A Kalman filter for calibration,evaluation of unknown samples and quality control in drifting systems : Part 3. Variance reduction

The performance of fixed-interval smoothing is investigated for a linear calibration graph with drifting parameters. When all the calibration measurements are processed on-line by the Kalman filter, the quality of the evaluated results may be improved by later off-line smoothing. It is shown that a considerable reduction in variance can be obtained.     

A Kalman filter for calibration,evaluation of unknown samples and quality control in drifting systems : Part 4. Flow Injection Analysis

The application of state estimation in flow injection analysis is described. The linear calibration graphs normally provided often suffer from drifting parameters. The entire system is absed on a set of algorithms for prediction, filtering, smoothing, evaluation, control and optimization. Selection and verification of the calibration model and the noise covariances used are investigated. The experimental results demonstrate the applicability of the calibration system in practice as a simple intelligent analyzer. The spectrophotometric determination of chloride in aqueous samples serves as the example.     

A kalman filter for calibration,evaluation of unknown samples and quality control in drifting systems: Part 2. Optimal Designs

It is well known that the optimal design for linear calibration is found at the extremes of the concentration range. For the evaluation of unknown samples, the precision is maximal at the mean value of the calibration standards. If the static model is replaced and stochastic behaviour of the parameters with extension to drift is assumed, only minor differences on these generalizations are obtained. The intelligent analyzer described here integrates on line procedures for calibration, evaluation, quality control and optimization.     

Heterogeneous samples in flow-injection systems : Part 1. Whole Blood

It is shown that the direct analysis of heterogeneous samples by non-steady state flow methods is associated with error because of undefined dilution and dispersion. This problem is examined theoretically and confirmed experimentally on determinations of pH and CO₂ in whole blood. It is also shown that microbubbles attached to the surface of a microelectrode or CHEMFET can substantially reduce the precision of the results.     

Comparison of the Kalman filter and dedicated algorithms for processing data for solution equilibria,noise smoothing and calibration

The suitability of the Kalman filter for extracting acidity (protonation) constants from titration curves, for noise removal, and for multicomponent determinations in the presence of sample-related interferences is described. The performance of the algorithm is illustrated with simulated examples and checked by comparing the results with those obtained by dedicated methods (Savitzky-Golay and Fourier-transform procedures and the general standard-addition procedure). The ability of a combination of two Kalman filters as a fixed-interval smoother for noise removal is stressed.     

Heterogeneous samples in flow-injection systems : Part 2. Standard Addition

It is shown that the effect of undefined dispersion in flow injection analysis (f.i.a.) of heterogeneous samples can be eliminated by the method of standard addition. This is a significant improvement over the direct calibration method. However, because f.i.a. is basically a precise dilution method, the initial free volume of the sample (e.g., total volume minus hematocrit, for whole blood)_must be known in order to produce accurate results for such samples. The Gran plot technique is adapted for f.i.a. and it is shown that the dispersion, D, can be obtained from these experiments.     

Simulations for evaluation of kinetic methods in differential scanning calorimetry. Part 1. Application to single-peak methods: Freeman-Carroll, Ellerstein, Achar-Brindley-Sharp and multiple linear regression methods

In order to simplify the choice between different kinetic methods used in differential scanning calorimetry, an interesting way for testing kinetic treatments is proposed, using simulated thermoanalytical curves computed from given kinetic parameters. Applied to the study of a polymerization, we tested the Freeman-Carroll, Ellerstein, multiple linear regression (reaction-order model) and Achar-Brindley-Sharp methods. The test of the validity of the methods is performed using the LSM parameter that represents the fit between the mathematical treatment used in the kinetic model and known data. The study reveals the importance of the number of points used, i.e. the resolution, in the thermoanalytical curve recording, especially for the Freeman-Carroll and Ellerstein methods, there being an increase in the relative error on all the kinetic parameters when the number of points is decreased. Maximum relative errors are reported for the pre-exponential factor calculations. Evaluation of the enthalpy error on the determination of the kinetic parameters has been performed. Simulations obtained with various enthalpies indicate the necessity in such cases of computing a relative dimensionless LSM parameter (relative to the amplitude of the phenomena) in order to compare different thermal effects.     

Theory of helicenic hydrocarbons. Part 1: Invariants and symmetry

Helicenes form a subclass of polyhexes and correspond to hydrocarbons of considerable chemical interest. This paper is the first part of a general graph-theoretical treatment of helicenes. The invariants are studied: the relations between them, their possible values, and their upper and lower bounds in helicenes. Extremal helicenes and circular helicenes are useful definitions of subclasses of the systems under consideration. Finally an account of symmetry of helicenes is given.On leave from: Department of Mathematics, Xinjiang University, Wulumuqi Xinjiang 830046, People's Republic of China.     

Collaborative study for the quality control of trace element determinations in paint coatings Part 1. Interlaboratory study

Since the adoption of the European Standard EN71: Part 3 on toy safety, there has been dissatisfaction with the poor reproducibility obtained between laboratories using the test method for the determination of the migration of certain elements from paints to toys. This lack of quality control could result in toys being judged unacceptable with regard to the requirements of the EC Directive 88/378/EEC, which creates a potential barrier to trade. In order to improve the methods of measurements and testing, the Standards, Measurements and Testing Programme (SM&T) is currently supporting a project of which the final aim is to produce paint reference materials. The first step of this collaborative project is aimed to assess and possibly improve the state-of-the-art of trace element determinations in paint coatings through an interlaboratory study, the results of which are presented in this paper.     

