Torbjörn Anfält

Determination of oxidized ketone bodies in milk by flow injection analysis

Abstract A flow injection method is described for the determination of oxidized ketone bodies in milk. Acetoacetate is decarboxylated to acetone at 100°C. Acetone is separated from the sample by gas diffusion through a teflon membrane and measured spectrophotometrically. The detection limit is 0.1 mM. Accuracy and reproducibility are good up to 5 mM. The sample capacity is up to 100 samples/h.

A Urea Electrode Based on the Ammonia Probe

Abstract An enzyme electrode specific for the substrate urea is described. The electrode consists of a layer of urease polymerized directly on to the surface of the gas diffusion membrane of an ammonia probe by means of glutaraldehyde. The calibration curves obtained when the electrode is allowed to measure in buffered solutions are discussed in terms of enzyme activity and pH-gradients in the membrane.

The precision and accuracy of some current methods for potentiometric end-point determination with reference to a computer-calculated titration curve

Abstract Accurately calculated titration curves make it possible to select the optimal method for evaluating the end-point of a particular potentiometric titration, with respect to systematic error, precision and time required. The potentiometric titration of fluoride with thorium(IV) solution is used as an example. Decreasing systematic error is obtained by the different methods in the following order: methods based on sigmoid curves > differential methods based on Δ E /Δ v plots > differential methods based on Δ v /Δ E plots > methods based on mass-balance and equilibrium equations. Increasing precision is obtained in approximately the same order. The conclusions appear to be generally applicable and are useful in the construction of automatic titrators.

Effect of carboxylic acid buffers on the potentiometric titration of fluoride with lanthanide nitrates using a lanthanum fluoride membrane electrode

Abstract By means of potentiometric titration of fluoride with lanthanide nitrates in the presence of carboxylate buffers it has been shown that formate, acetate, propionate and n-butyrate (A-) interfere with the precipitation reaction. Precipitates with the formula LnF3-xAx (Ln=La, Ce, Pr, Nd, Sm) are formed and the carboxylates cause the lanthanum fluoride membrane electrode to work sluggishly after the titration. Chelating ligands such as lactate, malonate, citrate and acetylacetonate also affect the lanthanum fluoride membrane, and, after titrations in such media, the electrode could be regenerated only by polishing its surface with diamond paste and then immersing it in dilute sodium fluoride saturated with lanthanum fluoride.

Effect of acetate buffer on the potentiometric titration of fluoride with lanthanum using a lanthanum fluoride membrane electrode

Precipitation titrations of fluoride with lanthanum nitrate using a lanthanum fluoride electrode have been carried out at constant ionic strength and different acetate concentrations. The titration curves have been analysed by rigorous equilibrium calculations with the computer program HALTAFALL. Acetate ions have been shown to enter the solid phase, forming precipitates with the formula LaF3-xAcx (0<x<1). The presence of acetate causes the electrode to work sluggishly and to deviate from the Nernst law. These effects increase with increasing acetate concentrations and may possibly even occur at high nitrate concentrations.

SPECIES FORMED IN THE POTENTIOMETRIC TITRATION OF FLUORIDE WITH THORIUM OR LANTHANUM NITRATE AND FUNCTIONS SUITABLE FOR THE EVALUATION OF THE EQUIVALENCE POINTS.

Abstract Calculations by means of SILLENs HALTAFALL program have been performed on experimental curves by LINGANE for the potentiometric titration of fluoride with thorium and lanthanum in different media. After adjusting the stability constants for some of the main species formed during the titration a good fit was obtained between the experimental data and the calculated titration curves. In the cases where the solution was buffered with acetate it was necessary to consider the formation of mixed fluoride-acetate complexes. Suitable functions for the evaluation of the equivalence point could be derived from the calculations. If the functions: F 1 =( v 0 + v )[F - ] and F 3 =( v 0 + v )[F - ] -3 are used before and after the equivalence point, respectively, it ought to be possible to determine fluoride very accurately by titration with lanthanum nitrate in an unbuffered solution. A value proportional to [F - ] is obtained from 10 exp (—EF/RT In 10), the Nernst e.m.f. equation.

A computer-processed semi-automatic titrator for high-precision analysis

Abstract A mini-computer processed semi-automatic titrator equipped with an analogue scanner, a digital voltmeter and a 16-bit relay register is described. The scanner has 100 channels available for input voltages and the voltmeter can measure signals in the range 0–100 V at a maximum rate of 20 readings sec−1. The relay register can be used to process simultaneously a maximum of 16 motor-driven syringe burets independently of each other. The titrator can be programmed in Assembler, Fortran and Basic. A major principle behind the design of the titrator is simplicity in programming, and this is achieved by the use of Basic callable subroutines to all peripheral equipment e.g. scanner, voltmeter and relay register. The titrator is therefore especially suitable for use in the research analytical laboratory.

The determination of bromide in natural waters by flow injection analysis

Abstract Bromide can occur in well waters as a result of sea water intrusion. The phenol red method is adapted to a flow-injection system and interferences are studied by using a two-channel valve. Standards are injected from one loop of the valve while the possible interferent is injected from the other loop; this provides a fast means of evaluating interferences. Ammonia, cyanide and humic substances interfere. Bromide can be determined down to 2 μM at a rate of 80 samples per hour

A micro-computer system for potentiometric stripping analysis

Abstract In potentiometric stripping analysis, trace metals are first amalgamated into a mercury film electrode and then oxidized back into solution by an oxidant. The potential vs. time curve is recorded. Microcomputer-controlled equipment for automation of the potentiometric stripping analysis is described. The higher resolution of time compared to manual equipment increases the sensitivity of the method. A resident, 3-kB BASIC interpreter with routines for handling the hardware makes the programming simple and the instrumentation flexible for changes in the analytical scheme. Printer and keyboard are incorporated in the equipment which makes the whole analyser compact.

A simple automatic phototitrator for the determination of total carbonate and total alkalinity of sea water

Abstract An automatic photometric analyser based on the reversed use of a conventional motor syringe buret and modern optoelectronic components is described. The buret serves as a photometric titration vessel into which sample and reagents are selectively drawn through a set of solenoid valves. It has been applied to the photometric titration of total alkalinity and total carbonate concentration of sea water, giving precisions of 0.10% and 0.13%, respectively.