Proficiency testing in the light of a new rationale in metrology

The novel proposed definition of measurement result in the international metrology vocabulary requires a revision of standards and guidelines for proficiency testing (PT), and a new approach to processing proficiency data is needed to test the ability of laboratories to present not only unbiased quantity values, but reliable estimates of their uncertainty. Hence, an accepted reference value with the smallest possible uncertainty is needed to ascertain the proficiency of laboratories reporting results with lower than average uncertainty. A strategy based on the T-statistic is proposed leading to an accepted reference value that fully reflects the uncertainties reported by participants in a PT scheme and permits calculation of E _n numbers to distinguish whether or not measurement results are consistent with the accepted definition of the measurand. The strategy is applied to PT data from a recent international laboratory intercomparison of uranium isotopic ratios.     

Evaluation of laboratory performance in IMEP water interlaboratory comparisons

The aim of International Evaluation Programme (IMEP) is to present objectively the quality of chemical measurements. Participants in IMEP compare their reported measurement results with independent external certified reference values with demonstrated traceability and uncertainty, as evaluated according to international guidelines. Three major interlaboratory comparisons (ILCs), IMEP-6, IMEP-9 and IMEP-12, on trace elements in water were carried out from 1994 to 2000. Participants' results for Cd, Fe and Pb concentrations from these three different IMEP water ILCs were compared by means of suitable performance indicators. The performance evaluation criteria were set according to the requirements stated in the Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption. Two different performance indicators were selected for evaluation of the individual participants' results: the commonly used z-score and the not so well-known E _n number. The group performance indicator is based on the variation of z-scores. To assess the individual measurement performance, not only the deviation of the reported measurement values from the certified reference value, but also criteria for maximum and minimum acceptable uncertainties were taken into account. The participants' performance is also reviewed by means of using a simple graphical tool, called “Naji-plots”.     

The application of data from proficiency testing to laboratory accreditation according to ISO 17025

Current methods of testing laboratories for their proficiency in reporting correct measurement results are liable to substantial errors of the second kind. This means that laboratories with deflated uncertainties are accepted as proficient, even though their reported measurement results pave the way for erroneous conclusions. Only by using E _n numbers based on an accepted reference value with the lowest possible uncertainty can the risk of recognising incorrect measurement results be kept at an acceptable level. Based on an actual set of proficiency test (PT)-data for the concentration of Pb in water, this paper compares PT results obtained by methods using E _n numbers with methods based on z-scores. Kaj Heydorn is a technical assessor at The Danish Accreditation and Metrology Fund (DANAK).     

Visualization technique for uncertainty budgets: Onion charts

A concise graphical depiction, the “onion” chart, is described for presenting uncertainty budgets for any measurand, y, having a set of component variances, . The onion chart consists of a concentric series of rings. Each ring is constructed from the set of fractional contributions, . The outer ring includes all and depicts the combined standard uncertainty, u _c (y), where u _c ²(y) ≡ ∑u _i ²(y). Moving inward, each successive ring deletes the largest remaining . A “reduced” is calculated for that ring from the remaining set of , with the fractional contributions calculated using the “reduced” . This format facilitates rapid visual comparison of the importance of each component, with minor components becoming visible as the larger components are successively deleted. An example is presented using data from pH metrology, including the physical interpretation of the resulting diagram.     

Synthesis and magneto-structural correlation of a new maleato bridged copper(II) coordination polymer

A one-dimensional (1-D) copper(II) coordination polymer [Cu(maleate)(2,2′-bipyridyl)] _n ·2H₂O has been synthesised. Single crystal X-ray diffraction study reveals that maleate ion bridges two adjacent copper(II) centres along the chain in a syn–anti fashion. A complete cryomagnetic investigation of the title complex correlates well with the distorted square pyramidal geometry of the central copper(II) ion and bridging nature of the maleate. A τ value of 0.26 indicates the distortion towards tbp coordination allowing the magnetic orbital to acquire some character leading to a weak antiferromagnetic interaction having J = −0.26 cm⁻¹. The complex has also been firmly established from several other instrumental techniques like Fourier transform infrared (FT-IR) and EPR spectroscopies.     

