Differentielle Spektralphotometrie als ein genaues Analysenverfahren

Zusammenfassung Ein Überblick zur Entwicklung theoretischer Vorstellungen über die Fehlerquellen der konventionellen und differentiellen Spektralphotometrie wird gegeben. Unter einer Vielzahl der differentiellen Methoden wird nur die Methode von Hiskey-Bastian betrachtet, welche es gestattet, die obere Konzentrationsgrenze der photometrischen Bestimmung zu erweitern. Es werden drei Hypothesen über die Fehlerquellen der photometrischen Messungen vorgestellt, die in unterschiedlichem Maße das Rauschen beim Ablesen der Absorbanz des Analyten sowie beim Abgleich von Leerwert und Dunkelstrom berücksichtigen. Die Ausdrücke für die Fehlergleichungen werden vorgestellt. Der Weg zum Auffinden der optimalen Bereiche, innerhalb welcher die Absorbanzen mit einem minimalen Fehler behaftet sind, wird aufgezeigt.

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Differential spectrophotometry as an accurate analytical method1. The development of the conceptions about sources of errors in photometric measurements

Summary A historical review about the development of conceptions about sources of errors in conventional and differential photometry is given. Among several differential methods the method of Hiskey-Bastian will be taken into account. This method allows to expand the upper range of concentrations, which are applied to the photometric measurements. Three hypotheses about the sources of errors in photometric measurements are discussed. They take into account, to a different extent, the noise in reading the absorbance of the sample solution as well as in setting the unit transmittance point on the scale and setting the zero (dark current). The expressions for the error equation are presented. The possibility of finding the optimum range of absorbance with the minimum error is shown.

     

Where is analysis of trace elements in biotic matrices going to?

Summary Accomplishing the act of balancing our technological progress with the accompanying risks for safety and health in our life quality, calls for modern analytical science. It should serve as an indicator for the correct balance of forces in the substantial sphere. However, today such an indicating role is based on rough estimations, or on insufficient or unconfirmed information with respect to concentrations, binding forms and local distributions of toxic or of essential substances within a sample. Moreover, many complex mechanisms of synergetic and antagonistic physiological interactions have not yet been clarified — and consequently, we have to take into account severe misjudgements of risks.In addition, one has reached the limits of financial means required for the increasing control and survey tasks of daily analytical routine. Accordingly, only a long-term planned strategy for the development of more powerful, more reliable and more economic analytical methods, which moreover guarantee a better local distribution (microdistribution analysis), are the prerequisites for an improvement of this situation in analytical sciences.In view of the future tasks and the ultimate limits of trace- and micro-distribution analysis of the elements, the present state and an outlook on reaching the limit of analysis are critically discussed. Main emphasis is placed here on the possibility of improving conventional determination methods such as AAS, OES, XRFA, MS, NAA with regard to better power of detection and reliability. But also innovative analytical principles such as laser atomic spectroscopy (RIS, LEI, LIF) are introducted. They promise to develop into an essential basis for micro and trace element analysis of tomorrow.As instrumental methods are always the last step in an analytical procedure, a brief reference will be made to the problem of sample preparation, mainly with regard to the sources of systematic errors. As for trace analysis at the ng/ ml- or pg/ml-levels there are no reliable or certified standard reference materials available up to now, multistep procedures are still necessary. They must combine decomposition, preconcentration and determination methods in an optimal way to minimize systematic errors. The state-of-the-art of such multistep procedures in extreme elemental trace analysis will also be presented.

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über die zukünftige Entwicklung der Spurenelementanalyse in biotischen Matrices

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Dedicated to Prof. Dr. W. Fresenius in gratitude on the occasion of his 75th birthday.     

