LCEC Detector with Graphite-Teflon Electode

Abstract

A compression molded graphite-Teflon electrode is evaluated as a detector for the electrochemical detection of phenolic compounds, separated by reverse-phase high-performance liquid chromatography. Detection limits for these phenolic compounds range from 0.5–1 ng. Repetitive injections yield peak heights with RSDs less than 1%. Passivation of electrode surface by phenols is discussed. In addition, construction of a flow cell to be used in conjunction with graphite-Teflon electrode is also described.     

AgI-Ag2O-V2O5 glasses as ion-to-electron transducers for the construction of all-solid-state microelectrodes

A method for the fabrication of ion-selective all-solid-state microelectrodes is presented. The ion-to-electron transduction process takes place into the transducer material. In this approach, AgI-Ag₂O-V₂O₅ glasses, which exhibit ionic and electrical conductivity are applied as ion-to-electron transducers of polymeric membrane microelectrodes. All-solid-state electrodes based on potassium-sensitive poly(vinyl chloride) membranes, deposited directly on the surface of glass composites, exhibited theoretical responses. Their selectivity and durability were comparable to planar microelectrodes containing an internal electrolyte immobilized in the intermediate hydrogel layer. The only disadvantage of the proposed structures was their limited reproducibility. Moreover, it was found that the unmodified AgI-Ag₂O-V₂O₅ glasses can be applied as ion-sensitive membrane of solid-state microelectrodes for the determination of Ag⁺ and I⁻ ions.     

Miniaturization of a standard liquid chromatographic system

Summary Methods for the construction of micro-columns equipped with low dead volume end fittings and an easy way to miniaturize a standard flow-cell to a volume of 0.67 mm³ are described. Operation characteristics of the microcolumns were evaluated by plate height versus linear velocity and plate height versus capacity factor plots. The influence of the volume of the flow-cell on the resolution is also demonstrated. An improvement of the resolution factor (R_S) from 0.9 to 1.45 between sulphapyridine and sulphamerazine was obtained by using the 0.67 mm³ flow-cell instead of the 12.5 mm³ original flow-cell. The influence of the sample volume on the separation efficiency is also shown.     

In-Stream Masking of Aluminium in the Determination of Fluoride by Flow-Injection Potentiometry

Abstract

The ability of selected complexing agents to mask aluminium and release fluoride for potentiometric determination in-stream has been assessed. The experimental manifold incorporated a cascade flow cell and comprised two flow paths, the first for conventional flow-injection and the second enabling stopped-flow analyses to be performed. For solutions containing equimolar quantities of Al and F at concentrations up to 10^?3 M in each ion, better than 90% fluoride recovery was achieved in 16s using Tiron. At higher aluminium loadings, fluoride was released more slowly, with citrate and DCTA being found to be more efficient than Tiron. At an Al. F ratio of 4:1 (10^?3 M F), relative release rates for fluoride over a 10 minute period occurred in the following order:

citrate > DCTA > Tiron > tartrate > EDTA

Acetate and hexamine buffers, often recommended as components in TISAB formulations, were as effective as EDTA in releasing fluoride. Using an acetate buffer with citrate as the decomplexing agent slowed this release. Aged Al/F solutions responded almost as quickly as fresh solutions to Tiron and DCTA, with small pH-related effects being observed for solutions 20 days old.     

Electrocatalytic Functionalized Specialty Paper as Low-Cost Porous Transport Layer Material in CO2-Electrolysis

The development of low-cost and efficient electrolyzer components is crucial for practical electrochemical carbon dioxide reduction (ECR). In this study, facile non-woven cellulose-based porous transport layers (PTLs) were developed for high current density CO₂-to-CO conversion. By depositing a cobalt phthalocyanine (CoPc) catalyst-layer over the PTLs, we fabricated ECR-functioning gas-diffusion-electrodes (GDEs) for both flow-cell and zero-gap electrolyzers. Under optimal conditions, the Faradaic efficiency of CO (FE_CO) reached 92 % at a high current density of 200 mA cm⁻². Furthering the architecture of the GDEs, CoPc was incorporated into the initial PTL slurry, forming ECR-active PTLs without the need for an additional catalyst-layer. The new GDE-architecture favored the CoPc-distribution by enhancing the contact and interactions with the carbon substrate and demonstrated a stable electrolysis process for over 50 h in a zero-gap cell at 200 mA cm⁻² with a FE_CO of 80 %.     

Continuous Blood Monitoring of Hard Beta-Emitting Isotopes in Small Laboratory Animals

Abstract

A monitoring system for recording very fast variations in blood levels of ³²P-labeled compounds is described. The flow-cell used is suitable for continuous determinations in anesthetized small laboratory animals (e.g. rats). The technique reported has been developed for hard beta-emitting isotopes. However, changing the counting unit, the described flow-cell can be adapted for gamma-emitting isotopes. With our system, efficiencies of the order of 40% have been obtained for ³²P in whole blood.