A precise instrumental neutron activation analysis method for determining the elemental composition of Mn−Mg−Zn ferrites

An accurate instrumental method is developed for analyzing nine Mn−Mg−Zn ferrite compositions with a wide range of macrocomponent concentrations. For the overall error of instrumental neutron activation analysis an expression is formulated where partial errors are most accurately taken into account. Brief analysis of the error sources is given. An expression is obtained allowing for the effects of contamination of the standard by the element under investigation with the accuracy of analysis being within 1–2 relative per cent.     

Hidden contributors to uncertainty and accuracy of results of residue analysis

Accurate analytical results with known uncertainty are required for the safety assessment of pesticides and testing the conformity of marketed food and feed with the maximum residue limits. The available information on various sources of errors was examined with special emphasis to those which may remain unaccounted for based on the current practice of many laboratories. The method validation typically covers the steps of the pesticide residue determination from the extraction of spiked samples to the instrumental determination, which contribute to only 10–40% of total variance of results. Though the variability of sampling, sample size reduction and sample processing may amount to the 60–90% of total variance, it generally remains unnoticed leading to wrong decisions. Another important source of gross error is the mismatch of the residues analysed and those included in the relevant residue definition. Procedures which may be applied for eliminating or reducing the errors are discussed.     

Accuracy in the determination of the compositions of main rockforming silicates and oxides on a JXA-8100 microanalyzer

The individual sources of errors in procedures used for considering matrix effects were studied. The ZAF and PRZ analytical programs provided good correction in the predominance of one of the matrix effects, namely, absorption or the atomic number. Their simultaneous occurrence increased the total error to 2–4 rel %. In the ZAF method, normalization to oxygen in terms of stoichiometry introduced errors if the sample simultaneously contained the test element in various oxide forms. The greatest error of up to 1–2 wt % appeared in simple and double oxides. In the analysis of the main rockforming silicates with the determination of total iron as FeO, the presence of Fe₂O₃ can change the concentration of components to ∼0.2%.     

Some features of X-ray registration using a JXA-8100 electron-probe microanalyzer

Specific sources of measurement errors have been studied. In the presence of perturbing radiation, the automatic setting of the spectrometer discrimination mode is not reasonable. When choosing the transmittance window, the dependence of the shift of the amplitude distribution on the counting rate should be taken into account. Losses of intensity can be significant. The value of effective dead time is 1.3 μs for spectrometers with flow methane-argon counters and 1.2–1.5 μs for spectrometric channels with sealed xenon counters. The mode of constant dead time is retained till the intensities of 100–150 kcps. The instrumental error of routine analysis is insignificant as compared with the statistical error of count collection. In the spectra from LiF crystals, a dip in intensities is adjacent to the shortwave wing of the AuL _α radiation line. Measuring intensities on it results in overestimates of the analyte concentration, and line weakening, which occurs because of the spectral hole, in contrast, leads to its underestimation. For this reason, in determining small concentrations of gold, using the L _α line as an analytical one seems unreasonable.     

Electrooxidative coupling of salts of nitro compounds with halide,nitrite, cyanide,and phenylsulfinate anions

Electrolysis of salts of primary and secondary nitro compounds (nitroethane, 1- and 2-nitropropanes, nitrocyclohexane, and nitrocycloheptane) in the presence of excess halide, nitrite, cyanide, and phenylsulfinate anions under undivided and divided amperostatic electrolysis conditions in a two-phase medium (CH₂Cl₂/H₂O) produces geminal nitrohalides (35–85% yields), dinitro compounds (15–51%), nitronitriles (6–27%), and nitrosulfones (50–70%). The salts of secondary nitro compounds form the products of oxidative coupling with halide and phenylsulfinate anions under the undivided electrolysis conditions. In all other cases, divided electrolysis is required. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1539–1546, July, 2005.     