Criteria and algorithms for the choice of analytical wave-lengths in the quantitative spectrophotometric analysis of multicomponent mixtures

Summary The criteria and methods for the choice of the number and position of analytical wave-lengths (AWL) for the quantitative spectrophotometric analysis of multi-component mixtures by the least squares method were studied by means of five three- and four-component model systems. Comparison of the results of using various criteria and selection methods with the data of an exhaustive search of all the possible AWL combinations suggests that the sums of squares of the computer matrix elements, P and P _j, could be recommended as the most efficient criteria. The most efficient selection method is that of successive screening of the wave-lengths which, after being eliminated from the initial AWL set, cause the least changes in the P or P _j values. From the obtained dependences of P and P _j on the number of AWL (n), the value of n can be chosen which provides the greatest reproducibility of the method for a given labour input, with the possible increase in the number of parallel determinations for each AWL being taken into account. The volume of computing can be diminished by ranking the AWL in the initial set and applying the method of successive screening or exhaustive search so as to diminish the number of AWL combinations. The above criteria and selection methods provide minimization of the effect of experimental errors in the optical densities of mixtures on the analytical results.

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Kriterien und Algorithmen zur Wahl analytischer Wellenlängen für die spektralphotometrische Analyse von Mehrkomponenten-Gemischen

     

Konzentrationsbestimmung an Textilf?rbungen mit Hilfe der Photo-Akustik-Spektroskopie

Zusammenfassung Das Beispiel der Direktbestimmung von Farbstoffkonzentrationen auf Textilfärbungen zeigt die quantitativ-analytische Anwendbarkeit der PAS. In Verbindung mit einem halbempirischen Auswertungsverfahren kann diese Methode auch bei hohem Chromophorgehalt angewandt werden. Der Einfluß verschiedener Störfaktoren auf das Analysenergebnis wird untersucht.

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Determination of dyestuff concentrations on textiles by photo-acoustic-spectroscopy

Summary The direct determination of dyestuff concentrations on textile samples shows PAS to be a reliable quantitative analytical tool. Using a semi-empirical analysis of data this method can be applied even to high loadings of chromophor. The influence of different sources of error on the analytical result is investigated.

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Die vorliegenden Untersuchungen wurden durch Zuwendung der DFG und des Fonds der Chemie unterstützt, wofür wir uns herzlich bedanken.     

Reliability of synthetic powder standards for atomic emission spectrometry

Summary The reliability of synthetic quartz and graphite powder standards for AES determination of sodium and potassium has been investigated. The study was concerned with the evaluation of the influence of the following factors on the overall variation of the results: irreproducibility of the mean chemical composition between standards, inhomogeneity within standard preparations, spectrographic technique of excitation and recording of spectra, photometric measurement of line intensities. In an experiment designed according to an hierarchical, orthogonal plan followed by analysis of variance applied to the results, the influence of all these factors could be evaluated. It was found that besides the most serious contribution of the spectrographic technique to the overall accidental error the irreproducibility of the mean chemical composition between standard preparations should be taken into account. This leads to the conclusion that in the case of powder standards the assumption is of no general validity that their composition is not subject to error. Therefore, calibration of AES methods with the use of powder standards should rather be based on the regression technique which allows for both variables (composition and analytical signal) being subject to errors.

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Zuverlässigkeit von pulverförmigen Eichsubstanzen für die Atomemissionsspektrometrie

     

Ermittlung, Auswertung und Ursachen von Fehlern bei Betriebsanalysen

Zusammenfassung Die vielfach zu Vergleichen herangezogene Streuung analytischer Bestimmungen hängt in hohem Ma\e vom gewählten Ermittlungsverfahren ab. Ähnliches gilt für die Art der Feststellung von Ausrei\ern, welche die Werte der Streuung eines Kollektivs wesentlich beeinflussen. Ein der Betriebsüberwachung dienendes Laboratorium hat bei der Ermittlung dieser Daten auch auf die Aussagekraft seiner Ergebnisse für den Betrieb Rücksicht zu nehmen.Gro\zahluntersuchungen aus verschiedenen Laboratorien lie\en erkennen, daß bei den meisten Bestimmungsverfahren eine charakteristische Abhängigkeit des Fehlers vom Gehalt besteht, nach der innerhalb eines begrenzten Bereiches eine Fehlerursache dominiert. Durch eine einfache Darstellung lassen sich die Fehler eines Verfahrens nicht nur rasch überblicken sondern auch gezielt aufsuchen.