Formation and Characterization of Large (Ar) n , (N2) n , and Mixed (Ar) n (N2) m van der Waals Clusters Produced by Supersonic Expansion

This paper reports the formation and characterization of large (Ar) _n , (N₂) _n , and mixed binary (Ar) _n (N₂) _m van der Waals clusters produced at room temperature in the process of supersonic expansion. The average cluster size is determined by the buffer gas induced beam-broadening technique. For both Ar and N₂ clusters, power variations of the average cluster size with the gas stagnation pressure P ₀ give size scaling as . The average cluster sizes of argon vary from 2950 to more than 30900 atoms per cluster with the argon gas stagnation pressures ranging from 4 to 14 bars, and of nitrogen vary from 600 to more than 10400 molecules per cluster with the nitrogen gas stagnation pressures ranging from 8 to 38 bars. The mixed binary (Ar) _n (N₂) _m cluster is produced by supersonic expansion of an Ar–N₂ mixture. The large mixed binary (Ar) _n (N₂) _m clusters with the average sizes n + m between 1000 and 16000 are obtained. In coexpansion of Ar–N₂ mixture, we find that the argon concentration becomes higher in the beam than before the expansion. This finding is discussed and may be helpful for further insight into the phenomenon of clustering.     

Studies on the thermal decomposition kinetics of LiPF6 and LiBC4O8

Thermal decomposition of LiPF₆ and LiBC₄O₈ (lithium bis(oxalate)borate, abbreviated as LiBOB) were studied using TG (thermogravimetry)-DTG (derivative thermogravimetry) method with different heating rate β of 5, 10, 20 and 40°C min⁻¹ or at different constant temperature θ _C (109·80, 118·79, 148·41, 176·86°C for LiPF₆ and 278·51, 298·13, 317·65, 336·13 for LiBOB). From the non-isothermal kinetics we calculate that is 1·01, n _LiBOB is 1·04, is 91907·61 J/mol, and E _LiBOB is 205179·88 J/mol; from the isothermal kinetics we calculate that n for both LiPF6 and LiBOB are 1, E_LiPF6 is 91907·61 J/mol, E _LiBOB is 205179·88 J/mol, is 16·89 s⁻¹, and lnA_LiBOB is 31·96 s⁻¹. The results obtained from the two ways have minor differences and can validate each other.     

On the charge storage mechanism at RuO<Subscript>2</Subscript>/0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript> interface

Comparative study of capacitative properties of RuO₂/0.5 M H₂SO₄ and Ru/0.5 M H₂SO₄ interfaces has been performed with a view to find out the nature of electrochemical processes involved in the charge storage mechanism of ruthenium (IV) oxide. The methods of cyclic voltammetry and scanning electron microscopy (SEM) were employed for the investigation of electrochemical behavior and surface morphology of RuO₂ electrodes. It has been suggested that supercapacitor behavior of RuO₂ phase in the potential E range between 0.4 and 1.4 V vs reference hydrogen electrode (RHE) should be attributed to double-layer-type capacitance, related to non-faradaic highly reversible process of ionic pair formation and annihilation at RuO₂/electrolyte interface as described by following summary equation:

Characterizations for Some Types of DNA Graphs

Vertex induced subgraphs of directed de Bruijn graphs with labels of fixed length k and over α letter alphabet are (α,k)-labelled. DNA graphs are (4,k)-labelled graphs. Pendavingh et al. proved that it is NP-hard to determine the smallest value α _k (D) for which a directed graph D can be (α _k (D),k)-labelled for any fixed . In this paper, we obtain the following formulas: and for cycle C _n and path P _n . Accordingly, we show that both cycles and paths are DNA graphs. Next we prove that rooted trees and self-adjoint digraphs admit a (Δ,k)-labelling for some positive integer k and they are DNA graphs if and only if Δ ≤ 4, where Δ is the maximum number in all out-degrees and in-degrees of such digraphs.     

