Hydrocarbon acidities calculated with MINDO/3, MNDO,and AM1

Acidities of 32 hydrocarbons have been calculated using MINDO/3, MNDO, and AM1. All three semiempirical procedures have systematic errors and reproduce experimental acidities poorly. A linear correlation, however, does exist between the calculated and experimental results. Correction of the AM1 or MNDO acidities leads to good agreement with literature values even for acids, such as methane and ethylene, whose conjugate bases are small localized anions. Predictions for several hydrocarbons are given.     

Studies on the non-uniformity of fine dispersive mixtures by instrumental activation method

The uniformity of ferrit charge component distribution affects significantly the magnetic properties of the final products. A characteristics feature of mixing efficiency is the concentration distribution of the components present in low concentration. It was the aim of the present research to investigate the variants of the instrumental activation technique to measure cobalt, sodium, and copper in ferrite charge. All data obtained were treated by the technique of the simple dispersion analysis. The effect of some systematic errors on the statistical parameters under consideration have been studied. Means of quantitative estimation of non-uniformity have also been discussed.     

Limits of detection and decision. Part 4

Probability density functions (PDFs) have been derived for a number of commonly used limit of detection definitions, including several variants of the Relative Standard Deviation of the Background–Background Equivalent Concentration (RSDB–BEC) method, for a simple linear chemical measurement system (CMS) having homoscedastic, Gaussian measurement noise and using ordinary least squares (OLS) processing. All of these detection limit definitions serve as both decision and detection limits, thereby implicitly resulting in 50% rates of Type 2 errors. It has been demonstrated that these are closely related to Currie decision limits, if the coverage factor, k, is properly defined, and that all of the PDFs are scaled reciprocals of noncentral t variates. All of the detection limits have well-defined upper and lower limits, thereby resulting in finite moments and confidence limits, and the problem of estimating the noncentrality parameter has been addressed. As in Parts 1–3, extensive Monte Carlo simulations were performed and all the simulation results were found to be in excellent agreement with the derived theoretical expressions. Specific recommendations for harmonization of detection limit methodology have also been made.     

Performance of density functionals for first row transition metal systems

This article investigates the performance of five commonly used density functionals, B3LYP, BP86, PBE0, PBE, and BLYP, for studying diatomic molecules consisting of a first row transition metal bonded to H, F, Cl, Br, N, C, O, or S. Results have been compared with experiment wherever possible. Open-shell configurations are found more often in the order PBE0>B3LYP>PBE approximately BP86>BLYP. However, on average, 58 of 63 spins are correctly predicted by any functional, with only small differences. BP86 and PBE are slightly better for obtaining geometries, with errors of only 0.020 A. Hybrid functionals tend to overestimate bond lengths by a few picometers and underestimate bond strengths by favoring open shells. Nonhybrid functionals usually overestimate bond energies. All functionals exhibit similar errors in bond energies, between 42 and 53 kJmol. Late transition metals are found to be better modeled by hybrid functionals, whereas nonhybrid functionals tend to have less of a preference. There are systematic errors in predicting certain properties that could be remedied. BLYP performs the best for ionization potentials studied here, PBE0 the worst. In other cases, errors are similar. Finally, there is a clear tendency for hybrid functionals to give larger dipole moments than nonhybrid functionals. These observations may be helpful in choosing and improving existing functionals for tasks involving transition metals, and for designing new, improved functionals.     

Validity and accuracy in evaluating surface tension of solids by additive approaches

The validity and the accuracy of both the Owens and Wendt and the Lifshitz-van der Waals/acid-base (LW/AB) methods for the determination of surface tensions of solids have been examined for a wide variety of situations. In each case, the allowed range of contact angles that result in positive values of all the square roots of the surface tension components of the solid has first been determined. Then the maximum relative errors in the surface tensions of solids that result from errors in contact angle measurements have been calculated within the allowed range. For both methods, it has been found that the maximum relative errors are minimal if one of the liquids is apolar. In the case of the LW/AB method, minimal errors are obtained if, in addition, the other two liquids are monopolar with different polarities. However, the more similar are the properties of the liquids, the narrower is the allowed range, and the larger are the maximum relative errors.     

Ammonium Determination in Water Samples by Using Opa-Nac Reagent: A Comparative Study with Nessler and Ammonium Selective Electrode Methods

A selective and sensitive method based on the ammonium derivatisation with o -phthaldialdehyde (OPA) and N -acetyl-cysteine (NAC) has been developed for ammonium determination in real water samples. The proposed procedure has been compared with ammonium reference methods such as Nessler reagent method and ammonium selective electrode. All procedures have been chemometrically tested and compared in terms of the main analytical properties. These procedures have been used to determine ammonium in unknown water samples. The OPA-NAC reagent method does not present any systematic error (proportional or constant), while Nessler reagent presents both of them for some samples assayed. The ammonium selective electrode is free of corrigible systematic errors, however presents amine interference. The OPA-NAC ammonium method is able to achieve a detection limit (LOD) of 0.07 mg/L in the sample, with a linear dynamic range up to 1.4 mg/L of ammonium.     