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Investigation, evaluation and sources of error of plant analyses

Though standard deviation commonly is used to compare analytical methods, it depends very much on the kind of experiment and evaluation. Mavericks also influence the standard deviation in a substantial manner. The evaluation of standard deviation in a plant laboratory has to consider also the way of production, which is controlled.Statistical interpretations from various laboratories showed, that for most analytical methods there exists a dependence between error and concentration in such a way that one kind of error dominates within a limited reach. By means of a simple diagram the different errors of an analytical method can be quickly surveyed and identified.

     

PARAFAC Decomposition of Three‐Way Kinetic‐Spectrophotometric Spectral Matrices Based on Phosphomolymbdenum Blue Complex Chemistry for Nitrite Determination in Water and Meat Samples

Abstract

A three‐way analytical methodology experimentally based on kinetic‐spectrophotometric and parallel factor analysis (PARAFAC) chemometrics analysis was assessed for the quantification of nitrite in water and meat samples. This method is based on the reduction of phosphomolybdic acid to phosphomolymbdenum blue complex by sodium sulfide. The obtained phosphomolymbdenum blue complex is oxidized by the addition of nitrite and this causes a reduction in intensity of the blue color. Three‐way data matrices were generated by acquisition of ultraviolet‐visible (UV‐Vis) spectra (600–900 nm) as a function of the time and of different relative concentration of the nitrite (0.10–2.10 µg mL^?1). The PARAFAC trilinear model, without restrictions, was used in the data analysis. A full decomposition of the data matrices was obtained (spectra, concentration, and time profile). It was shown that kinetic methods coupled to three‐way chemometrics analytical methods can be used for the development of robust sensors for the analysis of nitrite in water and meat samples. The accuracy of the method, evaluated through the root mean square error of prediction (RMSEP), was 0.0515 and 0.1181 for nitrite by PARAFAC and partise least squares (PLS) models respectively. The results with the PARAFAC model are better than those of the PLS model, according to results, it being possible to recover the spectra and kinetic profiles, as well as the initial concentration of nitrite with good accuracy.     

Gesammelte Erfahrungen bei der Routinebestimmung von3H und14C Durch Flüssig-Szintillationsspektrometrie

Experience accumulated in several years of routine work on liquid scintillation counting is presented, together with an analysis of the main sources of error and the mention of some means to reduce them. A precise method based on comparing analytical samples with known standards is described.      

Comparison of the efficiency of spark source, laser, glow discharge and secondary ion mass spectrometry for bulk analysis

Summary After describing the design and properties of the ion sources, the analytical performances of spark source, laser, glow discharge and secondary ion mass spectrometry are compared. The criteria are the sample requirements, the detectable elements, the detection limits, element sensitivity factors and the achievable accuracy. Typical areas of use for these methods are derived from these properties.

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Vergleich der Leistungsfähigkeit von Funkenquellen, Laser, Glimmentladungs- und Sekundärionen-Massenspektrometrie für die Bulk-Analyse

     

Anwendung und Bedeutung der spektrochemischen Analyse in den Geowissenschaften

Zusammenfassung Historisch gesehen ist die erste entscheidende Rolle der spektrochemischen Analyse bei der Entdeckung und Identifizierung chemischer Elemente, d.h. in geochemischen Untersuchungen zu suchen. Die Gründung und Entwicklung der Geochemie ist ohne spektroskopische Angaben kaum denkbar. Die Problematik und die Ziele des neuen, zwischen der analytischen Chemie und der Geochemie entstandenen interdisziplinären wissenschaftlichen Zweiges, der analytischen Geochemie, werden dargestellt. Die Leistungsfähigkeit der halbquantitativen und quantitativen Methoden wird gezeigt. Die Behandlung spektrochemischer Ergebnisse zur Gewinnung von geochemischen Informationen (Verteilungsart, Mittelwertbildung, Dispersion, Einfluß des analytischen Fehlers) wird diskutiert und Beispiele gezogener Rückschlüsse werden angeführt.

