Precise coulometric determination of redox inert anions based on electrolysis at the aqueous|organic solution interface

The flow cell proposed previously for the rapid and coulometric determination of cations based on the electrochemical ion transfer at the aqueous|organic solution interface was improved to be applicable to the determination of anions. The developed cell was composed of a porous poly(tetrafluoroethylene) tube (1.0 mm in inner diameter), a copper wire (0.8 mm in diameter) inserted into the tube, a platinum wire placed outside the tube, an organic solution into which the tube was immersed and a reference electrode in the organic solution. The aqueous solution containing a species of interest was flowed through the narrow gap between the tube and the copper wire. A potential difference was applied at the aqueous|organic solution interface by using the copper wire and the reference electrode in the organic solution in order to realize the ion transfer at the interface, and the current due to the interfacial ion transfer was detected by the copper and platinum wires. The developed cell was evaluated adopting the transfer of an anion such as perchlorate, picrate or alkylsulphonates from the aqueous solution to 1,2-dichloroethane (used as the organic solution), and demonstrated that the anions of 10⁻⁴ mol dm⁻³ level could be determined with coefficients of variations better than 0.2% (n = 5). The applicability of the developed cell to the flow injection analysis of anions was also discussed.     

解热静口服液的薄层色谱鉴别及总蒽醌的含量测定

对解热静口服液中的大黄、大青叶、黄芩、青蒿、草果进行了薄层色谱鉴别，方法简便、重现性好。还以大黄素为代表成分，采用比色法测定了该口服液中大黄总蒽醌的含量，平均回收率为９７．５４±１．６８％（ｎ＝６）。     

Using of HPLC coupled with coulometric detector for the determination of biotin in pharmaceuticals

The method for the determination of biotin by high performance liquid chromatography (HPLC) coupled with coulometric detector is presented here. Chromatographic and detection conditions were tested. A LiChrospher 60RP-select B column (250 mm × 4 mm; 5 μm) and the mobile phase containing 0.24 mol/L aqueous solution of acetic acid and acetonitrile in the ratio 85:15 (v/v) were found as the most suitable. The flow rate was 1 mL/min and the injected volume of the sample was 20 μL. The hydrodynamic voltammogram of biotin was measured and according to obtained data the detection parameters were set – channel I 600 mV, channel II 900 mV, sensitivity 1 μA. The developed method has been validated. The calibration curve is linear in the range 15–3600 ng/mL, correlation coefficient is 0.9998, limits of detection and quantification are 5 and 15 ng/mL, respectively. Recovery of the spiked samples was 98.67% with R.S.D. 0.255% on average. The developed method has been successfully applied for determination of biotin in pharmaceutical preparations.     

薯蓣属植物中薯蓣皂甙元的测定

本文介绍了一个简单、准确的测定薯蓣属植物中薯蓣皂甙元的方法。生药经水解、提取后,以薄层层析法分离薯蓣皂甙元,然后用库伦滴定法进行测定,并用此法分析了十多个不同品种和产地的薯蓣属植物的含量,为生产提供了参考数据。     

萹蓄中萹蓄甙的含量测定

本文介绍了萹蓄草用80%乙醇提取后,以薄层色谱法分离出篇蓄甙,用库伦滴定法或紫外分光法进行定量。本法操作简单,需样量少,重现性好。测定生药的变异系数约为2%。     

Real-time stoichiometry monitoring of electrodeposited chalcogenide films via coulometry and electrochemical quartz-crystal microgravimetry with hydrodynamic control. Ag2+δSe case

Potentiostatic coulometry is used in conjunction with electrochemical quartz-crystal microgravimetry (EQCM) with controlled hydrodynamics to develop a new electroanalytical protocol for in situ composition monitoring of metal chalcogenide thin films. The approach, its application scope and limitations, are illustrated using the example of electrosynthesized Ag_ySe thin films, successfully used previously for developing ion-selective sensors for Ag(I), cyanide and Hg(II). Well-defined flowing electrolyte conditions are achieved by the EQCM/submerged wall jet (SWJ) cell arrangement. The electrolyte flow rate through the nozzle is maintained constant between 5.5 and 250 cm³ min^?1. The hydrodynamic control makes it possible to extend the range of the combined EQCM/coulometric approach to greater layer thickness consistent with that of membranes practically used in sensor preparation. The stoichiometric coefficient (y) profile of Ag_ySe is monitored in situ for comparatively thick electrodeposited films (up to 800 nm). Two distinct features are clearly distinguished in the electrochemical formation of non-stoichiometric layers: in the zone adjacent to the substrate (i.e. between 170 and 270 nm) and for greater thickness (up to 800 nm). A mean value for y=2.24±0.06 is determined for the deposited layers, which is in good agreement with the values previously obtained by ex situ energy dispersive X-ray fluorescent microanalysis (EDAX).     

Electrochemical study of some three-derivative compounds of 1-phenyl-4-butyldithiocarboxylate-5-hydroxypyrazol (3D-FBDTCHP)

An electrochemical study related to the electrooxidation of the 3-hydroxyl and 3-methyl derivatives of 1-phenyl-4-butyldithiocarboxylate-5-hydroxypyrazol in aqueous ethanolic solutions covering a wide pH interval has been performed. In this study, these compounds are considered as potential collector agents for copper mineral sulfide flotation. From the potentiodynamic parameters for both compounds in solution, as well as for the 3-methyl derivative adsorbed on a glassy carbon electrode surface, it was established that these compounds undergo a dimerization process involving the formation of the respective bisthiocarbonyl disulfide derivative. On the basis of the voltammetric and coulometric data, as well as from the analysis of the product obtained after a preparative electrolysis carried out with the 3-methyl derivative, a mechanism accounting for the nature of the reaction product in aqueous ethanolic solutions is proposed.