Electroanalysis of ascorbic acid using poly(bromocresol purple) film modified glassy carbon electrode

We report a simple method for determination of ascorbic acid (AA) by using a glassy carbon electrode (GCE) modified with poly(bromocresol purple) (poly(BCP)/GCE). Compared with a bare GCE, the poly(BCP) film exhibited the obvious electrocatalytic effect towards ascorbic acid oxidation, which reduced the oxidation overpotential about 240 mV with obviously increased current response. Under the optimized conditions, the catalytic current increased linearly with the concentration of AA in the range of 2.0 × 10⁻⁵–7.0 × 10⁻⁴ M with the detection limit of 6.5 × 10⁻⁶ M (S/N = 3) in 0.1 M phosphate buffer solution (pH 6.5). The interferences from different species and the repeatability of the poly(BCP)/GCE for the determination of AA were also investigated. The proposed method has been successfully applied to the determination of AA in vitamin C injection and tablet with satisfactory results.     

Nafion-石墨烯-纳米金修饰电极测定尿酸

将Nafion和石墨烯及纳米金复合后修饰在玻碳电极上制成修饰电极,用于尿酸电化学行为的研究。在pH 5.8的磷酸盐缓冲溶液中,该修饰电极对尿酸具有良好的电催化作用,尿酸浓度在2.0×10^-7 ～2.0×10^-5 mol/L范围内与其氧化峰电流呈较好的线性关系,相关系数为0.9843,检出限为1.0×10^-8 mol/L。方法用于实际样品的测定,加标回收率为96.8～103.2%,RSD为2.7～3.3%。     

高效液相色谱法同时测定三聚氰胺、三聚氰酸、尿酸

建立高效液相色谱法同时测定血浆、结石中三聚氰胺、三聚氰酸和尿酸的检测方法。样品经超声提取、离心等前处理后,采用C_(18)色谱柱进行分离,紫外检测测定,外标法定量。本法简便、定量准确、精密度高、回收率理想。     

Spectrofluorometric determination of ascorbic acid using thiamine and potassium ferricyanide

A simple and sensitive spectrofluorometry method for the determination of ascorbic acid was reported. In alkaline solution, the nonfluorescent thiamine was oxidized by potassium ferricyanide and formed the fluorescent thiochrome with an excitation maximum at 367?nm and an emission peak at 441?nm. However, the fluorescence intensity gradually decreased in the presence of ascorbic acid. The decreased fluorescence was linearly dependent under the optimum conditions with the concentration of ascorbic acid from 0.086–1.5?µmol?L^?1 with a correlation coefficient of 0.9996. The detection limit of 0.026?µmol?L^?1 was lower than many other methods. Additionally, the mechanism underlying the enhancement and quenching of this method was discussed. The protocol was used to determine ascorbic acid in tablets and juice with satisfactory results.     

高效液相色谱-荧光法测定尿液中尿靛甙

本文采用高效液相色谱-荧光检测法对尿液样品中的尿靛甙含量进行了测定,通过对前处理方法和色谱条件优化,建立了适用于尿液样品中尿靛甙含量测定的色谱分析方法。该方法的定量线性范围为5.0~250.0mg/L,其线性相关系数为0.9993;方法检出限为0.001mg/L,加标回收率为93~101%。该方法前处理简单易行,灵敏度高,检出限低,可应用于个体尿液化检验诊断,辅助指导个体化营养诊疗。     

Application of L-DOPA modified carbon nanotubes as a bifunctional electrocatalyst for simultaneous determination of ascorbic acid,adrenaline, acetaminophen and tyrosine

L-DOPA multi-wall carbon nanotube modified glassy carbon electrode (DOPA-MWCNT-GCE) was used as a bifunctional electrocatalyst for simultaneous quantitative determination of ascorbic acid (AA) and adrenaline (AD). Electrochemical experiments show that the modified electrode plays the role of an excellent bifunctional electrocatalyst for the oxidation of AA and AD in two different potentials. The kinetic parameters such as the electron transfer coefficient, α, and the heterogeneous electron transfer rate constant, k′, for the electrocatalytic oxidation of AA and AD at the DOPA-MWCNT-GCE surface were estimated. Through a different pulse voltammetric (DPV) method, the plot of the electrocatalytic current versus AA and AD concentrations emerged to be constituted of two linear segments with different sensitivities. In addition, detection limits of 1.5 μM for AA and 0.62 μM for AD were obtained. In DPV, the proposed bifunctional electrocatalyst could separate the oxidation peak potentials of AA, AD, acetaminophen (AC) and tyrosine (Tyr) present in a mixture though, at the bare GCE, the peak potentials overlap. Finally, DOPA-MWCNT-GCE was satisfactorily used for the determination of AA, AD, AC and Tyr in pharmaceutical preparations.     