Binding of nontarget microorganisms from food washes to anti-<Emphasis Type="Italic">Salmonella</Emphasis> and anti-<Emphasis Type="Italic">E. coli</Emphasis> O157 immunomagnetic beads: minimizing the errors of random sampling in extreme dilute systems

For most applications, 3–5 observations, or samplings (n), are utilized to estimate total aerobic plate count in an average population (μ) that is greater than about 50 cells, or colony forming units (CFU), per sampled volume. We have chosen to utilize a 6 × 6 drop plate method for bacterial colony selection because it offers the means to rapidly perform all requisite dilutions in a 96-well format and plate these dilutions on solid media using minimal materials. Besides traditional quantitative purposes, we also need to select colonies which are well-separated from each other for the purpose of bacterial identification. To achieve this goal using the drop plate format requires the utilization of very dilute solutions (μ < 10 CFUs per sampled drop). At such low CFU densities the sampling error becomes problematic. To address this issue we produced both observed and computer-generated colony count data and divided a large sample of individual counts randomly into N subsamples each with n = 2–24 observations (N × n = 360). From these data we calculated the average total mean-normalized (, n = 360) deviation of the total standard deviation (s _tot) from each jth subsample’s estimate (s _j ), which we call Δ. When either observed or computer-generated Δ values were analyzed as a function of , a set of relationships () were generated which appeared to converge at an n of about 18 observations. This finding was verified analytically at even lower CFU concentrations (). Additional experiments using the drop plate format and n = 18 samplings were performed on food samples along with most probable number (MPN) analyses and it was found that the two enumeration methods did not differ significantly. Any reference to a particular brand or company name does not constitute an endorsement of it by the U.S. Department of Agriculture over other similar brands or companies that are not mentioned.     

Formation,characterization and stabilization of water-soluble colloidal MnO<Subscript>2</Subscript> in the oxidation of methionine,thiourea and thioacetamide by permanganate

Stabilization and characterisation of water soluble colloidal MnO₂ during the oxidation of sulphur-containing organic reductants “thiourea, thioactamide and methionine” by permanganate in aqueous neutral media are reported for the first time. Upon addition of permanganate to a solution of methionine, a transient species appears within the time of mixing, which is stable for several weeks. On the other hand, the transient species is unstable in the presence of thiourea and thioacetamide, respectively. The nature of manganese (IV) species present in the solution was characterized by spectrophotometric and coagulation measurements. On addition of HClO₄, there is a decrease in the absorbance of the reaction mixture. Under pseudo first-order conditions ([reductants] > []), the reduction rate was very fast up to the formation of water soluble colloidal MnO₂. The effect of various parameters, such as hydrogen ion concentration, amount of and concentration of reductants were investigated. Mechanisms consistent with the observed results have been proposed and discussed.     

Structural and electronic effects involving pyridine rings in 4-methylpyridine Cu4OX6L4 complexes. I. Vibrational spectra of Cu4OBr n Cl(6−n)(4-Mepy)4 complexes

Gaussian analysis of bands between 500 cm⁻¹ and 600 cm⁻¹ attributed to the _as (Cu₄O) stretching vibration of the tetrahedral Cu₄O core in Cu₄OBr _n Cl_(6−n)(4-Mepy)₄ (n = 0–6) complexes showed two bands, symmetry reduction of the T ₂ mode of vibration towards the A ₁ and E modes and vibrational coupling with an R-sensitive in-plane pyridine ring bending. The Cu-O bond is considered as vibrationally coupled with the Cu-N bond and the pyridine ring through the donor-acceptor vibrational coupling and the corresponding equilibrium charge distribution. The linear correlation between _as(Cu₄O) and the number of bromides in Cu₄OBr _n Cl_(6−n)(4-Mepy)₄ complexes was used for the estimation of partial charges on the 4-Mepy ligands which were positive for the prevailing donors and negative for the prevailing acceptors thus evoking a π-back bonding between the Cu(II) atoms and the 4-Mepy ligands. Correlations involving selected bond lengths and bond angles in the molecular structure of the Cu₄OCl₆(4-Mepy)₄ complex with four symmetrically independent molecules present in the unit cell indicate a symmetry reduction of the T ₂ mode of vibration and the π-back bonding between the Cu(II) atoms and the 4-Mepy ligands.     

