A software package comparison for uncertainty measurement estimation according to GUM

Six commercial programs devoted to the estimation of measurement uncertainty were compared for feasibility in order to be applied in routine chemical analysis. The main features of each program were discussed. They were applied to two well-documented case studies. Several screen captures were considered for illustration.     

Evaluation of measurement uncertainty for thermometers with calibration equations

The method recommended by Eurachem did not mention the effect of adequateness of calibration equations on the measurement uncertainty. In this work, the sources of measurement uncertainty for two types of thermometer were evaluated. Three calibration equations were adopted to compare its predictive performance. These sources of combined uncertainty include predicted values of calibration equation, nonlinearity and repeatability, reference source, and resolution source. The uncertainty analysis shows that the predicted uncertainly of calibration equations is the main source for two types of thermometer. No significant difference of the uncertainty was found between the classical method and the inverse method. However, the calculation procedure of the inverse method was simpler and easier than that of the classical method.     

Implementing combined uncertainty according to GUM into a commercial gamma spectrometric software

Measurement uncertainty is an important part of a measurement result that still often is neglected. A complete combined uncertainty budget can be calculated for non-routine measurements. However, for routine measurements, this work becomes time-consuming since every measurement result requires an uncertainty analysis. By analysing the uncertainty on a measurement system level in e.g. high resolution gamma spectrometry, the uncertainty analysis will be universal for a particular measurement geometry. The problem is then reduced to implementing the combined uncertainty into measurement software. This work shows how this analysis can be done and implemented into a commercial software for gamma spectrometric measurements.     

Modelling the separation by nanofiltration of a multi-ionic solution relevant to an industrial process

The current work focuses on the application of nanofiltration (NF) to the isolation of a pharmaceutical product, clavulanate (CA⁻), from clarified fermentation broths, which show a complex composition with five main identified ions (K⁺, Cl⁻, NH₄⁺, SO₄²⁻ and CA⁻). Our aim is to predict the rejection rates of these five ions, with the NF membrane Desal-DK, which may influence the separation of CA⁻ and play a role in the whole downstream process.     

Modelling of ready biodegradability based on combined public and industrial data sources

ABSTRACT

The European Registration, Evaluation, Authorization and Restriction of Chemical Substances Regulation, requires marketed chemicals to be evaluated for Ready Biodegradability (RB), considering in silico prediction as valid alternative to experimental testing. However, currently available models may not be relevant to predict compounds of industrial interest, due to accuracy and applicability domain restriction issues. In this work, we present a new and extended RB dataset (2830 compounds), issued by the merging of several public data sources. It was used to train classification models, which were externally validated and benchmarked against already-existing tools on a set of 316 compounds coming from the industrial context. New models showed good performances in terms of predictive power (Balance Accuracy (BA) = 0.74–0.79) and data coverage (83–91%). The Generative Topographic Mapping approach identified several chemotypes and structural motifs unique to the industrial dataset, highlighting for which chemical classes currently available models may have less reliable predictions. Finally, public and industrial data were merged into global dataset containing 3146 compounds. This is the biggest dataset reported in the literature so far, covering some chemotypes absent in the public data. Thus, predictive model developed on the Global dataset has larger applicability domain than the existing ones.     

Correlation between repeated measurements: bane and boon of the GUM approach to the uncertainty of measurement

With measurement uncertainty estimation accounting for all relevant uncertainty contributions, the results of measurements using the same procedure on different objects or samples may no longer be considered as being independent, and correlations have to be taken into account. For this purpose, a simple approximation for the estimation of covariances is derived and applied to the estimation of uncertainty for some basic combinations of two measurement results. This covariance estimate is also applied to the estimation of uncertainty for the mean value of the results of replicate measurements on the same object or sample.

Estimation of the uncertainty of CRMs in accordance with GUM: Application to the certification of four enzyme CRMs

Uncertainties of four enzyme-CRMs that have recently been certified in a co-operation between the IRMM and the International Federation for Clinical Chemistry were estimated. Estimation was based on the sum of the uncertainties of characterization, homogeneity and stability. Data from the certification collaborative study were used to estimate laboratory uncertainties, which form the basis for the uncertainty of characterization. Estimations for the uncertainty of homogeneity were derived from classical homogeneity studies. The estimations of uncertainty of stability caused the most difficulties. Realistic uncertainties fitting the needs of customers while being derived from measurement data based on theoretical considerations were obtained. Received: 11 May 2000 / Revised: 21 June 2000 / Accepted: 27 June 2000     

Stratospheric ozone dynamics according to the Chapman mechanism

The photochemical mechanisms behind the ozone dynamics in the stratosphere have been studied for a long time. Though the differential equations describing the kinetics associated with them are well known, their mathematical properties have not been fully explored. In this work some of these mathematical properties as well as their physical implications are investigated in the simplest photochemical mechanism, namely, Chapman’s one.     

