Simultaneous determination of captopril and hydrochlorothiazide by time-resolved chemiluminescence with artificial neural network calibration

The combined use of chemometrics and chemiluminescence（CL）measurements,with the aid of the stopped-flow mixing technique,developed a simple time-resolved CL method for the simultaneous determination of captopril（CPL）and hydrochlorothiazide（HCT）.The stopped-flow technique in a continuous-flow system was employed in this work in order to emphasize the kinetic differences between the two analytes in cerium（IV）-rhodamine 6G CL system.After the flow was stopped,an initial rise of CL signal was observed for HCT standards,while a direct decay of CL signal was obtained for CPL standards.The mixed CL signal was monitored and recorded on the whole process of continuous-flow/stopped-flow,and the obtained data were processed by the chemometric approach of artificial neural network.The relative prediction error（RPE）of CPL and HCT was 5.9% and 8.7%,respectively.The recoveries of CPL and HCT in tablets were found to fall in the range between 95% and 106%.The proposed method was successfully applied to the simultaneous determination of CPL and HCT in a compound pharmaceutical formulation.

The Determination of Iodide Based on a Flow-injection Coupling Irreversible Biamperometry

A novel flow-injection irreversible biamperometric method is described for the direct determination of iodide. The method is based on electrochemical oxidation of iodide at the gold electrode and the reduction of permanganate at the platinum electrode to form an irreversible biamperometric detection system. Under the applied potential difference of 0 V, in the 0.05 mol/L sulfuric acid, iodidecan be determined over the range 4.00×10^-7-1.00×10^-5 mol/L with a sampling frequency of 120 samples per hour. The detection limit for I- is 3.0×10^-7 mol/L and the RSD for 40 replicate determinations of 4.0×10^-5 mol/L potassium iodide is 1.68%. The new method was applied to the analysis of iodide in table salt with satisfactory results.

An ionic liquid supported CeO_2 nanoparticles-carbon nanotubes composite-enhanced electrochemical DNA-based sensor for the detection of Pb^(2+)

An electrochemical sensor incorporating a signal enhancement for the determination of lead （II） ions （Pb2＋） was designed on the basis of the thrombin-binding aptamer （TBA） as a molecular recog- nition element and ionic liquid supported cerium oxide （CeO2） nanoparticles-carbon nanotubes compo- site modification. The composite comprises nanoparticles CeO2, multi-waU carbon nanotubes （MWNTs） and hydrophobic room temperature ionic liquid （RTIL） 1-ethyl-3-methylimidazolium tetrafluoroborate （EMIMBF4）. The electrochemical sensors were fabricated by immersing the CeOa-MWNTs-EMIMBF4 modified glassy carbon electrode （GCE） into the solution of TBA probe. In the presence of Pb2＋, the TBA probe could form stable G-quartet structure by the specific binding interactions between Pb2＋ and TBA. The TBA-bound Pb2＋ can be electrochemically reduced, which provides a readout signal for quantitative detection of Pb2＋. The reduction peak current is linearly related to the concentration of Pb2＋ from 1.0 ＊ 10-8 M to 1.0 ＊ 105 M with a detection limit of 5 ＊ 109 M. This work demonstrates that the CeOz-MWNTs-EMIMBF4 nanocomposite modified GCE provides a promising platform for immobi- lizing the TBA probe and enhancing the sensitivity of the DNA-based sensors.

Determination of Enantiomeric Compositions of Tryptophan by Chemometric Analysis of the Fluorescence Spectra of Bovine Serum Albumin Receptor-ligand Mixtures

In this work, a novel method was constructed to determine the enantiomeric composition of tryptophan （Trp） by bovine serum albumin （BSA） based on the fluorescence spectra of the receptor-ligand mixtures coupled with partial least squares （PLS-1） analysis. As a result the enantiomeric composition of Trp was accurately determined.