Determination of phenyl acetic acid by cyclic voltammetry with electrochemical detection

The phenyl acetic acid (PAA) has been determined by cyclic voltammetry with electrochemical detection using CuGeO₃ nanowires as the glassy carbon electrode (GCE) modified materials. The electrochemical behaviors of the PAA at the CuGeO₃ nanowire modified GCE in neutral solution show that two pairs of electrochemical CV peaks are observed. Two anodic CV peaks are located at 0.31 V and −0.02 V for cv peak 1 and cv peak 2, respectively. The intensities of two anodic peaks vary linearly with the increase of the PAA concentrations from 0.01 to 2 mM. The detection limit is 82.1 μM and 9.1 μM for cv peak 1 and cv peak 2, respectively. The CuGeO₃ nanowire modified GCE exhibits good reproducibility, stability and sensibility.     

松籽油中松油酸含量的快速测定

本文采用气相色谱法测定松籽油中松油酸含量,本方法简便、快速、准确、精密度高。     

气相色谱法测定月见草油中γ-亚麻酸含量

本文采用气相色谱技术 ,建立月见草油中γ -亚麻酸含量的测定方法 ,本方法简单、快速 ,精密度高 ,准确度较好。     

Adsorption effect of a cationic surfactant at carbon paste electrode as a sensitive sensor for study and detection of folic acid

The present study is the first report on the effect of cetyltrimethylammonium bromide (CTAB) on the electrochemical behavior of folic acid (FA) at the surface of carbon paste electrode (CPE) in real samples. The studies were performed by cyclic voltammetry (CV), chronocoulometry and differential pulse voltammetry (DPV). CTAB, with a hydrophobic C–H chain, could absorb at the CPE surface by hydrophobic interaction and then changed the electrode/solution interface, and eventually affects the electrochemical response of FA, confirming from the remarkable oxidation peak current enhancement. For investigation of the electrode properties, CV technique was used at the various scan rates. Electrochemical parameters including diffusion coefficient (D), electron transfer coefficient (α) and ionic exchanging current density (j_o) were determined for the FA at the surface of the electrode. Under optimized conditions, the proposed method showed acceptable analytical performances for FA in terms of linearity (over the concentration range from 0.01 to 1.5 and 1.5 to 10.0 μM), detection limit (2.89 nM), repeatability (1.37%) and stability (13% reduction in peak current after 60 days). After studying on the effect of probable interferences it was found that the method was free of the interferences. Finally, the proposed method was successfully applied for the determination of FA in real samples.     

Application of mixed self-assembled monolayers (Mixed SAMs) for nucleic acid detection

Mixed self-assembled monolayers (Mixed SAMs) consisting of 8-Ferrocenyl-1-octanethiol and 6-Mercapto-1-hexanol (FcOT:MCH) with probe PNA on gold electrodes were fabricated by using two-step after the optimization of immobilization temperature of FcOT:MCH SAMs. Using AC voltammetry, a novel nucleic acid detection platform, with mixed SAMs, was proposed. A negative formal potential shift was observed after complementary ssDNA hybridization while there was no significant difference after non-complementary ssDNA hybridization. Compatible results were obtained with the measurement of formal potential differences between mixed SAMs and target DNA (complementary and non-complementary DNA) in different target DNA concentrations. The formal potential difference between mixed SAMs immobilization and complementary ssDNA hybridization was measured in different ionic strength concentrations.     

血清中尿酸的测定方法及其研究进展

描述了尿酸的检测在涉及临床诊断研究方面具有重要意义。尿酸常用的检测方法有：酶法，伏安法，毛细管电泳法，高效液相色谱法和同住素稀释质谱法等。本文比较全面的总结了血清中尿酸的检测方法及其研究进展。     

A chamber for biomechanical,electrochemical and electrophysiological measurements in functional segments of peripheral nerves

The aim of the work was to develop the chamber to be used in biomechanical, electrochemical and electrophysiological measurements in functional segments of peripheral nerves, when electrical stimulating pulses are selectively applied to preselected locations along the nerve and neural responses are measured.     

Effects of the ascorbic acid supplementation on NADH-diaphorase myenteric neurons in the duodenum of diabetic rats.

We assessed the ascorbic acid (AA) supplementation on the myenteric neurons in the duodenum of rats. Fifteen rats with 90 days of age were divided into three groups: control (C), diabetics (D) and ascorbic acid treated diabetics (DA). After 120 days of daily treatment with AA, the duodenum was submitted to the NADH-diaphorase (NADH-d) histochemical technique, which allowed us to evaluate the neuronal density in an area of 8.96 mm2 for each duodenum, and also to measure the cellular profile area of 500 neurons per group. The supplementation promoted an increase on AA levels. The neuronal density (p < 0.05) was higher in the group DA when compared to group D. There were no significant differences in the neuronal areas, when we compared groups C (204 +/- 16.5) and D (146.3 +/- 35.84) to groups D and DA (184.5 +/- 5.6) (p > 0.05). The AA-supplementation avoided the density reduction of the NADHd myenteric neurons in the duodenum of diabetic rats.     