Synthesis and characterization by fast atom bombardment mass spectrometry of peptides related to the B-domain of staphylococcal protein A

Solid-phase synthesis was used to prepare several peptides related to Staphylococcal protein A, including a 58-residue sequence corresponding to the entire B-domain of the protein. These materials were characterized by a combination of fast atom bombardment mass spectrometry and microchemical methods, including Edman degradation and tryptic digestion. The errors identified included incomplete removal of blocking groups, premature chain termination and the dehydration of an aspartic add residue in the sequence. All of these problems would have been extremely difficult to elucidate by conventional techniques of protein chemistry, and demonstrate that mass spectrometry is the method of choice for verifying the structural integrity of the products of solid-phase synthesis.     

Efficient calculation of SAMPL4 hydration free energies using OMEGA,SZYBKI, QUACPAC,and Zap TK

Several submissions for the SAMPL4 hydration free energy set were calculated using OpenEye tools, including many that were among the top performing submissions. All of our best submissions used AM1BCC charges and Poisson–Boltzmann solvation. Three submissions used a single conformer for calculating the hydration free energy and all performed very well with mean unsigned errors ranging from 0.94 to 1.08 kcal/mol. These calculations were very fast, only requiring 0.5–2.0 s per molecule. We observed that our two single-conformer methodologies have different types of failure cases and that these differences could be exploited for determining when the methods are likely to have substantial errors.     

Fluid density predictions using the COMPASS force field

Calculations of liquid densities for nine systems, each at two different state points, have been performed as specified for the First Industrial Fluid Properties Simulation Challenge. All calculations have utilized the current Version (2.6) of the COMPASS force field, with addition of recently refined parameters for alcohols, in conjunction with the Discover simulation program. Periodic cells containing 1000–2000 atoms have been subjected to 1.0 ns molecular dynamics simulation under conditions of constant temperature and pressure. Detailed analysis of the simulations has been performed to quantify uncertainties arising from both sampling statistics and other model and simulation protocol related errors. Accuracy of the predictions has been discussed separately for the aqueous and non-aqueous systems, with the former being found to give reliable predictions under ambient conditions but average to poor performance at higher temperatures and pressures. For non-aqueous systems other than 1,2,3-trichloropropane, a member of a group of compounds which have not been rigorously parameterized, density predictions are excellent and, significantly, are of comparable accuracy at both pairs of state points studied.     

Die Bestimmung des Sauerstoffs mit hoher Präzision und Richtigkeit

Oxygen has been determined with high precision and accuracy by activation analysis via N-16, using a cyclic irradiation and counting technique. The sources of accidental errors have been revealed and eliminated by means of statistical tests and the systematic errors due to counting errors and matrix effects have been corrected. The standardization errors arising in stationary and birotary sandwich arrangement of sample and standard are compared and the procedure of statistical error analysis is discussed. The results of oxygen analysis in organic compounds, oxides, carbonates, sulfates and other compounds with a precision 0.05% and an accuracy <0.1% are reported.     

The kinetic equation under non-isothermal conditions

Data generated from selected model expressions for solid-state kinetics have been analysed in terms of expressions of closely-related form to test distinguishability of the models on which the expressions are based. Random errors have then been introduced into these data and the data have been re-analyzed in terms of the original and closely-related expressions. As is to be expected, introduction of errors decreases distinguishability further and estimates have been made of the accuracy of measurement of the extent of reaction, α, required, the most suitable ranges of α to use, from plots of residuals, and the acceptable levels of various statistical parameters, for reliable distinction between alternative models.     

Estimation of discrimination errors in the technique for determining the geographic origin of onions by mineral composition: interlaboratory study

Techniques to determine the geographic origin of foods have been developed for various agricultural and fishery products, and they have used various principles. Some of these techniques are already in use for checking the authenticity of the labeling. Many are based on multielement analysis and chemometrics. We have developed such a technique to determine the geographic origin of onions (Allium cepa L.). This technique, which determines whether an onion is from outside Japan, is designed for onions labeled as having a geographic origin of Hokkaido, Hyogo, or Saga, the main onion production areas in Japan. However, estimations of discrimination errors for this technique have not been fully conducted; they have been limited to those for discrimination models and do not include analytical errors. Interlaboratory studies were conducted to estimate the analytical errors of the technique. Four collaborators each determined 11 elements (Na, Mg, P, Mn, Zn, Rb, Sr, Mo, Cd, Cs, and Ba) in 4 test materials of fresh and dried onions. Discrimination errors in this technique were estimated by summing (1) individual differences within lots, (2) variations between lots from the same production area, and (3) analytical errors. The discrimination errors for onions from Hokkaido, Hyogo, and Saga were estimated to be 2.3, 9.5, and 8.0%, respectively. Those for onions from abroad in determinations targeting Hokkaido, Hyogo, and Saga were estimated to be 28.2, 21.6, and 21.9%, respectively.     

