Liliana Ilcheva

Effect of addition of main ion to carrier solution in potentiometric flow-injection measurements with solid state ion-selective electrodes

SummaryFlow-injection measurements were performed using chloride, fluoride, iodide and copper(II)-selective electrodes. A pronounced effect of addition of main ion to the carrier solution was observed for the fluoride- and iodide-selective electrode. Super-Nernstian slope observed for the fluoride- and copper(II)-selective electrode in the absence of the sensed ion in the carrier solution decreased to Nernstian values in the presence of the measured ion in the carrier solution. This phenomenon is explained by different response times at different concentrations of the sensed ion.

Flow injection analysis of chloride in tap and sewage water using ion-selective electrode detection

ZusammenfassungEs wird der Einsatz einer ionenselektiven Chloridelektrode in Verbindung mit der Fließinjektionsanalyse von Chlorid in Leitungs- und Abwasserproben beschrieben. Mittels einer extrem einfachen Anordnung lassen sich so zwischen 60 und 120 Proben stündlich analysieren. Die Standardabweichung beträgt bei Chloridgehalten >100 ppm ca. 5% und bei Gehalten um 10 ppm ca. 10%. Wenn eine AgCl-Einkristallmembranelektrode in Verbindung mit einer hohen Flußrate benutzt wird, stören die üblichen Störionen, wie Iodid, Bromid usw., um Größenordnungen weniger als üblich.SummaryThe application of a chloride-selective electrode in flow injection analysis of chloride in tap and sewage water samples is described. With an extremely simple experimental set-up, from 60 to 120 samples per hour can be analysed. The standard deviation lies at 5%, when the chloride content is above 100 ppm, and 10%, if 10 ppm are present. Using a AgCl single crystal ion-selective electrode and high carrier solution flow rates, interfering anions like iodide, bromide, etc. are kinetically discriminated against and interfere only at orders of magnitude less than usual.

A simple, selective and sensitive liquid-chromatographic or flow-injection detector for chloro-organic compounds based on ion-selective electrodes

ZusammenfassungEs werden erste Ergebnisse des Einsatzes einer ionenselektiven Chloridelektrode in Verbindung mit einer Fließinjektionsanalyse von Organochlorverbindungen beschrieben. Die organische Verbindung wird vor der Detektion entweder elektrochemisch oder durch UV-Bestrahlung unter Bildung von Chloridionen zerstört. Das Nachweisvermögen einer Anordnung, die ca. 30 Analysen pro Minute erlaubt, liegt bei wenigen Nanomol Chlor. Die Reproduzierbarkeit liegt bei Injektionen von 50 μl einer 10−3 mol/l Cl enthaltenden Verbindung bei ca. 5% rel. Brom, Jod und Thiolschwefel enthaltende Verbindungen werden ebenfalls angezeigt, lassen sich aber durch zusätzliche ISEs selektiv erfassen.SummaryThe application of a chloride-selective electrode in flow injection analysis of chloro-organic compounds is described. In this feasibility study, the organic compound is destroyed, liberating chloride ions, either electrochemically or by UV radiation before entering the electrochemical cell. The detection limit of an assay performing about 30 determinations per minute lies in the nanomole range. The standard deviation lies at about 5% if 50 μl of a 10−3 mol/l solution of a Cl-containing compound are injected. Compounds containing bromo-, iodo- or thiol groups are also detected. With additional ISEs they can be determined more selectively.

Coulometric detector cell for use with flow injection

A two-electrode cell for constant potential coulometric detection in flow injection systems has been developed. The cell has a saturated calomel electrode with a large surface area and a porous working electrode made of platinum particles. The calomel electrode is not polarised, the potential is kept constant and the electrode serves as both reference and counter electrode. This design of the calomel electrode provides a detector that is simple to construct and easy to use. The cell was tested with the coulometric determination of thallium(I) by means of its oxidation reaction to thallium(III) in a 0.1 M hydrochloric acid medium. A 1.025 V constant potential was applied. Amounts of 0.02–0.17 µequiv. of thallium(I) were determined at flow-rates of 0.2–1.0 ml min–1, respectively. The detection limit was 8 pequiv. of thallium(I) at a signal to noise ratio of 2:1 and a flow-rate of 1.0 ml min–1. Amounts between 0.006 and 5.80 µg of thallium(I) were determined by flow injection with a relative standard deviation of 3–6%. A procedure is proposed for calculation of the dispersion in a flow-injection system with coulometric detection.

Continuous flow and flow injection potentiometry of complex-bonded metal ions by the standard additions method

A new approach is proposed for the description of the dispersion of confluent streams. It offers the possibility to define, theoretically, a standard additions method in continuous flow and flow injection systems. This method allows the application of a single or multiple standard additions techniques as illustrated in the determination of the total content of complex-bonded silver ions in the presence of an excess of sodium thiosulfate. A silver ion-selective electrode was used. The method was checked within the concentration range 10–6–10–1 mol l–1 silver nitrate, the relative error varying between 2 and 8%.

Differential flow injection potentiometry

A differential flow injection potentiometric method, with two different ion-selective electrodes placed in series, is described. The dispersed sample contacts successively the two electrodes. In this situation, for a certain time interval each ion-selective electrode performs a reference function towards the other, which in this time interval reacts with the sample. In this way nitrate and chloride ions, and nitrate and ammonium ions could be determined simultaneously with nitrate and chloride-selective electrodes, and with nitrate and ammonium electrodes, respectively. It is shown, that by means of the differential flow injection technique it is possible to determine the nitrate content with a relative error of 10%, when the chloride ion concentration is thousand times higher.

Flow injection spectrophotometric determination of the biuret content in urea fertilisers

The flow injection spectrophotometric determination of biuret, based on the formation of the copper(II)-biuret complex with an absorption maximum at 550 nm, is described. The relationship between the peak height (absorbance) and the concentration of biuret was linear up to a concentration of 5.0 mg ml–1. The method is highly selective. Ammonia, which is the only interferent, was removed by a Dowex ion-exchange column built into the flow injection system. The method was applied to the determination of biuret in a commercial urea fertiliser. Fifty samples can be analysed per hour with a relative standard deviation of 1.2–2.5%.

HETEROGENEOUS EQUILIBRIUM BETWEEN SOLUTION AND SLIGHTLY SOLUBLE COMPOUND IN FLOW INJECTION ANALYSIS: PLATINUM(IV) DETERMINATION

SummaryA new principle of flow injection analysis using a precipitation reaction is suggested. It is based on a change of the equilibrium between solution and slightly soluble compound when passing the solution studied through a reaction column, containing a slightly soluble compound. H2PtCl6 is determined with a column containing Tl2PtCl6. The detection is performed by the current of thallium(I) oxidation to thallium(III) on a platinum electrode. Two different flow injection schemes are used. The determination of platinum(IV) is applied to platinum analysis in spent industrial alumoplatinum catalysts.