Computer graphics for quality control in the INAA of geological samples

A data reduction system for the routine instrumental activation analysis of samples is described, with particular emphasis on interactive graphics capabilities for evaluating analytical quality. Graphics procedures have been developed to interactively control the analysis of selected photopeaks during spectral analysis, and to evaluate detector performance during a given counting cycle. Graphics algorithms are also used to compare the data on reference samples with accepted values, to prepare quality control charts to evaluate long term precision and to search for systematic variations in data on reference samples as a function of time.     

Certification of reference materials for the quality control of major element determinations in groundwater Part 1: Feasibility study

 Analyses of groundwater are routinely performed by control laboratories within the European Union to monitor the levels of major elements. The quality control of such determinations requires the use of certified reference materials which are representative of natural samples. However, the preparation and stabilisation of natural groundwater for their major element composition is difficult to achieve and materials simulating the mean composition of real samples often represent the best alternative. In order to investigate the feasibility of preparation and stabilisation of simulated groundwater samples, various tests were necessary prior to the production of a large batch of candidate reference materials. This paper presents the preparation of simulated groundwater reference materials and the different stabilisation procedures tested. Received: 9 September 1996/Revised: 4 December 1996/Accepted: 14 December 1996     

Collaborative study to improve the quality control of trace element determinations in polymers. Part 1. Interlaboratory study

In order to control the quality of trace element determinations in polymer, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has started a project of which the final aim is to certify polymer reference materials for their contents of a range of trace elements. The first part of this project consisted in an interlaboratory study which aimed at testing the feasibility of preparation of candidate polymer reference materials and to detect and remove most of the pitfalls observed in trace element determinations. This paper presents the results of this interlaboratory study carried out prior to the certification campaign. Received: 22 April 1999 / Revised: 21 June 1999 / Accepted: 21 June 1999     

Collaborative study to improve the quality control of trace element determinations in polymers. Part 1. Interlaboratory study

In order to control the quality of trace element determinations in polymer, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has started a project of which the final aim is to certify polymer reference materials for their contents of a range of trace elements. The first part of this project consisted in an interlaboratory study which aimed at testing the feasibility of preparation of candidate polymer reference materials and to detect and remove most of the pitfalls observed in trace element determinations. This paper presents the results of this interlaboratory study carried out prior to the certification campaign. Received: 22 April 1999 / Revised: 21 June 1999 / Accepted: 21 June 1999     

Using synthetic multi-element standards (SMELS) for calibration and quality control of the irradiation facilities in the BR1 reactor

The thermal to epithermal neutron flux ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape (α) are essential parameters for the correct application of k ₀-standardized neutron activation analysis. Several methods are applied for the determination of f and α. They are based on Cd-covered multi-monitor or on bare-irradiations methods. The recently developed and characterized synthetic multi-element standards (SMELS) were designed as a validation tool for the proper implementation of the k ₀-NAA method in a laboratory. In particular, SMELS Type III contains Au and Zr, thus allowing the direct determination of f and α. It could, therefore, replace the traditional flux monitors. Furthermore, it could be used as a quality control material to monitor the stability of the irradiation facility and the detector. This paper presents the accuracy of the f and α determination and the feasibility of quality control using SMELS for irradiation channel Y4 of the BR1 reactor.     

Polymer crystallization dynamics,as reflected by differential scanning calorimetry. Part 1: On the calibration of the apparatus

In this paper a method for the calibration of the heat transfer coefficient between pan and furnace is given. This (second) calibration is necessary in addition to the usual calibration of the temperature scale. Indeed, with increasing cooling rates as required for kinetic measurements, the finite heat flow resistance between pan and furnace becomes evident anyway. We also propose to enlarge this resistance deliberately, in order to separate the time scales of the control system and of the exponential return of the heat flow curve to the base line, as occurring after completion of the phase transition. Only in this way can the heat transfer coefficient be determined with some accuracy. Another advantage of a lowered heat transfer coefficient will be treated in a third paper. It enables an approximate treatment of polymer crystallization kinetics.     

The evaluation of probabilistic classification methods : Part 1. A monte carlo study with ALLOC

Probabilistic classification (i.e., classification of individuals into one of several groups by assigning probabilities of classification to each individual) is desirable when the main interest is in individuals rather than the whole group. The evaluation of probabilistic assignments is described in detail, including statistical features such as measures for the sharpness of the classification, the predictive ability and the reliability of the probability values. In a simulation study, the influence of the objects—variable ratio and the interclass distance on the results was examined for the training data themselves (resubstitution method), an independent test set, and a pseudo-independent test set created from the training set (leave-one-out method). The results indicate that the leave-one-method can often be used instead of an independent test set. In many cases, the assignments cited as probabilities are not probabilities at all, because the classification system is too over-confident.