Determination of low concentrations by spectrophotometry: Uranium-thiocyanate system

Errors in the determination of low concentrations by spectrophotometry are investigated with the uranium-thiocyanate system as an example. The reagent blank has significant absorption and measurements are made at 375 nm instead of the λ_max. The error in the intercept of the calibration curve is an important factor in such measurements and the errors involved in the estimation of 1 μg/ml (normal working range 4–40μg/ml) are studied. It is shown that both random and systematic errors associated with the intercept are responsible for observed errors. The two types of errors are resolved by ANOVA (analysis of variance). The error in the measurement of a single value is estimated and compared with measured values for different calibration ranges. It is seen that two factors predominantly influence the error in the measured concentration — the variance from regression and the closeness of the measured value to the mean of the calibration range.     

Validation of multi-element isotope dilution ICPMS for the analysis of basalts

In this study we have validated a newly developed multi-element isotope dilution (ID) ICPMS method for the simultaneous analysis of up to 12 trace elements in geological samples. By evaluating the analytical uncertainty of individual components using certified reference materials we have quantified the overall analytical uncertainty of the multi-element ID ICPMS method at 1–2%. Individual components include sampling/weighing, purity of reagents, purity of spike solutions, calibration of spikes, determination of isotopic ratios, instrumental sources of error, correction of mass discrimination effect, values of constants, and operator bias. We have used the ID-determined trace elements for internal standardization to improve indirectly the analysis of 14 other (mainly mono-isotopic trace elements) by external calibration. The overall analytical uncertainty for those data is about 2–3%.In addition, we have analyzed USGS and MPI-DING geological reference materials (BHVO-1, BHVO-2, KL2-G, ML3B-G) to quantify the overall bias of the measurement procedure. Trace element analysis of geological reference materials yielded results that agree mostly within about 2–3% relative to the reference values. Since these results match the conclusions obtained by the investigation of the overall analytical uncertainty, we take this as a measure for the validity of multi-element ID ICPMS.     

An overlap criterion for selection of core orbitals

 An overlap criterion is defined that connects the identification of core orbitals in a molecular system, which can be problematic, to that in isolated atoms, which is well defined. This approach has been tested on a variety of troublesome systems that have been identified in the literature, including molecules containing third-row main-group elements, and is shown to remove errors of up to 100 kcal/mol arising from an inconsistent treatment of core orbitals at different locations on a potential-energy surface. For some systems and choices of core orbitals, errors as large as 19 kcal/mol can be introduced even when consistent sets of orbitals are frozen, and the new method is shown to identify these cases of substantial core–valence mixing. Finally, even when there is limited core–valence mixing, the frozen-core approximation can introduce errors of more than 5 kcal/mol, which is much larger than the presumed accuracy of models such as G2 and CBS-QB3. The source of these errors includes interatomic core–core and core–valence dispersion forces. Received: 31 August 2001 / Accepted: 11 October 2001 / Published online: 9 January 2002     

Determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in Milk, Cheese and Chocolate

 Combined analytical procedures consisting of wet digestion step followed by instrumental determination – differential pulse cathodic stripping voltammetry (DPCSV) or electrothermal atomic absorption spectrometry (ETAAS) – as well as a direct analysis method – slurry sampling ETAAS – for the determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in milk, cheese and chocolate are described and compared. Wet digestion using a mixture of HNO₃-HClO₄-H₂O₂ is proposed for complete matrix decomposition prior to trace analyte determinati on by DPCSV or ETAAS. A mixture of HNO₃-H₂O₂ is used for slurry preparation. Optimal instrumental parameters for trace analyte measurements are presented. The reliability of the procedures has been verified by analyzing standard reference materials. Results obtained are in good agreement with the certified values and the relative standard deviations (for these results) are in the range 5–10% for wet digestion DPCSV or ETAAS and 3–9% for slurry sampling ETAAS in the range of 2 μgċg⁻¹ (Cd) to 12 μgċg⁻¹ (Fe). Received August 24, 1999. Revision January 20, 2000.     

Application of fission track registration technique in the estimation of fissile materials

Analysis of fissile materials in solution by fission track registration technique has been extended to plutonium in solution of its alloys. In these estimations, the results agreed within 1–4% with the average of those obtained by other chemical and instrumental methods like potentiometry, mass-spectrometry and X-ray fluorescence. Some special practical problems encountered in the analysis of plutonium solutions are noted. Various factors affecting the results have been investigated and the necessary precautions for reducing these errors have been indicated. The advantages of the method over some other conventional methods have also been discussed. It is suggested that a source of about 10 μg of²⁵²Cf corresponding to a neutron flux of about 10⁷ n·cm⁻²·sec⁻¹ is ideal for these experiments.     

