the lowest NSB. A concentration detection limit of 52 ± 2 ng mL⁻¹ and an absolute detection limit of 5.2 ± 0.2 ng were achieved for neutravidin when this assay was performed using a 100 μL sample size.     

Nondestructive damage assessment in fiber reinforced composites with the pulsed ultrasonic polar scan

This study investigates the use of both amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) as a sophisticated non-destructive damage sensor for fiber reinforced composites. Focus is put on stiffness related damage phenomena, which are in general difficult to monitor nondestructively, and their associated signature in the P-UPS image. Various composite samples, with different damage states, have been inspected at multiple material spots with the P-UPS technique. The results demonstrate the capability of the P-UPS method to obtain a unique signature of the local material damage characteristics. Several indicators in the acquired P-UPS images have been identified from which the type and level of material degradation can be obtained. The P-UPS extracted characteristics are fully supported by simulations, conventional tests as well as visual inspection.     

肾上腺素电氧化过程的快速扫描循环伏安研究

以快速循环伏安法为主要手段,研究了肾上腺素电化学氧化反应机理.肾上腺素在1 m ol•dm－3 H2SO4中的电化学氧化反应,具有扩散控制的基本特征,并伴随着电活性质粒的 弱吸附现象.在快速电势扫描条件下,肾上腺素电氧化过程遵从EC反应机理.当肾上腺素浓度低于1.00×10－3 mol•dm－3时,吸附现象的特征趋于显现出来;在快速电势扫描速率下,电活性质粒吸附的特征更加明显.结合表面伏安法分析,估算了肾上腺素电氧化过程的传递系数α=0.264.电化学反应速率常数ks=31.81 s－1.     

A novel liquid chromatography Orbitrap mass spectrometry method with full scan for simultaneous determination of multiple bioactive constituents of Shenkang injection in rat tissues: Application to tissue distribution and pharmacokinetic studies

Shenkang injection is a traditional Chinese formula with good curative effect on chronic renal failure. In this paper, a novel, rapid and sensitive ultra‐high‐performance liquid chromatography coupled with Q Exactive hybrid quadrupole Orbitrap high‐resolution accurate mass spectrometry was developed and validated for simultaneous determination of seven bioactive constituents of Shenkang injection in rat plasma and tissues after intravenous administration. Acetonitrile was used as a protein precipitation agent in biological samples disposal with carbamazepine as internal standard. The chromatographic separation was carried out on a C₁₈ column with a gradient mobile phase consisting of acetonitrile and water (containing 0.1% formic acid). The MS analysis was performed in the full‐scan positive and negative ion mode. The lower limits of quantification for the seven analytes in rat plasma and tissues were 0.1–10 ng/mL. The validated method was successfully applied to tissue distribution and pharmacokinetic studies of Shenkang injection after intravenous administration. The results of the tissue distribution study showed that the high concentrations of seven constituents were primarily in the kidney tract. This is the first report of the application of Q‐Orbitrap with full‐scan mass spectrometry in tissue distribution and pharmacokinetic studies of Shenkang injection.     

Separation of Nucleobases Using High‐performance Liquid Chromatography Coupled with Voltammetric Scanning

In this paper, a method based on chromatographic separation of analytes and their quantification using on‐line cyclic voltammetry is reported. The method based on high performance liquid chromatography on reverse phase column was optimized using free nucleobases‐guanine, adenine, thymine, and cytosine. The optimal separation of nucleobases was detected when using 0.05 M borate buffer (pH 9.0) as the mobile phase, at isocratic flow rate 1 mL min⁻¹, and at separation column temperature of 30 °C. The accurate timing of the cyclic voltammetry enabled us to quantify the concentrations of individual nucleobases by oxidation on glassy carbon electrode.     