A covalent modified hydrophilic capillary for enhanced capillary electrophoresis of biopolymers

8-Gluconolactone was covalently coupled to aminopropyl derivatized capillary, which created hydrophilic brushes on the inner wall of the capillary. The coated capillary was shown to generate a stable electroosmotic flow （EOF） in the investigated pH range of 2.0-9.0 and to suppress effectively the adsorption of proteins. And it enabled separation of some biopolymer mixtures including basic proteins, DNA and tryptic digested bovine serum albumin （BSA） within 15 rain with efficiencies up to 450,000 plates/m. The intra- and inter-day reproducibility of the coating referring to the retention times of proteins were satisfactory with mean relative standard deviations （R.S.D.） of 0.8 and 1.7%, respectively. 2009 Yin Mao Wei. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All fights reserved.

Identification and Determination of Nicorandil and its Degradation Products by HPLC and GC/MS

A rapid and sensitive HPLC-DAD method is developed for simultaneous determination of nicorandil and its degradation products, N-（2-hydroxyethyl） nicotinamide, nitrate ion and nicotinic acid, using nicotinamide （NT） as internal standard, at wavelength 204 nm. Nicotinic acid is identified by HPLC and GC/MS. The method can also be applied to study kinetic of degradation processes of nicorandil in storage.

Determination of Vitamin B_1 in Pharmaceutical Preparations by Flow-injection Analysis with Biamperometric Detection

A new electrochemical method for the on-line determination of vitamin B1 is presented. Based on dead-stop endpoint biamperometry by using two platinum foil electrodes with an applied potential difference of 150 mV, vitamin B1 can be oxidized by hexacyanoferrate （ Ⅲ ） in a sodium hydroxide medium via a reversible indicating couple Fe（ CN）6^4- /Fe（CN）6^3- The cell current is linear with the concentration of vitamin B1 in the concentration range of 4. 0 × 10^-6-1.0 × 10^ -3 mol/L with a detection limit of 8.0 ×10 ^-7 mol/L（0. 27 μg/mL）. Most familiar excipients, ions and vitamins do not interfere with the determination of vitamin B1. The method displays the advantages of simplicity, high efficiency（ 180 samples/h）, and high selectivity, and is suitable for the determination of vitamin B1 in pharmaceutical preparations.

Indirect Flow Injection Chemiluminescence Method for the Determination of Tetracyclines Using Cu(Ⅱ) as a Probe Ion

This paper reported an indirect flow injection chemiluminescence （FI-CL） method for the determination of the drugs tetracycline （TC）, chlortetracycline （CTC） and oxytetracycline（OTC） using Cu（ Ⅱ ） as a probe ion. The CL reaction was induced on-line and after injection of the sample the negative peaks appeared as a result of complexation. The method was applied to the determination of TCs in pharmaceuticals and human urine with recoveries in the range95-105%.

氯离子选择电极瞬时电位分析法研究

0.1 mol/L KNO3空白液与Cl-切换时, AgCl电极响应的瞬时电位信号峰高度ΔEp有非常好的再现性, 40多天所测的10次标准曲线电位平均偏差小于2.0 mV, ΔEp～p(Cl-)直线平均斜率为55.4 mV, 其平均偏差小于1.0 mV, 电极响应下限和ΔEp～p(Cl-)直线截距都与经AgCl溶度积所计算的值一致. 瞬时信号峰电位上升时间小于1.5 s, 可实现小体积试液的快速准确分析. 用离子水合吉布氏自由能ΔGh(Cl-)的变化解释了瞬时信号不同阶段的电位变化速度. 实验中使用自制的活度阶梯自动切换装置, 该装置具有容积比为 4∶1的空白液和试液两个注射泵. 用该法已测定了维生素B6的含量.