Addition of internal standards to particulate sample matrices for routine trace analyses of semivolatile organic compounds: A source of systematical and random errors

This article is a criticism of the strategy of adding (isotope labelled) internal standards of semi volatile hydrophobic organic compounds directly on the surface of particulate samples matrix such as sediment, soil and fly ash, etc. in a small aliquot (mL) of solvent, before trace level analysis. The use of the internal standard is intended to compensate for incomplete extractions, clean-up losses, dilution errors and instrument variations. However, direct addition of internal standards to sample matrices creates two possibilities for inaccurate results by processes only affecting the internal standard: First, evaporation losses of standard from the sample matrix during evaporation of the carrier solvent. Second, the native analyte and internal standard sorb to the sample matrix with differing force. Both processes can introduce systematic and random error to the result. A systematic error of 74% due to evaporation losses of tetra chlorinated dibenzo-p-dioxins is observed, while the corresponding error for octa chlorinated dioxin is 0%. The associated random error is 45% for tetra down to 1–4% relative standard deviations for hepta and octa chlorinated dioxins. For laboratory staff the evaporation losses of standard (and native) compounds causes, besides dust, an additional risk of inhalation exposure. The internal standard should instead be added to the extraction solvent after the extraction. Smaller systematical errors (10–20%) and associated random errors due to irreversible sorption are discussed. Received: 4 September 1997 / Revised: 26 January 1998 / Accepted: 31 January 1998     

Determination of nitrogen,oxigen, fluorine,phosphorus, sulfur and chlorine in aluminium alloys by means of neutron activation

N, O, F, P, S, Cl can be mixed with aluminium during electrolysis, alloying operations and surface treatments. These elements allow changes in mechanical properties. We have adapted separation methods to neutron activation analysis of aluminium alloys down to the sub—ppm level. N, F, Cl, determinations need distillation. S and P separations are based on liquid extraction. O determination is carried out by instrumental method. Tracers and inactive carriers are used for separation study. Clearning of the surface is performed if necessary. 14 MeV neutron activation is applied to nitrogen, oxygen and fluorine determination. The sensitivity is about 200 imp/min/mg. Reactor neutron activation is performed for phosphorus, sulfur and chlorine analysis. The detection level is 0.1 μg/g. Interesting differences of N, O, F, and Cl contents are observed for Al−Zn or Al−Cu alloys in the range 0.1–10 μg/g.     

Quantification of Teicoplanin in Human Plasma by Liquid Chromatography with Ultraviolet Detection

A simple high-performance liquid chromatographic method was developed for determining five major components of teicoplanin, designated A2–1, A2–2, A2–3, A2–4 and A2–5, in human plasma. Using piperacillin sodium as internal standard, teicoplanin in plasma samples was extracted by coextractive cleanup procedure. The extracts were injected into a Nova-Pak C₁₈ column maintained at ambient temperature. The mobile phase consisted of acetonitrile–0.1% trifluoroacetic acid (27:73, pH = 2.2), at a flow rate of 1.0 mL min⁻¹. The analytes were detected at the UV wavelength of 218 nm. The method was found to be linear over the concentration range of 2.5–50 mg L⁻¹ for teicoplanin (r = 0.9993 ± 0.0038), which covered the clinically expected trough plasma levels. The percentage error of the analytical method was below 9%. The intra- and inter-day reproducibility was adequate with coefficients of variation less than 7%. The chromatographic running time was 11 min. Thus, the method can be effectively applied to measure teicoplanin concentrations in clinical samples.     