层状配位聚合物犤Pb(NCS)_2(bpea)_n的合成,结构和非线性光学性质(bpea=1,2-双(4-吡啶基)乙烷)(英文)

室温下Pb(OAC)2·3H2O,KNCS,和1,2-双(4-吡啶基)乙烷在甲醇中反应生成了八员环支撑的层状配位聚合物犤Pb(NCS)2(bpea)犦n。三阶非线性Z-扫描研究表明该化合物具有非线性折射行为:其非线性吸收系数α2=1.1×10-11m·W-1,非线性折射系数n2=6.055×10-18m2·W-1。     

Reverse scans in square wave voltammetry

Reverse scans in square wave voltammetry (SWV) leading to the regeneration of the substance initially present in solution are studied. Widths and peak potentials of waves in SWV performed with both negative and positive potential scans allow us to determine easily the kinetic parameters of a slow electrochemical reaction. The theoretical treatment is verified using the U(V)–U(VI) system in a carbonate medium, which has already been studied by Krulic, Fatouros and Chevalet [J. Electronal. Chem. 251 (1988) 151].     

The Electrochemical Behavior of α‐Ketoglutarate at the Hanging Mercury Drop Electrode in Acidic Aqueous Solution and Its Practical Application in Environmental and Biological Samples

The voltammetric behavior of α‐ketoglutarate (α‐KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH 4.5, 0.2 M NaAc‐HAc buffer solution), a sensitive reductive wave of α‐KG was obtained by linear scan voltammetry (LSV) and the peak potential was ?1.18 V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were α=0.3 and k_s=0.72 1/s. There was a linear relationship between peak current i_{p, α‐KG} and α‐KG concentration in the range of 2×10^?6–8×10^?4 M α‐KG. The detection limit was 8×10^?7 M and the relative standard deviation was 2.0% (C_α‐KG=8×10^?4 M, n=10). Applications of the reductive wave of α‐KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of α‐KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between α‐KG and aluminum, a linear relationship holds between the decrease of peak current of α‐KG Δi_p and the added Al concentration Cequation/tex2gif-inf-5.gif in the range of 5.0×10^?6–2.5×10^?4 M. The detection limit was 2.2×10^?6 M and the relative standard deviation was 3.1% (Cequation/tex2gif-inf-6.gif=4×10^?5 M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP‐AES. (3) It was also applied to study the effect of Al^III on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of α‐KG+NH +NADH?L ‐glutamate+NAD⁺+H₂O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD⁺ and α‐KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes.     

步进扫描差示扫描量热法研究不同链结构的聚乙烯类聚烯烃热力学特性

采用步进扫描差示扫描量热法研究了几种具有不同链结构的聚乙烯类聚烯烃的热力学性质.结果表明,不同链结构的聚烯烃在热力学平衡熔融态下,其绝对比热容的温度依赖性在实验误差范围内几乎相同;而无论链结构的变化如何,在极低温度下稳定结晶态的热容也非常接近.但在熔融温度范围内,比热容对不同聚烯烃的链结构非常敏感,这是由于在远低于聚烯烃主熔化峰温度范围内,聚乙烯晶体结构中的不同支链的影响.在时间-热流的步进扫描曲线中,具有长支链结构的聚烯烃表现出独特的熔融-再结晶行为,这可能是由于交联点之间较长的受约束链段的运动在熔融过程中得到释放并重排所致.     

Simultaneous Determination of Trace Ofloxacin and Enoxacin by TLC-Fluorescence Spectrodensitometry

Abstract

A new TLC-fluorescence spectrodensitometry method is described for the simultaneous determination of trace ofloxacin and enoxacin, using a optimized mobile phase of chloroformmethanolethyl acetatetetrahydrofuranaqueous ammonia (6:4.6:1.5:0.8:1.5, V/V). The influence of the silica gel plates previously treated with various concentrations of sodium edetate solution in various pH's are studied. Their R, values are 0.54 and 0.29 respectively. The excitation, wavelength is 335nm. The linear ranges are 0~75ng. The relative standard deviations are <6.9%. The mean recovery of the two antibiotics in body fluid ranged from 95.4% to 105.2%.