A multivariate calibration procedure for the tensammetric determination of detergents

A multivariate calibration procedure based on singular value decomposition (SVD) and the Ho-Kashyap algorithm is used for the tensammetric determination of the cationic detergents Hyamine 1622, benzalkonium chloride (BACl), N-cetyl-N,N,N-trimethylammonium bromide (CTABr) and mixtures of CTABr and BACl. The sensitivity and accuracy depend strongly on the nature of the detergent. Acceptable accuracy is obtained with a two-step calculation procedure in which calibration constants for the total concentration range of interest are used to guide the choice of a more specific set of calibration constants which are valid for a much smaller concentration span. For Hyamine 1622, concentrations in the range 5 × 10−6−2 × 10−4 M could be determined with an accuracy of ± 10−6 M. For CTABr, these numbers were 3 × 10−6−2 × 10−4 M and ± 5 × 10−7 M; for BACl, they were 2 × 10−3−9 × 10−2 g l−1 and ± 1 × 10−3 g l−1. In the mixtures of CTABr and BACl, the accuracies were ± 3 × 10−6 M and × 1 × 10−3 g l−1, respectively

The computerized determination of double-layer capacitance with the use of kalousek-type waveforms and its application in titrimetry

A method for the rapid determination of double-layer capacitance—potential curves of electrodes is described. An on-line computer is used to apply Kalousek-type waveforms to the electrochemical cell and to measure the accompanying current response. The capacitances are determined from the slope of the plots of log current against time. For 0.1 M KCl, the computerized method agrees well with the bridge method, except for the potential range of 0 to –0.15 V. The method is very useful for automating titrations with tensammetric detection of the end-point. The method is applied to the titration of barium with a macrocydic compound (kryptofix 222) and the titration of cetyl-trimethyl-ammonium bromide with bromocresol purple. The accuracy of the titrations is ±2%

Artificial neural networks as a multivariate calibration tool: modelling the Fe-Cr-Ni system in X-ray fluorescence spectroscopy

The performance of artificial neural networks (ANNs) for modeling the Cr---Ni---Fe system in quantitative x-ray fluorescence spectroscopy was compared with the classical Rasberry-Heinrich model and a previously published method applying the linear learning machine in combination with singular value decomposition. Apart from determining if ANNs were capable of modeling the desired non-linear relationships, also the effects of using non-ideal and noisy data were studied. For this goal, more than a hundred steel samples with large variations in composition were measured at their primary and secondary K¿ and Kß lines. The optimal calibration parameters for the Rasberry-Heinrich model were found from this dataset by use of a genetic algorithm. ANNs were found to be robust and to perform generally better than the other two methods in calibrating over large ranges

The effects of disruptive and stabilizing selection on body size in Drosophila melanogaster. III. Genetic analysis of two lines with different reactions to disruptive selection with mating of opposite extremes

A genetic analysis was made of two lines which when subjected to disruptive selection with compulsary mating of opposite extremes (D−) showed a different response viz. one, D−-1, showing predominantly an increase of environmental variance and possibly interaction variance, the other, D−-2, showing an increase of genetic variance. Crosses between extreme flies within lines revealed that D−-1 genomes from large flies are dominant to genomes from small individuals. In D−-2 the genetic variation is predominantly additive variance. Tests for dominant chromosome effect in crosses with an inbred stock with recessive markers showed clear third chromosome differences in D−-2 and not in D−-1. Chromosome exchange between extreme flies corroborated the importance of genetic differences in D−-2. A factor or complex of factors with large effect decreasing body size is located on third chromosomes from small flies in D−-2. Interaction between chromosomes has a similar magnitude in the two lines. Crowding and temperature experiments did not reveal an increased general sensitivity to environmental factors in D−-1, which was suggested by the enlarged environmental variance of this line

Resonant frequency measurements as an alternative to phase-selective A.C. polarography in tensammetry and pseudocapacitance determinations

A new method is proposed for the determination of the double-layer capacitance and pseudocapacitance of electrochemical cells. The method is based on the measurement of the resonant frequency of the circuit consisting of the electrochemical cell connected in series with a standard inductor. The performance of the method is demonstrated with double-layer capacitance measurements at the dropping mercury electrode in 1 M KCl and butanol-1/1 M KCl mixtures and with the determination of heterogeneous charge-transfer rate constants ranging from 10−2 to 10−5 m s−1

The anodic oxidation of bases in the solvent m-cresol

The oxidation of bases in the solvent m-cresol was investigated by polarography, voltammetry at the rotating platinum disc electrode and by chronopotentiometry. It was shown that the m-cresolate ion is the electroactive species in this reaction. The oxidation is a one-electron process giving a phenoxy radical. This phenoxy radical is converted in a chemical reaction of higher than first order, most likely to the dimer

Modelling the permeability of polymers: a neural network approach

In this short communication, the prediction of the permeability of carbon dioxide through different polymers using a neural network is studied. A neural network is a numeric-mathematical construction that can model complex non-linear relationships. Here it is used to correlate the IR spectrum of a polymer to its permeability. The underlying assumption is that the chemical information hidden in the IR spectrum is sufficient for the prediction. The best neural network investigated so far does indeed show predictive capabilities

Computerized kalousek polarography

A versatile online computer-based system for Kalousek polarography features simultaneous recording of oxidation and reduction currents, averaging over successive scans, and processing of the polarographic data by curve-fitting. The accuracy for determinations of cadmium, potassium and lithium down to 10-5 M is ± 5% for pulse rates up to 25 Hz

Automated injection of slurry samples in flow-injection analysis

Two types of injectors are described for introducing solid samples as slurries in flow analysis systems. A time-based and a volume-based injector based on multitube solenoid pinch valves were built, both can be characterized as hydrodynamic injectors. Reproducibility of the injections of dispersed solids ( 150 ¿m) was tested with several concentrations of slurry samples up to 30 mg/ml; the injected volume was 1 ml. For both injectors dye and slurry samples could be injected with good precision (relative standard deviation for the peak area less than 2%). Peak detection was performed turbidimetrically. Data analysis and operation of the injectors were automated. The usual peristaltic pumps in flow analysis are normally not capable of handling slurries of the type investigated, therefore a valveless piston pump was used instead

The kinetics of the methanol synthesis on a copper catalyst: An experimental study

The kinetics of the low pressure of methanol from feed gases containing solely CO and H2 were studied in an internally recycled gradientless reactor. As experimental accuracy impeded the application of high CO contents, the experimental range of mole fraction of CO was limited to 0.04 to 0.22. The total pressure was varied from 3 to 7 MPa and the temperature from 503 to 553 K. Residence time distribution experiments confirmed the assumption of perfect mixing on a macroscale. A maximum likelihood approach was used to fit possible kinetic equations. Although more accurate results and better fits—compared to previous experiments in a simple integral reactor—were obtained, no single rate expression could be selected as the most appropriate one. This was mainly attributed to the effects of small amounts of CO2 and H2O formed in the reactor. Three different reaction rate equations fit the experiments equally well. Arguments are given that we never can expect to elucidate the reaction mechanisms on the basis of kinetic experiments