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Application and role of spectrochemical analysis in geological sciences

Summary From the historical point of view the first decisive role of spectral analysis was played in the discovery and identification of chemical elements in natural materials. The creation of a florishing branch of geological sciences — the geochemistry — cannot be imagined without a high level of spectrochemical methods. Features and objectives of analytical geochemistry are presented. The contribution of outstanding spectroscopists to the analysis of geological materials and some special spectroscopic techniques developed for this field are remembered.The reliability of spectrochemical results and efficiency of appropriate methods is shown. The treatment of spectrochemical results for some geochemical informations (type of distribution, mean values, dispersion, influence of the analytical error) is discussed and examples of conclusions obtained on the basis of spectrochemical results are presented.

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Ich danke Frau Prof. Dr. R. Rautschke, Dr. sc., für fachliche und sprachliche Bemerkungen.     

Improvements in methylmercury determination prior to the certification of two tuna fish materials

An account is given of a systematic, collaborative investigation to detect problems and sources of error in the determination of methylmercury (MeHg) in biological samples. The work was done by a group of analytical laboratories under the auspices of the Community Bureau of References (BCR) of the Commission of the European Communities (EC). The paper presents the organization of three intercomparisons on organic mercury in solution and solid matrices, and the results obtained by the participants. The different analytical steps of the methods used (extraction, clean-up, separation, final detection) are compared and assessed.     

Zur Fehlerermittlung bei der photometrischen Eisenbestimmung in Glassanden

Zusammenfassung Zur Bestimmung des Eisengehaltes in Glassanden eignet sich die o-Phenanthrolinmethode, da diese Methode frei ist von störenden Einflüssen der im Sand neben dem Eisen vorliegenden Fremdionen.Der Analysenfehler wird dabei aus den Eichmessungen nach den Methoden der Ausgleichsrechnung und mathematischen Statistik rechnerisch ermittelt und bei der Auswertung des Analysenergebnisses in geeigneter Form berücksichtigt.

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Summary For the determination of the iron content in glass sands the o-phenanthroline method is suitable because it is unaffected by foreign ions occuring in the sand besides iron.The analytical error is calculated from the calibrating measurements according to the methods of balancing computation and mathematical statistics, and is taken into account on interpreting the analytical result in a suitable form.

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Herrn Dr. Moritz danken wir für die Anregung zu dieser Arbeit, Herrn Dr.-Ing. habil. Klaus Doerffel für wertvolle Hinweise zur mathematischen Auswertung.     

Reliability of measurements of pesticide residues in food

This paper accounts for the major sources of errors associated with pesticide residue analysis and illustrates their magnitude based on the currently available information. The sampling, sample processing and analysis may significantly influence the uncertainty and accuracy of analytical data. Their combined effects should be considered in deciding on the reliability of the results. In the case of plant material, the average random sampling (coefficient of variation, CV=28–40%) and sample processing (CV up to 100%) errors are significant components of the combined uncertainty of the results. The average relative uncertainty of the analytical phase alone is about 17–25% in the usual 0.01–10 mg/kg concentration range. The major contributor to this error can be the gas-liquid chromatography (GLC) or high-performance liquid chromatography (HPLC) analysis especially close to the lowest calibrated level. The expectable minimum of the combined relative standard uncertainty of the pesticide residue analytical results is in the range of 33–49% depending on the sample size.The gross and systematic errors may be much larger than the random error. Special attention is required to obtain representative random samples and to eliminate the loss of residues during sample preparation and processing.     

钢中氧化物夹杂分析的误差来源及结果的可靠性

本文综述了采用化学-电化学方法分析钢中氧化物夹杂的误差来源。基体元素的水解、钝化、共存相的干扰和包裹相等引起正偏差;化学溶损、沉淀处理等引入的负偏差;以及随机误差。相应地提出了提高分析精度的具体措施。对这种既无标样又无标准可循的分析其结果的可靠性不仅需根据钢中氧含量而定,还需根据夹杂物的总量与分量的吻合程度来判定,此外要结合钢的化学成份,冶炼工艺,脱氧制度来综合判断。     