Investigation on Voltammetric Behavior of Camptothecin and Its Analytical Application

The voltammetric behavior of camptothecin （CPT） in Britton-Robinson （B-R） buffer solutions （pH 2.09-9.07） was studied by the means of linear sweep voltammetry （LSV）, cyclic voltarnmetry （CV） and normal pulse voltammetry （NPV） at a hanging mercury drop electrode. In different pH range of B-R buffer solutions, CPT could cause three reduction waves. In B-R buffer solutions （pH 2.09-5.46）, wave P1 yielded by CPT was a two-electron wave. Between pH 6.01 and 9.07, CPT could yield two reduction waves P2 and P3. In addition, the pure CPT obtained from camptotheca acumina grown only in China was determined by NPV, and a linear response was observed in the range of 2.0 × 10^-3-4.0 × 10^-2 mmol·L^-1 with a 0.9991 correlation coefficient and a 8.0 × 1^-4 mmol·L^-1 detection limit for CPT.

In situ generation and detection of methyl radical by voltammetry

In persulfate-acetate, dimethyl sulfoxide or tert-butyl alcohol systems, in situ generation and detection of methyl free radical are realized with voltammetry. It includes the following successive processes. The persulfate S2O82 is polarographically reduced via one-electron addition to sulfate radical SO4, the SO4 initiates chain reaction with acetate, dimethyl sulfoxide, or tert-butyl alcohol on the electrode surface to produce a methyl radical, and one-electron reduction of the methyl radical yields its polarographic reduction wave. In comparison with the known techniques such as ultraviolet radiolysis coupling with electron spin resonance, etc., the proposed method is simple, sensitive and selective.

Direct Electrochemistry and Electrocatalysis of Hemoglobin Based on Nation-Room Temperature Ionic Liquids- Multiwalled Carbon Nanotubes Composite Film

A robust and effective composite film combined the benefits of Nation, room temperature ionic liquid （RTIL） and multi-wall carbon nanotubes （MWNTs） was prepared. Hemoglobin （Hb） was successfully immobilized on glassy carbon electrode surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Hb were investigated in detail. A pair of well-defined and quasi-reversible redox peaks of Hb was obtained in 0.10 mol,L^-1 pH 7.0 phosphate buffer solution （PBS）, indicating that the Nafion-RTIL-MWNTs film showed an obvious promotion for the direct electron transfer between Hb and the underlying electrode. The immobilized Hb exhibited an excellent electrocatalytic activity towards the reduction of H2O2. The catalysis current was linear to H2O2 concentration in the range of 2.0× 10^-6 to 2.5× 10-4mol·L-1, with a detection limit of 8.0× 10-7 moloL-1 （S/N=3）. The apparent Michaelis-Menten constant （ Kapp ） was calculated to be 0.34 mmolo·L^-1 Moreover the modified electrode displayed a good stability and reproducibility. Based on the composite film, a third-generation reagentless biosensor could be constructed for the determination of H2O2.

β_2-Adrenoceptor affinity chromatography and its application in the screening of the active compounds from Semen Armeniacae Amarum

β2-Adrenoceptor (β2-AR) was purified from the rabbit lung tissue by sepharose-salbutamol affinity chromatographic column. To prepare the β2-AR stationary phase, β2-AR was evenly immobilized on the surface of macro-pore silica with a mild chemical coupling method through covalent bond. The reten- tion properties of β2-AR stationary phase were characterized by four ligands, salbutamol sulfate, noradrenaline bitartrate, adrenaline hydrochloride and propranolol hydrochloride, to establish the β2-AR affinity chromatography. Then, the method was used to screen the active compounds from the total extracts of Semen Armeniacae Amarum. The results showed that β2-AR on the surface of the sta- tionary phase could keep its original bioactivity and selectivity. Amygdalin retained in the chroma- tographic column was proved to be the active compound of the total extracts of Semen Armeniacae Amarum. Compared with the existing chromatographic screening approaches, this method showed a good stability and high selectivity. The active compounds which could interact with β2-AR in traditional Chinese medicine (TCM) could be screened efficiently by this method, providing a new way to screen the active compounds in complicated samples such as TCM.

