Gillis Johansson

An enzyme reactor electrode for urea determinations.

Abstract An enzyme reactor electrode system for the determination of urea is described. A buffer is pumped through an enzyme reactor (0.4 ml) containing urease immobilized with glutaraldehyde to glass. The effluent is mixed with sodium hydroxide pumped through a second channel and fed through an ammonia gas electrode. Samples are introduced via a third flow channel and mixed with the buffer. The conversion of urea to ammonia is quantitative for sample concentrations of less than 0.03 M for a flow rate of 40 ml h-1. The reactor electrode shows a Nernstian slope of 57 mV/decade for 5·10-5–3·10-2 M urea. The response is independent of variations in the flow rate, enzyme activity or temperature of the reactor.

Studies of copper(II) sulphide ion-selective electrodes

Changes in liquid junction potentials in copper(II) solutions were measured when different reference electrodes were used. The slope and intercept of a calibration curve for a copper-selective electrode will depend on the selection of reference electrode. The condition of the electrode surface of an Orion copper-selective electrode was studied microscopically and the influence of redox potential on stability of the electrode against corrosion is discussed. Oxidizing solutions will produce pits at dislocations in the material and there will be a mixed electrode potential. The slope, stability, and speed of response are much lower when the surface contains pits. Diamond-polishing was shown to improve the electrode significantly.

Ion-selective electrodes based on 7,7,8,8-tetracyanoquinodimethane-radical salts

Abstract Ion-selective solid-state electrodes were prepared from ion-radical salts of TCNQ. The copper-selective and the silver-selective electrodes showed only a few interferences and behaved according to Nernsts law over 5 and 6 decades of activities, respectively. The tetraethylammonium compound resulted in an electrode selective to this ion compared to ammonium and other tetraalkylammonium ions. The same was true for the tetraphenylarsonium electrode. The electrode response was reasonably fast and the stability acceptable for use as sensors in various applications.

A temperature-controlled graphite tube furnace for the determination of trace metals in solid biological tissue

A temperature-controlled graphite furnace for atomic-absorption analysis has been built and tested. The temperature of the graphite tube was monitored with an infrared-sensitive detector. Samples were introduced directly or via a separately heated graphite cup. Micro-samples of solid biological tissue were analysed directly for Zn, Mn and Co and the sensitivities for 1% absorption were 0.05,2 and 10 pg respectively. The salt content of the tissue limits the sample sizes, owing to non-specific absorption. The ashing conditions were investigated and found to be especially critical for Zn.

The resistance and intrinsic time constant of glass electrodes

Summary The resistance as well as the time constant of a glass membrane can be separated into one part originating in the glass body and one part in the surface. The surface glass time constant decreases rapidly with temperature, at room teperature it is of the size tens of seconds, while the glass time constant is in the millisecond range. By subdividing the parts further the results could be used for calculating jump distances of the conductive lithium ions. the size of the surface resistance was dependent on the hydration and is presumably caused by an energy barrier. A very accurate pulse technique was developed for the measurements.

An enzyme reactor electrode for determination of amino acids.

Abstract L -Leucine can be determined with an enzyme reactor electrode containing L-amino acid oxidase immobilized with glutaraldehyde to glass. The reactor also contains immobilized catalase which splits the hydrogen peroxide formed. Oxygen for the reaction is also supplied by adding hydrogen peroxide to the samples. The electrode is an ammonia gas sensor. The calibration curve is strictly linear with Nernstian slope between 3·10-5 and 10-3 M leucine.

The hydrogen-ion selective glass electrode.

The properties and mechanism of operation of hydrogen-ion selective glass electrodes are reviewed and a model using information from recent research is presented. In the gel layer of a pH-glass protons or hydronium ions are bound to negative charges in a silicon network cross-linked with bi- or tervalent metal ions. The composition of the gel layer is discussed; it is known that the outer part contains water. The formation of a gel layer and its destruction in alkaline solutions are discussed. Between the gel layer and the dry glass there is a transition layer characterized by a very high resistivity. This forms a barrier to ion transport and prevents rapid corrosion of the glass. The ionic mobilities of various ions change drastically with distance inwards towards the dry glass. The alkaline and acid errors are discussed as well as the asymmetry potential. By etching away the gel layers and the transition layers on both sides of the glass and then starting hydration simultaneously on both sides, two symmetric layers can be produced. This will result in an almost complete cancellation of the asymmetry potential. Some applications to precision measurements and measurement in non-aqueous solvents are discussed.

Single-point titrations: Part-I. The determination of bases

Abstract Equations are derived for the calculation of acid mixtures, which upon titration with base show a linear relation between pH and the amount of base. Three to five weak acids were used and a linearity of better than ±0.02 pH units was obtained. The use of such mixtures for analysis of the base content of samples by means of a single pH measurement is described. A procedure for obtaining conditional p K a values of the components of the acid mixture is also described. The single-point titration method is advocated for use when better accuracy than that of direct potentiometry is desired but less than that of an ordinary titration can be accepted. It is not necessary to know the p K b or the number of weak bases.

Alkaline errors of glass electrodes in non-aqueous solvents

Alkaline errors of glass electrodes in isopropanol were obtained from a comparison with the hydrogen electrode. Electrode glasses which show low alkaline errors in water are also more ideal in isopropanol. Univalent metal ions cause larger deviations than bivalent. Hysteresis effects were found in going from alkaline to acid solutions but not for the reverse direction.

Determination of nitrate in pickling baths with a nitrate-selective electrode and a standard addition procedure

Abstract A reverse addition method for the determination of nitrate in pickling baths is described. Calibration solutions of nitric acid were added to the standard solution so that the slope and intercept of the electrode response function could be determined. The standard deviation of the method was better than 1 %. Nitrate in pickling baths containing hydrofluoric and nitric acids was measured and compared to measured hydrogen ion concentrations as a function of running time for the bath. The effects of iron(III) and hydrofluoric acid on the results were studied.