High accuracy in the element analysis by mass spectrometry

Summary Accurate analysis results are a common problem in trace and micro determinations of elements, as found in particular in a number of interlaboratory studies. The difference between precision and accuracy of an analysis is shown in this review and a possible hierarchy of analytical methods is given. Isotope dilution mass spectrometry is the most accurate method of all mass spectrometric techniques. Possible element analyses by isotope dilution mass spectrometry are discussed using different ionization methods in the mass spectrometer (thermal ionization, spark source mass spectrometry, electron impact ionization, ICP and MIP, field desorption mass spectrometry). If MIP-MS and spark source mass spectrometry are applied, the difference between analysis results where the isotope dilution technique is and is not used is shown. The precision and accuracy of spark source mass spectrometry increases significantly when the isotope dilution method is applied. Accurate results by mass spectrometry are shown in comparison with certified values of standard reference materials using food samples, biological samples, geological samples, nuclear reactor materials, metals, and samples from the environment as examples. Possible sources of error by isotope dilution mass spectrometry are discussed. In contrast to the analysis of metal traces, only a few alternative methods can be applied to the trace analysis of non-metals and their anion forming compounds. In this case the production of negative thermal ions in a mass spectrometer in connection with the isotope dilution technique is a useful tool for accurate anion and non-metal analyses.

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Hohe Richtigkeit in der Elementanalyse durch Massenspektrometrie

Zusammenfassung Richtige Analysenergebnisse sind ein allgemeines Problem bei der Spuren- und Mikrobestimmung der Elemente, wie sich vor allem immer wieder im Rahmen von Ringanalysen herausstellt. Der Unterschied zwischen Reproduzierbarkeit und Richtigkeit eines Analysenergebnisses wird in diesem Übersichtsartikel aufgezeigt und eine mögliche Hierarchie von Methoden aufgestellt. Im Bereich der Massenspektrometrie gilt die Isotopenverdünnungsanalyse als diejenige Methode, mit der die richtigsten Ergebnisse erhalten werden können. Für die Anwendung verschiedener Ionisationsmethoden im Massenspektrometer (Thermionisation, Funkenquellen-Massenspektrometrie, Elektronenstoßionisation, ICP und MIP, Felddesorptions-Massenspektrometrie) werden die Möglichkeiten der Elementanalyse durch die Isotopenverdünnungstechnik diskutiert. Bei Verwendung der MIP-MS und der Funkenquellen-Massenspektrometrie wird auch der Unterschied zwischen Ergebnissen, die mit und ohne Isotopenverdünnungsanalyse erhalten werden, aufgezeigt. Dabei ergibt sich für die Funkenquellen-Massenspektrometrie eine wesentliche Verbesserung der Analysenergebnisse, wenn die Isotopenverdünnungsmethode angewendet wird. Anhand von Beispielen (Lebensmittelproben, biologische Proben, geologische und kerntechnische Proben, Metalle, Umweltproben) wird die Richtigkeit der massenspektrometrischen Ergebnisse verdeutlicht, wobei häufig ein Vergleich zu zertifizierten Werten von Standard-Referenzmaterialien gegeben wird. Mögliche Fehlerquellen der Isotopenverdünnungsanalyse werden diskutiert. Da bisher zur Bestimmung von Anionen- und Nichtmetallspuren nur vergleichsweise wenige Verfahren zur Verfügung stehen, hat sich hier die Erzeugung negativer Thermionen in einem Massenspektrometer bei gleichzeitiger Anwendung der Isotopenverdünnungsanalyse bewährt.

     

The role of statistics in quality assurance

Summary The quality of data, which is to say its accuracy, must be known whenever it is to be used for purposes of decision. This is only possible as it is produced by a valid analytical system operating in a state of statistical control. A quality assurance program should be established, consisting of quality control of the analytical system and quality assessment of the data that are produced. Data quality objectives should be established for every measurement situation and the accuracy attained must be within these limits. Ideally, the attained accuracy should exceed the required accuracy by a factor of three, at a minimum. The estimation of attained accuracy is best made using reliable reference materials. When they are not available, spikes may be used with lesser confidence. No matter what estimation techniques are used, decisions must be made on the basis of statistical tests of significance. The evaluation of accuracy is a continuing operation and facilitated by the use of appropriate control charts. The paper discusses the above described concepts and summarizes the techniques most useful for evaluating the accuracy of analytical data.

