Uranium determination using atomic spectrometric techniques: An overview

This review focuses on the determination of uranium using spectroanalytical techniques that are aimed at total determination such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma optical emission spectrometry (ICP-OES); and inductively coupled plasma mass spectrometry (ICP-MS) that also enables the determination of uranium isotopes. The advantages and shortcomings related to interferences, precision, accuracy, sample type and equipment employed in the analysis are taken into account, as well as the complexity and costs (i.e., acquisition, operation and maintenance) associated with each of the techniques. Strategies to improve their performance that employ separation and/or preconcentration steps are considered, with an emphasis given to solid-phase extraction because of its advantages compared to other preconcentration procedures.     

An uncertainty evaluation for multiple measurements by GUM, III: using a correlation coefficient

After a measurement, a measured value and a measurement uncertainty are produced as a measurement result. By a repeated measurement, another measurement result is produced. Between the individual results of the two measurements, it is shown that there may be a significant correlation. A correlation coefficient can be determined when a GUM-compliant uncertainty budget for a measurement is available. Utilizing the correlations between the N individual results, an equation is derived to combine the N individual uncertainties of N measurements. Using the newly derived equation including the correlation coefficient, three measurement uncertainties of three measurement results are combined as an example. The combined uncertainty is compared with the uncertainty of a measurement which treats the three individual measurements as one process. Papers published in this section do not necessarily reflect the opinion of the editors, the editorial board, or the publisher.     

An automatic gravimetric titrator and its use for the potentiometric determination of uranium by the Davies and Gray method

Summary Construction and mode of operation of an automatic gravimetric titrator are described. Center of the system is a Titroprint E 475 which was modified on a few points. The titrant is added by use of two automatically controllable motor burettes as a main volume, and then in steps of 0.01 ml. The losses of weight of the reservoir vessel are correspondingly recorded by an electronic balance. The measured data are obtained on a punched tape and allow evaluations of the analysis as gravimetric and volumetric titration by use of two Basic computer programs. When the system was used for the potentiometric determination of uranium a relative standard deviation of 0.48 (gravimetric and volumetric) and relative deviations from the nominal value of –0.41 (gravimetric) and –0.79 (volumetric) were obtained as mean values for 14 groups of 5–6 samples.

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Ein automatischer gravimetrischer Titrator und seine Anwendung für die potentiometrische Bestimmung von Uran nach Davies und Gray

Zusammenfassung Es werden Aufbau und Betriebsweise eines automatischen gravimetrischen Titrators beschrieben, dessen Hauptkomponente ein in mehreren Punkten modifizierter Titroprint E 475 ist. Das Titrationsmittel wird mit zwei elektronisch steuerbaren Motorbüretten grob- bzw. feindosiert, wobei eine elektronische Waage die entsprechenden Gewichtsverluste des Reservoirgefäßes registriert. Die auf Lochstreifen ausgegebenen Meßdaten lassen Auswertungen der Analyse als gravimetrische und volumetrische Titration über entsprechende Basic-Computerprogramme zu. Bei Benutzung des Systems für die potentiometrische Bestimmung von Uran wurden für Gruppen von 5–6 Proben mittlere relative Standardabweichungen von 0,48 (gravimetrisch und volumetrisch) sowie mittlere relative Abweichungen vom Sollwert von –0,41 (gravimetrisch) bzw. –0,79 (volumetrisch) erhalten.

     

A validation concept for purity determination and assay in the pharmaceutical industry using measurement uncertainty and statistical process control

 The analytical chemists in process development in the pharmaceutical industry have to solve the difficult problem of producing high quality methods for purity determination and assay within a short time without a clear definition of the substance to be analyzed. Therefore the quality management is very difficult. The ideal situation would be that every method is validated before use. This is not possible because this would delay the development process. A process-type quality development approach with an estimation type fast validation (measurement uncertainty) is therefore suggested. The quality management process consists of the estimation of measurement uncertainty for early project status. Statistical process control (SPC) is started directly after measurement uncertainty estimation and a classical validation for the end of the project. By this approach a process is defined that allows a fast and cost-efficient way of supporting the development process with the appropriate quality at the end of the process and provides the transparency needed in the development process. The procedure presented tries to solve the problem of the parallelism between the two development processes (chemical and analytical development) by speeding up the analytical development process initially. Received: 25 March 1997 · Accepted: 17 May 1997     

Commercialized rapid immunoanalytical tests for determination of allergenic food proteins: an overview

Food allergies have become an important health issue especially in industrialized countries. Undeclared allergenic ingredients or the presence of “hidden” allergens because of contamination during the food production process pose great health risks to sensitised individuals. The EU directive for food labelling lists allergenic foods that have to be declared on food products by the manufacturers. The list includes gluten-containing cereals, crustaceans, eggs, fish, peanuts, soybeans, milk, various nuts (e.g. almond, hazelnut, and walnut, etc.), celery, mustard, sesame seeds, lupin, and molluscs. Reliable methods for detection and quantification of food allergens are needed that can be applied in a fast and easy-to-use manner, are portable, and need only limited technical equipment. This review focuses on the latest developments in food allergen analysis with special emphasis on fast immunoanalytical methods such as rapid enzyme-linked immunosorbent assays (ELISA), lateral-flow immunochromatographic assays (LFA) and dipstick tests. Emerging technologies such as immunochemical microarrays and biosensors are also discussed and their application to food allergen analysis is reviewed. Finally, a comprehensive overview of rapid immunochemical test kits that are currently available commercially is given in tabular form.     