气相色谱法快速测定松籽油中松油酸的含量

介绍了用气相色谱法测定松籽油中松油酸的含量，方法具有前处理简单、快速、准确，精密度高等特点。     

茶籽油中脂肪酸成分的气相色谱/质谱分析

建立茶籽油中脂肪酸的气相色谱/质谱 (GC/MS) 测定方法。茶籽油经正己烷提取和三氟化硼衍生,用HP-5MS毛细管柱分离。用所建立的方法比较茶籽油、橄榄油和其它植物油中的脂肪酸含量。并分析茶籽油、茶籽及加工副产物中的脂肪酸水平。     

Silver nanoparticles/polymethacrylic acid (AgNPs/PMA) hybrid nanocomposites-modified electrodes for the electrochemical detection of nitrate ions

AgNPs/PMA hybrid nanocomposite materials with different Ag loadings have been synthesized using a simple chemical route assisted by UV irradiation. The hybrid composites were characterized by means of SEM and TEM, UV–vis spectroscopy and XPS. The as synthesized hybrid samples, composed of small Ag nanoparticles (AgNPs) embedded within the PMA (poly-methacrylic-acid) matrix, have been used to modify the working electrode of disposable screen printed carbon electrodes (SPCEs). It has been observed that hybrid composite with the lowest Ag loading forms dendritic silver structures on the surface of working electrode, whereas at higher loadings massive structures were formed. The electrocatalytic properties of the AgNPs/PMA/SPCEs were investigated toward the reduction of nitrate at neutral pH. Based on these modified electrodes, both voltammetric and amperometric sensors were developed for the electrochemical sensing of nitrate. Voltammetric sensor showed a wide linear range (0–20 mM) and high sensitivity (130 μA mM⁻¹ cm⁻²).     

水环境痕量重金属检测的电化学传感器的研究

重金属是一种危险的污染物,往往长期积累在生物体内不可降解,在极其微量的情况下也会对各种生态系统产生不同程度的危害.文中采用汞膜玻碳圆盘电极,研制了一种用于监测水环境痕量重金属浓度的电化学传感器,基于差分脉冲阳极溶出伏安法(differential pulse anode stripping voltammetry,DPASV),实现了锌、镉、铅和铜4种元素的同时测定.结果表明:该传感器用于检测锌、镉、铅和铜的检出限分别为2.0 μg/L、1.9 μg/L、0.8 μg/L和0.7 μg/L.与其他重金属检测方法相比,该电化学传感器的特点是可同时快速检测多种重金属元素,传感器体积小,价格低,操作简单,灵敏度高,易于实现现场自动检测分析.     

Morphological changes of poly(DI‐lactide‐co‐glycolide) nano‐particles containing ascorbic acid during in vitro degradation process

Poly(dl ‐lactide‐co‐glycolide) powder composed of uniform particles with the mean particle size in the range of 110–170 nm was obtained from commercial granules. Ascorbic acid in different concentrations was encapsulated into the poly(dl ‐lactide‐co‐glycolide) particles. Degradation of the latter in terms of morphological changes in the physiological solution was followed. Within a period of 2 months, the particles completely degrade and all the ascorbic acid is released. The samples were characterized by ultraviolet spectroscopy and scanning electron microscopy.     

基于脉冲压缩技术的高温连铸坯壳厚度测量EMAT设计及应用

采用非接触电磁超声技术实现高温连铸坯壳厚度测量,实时调整辊压力、冷却喷水量、压下位置和压下速度等工艺参数,避免出现中心偏析和松散问题,具有重要的工程应用价值。为了进一步提高电磁超声换能器(EMAT)在晶粒粗大和表面振痕的高温铸坯中的信噪比和空间分辨率,建立了基于Chirp信号激励的跑道线圈电磁超声检测过程的有限元模型,分析了EMAT设计参数、Chirp信号频宽和脉宽等因素对脉冲压缩后的超声回波信噪比和空间分辨率的影响,并通过实验予以验证。结果表明:经过脉冲压缩后,超声回波的SNR提高19 d B以上,波包宽度减少62. 4%以上; Chirp信号脉宽和永磁体尺寸对信噪比有显著影响,Chirp信号频宽、永磁体间距和宽度、跑道线圈导线直径及其阻抗匹配参数影响空间分辨率。