Analytical techniques for corrosion studies on noble metals

The suitability of various analytical methods for studying the corrosion of gold, silver and palladium in various electrolytes has been investigated. The methods included potentiometry with ion-selective electrodes, polarography and atomic-absorption spectrophotometry. All three methods are useful for monitoring low corrosion rates by solution analysis but each has its limitations. Concentrations in the ng/ml range can be measured routinely with errors of 10% or less.     

Dynamic rather than static performance measures are needed to improve patient safety

Selected performance measures have been proposed to reduce clinical laboratory errors as a means of reducing medical errors. Yet, whereas this static list of measures are all quality-related, they are not all patient-safety related. For example, the specimen rejection rate is actually measuring a laboratory's ability to detect errors, which is a good thing. Moreover, a static list does not account for new errors or an improved error rate for items on the list. A dynamic list of patient-safety errors, informed by a FRACAS (Failure Review and Corrective Action System) overcomes these objections, since the list of performance measures is periodically refreshed by error data from the clinical laboratory. While new to clinical laboratories, FRACAS has been successfully used in the medical device industry.     

Precise controlled-potential coulometry: Instrumental errors

Instrumental errors in modern controlled-potential coulometry are analyzed. The instrumental errors are classified into two main groups, namely, errors of determining the degree of completion of analyte electrolysis and errors of measuring the quantity of electricity taken for electrolysis. Various components of these errors have been estimated numerically. It has been demonstrated that, with the use of currently available electronic components, the total instrumental error can be as low as 0.01–0.02%, which allows the analysis error to be reduced down to 0.05–0.1%. Presented at the V All-Russian Conference with the Participation of CIS Countries on Electrochemical Methods of Analysis (EMA-99), Moscow, December 6–8, 1999.     

Comparison of the application of Debye-Huckel and specific ion interaction theories for the complexation of tungsten(VI) with ethylenediaminediacetic acid

Equilibrium of the reaction of tungsten(VI) with ethylenediaminediacetic acid (EDDA) has been investigated in aqueous solution of pH 7.5 and 25°C. All measurements have been carried out at different ionic strengths ranging from (0.1 to 1.0) mol dm⁻³ (NaClO₄). According to our results the metal to ligand ratio is 1: 1. Stability constants and stoichiometry of the complex have been determined from a combination of potentiometric and UV spectroscopic measurements. In this semi-empirical model, two parameters have been introduced in a Debye-Huckel type equation based on the Gauss—Newton nonlinear least-squares method and minimizing the sum of the squares of the errors. Comparison of the ionic strength effect on these complex formation reactions has been made using a Debye-Huckel type equation and Bronsted—Guggenheim—Scatchard specific ion interaction theory (SIT). Published in Russian in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 5, pp. 864–868. The article is published in the original     

DFT-B3LYP and SMD study on the interactions between aza-, diaza-, and triaza-12-crown-4 (A n -12-crown-4, n = 1, 2, 3) with Na+ in the gas phase and acetonitrile solution

B3LYP/6-311G level of theory is used to study the interactions between aza-, diaza-, and triaza- 12-crown-4 ligands as host molecules and Na⁺ ion as a guest species. Minimum energy structures, complexes binding energies, basis set superposition errors, and various thermodynamic parameters of free ligands, ion, and complexes have been calculated based on the proposed level of theory. A simple thermodynamic cycle with and without different acetonitrile cluster sizes inside the cavity of Na⁺, has been used to calculate the stability constants of aza-12-crown-4 complex. All solvation free energy estimations have been done with using SMD model. Results show that with introducing more acetonitrile molecules in the cavity of guest species, the absolute deviation is reduced. In addition, a good linear correlation between experimental complex formation constants and binding energies of complexes has been obtained. Calculated results, which are in agreement with the experimental data, predict that the interaction energy of triaza- is more than diaza-12-crown-4, which in turn is greater than aza-12-crown-4 with Na⁺ ion.     

Structure and Mechanism in Cinchona Alkaloid Chemistry: Overturning a 50-Year-Old Misconception

Long-standing errors of the supposedly established literature, including textbooks and data bases have been corrected: The structure of the hetero-cinchona bases in the crystal and in solution (see scheme) and the mechanism of their formation from quinine and quinidine have been elucidated.     

高灵敏电荷耦合器件荧光检测—卡尔曼滤波影响因素研究

本文应用高灵敏电荷耦合器件荧光检测，根据实际测量数据叠加一定程度误差得到的模拟数据及选取不同的计算参数，对影响卡尔曼滤波结果因素，进行了较为系统的研究，找到了一些规律，提高了多组份分析的准确度。     

Precision in 14 MeV neutron activation analysis

The errors of analysis due to the different parameters involved in 14 MeV neutron activation analysis method are studied. Formulae to calculate these erros have been developed when possible. Otherwise they have been evaluated for special experimental situations. Special cases where some parameters become critical, as far as precision is concerned, have been mentioned.