Precise determination of boron by titration with a multiparametric curve-fitting procedure for data evaluation

A precise method is described for the determination of boric acid and boron in metal borides by potentiometric titration of the mannitol/boric acid complex with a strong alkali. Titration data are evaluated by a multiparametric curve-fitting procedure on the basis of model functions for this type of titration. The initial boric acid concentration, or parameters like the conditional acidity constant and the association number of the mannitol/boric acid complex can be determined. For a sample of titanium boride, the standard deviation was 0.15% on a boron content of 29.18%.     

Conditions for calibration of an isothermal titration calorimeter using chemical reactions

The reaction of protonation of 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) is a suitable one for the calibration of isothermal titration calorimeter (ITC), providing that experimental conditions are appropriately chosen. The conditions and methods for handling experimental data from a nanowatt-ITC are discussed. Also, the binding of Ba²⁺ to 18-Crown-6 is successfully used to check the accuracy and precision of the chemical calibration performed with TRIS. This latter reaction has the additional advantage that the data can also be used for a check on the determination of the value of a binding constant. The anomaly of the first injection in ITC is analyzed and, by combining calorimetric and spectroscopic measurements, it is shown that it mainly results from a backlash effect of the syringe plunger rather than from a diffusion effect.     

Quantitative determination of transferrin in cerebrospinal fluid using an enzyme linked immunosorbent assay

An enzyme linked immunosorbent assay (ELISA) based method for the determination of transferrin in cerebrospinal fluid (CSF) is described. This method allows transferrin determinations in ultra-small ( 5 L) sample volumes. The proposed method offers the possibility to determine transferrin at very low concentrations at which existing methodologies fail because of their insufficient detection limits. The accuracy of the proposed technique was validated by comparing the results of 20 CSF samples obtained by ELISA to those measured by nephelometry yielding mean ± SD values of 21.1±5 mg/L and 20.6 ± 6 mg/L, respectively (y = 1.13X – 2.97, r = 0.899). The interassay CV was below 10% whereas the detection limit was 2.9 g/L.     

Separation and preconcentration by a cloud point extraction procedure for determination of metals: an overview

Recently, cloud point extraction (CPE) has been an attractive subject as an alternative to liquid–liquid extraction. The technique is based on the property of most non-ionic surfactants in aqueous solutions to form micelles and become turbid when heated to the cloud point temperature. This review covers a selection of the literature published on applications of CPE in determination of metal ions over the period between 2004 and 2008.     

Measurement uncertainty evaluation for a non-negative measurand: an alternative to limit of detection

The interpretation and reporting the results of measurements on materials where the concentration of the analyte is close to or may even be zero has been the subject of much discussion with the use of such concepts as limit of detection (LOD) and limit of quantification (LOQ). While these concepts have taken into account the measurement uncertainty, they have not utilised the fact that the value of the measurand, i.e., the concentration, is constrained to be zero or greater. Taking this into account the distribution of values attributable to the measurand can be derived from the probability density function (PDF) that determines the distribution of the observed values. When this PDF is normal the distribution of the values attributable to the measurand is a truncated t distribution with a lower limit of re-normalised so that the total probability is one, where x _m is the mean of the n observed values and s their standard deviation. When x _m much greater than then the distribution reverts to the unmodified t distribution. The probability that the value of the measurand is above or below a limit can be calculated directly from this truncated t distribution and the interpretation of the result does not require the use of concepts such as LOD and LOQ. Also it deals with the problem of negative observations. This Report was written by Alex Williams (e-mail: aw@camberley.demon.co.uk) for the Statistical Subcommittee and approved by the Analytical Methods Committee.     

Measurement uncertainty procedures revisited: Direct determination of uncertainty and bias handling

This article is based on a lecture presented at the Analytica Conference, where the basic principles for evaluating and expressing the uncertainty of analytical measurements, as set out in the guides published by ISO and EURACHEM, were reviewed, and the inventory of procedures and tools for effective implementation of these principles was examined. While the emphasis in the lecture was on basic principles, this article presents a more detailed elaboration of one of the main practical procedures outlined in the lecture: direct determination of uncertainty and handling of bias.     