Hemoglobin-glucose oxidase catalyzed polymerization of aniline:Electrochemical study and application

A new method for the formation of electroactive polyaniline （PANI） biocatalyzed by hemoglobin coupled with glucose oxidase in neutral medium on the polystyrene nanospheres （PS） modified glassy carbon electrode, was investigated. The bio-polymerized PANI formed on the PS was confirmed by the obvious increase of the diameter of the particles on the scanning electron microscopy image. The cyclic voltammetric behavior of the PANI was also investigated. PANI produced an oxidative peak at 0.28 V and a reductive peak at 0.23 V. Based on the glucose-dependent bio-polymerization, a new electrochemical protocol for the estimation of glucose was developed. The square wave voltammetric response of PANI deposited on the modified electrode increased linearly with glucose concentration in the range of 0.1- 10.0 μmol/L. The efficient performance of hemoglobin-oxidase biocatalyzed polymerization of aniline provides a new concept for the synthesis of nanomaterials, and a general protocol for the development of the biosensors.

Catalytic Adsorptive Stripping Voltammetry at a Carbon Paste Electrode for the Determination of Amiodarone

Voltammetry using solid electrodes usually suffers from the contamination due to the deposition of the redox products of analytes on the electrode surface. The contamination has resulted in poor reproducibility and overelaborate operation procedures. The use of the chemical catalysis of oxidant on the reduction product of analyte not only can eliminate the contamination of analyte to solid electrodes but also can improve the faradaic response of analyte. This work introduced both the catalysis of oxidant K2S2O8 and the enhancement of surfactant Triton X-100 on the faraday response of amiodarone into an adsorptive stripping voltammetry at a carbon paste electrode for the determination of amiodarone. The method exhibits high sensitivity, good reproducibility and simple operation procedure. In 0.2 mol·L^-1 HOAc-NaOAc buffer （pH=5.3） containing 2.2×10^-2 mol·L^-1 K2S2O8 and 0.002% Triton X-100, the 2.5th-order derivative stripping peak current of the catalytic wave at 0.3 V （vs. Ag/AgCl） is rectilinear to amiodarone concentration in the range of 2.0×10^-10-2.3×10^-8 mol·L^-1 with a detection limit of 1.5×10^-10 mol·L^-1 after accumulation at 0 V for 30 s.

Leojaponic acids A and B, two new homologous terpenoids, isolated from Leonurus japonicus

The present study aimed at isolation and purification of the bioactive terpenoids from the herb of Leonurus japonicus by chromatographic separations such as silica gel, sephadex LH-20 and C18 reversed phase silica gel, as well as preparative HPLC. As a result, leojaponic acids A(1, C_(17)H_(24)O_4) and B(2, C_(18)H_(26)O_4), two homologous terpenoids, together with(-)-loliolide(3), 1-(3-ethylphenyl) ethane-1, 2-diol(4) and dibutyl phthalate(5), were isolated from the Et OH extract of L. japonicus. All the chemical structures of the isolates were elucidated on the basis of 1D and 2D NMR analyses. Compounds 1 and 2 were new terpenoids, and Compounds 3 and 4 were isolated and identified for the first time from this plant. In addition, the a-glucosidase and tyrosinase inhibitory activity of the new compounds were evaluated.

Soluble and Degradable Polyimides with Phenyl-2-pyridyl Ether Structure:Synthesis and Characterization

A diamine monomer o-phenylenedioxybis（5-amino-2-pyridine） was synthesized via reduction of a dinitro compound o-phenylenedioxybis（5-nitro-2-pyridine）, producing a series of new polyimides from this diamine and various commercially available aromatic dianhydrides via conventional two-stage processes. The resulting polyimides are able to form tough and transparent films, with decomposition temperatures in the range of 529-551 ℃, and can be dissolved in organic polar solvents. Meanwhile, these polyimides can be degraded in a hydrazine hydrate medium, a degradation mechanism proposed by analyzing the degradation products suggests that the degradable properties could be attributed to the phenyl-2-pyridyl ether structure in the polymer. In addition, the transformation of the compound structure from dinitro compound to damine monomer in the synthetic process is discussed in respect to X-ray structure.