The effects of preparation temperature on the main electrical parameters of Al/TiO<Subscript>2</Subscript>/p-Si (MIS) structures by using sol–gel method

In this study, the forward bias current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the Al/TiO₂/p-Si (MIS) structures derived using the sol–gel method have been investigated and compared at various preparation temperatures. Experimental results show that the preparation temperatures strongly affect the electrical characteristics, such as ideality factor (n), zero-bias barrier height (), series resistance (R _s ) and interface states (N _ss ). The MIS structures show non-ideal behavior of I–V characteristics with an n varying between 2.17 and 4.61. We have found that the and R _s increase as the n decrease with increasing preparation temperature. The energy distribution profile of N _ss of the Al/TiO₂/p-Si (MIS) structures was obtained from the forward bias I–V characteristics by taking into account both the bias dependence of the effective barrier height () and R _s for various preparation temperatures. The values of N _ss increase from the midgap towards the top of valance band for various preparation temperatures.     

Dynamics of H+O2 collisions on anab initio potential energy surface

The dynamics of elementary rate processes for H+O₂ collisions on an ab initio potential energy surface have been simulated by quasiclassical trajectory theory (QCT). For H+O₂ (v=0,j=1), we have obtained the reaction probabilityP _r (E,b) as a function of collision energy E and impact parameterb, the reaction cross sectionS _r as a function ofE, and the average values of the product quantum numbers of OH.For H+0₂ (v=2,j=1, 20, 40, 60, 80, 100;v=1, 3, 4, 5,j=1) atE=0.3 eV, we have found thatb _max is about 4.5a ₀ and the impact parameter at whichP _r is maximum decreases asj increases. The reaction cross section increases asj andv become large. For inelastic collisions, whenb is small andj is large, the and are both small. For reactive collisions, almost equals zero, but the probability of being larger than zero increases with increasingj; and¯v _OH even shows population inversion forj=100. Additional details of the dynamics are shown in figures of interparticle distance and stereographs.     

Uncertainty of measurement for the determination of fluoride in water and wastewater by direct selective electrode potentiometry

A procedure to estimate the uncertainty of measurement applied to the fluoride determination of waters and wastewaters matrices by selective electrode potentiometry was implemented based on Eurachem Guide. The major sources of uncertainty were identified as the calibration standard solutions, fluoride concentration obtained by potential interpolation of the regression line and the precision. However the relative uncertainties depend on the anion concentration levels. The methodology proposed was presented to two fluoride concentration levels that are in the range of surface water samples (C _sample=1.12 mgF l⁻¹) and of wastewater matrices (C _sample=101.4 mgF l⁻¹). The expanded uncertainties calculated were 0.40 and 9.1 mg l⁻¹ for low and high concentration levels, respectively, using the reproducibility uncertainty as precision evaluation. The relative expanded uncertainty was around ±10% for the highest concentration, which can be considered acceptable for the ion selective electrode potenciometric methods and ±36% for the lowest concentrations. In this case the sample fluoride content is very close to the limit of quantification which has a relative uncertainty of about ±30%. If the repeatability was used in spite of duplicate analysis the same conclusions were obtained (C _sample=1.12 ± 0.39 mgF l⁻¹ and C _sample=101.4 ± 7.0 mgF l⁻¹). Although the calculated expanded uncertainties and consequently the combined uncertainty, do not vary significantly in the cases where it was used the repeatability or reproducibility for evaluating the precision, each relative variances uncertainty contributions do. When the repeatability is used to determine the combined uncertainty, the CSS and uncertainties contributions are the most dominant ones. However, if reproducibility is used, relative uncertainty variance contributions are distributed among CSS, C _F, and precision. In both cases, the contribution increases and r _CSS contribution decreases with the increasing of the concentration level. The precision variance contribution is only significant in the case where the reproducibility is used, and increases with the increasing of the concentration level. The uncertainty in the result calculated using the proposed methodology (C _sample ± U _sample = 2.17 ± 0.42 mgF l⁻¹) is in satisfactory agreement with the estimated expanded uncertainty obtained using the relative reproducibility standard deviation obtained in interlaboratory studies ().     