Rapid colorimetric determination of reduced and oxidized glutathione using an end point coupled enzymatic assay

A simple and rapid colorimetric coupled enzymatic assay for the determination of glutathione is described. The proposed method is based on the specific reaction catalyzed by γ-glutamyltransferase, which transfers the γ-glutamyl moiety from glutahione to an acceptor, with the formation of the γ-glutamyl derivative of the acceptor and cysteinylglycine. The latter dipeptide is a substrate of leucyl aminopeptidase, which hydrolyzes cysteinylglycine to glycine and cysteine that can be easily measured spectrophotometrically. The proposed method was used to measure the content of glutathione in acid extracts of bovine lens, to follow the NADPH-dependent reduction of glutathione disulfide (GSSG) to reduced glutathione (GSH) catalyzed by the enzyme glutathione reductase and to determine the glutathione content in human astrocytoma ADF cells subjected to oxidative stress. The results obtained showed that the method can be suitably used for the determination of GSH and GSSG in different biological samples and to monitor tissue or cell redox status under different conditions. It is also applicable for following reactions involving GSH and/or GSSG.

Derivatizing assay for the determination of aldehydes using micellar electrokinetic chromatography

In this work, the use of a novel derivatization agent for the determination of aldehydes (in this particular case: formaldehyde, acetaldehyde, propionaldehyde, and valeraldehyde) using micellar electrokinetic chromatography is reported. The derivatization reaction is based on the reaction of aldehydes with benzhydrazide to form the corresponding derivates with maximum absorbance at 250 nm. The experimental conditions of the derivatization reaction as well of the separation were optimized. The adducts were separated with a +22 kV voltage at a temperature of 29°C. The adducts’ separation was performed in less than 14 min using as the running buffer a mixture containing 110 mmol/L of sodium dodecyl sulfate and 27 mmol/L of sodium tetraborate at pH 9.45. Samples were injected using hydrodynamic mode (50 mbar × 5 s). The calibration curves were linear up to 15.0 mg/L with r ² above 0.99. Intra and inter‐day precisions were in average 3 and 4%, respectively, and recoveries were in average of 95%. Limits of detection and quantification were around 0.5 and 1.5 mg/L, respectively. The developed method was successfully applied in the analysis of low molar weight aldehydes in yogurt and vinegar samples.     

Quantitative NMR spectroscopy for accurate purity determination of amino acids,and uncertainty evaluation for different signals

Purity evaluation of amino acids using nuclear magnetic resonance spectroscopy is reported. Three amino acids (aspartic acid, valine, and arginine) and certified reference materials (CRMs), such as acidic, neutral, and basic amino acids, as well as a low pure sample of valine were used as the analytes. DCl solution, D₂O, and NaOD solution were used as the preparation solvents. The quantitative values were obtained from all observed signals and compared with the certified values of the CRMs. When an amino acid was dissolved in water, a strong HOD signal due to proton exchange was observed. When the signal adjoining the HOD signal was considered in the evaluation, the accurate quantitative value could not be obtained. Therefore, under optimized conditions, the analyte signals separated from the HOD signal were chosen for purity determination of amino acids. As a result, the quantitative values were in agreement with the certified values of CRMs. An expanded uncertainty was estimated to be approximately 0.002 kg kg^?1. We also discuss the effect of impurities on purity determination based on all signals and conclude that agreement of quantitative values determined from different signals in a molecule is a good indication of the accuracy of the results.     

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.

A definitive RNAA method for determination of selenium in biological samples: uncertainty evaluation and assessment of degree of accuracy

This article describes work on the development of a highly accurate RNAA method for determination of selenium in biological samples. The analytical post-irradiation procedure is based on a combination of cation-exchange and extraction chromatography with final selective and quantitative fixation of selenium on a column packed with 3,3′-diaminobenzidine (DAB) supported on Amberlite XAD4, followed by gamma-ray spectrometric measurement. The suitability and accuracy of the method was demonstrated by analysing CRMs with certified selenium content. The uncertainty budget for Se determination in standard reference material Peach Leaves NBS 1547 was estimated; the combined standard uncertainty was calculated as 1.7%. The described method fulfils all the criteria for definitive methods. It was subsequently used for determination of selenium in biological materials intended as new CRMs and proficiency test samples.     

Stability-indicating LC assay for butenafine hydrochloride in creams using an experimental design for robustness evaluation and photodegradation kinetics study

A stability-indicating liquid chromatography method for the determination of the antifungal agent butenafine hydrochloride (BTF) in a cream was developed and validated using the Plackett-Burman experimental design for robustness evaluation. Also, the drug photodegradation kinetics was determined. The analytical column was operated with acetonitrile, methanol and a solution of triethylamine 0.3% adjusted to pH 4.0 (6:3:1) at a flow rate of 1 mL/min and detection at 283 nm. BTF extraction from the cream was done with n-butyl alcohol and methanol in ultrasonic bath. The performed degradation conditions were: acid and basic media with HCl 1M and NaOH 1M, respectively, oxidation with H(2)O(2) 10%, and the exposure to UV-C light. No interference in the BTF elution was verified. Linearity was assessed (r(2) = 0.9999) and ANOVA showed non-significative linearity deviation (p > 0.05). Adequate results were obtained for repeatability, intra-day precision, and accuracy. Critical factors were selected to examine the method robustness with the two-level Plackett-Burman experimental design and no significant factors were detected (p > 0.05). The BTF photodegradation kinetics was determined for the standard and for the cream, both in methanolic solution, under UV light at 254 nm. The degradation process can be described by first-order kinetics in both cases.