An analysis of avidin, biotin and their interaction at attomole levels by voltammetric and chromatographic techniques

The electroanalytical determination of avidin in solution, in a carbon paste, and in a transgenic maize extract was performed in acidic medium at a carbon paste electrode (CPE). The oxidative voltammetric signal resulting from the presence of tyrosine and tryptophan in avidin was observed using square-wave voltammetry. The process could be used to determine avidin concentrations up to 3 fM (100 amol in 3 l drop) in solution, 700 fM (174 fmol in 250 l solution) in an avidin-modified electrode, and 174 nM in a maize seed extract. In the case of the avidin-modified CPE, several parameters were studied in order to optimize the measurements, such as electrode accumulation time, composition of the avidin-modified CPE, and the elution time of avidin. In addition, the avidin-modified electrode was used to detect biotin in solution (the detection limit was 7.6 pmol in a 6 l drop) and to detect biotin in a pharmaceutical drug after various solvent extraction procedures. Comparable studies for the detection of biotin were developed using HPLC with diode array detection (HPLC-DAD) and flow injection analysis with electrochemical detection, which allowed biotin to be detected at levels as low as 614 pM and 6.6 nM, respectively. The effects of applied potential, acetonitrile content, and flow rate of the mobile phase on the FIA-ED signal were also studied.     

Nickel pentacyanonitrosylferrate film modified aluminum electrode for electrocatalytic oxidation of hydrazine

The electrocatalytic oxidation of hydrazine at the aluminum electrode, modified by electroless deposition of nickel pentacyanonitrosylferrate (NiPCNF) on the surface of the electrode has been studied by cyclic voltammetry, chronoamperometry and rotating disk electrode voltammetry and the kinetics of the catalytic reaction were investigated. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. It was found that a one-electron charge-transfer process is rate limiting and that the average values of the rate constant for the catalytic reaction and the diffusion coefficient, evaluated by different approaches, are 5.2×10³ M^–1s^–1 and 8.5×10^–6 cm²s^–1, respectively. Further examinations of the modified electrodes show that the modifying layers (NiPCNF) on the aluminum substrate have reproducible behavior and a high level of stability, after exposing them in air and hydrazine solutions for a long time. Electronic Publication     

The analysis of lubricating oil additives by supercritical fluid chromatography with packed and open tubular capillary columns

Lubricating oil additives have been analyzed by supercritical fluid chromatography on open tubular and packed capillary columns. Carbon dioxide and modified carbon dioxide were used as mobile phases and detection was accomplished by flame ionization and micro UV. Rapid and efficient analysis of the lubricating oil additives was demonstrated.     

Electroless preparation and electrochemical behavior of a platinum-doped nickel hexacyanoferrate film–zinc modified electrode: catalytic ability of the electrode for electrooxidation of methanol

The use of a zinc substrate as an electrode and the modification of its surface by means of a thin film of platinum-doped nickel hexacyanoferrate (Pt-NiHCF) were developed. The modification conditions of the zinc surface including the electroless deposition of metallic nickel on the electrode surface from NiCl₂ solution, chemical derivatization of the deposited nickel to the NiHCF film in 0.5 M K₃[Fe(CN)₆] solution, and electrochemical penetration of metallic platinum into the modified film are described. The modified zinc electrodes prepared under optimum conditions show a well-defined redox couple due to the [Ni^IIFe^III/II(CN)₆]^1–/2– system. The effects of pH, the alkali metal cation, and the anion of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied in detail. The diffusion coefficients of hydrated alkali metal cations in the film (D), the transfer coefficient (), and the transfer rate constant for the electron (k_s) were calculated in the presence of some alkali metal cations. The electrocatalytic activity of the modified electrode for methanol oxidation was demonstrated. The stability of the modified electrode under various experimental conditions was investigated.     

