Antonín Trojánek

The continuous removal of oxygen from flowing solutions

Abstract An apparatus for continuous removal of oxygen or other dissolved gases from liquid samples is described; it is useful in continuous analyses. The gas diffuses through a semipermeable membrane into a space with a lower partial pressure of the particular gas. The separation unit consists of two concentric tubes and is practical and efficient. The mathematical model for transport under conditions of stationary gas diffusion with laminar flow of the liquid in the tube did not correspond satisfactorily to the experimental relationship, probably because of turbulence in the flow.

A wall-jet conductometric detector for determination of sulphur dioxide in air after preconcentration in water in an aerodispersion unit

Abstract Sulphur dioxide is preconcentrated from air into a polydispersed aerosol of water. The aerosol condenses on impact on the detector, on the surface of which a film of the condensate is maintained. The conductance of the liquid film is measured with a pair of platinum electrodes. The calibration dependence is nonlinear but corresponds to the theoretical model. The concentration range 0.05–2.2 mg SO2 m−3 was studied. The detection limit was 2 × 10−3 mg m−3; the relative standard deviation for 0.38 mg m−3 was 2.4%. A steady-state response to a change in SO2 concentration was attained within ca. 70 s. Ammonia is the only interferent.

Flow-through coulometric stripping analysis and the determination of manganese by cathodic stripping voltammetry

Abstract A simple flow-through system is described for collection of liquid samples into a closed loop. This arrangement can be used for coulometric determinations by the stripping method without previous calibration. The usefulness of the system is demonstrated on the determination of manganese (ca. 10 -6 M) in acetate buffer by cathodic stripping voltammetry.

Thin-layer polarographic detector for the high-performance liquid chromatographic detection of thiourea derivatives

A polarographic thin-layer detector for high-performance liquid chromatography, was devised. The detector has a sandwich structure with a working surface area of the mercury electrode of 0.25 mm2. The detector was applied to the direct amperometric detection and for detection with reactivation of the electrode surface by voltage pulses. It is shown that the latter detection mode is suitable for the determination of compounds that form insoluble or complex mercury salts, e.g., thiourea. Thiourea and its derivatives can be separated and determined in a wide concentration range and the detection limit for thiourea corresponds to 2 ng injected. Thiourea can be determined directly in urine.

Current sampling in polarography without synchronization with the drop time

Abstract The circuit proposed for sampling of polarographic currents enables oscillations on the recorded curves to be eliminated without distortion of the curve. The apparatus, based on a peak detector, can be used regardless of the shape and character of the curves, and does not require indication of drop disconnection. When the necessary conditions are fulfilled, the output signal is identical with the signal from a Tast polarograph.

Improved low noise differential pulse polarography

Abstract A method for the improvement of the signal to noise ratio in differential pulse polarography is proposed. The electrode is polarized by means of a double voltage step during which the current is sampled using an integration technique in which line and random noise is cancelled.

Amperometric detection of nitrates using a flow-through membrane detector

Abstract A flow-through amperometric detector has been developed based on the electrochemical reduction of nitrates at a silver cathode. The nitric oxide formed is detected by a gold-plated porous membrane electrode placed downstream in the detector. Nitrates were mostly determined in samples containing 5 × 10 −2 M H 2 SO 4 . The sensitivity of the determination is expressed as the slope of the regression straight line was 0.85 nA μ M −1 in the range 5 × 10 −6 to 10 −3 M NO − 3 . The limit of quantitation determined as ten times the peak-to-peak background noise amplitude was 8 × 10 −7 M NO − 3 . The relative standard deviation for the determination of 5 × 10 ∂ and 10 −4 M NO − 3 was 3.6 and 0.8%, respectively. The most important interference in the determination of nitrate is that from nitrite, which exhibits identical behaviour in the determination. A method has been proposed which eliminates the effect of nitrite and permits its simultaneous determination in the presence of nitrate.

Determination of the flotation collector ethyl xanthate by flow-injection analysis.

A flow-injection method for determination of xanthate with amperometric detection is presented. A composite carbon electrode modified with silica gel is used for detection. Very good reproducibility (1.5% r.s.d.) results from renovation of the electrode surface by three potential scans between measurements. In the analysis of flotation liquor, the interfering effect of metal complexes, formed by leaching of the ore in water, is eliminated by addition of EDTA. The method can be used to determine ethyl xanthate in the concentration range 0.10-10.0 mg/1, with a detection limit of 0.04 mg/1.

Determination of ruthenium as ruthenate by stripping voltammetry

Abstract Stripping voltammetric analysis of ruthenium with a platinum RDE was studied in the concentration range from 5×10 −7 to 1.2×10 −5 M RuO 4 2− , where linear dependence of the anodic peak height on the ruthenate concentration was obtained. Special attention has been paid to a simple preparation of the sample for analysis. Ruthenate can be prepared directly in the electrolytic vessel from the ruthenium compounds by oxidation with potassium persulphate in alkaline medium. As a supporting electrolyte 10 −2 to 5×10 −2 M K 2 S 2 O 8 with 10 −1 to 1 M KOH was used.

Oxidation of organic compounds with electrogenerated oxidant: V. Oxidation of some unsaturated organic compounds

Summary By means of electrogenerated Os(VIII) the oxidation of some unsaturated organic compounds such as styrene, cyclohexene and maleic acid was studied. For maleic acid the effect of the substrate concentration on the reaction rate was demonstrated. The observed deviation from the first order dependence was explained taking into account a mechanism proceeding via intermediate complex oxidant-substrate formation.