Mechanism of the catalyzed by cysteine electroreduction of the insoluble in water cobalt(II) salt as a component of carbon paste electrode

The mechanism of the Co(II) catalytic electroreduction of water insoluble CoR₂ salt in the presence of cysteine was developed. CoR₂ = cobalt(II) cyclohexylbutyrate is the component of a carbon paste electrode. Electrode surface consecutive reactions are: (a) fast (equilibrium) reaction of the complex formation, (b) rate-determining reversible reaction of the promoting process of CoR(Ac⁺) complex formation, (c) rate-determining irreversible reaction of the electroactive complex formation with ligand-induced adsorption, and (d) fast irreversible reaction of the electroreduction. Reactions (a,b) connected with CoR₂ dissolution and reactions (c,d) connected with CoR₂ electroreduction are catalyzed by . Regeneration of (reactions “b,d”) and accumulation of atomic Co(0) (reaction “d”) take place. Experimental data [Sugawara et al., Bioelectrochem Bioenergetics 26:469, 1991]: i _a vs E (i _a is anodic peak, E is cathodic accumulation potential), i _a vs , and i _a vs pH have been quantitatively explained.     

Thick Fe2O3, Fe3O4 films prepared by the chemical solution deposition method

Fe₂O₃, Fe₃O₄ films have been prepared from Fe(OCH₂CH(CH₃)₂)₃–(CH₃)₂CHCH₂OH–2.2′-diethanola- mine (DEA)–poly(vinylpyrrolidone) (PVP) solutions by the spin-(SC) and dip-coating (DC) technique on SiO₂ and Si substrates. The maximum film thickness achieved without crack formation has been increased by incorporation of PVP (relative molecular weights 40000 and 360000) into the precursor solution. The stability of the precursor solutions was remarkably increased by addition of DEA. Compact, dense, and crack-free Fe₂O₃ films with thicknesses 900 nm (DC), 450 nm (SC), have been obtained via single-step deposition cycle. Higher-molecular-weight PVP has been more effective in increasing the thickness. The minimum concentration of DEA, which results in pronounced increase of solutions stability, is about R _P (n(DEA)/n(Fe) = 0.1). The high content of carboneous residue in the pyrolysed Fe₂O₃ films promotes the formation of Fe₃O₄ films via reduction in a gas flow of H₂/N₂ gas mixture. Microstructure, surface morphology, and magnetic properties of the films have been also investigated using SEM, AFM, and SQUID, respectively.     

An exact expression for the wiener index of a TUC<Subscript>4</Subscript>C<Subscript>8</Subscript>(R) nanotorus

The Wiener index of a graph G is defined as , where V(G) is the set of all vertices of G and for denotes the length of a minimal path between x and y. A C ₄ C ₈ net is a trivalent decoration made by alternating squares C ₄ and octagons C ₈. It can cover either a cylinder or a torus. In this paper, an algorithm for computing the distance matrix of a C ₄ C ₈(R) nanotorus T = T[p,q] is given. Using this matrix, the Wiener index of T is computed.     

The first and second largest Merrifield–Simmons indices of trees with prescribed pendent vertices

The Merrifield–Simmons index of a graph G is defined as the number of subsets of the vertex set, in which any two vertices are non-adjacent, i.e., the number of independent-vertex sets of G. By T(n,k) we denote the set of trees with n vertices and with k pendent vertices. In this paper, we investigate the Merrifield–Simmons index for a tree T in T(n,k). For all trees in T(n,k), we determined unique trees with the first and second largest Merrifield–Simmons index, respectively.