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Die Rolle der Statistik in der Qualitätssicherung

     

Robust regression methods to calibrate a continuous flow analyzer in the colorimetric analysis of inorganic phosphorus in seawater

The presence of a salinity effect in the automated analysis of phosphorus in seawater performed by a phosphomolybdate complex can cause the inaccurate estimation of the true amount, because the calibration procedure performed by least-squares regression does not take into account the different analytical response of samples and standard solutions. The error arising from this salt effect is corrected by calibrating the autoanalyzer with robust regression methods (RRMs), which allow definition of the range of salinity in which the analytical response of the autoanalyzer is only dependent on the concentration of marine nutrients. The RRMs are especially helpful in the analysis of oligotrophic samples where the salinity effect is particularly relevant.     

Differentielle Spektralphotometrie als ein genaues Analysenverfahren

Zusammenfassung Die Präzision der differentiellen photometrischen Messung an dem mikrorechnergesteuerten Zweistrahl-Spektralphotometer SPECORD M 40 (Carl Zeiss Jena) wurde untersucht. Die gewonnenen Daten wurden zur Interpretation der Fehlerquellen, die den Gesamtfehler wesentlich beeinflussen, benutzt. Es zeigte sich, daß hier die gleiche Beziehung wie auch für den Fall eines Einstrahl-Spektralphotometers gilt. Das heißt, daß das Rauschen an beiden Enden der Transmissionsskala sowie die Empfindlichkeit des Gerätes die Präzision der photometrischen Messung bestimmen. Das Rauschen beim Dunkelstromabgleich ist auch in diesem Fall kleiner als beim Leerwertabgleich.Es ist gezeigt worden, daß unter der Berücksichtigung der Gültigkeitsbereiche des Bouguer-Lambert-Beerschen Gesetzes die differentielle Methode richtige und präzise Werte liefern kann, wenn als Leerwert eine Lösung von der Absorbanz A ₁₀=1 benutzt wird und die Absorbanz des Analyten A ₂₀ im Bereich 1,1–1,6 liegt.

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Differential spectrophotometry as an accurate analytical method3. Experimental test of the hypotheses about the error sources in the differential photometric measurements on a double-beam photometer

Summary The precision of the differential photometric measurement by the microcomputer double-beam spectrophotometer SPECORD M 40 (Carl Zeiss Jena) is investigated. The data obtained are used to interpret the error sources influencing essentially the total error. It was shown, that in this case the same equation is valid as in the case of the one-beam spectrophotometer. That means, that the noise at both ends of the transmittance scale as well as sensitivity of the device influenced the precision of the given spectrophotometer. The noise of the dark current is here also smaller than the noise at the setting of unit transmittance point. Furthermore it was shown, that taking the validity range of the Beer's Law into account, precise and accurate results can be achieved by the differential method, if the reference solution shows the absorbance A ₁₀=1, and the absorbance of the analyte A ₂₀ lies between 1.1 and 1.6.

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Teil 2: siehe [4]     

Do we really need to account for run bias when producing analytical results with stated uncertainty? Comment on 'Treatment of bias in estimating measurement uncertainty' by G. E. O'Donnell and D. B. Hibbert

Treatment of bias is an important issue relating to analytical quality. Recently, G. E. O'Donnell and D. B. Hibbert (Analyst, 2005, 130, 721) recommended to always correct analytical results for 'run bias' determined by a single analysis of a certified reference material (CRM) in each analytical run. In the authors' opinion, this is necessary for the results obtained to be comparable from run to run. It is argued here that such a recommendation is logically inconsistent and stems from misinterpretation of measurement uncertainty as being estimated under repeatability conditions. The fundamental principle underlying the measurement uncertainty methodology is that all relevant sources of error should be taken into account, which results in overall uncertainty assessment and thus provides a means for a global comparability of measurement and test results. The local, i.e. run-to-run, comparability is not a factor if analytical results are interpreted on the basis of their associated uncertainty.     

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.