Study of volatile aroma components in young Tokaji Aszu wines by GC-MS

Summary “Tokaji Aszu”. is the most famous Hungarian wine type with a very delicious, unique aroma. Tokaji Aszu wines are produced from noble rotten grapes by a special vinification technology. In the last few years certain wineries have made an effort to introduce some changes into this traditional process. The present work examines the effect of different vinification technologies on some aroma components in one year old Aszu wines. The volatile aroma components were determined by gas chromatography-mass spectrometry using a Supelcowax 10 60m×0.32 mm capillary column. Wine samples were extracted with Freon 11 prior to the analysis. The chromatograms contained 150–190 peaks. About 40 aroma components were used for comparison of the wines. The results show some limited changes in the aroma composition of the wines due to vinification technological changes. Higher levels of several hydroxy-, oxo-, dicarboxylic acid esters and lactones were found in Aszu wines produced in the traditional way. Attempts have been made to compare instrumental data to sensory properties of the wines. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Potentiometric sensors based on organic ion exchangers of tetraalkylammonium and silver complexes with ampicillin,oxacillin, and cefazolin

Potentiometric sensors with plasticized polymer membranes based on tetraalkylammonium organic ion exchangers and silver(I) complexes with ampicillin, oxacillin, and cefazolin are proposed for the quantification of antibiotics in model mixtures. The quantitative parameters of complex species of silver with β-lactam antibiotics (β-lac) are established. The complexes (β-lac)₂Ag are shown applicable as electroactive components of membranes of potentiometric sensors with tetraalkylammonium cations as counterions. For the information on potentiometric selectivity coefficients and the parameters of cross-sensitivity of sensors in solutions of β-lactam antibiotics they might be used in multisensor systems of the electronic tongue type. The analytical signals are processed by the method of neural network. The average relative error of the individual quantification of β-lactam antibiotics in three-component model mixtures was 4–6%.     

Determination of some trace elements in the industrial process of aluminium production

Some trace elements in samples from the aluminium industry (Aluminium Kombinat, Titograd, Yugoslavia) were determined by instrumental neutron activation analysis. Samples characteristic for alumina production (bauxite, red sludge), reduction cell components (alumina, anode, AlF₃, cryolite) and aluminium produced (purity 99.5–99.7%) have been analyzed. 10 trace elements were determined under a given set of working conditions and followed through the routine production.     

Color reactions of hederagenin and its glycosides

The spectrophotometric reactions of triterpene compounds with concentrated sulfuric acid, a mixture of sulfuric acid and ethanol, and a mixture of sulfuric and acetic acids has been studied with hederagenin and its glycosides — caulosides A, C, and D, isolated from the Far Eastern plantCaulophyllum robustum Maxim — as examples. Conditions for performing the reaction which exclude the influence of the carbohydrate components of the glycosides from the determination of hederagenin have been suggested. The reaction with a mixture of sulfuric acid and ethanol has been used to determine the amounts of caulosides A and C in a total preparation after their separation by the TLC method. The relative error of the determination did not exceed 5 rel.%. Pacific Ocean Institute of Bioorganic Chemistry, Far-Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 643–646. September–October, 1980.     

Investigations on the comparator technique used in epithermal neutron activation analysis

The possible extension of the comparator technique of reactor neutron activation analysis into the field of epithermal neutron activation has been investigated. Ruthenium was used for multi-isotopic comparator. Experiments show that conversion of the so-called reference k-factors—determined by irradiation with reactor neutrons—into k_epi-factors usable at activation under cadmium filter, can be evaluated with fair accuracy. Sources and extent of errors and their contribution to the final error of analysis are discussed. Based on the paper presented at the 2nd European Conference on Analytical Chemistry, 25–30 August, 1975, Budapest, Hungary.     

Relation between prediction errors of inverse and classical calibration

The formulae for prediction errors of inverse and classical calibration derived by Centner, Massart and de Jong in the Fresenius’ Journal of Analytical Chemistry (1998) 361 : 2–9 are reconsidered. All calculations assume univariate calibration by ordinary least squares regression applied to an infinite number of data pairs. Inverse calibration gives rise to an error variance which is smaller by a certain factor than that of classical calibration. This factor amounts to unity plus the ratio of the variances of the measurement errors and of the responses used for the calibration. The root mean squared error of prediction is also smaller for inverse than for classical calibration, namely by the square root of this factor. A prediction error calculated in that way agrees well with a result obtained by Monte Carlo simulations. Received: 23 December 1999 / Revised: 14 February 2000 / Accepted: 15 February 2000