改性累托石吸附水溶液中苯酚的研究I吸附条件的确定

用十二烷基二甲基苄基氯化铵 (1227)、十六烷基三甲基溴化铵 (1631)、十八烷基三甲基溴化铵 (1831) 3种表面活性剂改性天然累托石 (REC) 粘土,分别得到3种有机改性累托石:1227-REC、1631-REC和1831-REC。用有机改性累托石作吸附剂,对水溶液中的苯酚进行吸附研究,考察了pH值、吸附时间、吸附剂用量、温度等因素对吸附效果的影响。结果发现,在本文研究条件下,3种吸附剂对苯酚达到较理想吸附效果的合理条件是:pH值分别为6、8、8;吸附平衡时间分别需要90、20、40min;吸附剂用量均为20g/L;常温。在确定的合理条件下,去除率分别能达到66.2%、99.0%、99.8%。     

2,4,6-三硝基苯酚改性锆铝复合氧化物固定相分离富勒烯的色谱性能研究

制备了用于分离C60和C70的2，4，6－三硝基苯酚改性锆铝复合氧化物高效液相色谱固定相，考察了流动相中甲苯的含量、柱温及流速对C60和C70分离的影响，同时比较了酸腐蚀前后锆铝复合氧化物基质对分离的影响，结果表明，2，4，6－三硝基苯酚改性酸腐蚀后锆铝复合氧化物填料对富勒烯表现出较强的分离能力，具有作为富勒烯制备分离的潜力。     

神经网络法用于多元混酸同时测定

利用多层神经网络误差反向传播算法处理酸碱电位滴定数据，求得出多元混合酸各组分的浓度，优化了神经网络的结构和参数，测定了三组分有机酸混合样品，结果良好，平均相对偏差ＲＳＤ≤４％。     

Electroredox Behavior of Novel Poly viol ogens Modified Electrodes

The electroredox behavior of novel modified electrodes coated with complexes of different polyviologens was investigated using cyclic voltammetry. The influences of compositions of electrolyte complex on the reversibility of the modified electrode and the electrochromic properties were studied also. It was found that all the ratios of integrated charges of cathodic to anodic scan (Qc/QA) are close to 1, which indicates that these modified electrodes have good reversible behavior. Repeated stepping over the first wave for 500 scans, the PSS-PX(p)V modified electrode showed excellent stability. The first reduction potential (E1), decrease of current height (Dec%), response time (tre tox) of various polyviologen modified electrodes were reported. In addition, the effect of the coverage of polyviologen on the electrode surface was also examined. The rate of electron transfer in this heterogeneous system is diffusion-controlled, consistent with the Conttrell equation.     

聚邻苯二胺修饰电极抗坏血酸氧化酶生物传感器的研究

本文报道了聚邻苯二胺／抗坏血酸氧化酶生物传感器，用这种传感器测定人体血清中的抗坏血酸，线性范围在１．０×１０＾－４～２．５×１０＾－７ｍｏｌ／Ｌ之间，响应时间为７ｓ，检测限为１．０×１０＾－８ｍｏｌ／Ｌ。该传感器具有选择性好、灵敏度高和响应时间短等特点。     

Preparation and Characterization of a Lignin Modified Electrode

Alkali lignin undergoes strong adsorption on polycrystalline gold electrodes. Subsequent oxidation in a sulfuric acid solution leads to a restructured redox‐active polymer that shows features characteristic for surface confined species. Surface coverage of up to 4.40×10^?10 mol cm^?2 may be obtained depending on the adsorption time or lignin concentration in the adsorption solution. Using Laviron's approach the electron‐transfer rate constant and the transfer coefficient were found to be 8.9 s^?1 and 0.35, respectively. The formal potential of the redox couple shifted negatively with pH at a rate of ca. 60 mV/pH unit, suggesting a 2 e/2 H⁺ reaction. The redox couple was also found to be a good mediator for electrochemical ascorbic acid oxidation in neutral phosphate buffer with ca. 250 mV reduction of the oxidation overpotential.