Using the L1 norm to select basis set vectors for multivariate calibration and calibration updating

With projection based calibration approaches, such as partial least squares (PLS) and principal component regression (PCR), the calibration space is spanned by respective basis vectors (latent vectors). Up to rank k basis vectors are formed where k ≤ min(m,n) with m and n denoting the number of calibration samples and measured variables. The user needs to decide how many and which respective basis vectors (tuning parameters). To avoid the second issue, basis vectors are selected top‐down starting with the first and sequentially adding until model criteria are satisfied. Ridge regression (RR) avoids the issues by using the full set of basis vectors. Another approach is to select a subset from the total available. The presented work develops a process based on the L₁ vector norm to select basis vectors. Specifically, the L₁ norm is used to select singular value decomposition (SVD) basis set vectors for PCR (LPCR). Because PCR, PLS, RR, and others can be expressed as linear combination of the SVD basis vectors, the focus is on selection and comparison using the SVD basis set. Results based on respective tuning parameter selections and weights applied to the SVD basis vectors for LPCR, top‐down PCR, correlation PCR (CPCR), PLS, and RR are compared for calibration and calibration updating using spectroscopic data sets. The methods are found to predict equivalently. In particular, the L₁ norm produces similar results to those obtained by the well‐studied CPCR process. Thus, the new method provides a different theoretical framework than CPCR for selecting basis vectors. Copyright © 2016 John Wiley & Sons, Ltd.     

Estimation of the uncertainty of CRMs in accordance with GUM: application to the certification of four enzyme CRMs

Uncertainties of four enzyme-CRMs that have recently been certified in a co-operation between the IRMM and the International Federation for Clinical Chemistry were estimated. Estimation was based on the sum of the uncertainties of characterization, homogeneity and stability. Data from the certification collaborative study were used to estimate laboratory uncertainties, which form the basis for the uncertainty of characterization. Estimations for the uncertainty of homogeneity were derived from classical homogeneity studies. The estimations of uncertainty of stability caused the most difficulties. Realistic uncertainties fitting the needs of customers while being derived from measurement data based on theoretical considerations were obtained.     

Linear calibration graph applicable to the indirect determination of sulphate

Equations based on the equilibrium relationship between a sulphate-containing solution and solid lead sulphate were derived and applied to calibration graphs for the determination of sulphate. The special character of the linear graphs extends not only the applicability of linear calibration and standard addition procedures to the indirect determination of sulphate, but also the reliability of the analytical results. Experiments with the flow-injection technique confirmed the applicability of the proposed linear graphs.     

Applicability of the polysulphone horizontal calibration to differently inclined dosimeters

Polysulphone (PS) dosimetry has been a widely used technique for more than 30 years to quantify the erythemally effective UV dose received by anatomic sites (personal exposure). The calibration of PS dosimeters is an important issue as their spectral response is different from the erythemal action spectrum. It is performed exposing a set of PS dosimeters on a horizontal plane and measuring the UV doses received by dosimeters using calibrated spectroradiometers or radiometers. In this study, data collected during PS field campaigns (from 2004 to 2006), using horizontal and differently inclined dosimeters, were analyzed to provide some considerations on the transfer of the horizontal calibration to differently inclined dosimeters, as anatomic sites usually are. The role of sky conditions, of the angle of incidence between the sun and the normal to the slope, and of the type of surrounding surface on the calibration were investigated. It was concluded that PS horizontal calibrations apply to differently inclined dosimeters for incidence angles up to approximately 70° and for surfaces excluding ones with high albedo. Caution should be used in the application of horizontal calibrations for cases of high-incidence angle and/or high albedo surfaces.     

