Siegbert Pantel

SOME NEWER EXAMPLES OF THE APPLICATION OF CATALYZED INDICATOR REACTIONS IN TITRIMETRIC ANALYSIS.

Abstract The principles of the application of catalyzed reactions for the indication of end-points in titrimetric analysis are discussed. Some newer examples are given for this type of titration. An argentimetric titration (Cl-, Br-, I-), in which the indicator reaction is followed visually, and three compleximetric titrations in which the indicator reactions are observed photometrically (Mn), biamperometrically (Mn) and thermometrically (Cu), are described.

Catalytic-kinetic determination of copper and l-histidine with the use of a luminostat

Abstract A luminostat, a new type of “stat”-method is described. Copper(II) catalyzes the chemiluminescent reaction between luminol and hydrogen peroxide. The intensity of the luminescence is used via a photomultiplier and a current-voltage transducer to regulate the addition of hydrogen peroxide from an automatic burette. The rate of this addition necessary to keep constant a preset luminescence is a measure of the copper(II) concentration. As L-histidine acts as an inhibitor for copper(II) in this reaction, it can be determined indirectly. Copper (II) can be determined in the range 10–100 μg 20 ml , and L-histidine in the range 50–400 μg 20 ml .

Katalytisch-kinetische bestimmung von katalase, kupfer, molybdän und jodid mit hilfe eines biamperostaten

Zusammenfassung Biamperometrisch erfassbare Reaktionen konnen durch Verwendung eines Strom-Spannungs-Wandlers mit Hilfe der “Potentiostat”-Methode ausgewertet werden. Die durch Katalase katalysierte Zersetzung von Wasserstoffperoxid, die Kupfer-katalysierte Oxydation von Jodid mit Peroxidisulfat, die Molybdan(VI)-katalysierte Oxydation von Jodid mit Wasserstoffperoxid und die Jodid-katalysierte Oxydation von Arsen(III) mit Cer(IV) werden zur Illustration dieser Moglichkeit verwendet. Es werden die Katalysatoren Katalase, Kupfer, Molybdan-(VI) und Jodid sowie Azid als Inhibitor fur Katalase im p.p.b.-p.p.m.-Bereich bestimmt.

Catalytic-kinetic absorptiostat technique with the indigo carmine—hydrogen peroxide reaction as the indicator reaction

Abstract The absorptiostat method previously described is used for the catalytic-kinetic determination of sulphur compounds (sulphide, thioacetamide. thiourea and thiosulphate) in the micromolar range by means of their catalytic action for the indigo carmine—hydrogen peroxide indicator reaction. The thiosulphate catalyst is activated by iron(III) or aluminium(III); aluminium(III) is deactivated by fluoride. On this basis, iron(III) is determined in the ng range, and aluminium(III) and fluoride in the μg range.

Some new applications of the biamperostat catalytic-kinetic determination of copper, peroxidase, glucose oxidase, thyroxine and 5-chloro-7-iodo-8-hydroxyquinoline.

Abstract Biamperometrically observable reactions can be evaluated by the “potentiostat” method with a current-to-voltage transducer. Some further examples of the application of this “biamperostat” are described: the copper(II)-catalyzed autodecomposition of hydrogen peroxide, the horseradish peroxidase-catalyzed oxidation of iodide with hydrogen peroxide, the glucose oxidase-catalyzed oxidation of glucose with molecular oxygen and the iodine (in organic compounds )-catalyzed oxidation of arsenic(III) with cerium(IV). 1,10-Phenanthroline is determined indirectly by its inhibitory action on copper(II).

Catalytic-kinetic determination of thioureas by a biamperostatic method with iodine-azide as the indicator reaction

Abstract A biamperostat method is described, in which the iodine concentration in the iodine-azide reaction mixture is kept very low and constant by the automatic addition of increments of a potassium triiodide solution. This is used to determine the catalysts thiourea, phenylthiourea, benzoylthiourea and tetramethylthiuram sulphide in the nanomolar range in aqueous as well as in 20% ethanolic solution. The catalytic activities of another fifteen substituted thioureas are measured and listed.

Catalytic—kinetic determination of some iodine-containing organic compounds with different catalytic activities by a biamperostatic method

Abstract Iodine-containing organic compounds of the general formula X—C6H4—I catalyze the Sandell—Kolthoff reaction to different extents; the catalytic activities depend on the other substituent and on the relative positions of the X and iodine substituents. 4-Iodophenol, 2-iodophenol and 4-iodo-N,N-dimethylaniline can be determined in the microgram range.

Catalytic end-point detection in titrimetric analysis

Abstract In catalytic end-point detection, the first drop of titrant in excess is not used for a stoichiometric reaction with the indicator (as in conventional titrations) but acts as, or liberates, a catalyst for the indicator reaction. A very small excess of titrant thus suffices to catalyze large amounts of the indicator reaction mixture. Such catalytic end-points are therefore very sensitive. Terminology is discussed briefly. The various types of titration (direct, with a “brake”, reversed, indirect and substitution) and of end-point detection (visual, olfactory, photometric, thermometric and electrometric) are described. Applications of these techniques are summarized.

Stat methods in analytical chemistry : Kinetic techniques for catalyzed and uncatalyzed reactions

Abstract An important group of (catalytic-) kinetic methods uses “open systems”, in which, during the course of the reaction, a reactant is added or a product is removed, or even both. The “Stat methods” belong to this group. In the Stat methods, a preset stationary state within a catalyzed or uncatalyzed system is kept constant by stepwise addition of a suitable reagent, so that any change in a concentration is just compensated. Methods based on electrochemical techniques (pH-stat, potentiostat, amperostat and biamperostat) and on spectrophotometric and luminescence techniques (absorptiostat, fluorostat and luminostat) are described and their applications are summarized.

Thermometric and conductometric observation of copper(ii)-catalyzed reactions in the catalytic-kinetic difference method : Determination of microgram amounts of copper(ii)

Abstract The course of reactions in the catalytic-kinetic difference method, previously described, can also be followed by conductometry and thermometry. The copper-catalyzed decomposition of hydrogen peroxide can be followed by thermometry, and the copper-catalyzed oxidation of thiosulfate with hydrogen peroxide by conductometry. Both reactions can be used for the determination of microgram amounts of copper(II).