Volatile Metal Alkoxides according to the Concept of Donor Functionalization

Since the fundamental works of D. C. Bradley and R. C. Mehrotra, metal alkoxides have attracted attention because of the diversity of their low- and high-molecular-weight structures; they are also generating increasing interest as precursor compounds for solving technical materials problems. The understanding of the hydrolytic nucleation behavior is a prerequisite for the optimization of materials from sol–gel processes. For metal alkoxides to be precursors in chemical vapor deposition (CVD) processes in the preparation of inorganic oxidic materials, they should be sufficiently volatile, and sublimation should occur without decomposition at as low a temperature as possible (< 150 °C). Only recently, using the “donor functionalization” concept, was a ligand type systematically developed that unifies the advantages of both steric demands and σ-donor stabilization and so stabilizes low-molecularweight metal alkoxides. Even large metal ions of low charge (for example Ba²⁺) can thus form volatile alkoxides. O- and N-donor functions in bidentate and multidentate alkoxo ligands are particularly advantageous; hence, for example, the vanadium derivative [V(OCMe₂CH₂OMe)₃] is one of the most volatile metal alkoxides known to date. The first alkoxides of the alkaline earth metals calcium, strontium, and barium, which sublime without decomposition, have the formula [M₂{OC(CH₂OiPr)₂tBu}₄]. This article presents a critical inventory of the metal alkoxides with particular regard to the aspect of volatility. It also describes successes of the donor functionalization concept and shows—in prespective—how alkoxo ligands can be “tailor made” for metals according to their charge-to-radius ratio by further development of the concept.     

The masses of elementary particles according to the pionic theory

We express the masses of elementary particles as simple polynomials of (=3.14...). The calculated masses differ only slightly from the experimentally found ones and, in most cases, are within the error margins accepted in the experiments. This method of calculation is part of our work titled The pionic theory of matter.     

The susceptibility of calibration methods to errors in the analytical signal

Calibration methods differ as to the number and concentration of calibration standards, and whether these are added to the samples or separate from them. The four main calibration mehods (single separate or added standard and multiple separate or added standards) and some modifications are desribed mathematically and subjected to error-propagation analysis, to examine the likely effects of errors in the analytical signal on the overall accuracy and precision of the concentration estimate. Comparison of the results throws light on the influence of the number, concentration and nature of the calibration standards, the effects of sample and standard replication, and the costs and the benefits of blank measurements. It is shown that all standard-addition methods are immune to proportional signal error, but more sensitive to nonlinearity. In separate-standard methods, all bias disappears when the true sample concentration (x_s) is equal to the standard concentration or to the mean standard concentration ($\text{x}$). Only the multiple separate standard method is unaffected by constant error common to sample and standards, without blanking. In multiple-standard methods, precision is best at x_s = $\text{x}$. Precision is always improved by increasing the number of sample and standard measurements; standard-addition methods respond best to sample replication. Whichever calibration method is used, recovery correction will eliminate proportional concentration error, at the cost of decreased precision.     

Measurement of low vapour pressures according to the Knudsen effusion method

The exact measurement of low vapour pressures during recent years has become increasingly important, particularly for environmental problems caused by organic chemicals. Not only for this but for many other fields information about the phase transition solid - gas and liquid - gas is of great scientific interest. In this work a brief survey of the determination of vapour pressures with thermo-analytical methods is made. In particular the thermo-gravimetric vapour pressure measurements by means of a Knudsen cell and a newly developed vapour pressure balance for exact measurement of very low vapour pressures are described. Applications for organic materials (fungicides, benzoic acid, oils) are discussed.     

Modelling the background current with partial least squares regression and transference of the calibration models in the simultaneous determination of Tl and Pb by stripping voltammetry

With the aim of carrying out a calibration transfer for routine analysis, partial least squares (PLS) regression was successfully applied to simultaneously determine thallium and lead by stripping voltammetry when an interfering background current is present. The presence of a significant blank signal that overlaps the thallium peak, together with the overlapping thallium and lead signals were both suitably modelled by this multivariate regression technique. Moreover, once the PLS models are built, the piecewise direct standardization (PDS) method can be used to transfer these models over time in such a way that the number of calibration samples that will be needed in future determinations is reduced from 25 to 9, without a loss of quality in the analyses. The mean of the relative errors (in absolute values) obtained for thallium and lead is below 4.94% and 3.19%, respectively.     

Application of calibration standardization method to the analysis of diuretic pharmaceutical herbs

Calibration standardization of X-ray fluorescence method was carried out for the determination of the anorganic contents in diuretic herbs as calledFolia Betulae, Stylus Maydis, Flores Verbasci, Equisetum Arvense andFlos Helichrysi, growing in Turkey. These herbs are widely used in pharmacy and public health for kidney disease theraphy. Herb samples were steeped in the water and mixed through the pure cellulose, then pelletized in the intermediate thickness. An annular source of¹⁰⁹Cd (3.7 MBq) was used for excitation of fluorescent K lines of elements lying between potassium and zirconium. Toxic elements in considerable amounts were not found.     

Generating functions for the Harary-Read numbers classified according to symmetry

The studies of the Harary-Read numbers for catafusenes are continued. The generating functions were derived separately for the different symmetries of interest. Numerical values are supplemented.