Substoichiometric determination of heavy rare earths by isotopic dilution analysis

A substoichiometric method for the determination of heavy rare earths (holmium, thulium) has been developed. After the addition of a substoichiometric amount of EDTA to the test sample of rare earth labelled with its radioactive isotopes, the negatively charged complex formed was separated by passage through a column of Dowex 50 x 8. Interfering metals can be removed by preliminary cupferron and diethylammonium diethyldithiocarbamate extraction. Concentrations of rare earth down to 4 x 10(-7)g 5 ml have been determined.     

The separation and determination of fatty acids by isotopic dilution and radiogas-liquid chromatography

A number of static phases have been evaluated for the GLC separation of fatty acids. Of those investigated, only AT 1200 was capable of resolving the isomeric forms of the acids. A radiogas-liquid chromatographic method incorporating isotopic dilution analysis has been developed for the determination of n-butyric acid. The proposed method has been applied to the determination of the acid in hydrolysed butter fat and milk chocolate extracts.     

The determination of selenium in biological material by thermal neutron activation analysis and atomic absorption spectrometry

Neutron activation analysis and atomic absorption spectrometry (graphite furnace) methods for the analysis of selenium in human tissue are described. The sensitivity (10–30 ng/sample), accuracy and precision are of the same order for both techniques and the choice can only be made on grounds of urgency or convenience. AAS should be chosen for the analysis of wet tissue or the urgent analysis of small numbers of dry tissue. NAA should be chosen for the analysis of large numbers of dry tissue samples where time is not important. The selenium concentration of human liver is shown to be in the region of 1 to 2 ppm (dry weight). Selenium may be lost from tissue during freeze drying if the samples are not maintained at −35°C.     

Total sulphur determination in plant material

Summary A simple method for the determination of total sulphur in plant material is proposed. Wet ashing with a HClO₄-H₂O₂ mixture is performed in a simple semi-closed system without losses of sulphur. Even the difficultly oxidizable compounds like methionine are completely recovered. The determination is performed by turbidity measurement using barium chloride. Reproducibility of the procedure is good (rel. st. dev. 3–4%).

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Bestimmung von Gesamtschwefel in Pflanzenmaterial

Zusammenfassung Für die Analyse wird die Naßveraschung mit einem HClO₄-H₂O₂-Gemisch in einem halbgeschlossenen System verwendet. Schwefelverluste treten nicht auf. Selbst schwer oxidierbare Verbindungen, wie Methionin, werden vollständig erfaßt. Die Bestimmung erfolgt turbidimetrisch mit Bariumchlorid. Die Reproduzierbarkeit ist gut (relative Standardabweichung 3–4%).

     

Trace-level determination of 1,4-dioxane in water by isotopic dilution GC and GC-MS

The volatile and polar solvent 1,4-dioxane has recently been reported as a contaminant of ground and surface waters, establishing the need to determine this substance in drinking water. This investigation established that 1,4-dioxane can be determined in water by various techniques including direct aqueous injection (DAI) gas chromatography (GC) and purge and trap GC-mass spectrometry (MS). Purge and trap GC-MS is limited by 1,4-dioxane's poor purge efficiency, resulting in detection limits up to 100 times greater than the efficiently purged volatile organic compounds. To attain the sensitivity required for drinking water monitoring, a method based on continuous liquid-liquid extraction with dichloromethane was developed. Isotope dilution was more accurate and reproducible than quantification with external standards, and the improvement in precision led to a lower method detection limit, 0.2 microgram L-1, using a quadrupole ion trap instrument in the electron ionization mode. Isotope dilution accuracy approached 100% in ppb determinations. Isotopic dilution quantification was also possible using a non-selective GC detector owing to the high efficiency of capillary GC columns that resolve the deuterium-labeled solvent from the natural isotopes.     

Simultaneous determination of bisphenol A and alkylphenol in plant oil by gel permeation chromatography and isotopic dilution liquid chromatography-tandem mass spectrometry

A simple analytical method was developed for the simultaneous analysis of bisphenol A (BPA), nonylphenol (NP) and octylphenol (OP) in plant oil. The target compounds were extracted by cyclohexane/ethyl acetate (1:1), purified by gel permeation chromatography (GPC), and analyzed by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) in the negative ion mode. An isolator column was attached in front of the injection valve of the LC to separate background contaminants. Recovery studies were performed at three fortification levels. Mean recoveries were from 92.9% to 119.0%, with an acceptable coefficient of variation (4.4-18.5%, n=6). The limits of quantification of the method were 2, 2 and 0.5 μg/kg for BPA, NP and OP, respectively. This method can be applied for screening and confirming target compounds in plant oil.     

A convenient isotopic dilution method for the direct determination of oxygen in fluorinated organic materials

Summary A method is described for the microdetermination of oxygen in fluorinated organic compounds. The unknown material is pyrolyzed together with¹⁸O-containing succinic acid, in a sealed, evacuated, specially-purified copper tube. After equilibration at 850°C, the tube is punctured and the pyrolysis gases are admitted to a mass spectrometer. Comparison of the m/e-46/44 ratio (C¹⁶O¹⁸O/C¹⁶O¹⁶O) to the ratio obtained from similar pyrolysis of the oxygen-18 compound only, provides a means of calculating the oxygen content of the unknown.The copper tubes are made from ordinary, rigid, 1/4 o. d. tubing, which is purified by reduction in hydrogen and heating under vacuum. They are sealed by induction welding.The procedure has been used successfully for a variety of fluorinated compounds including several metal salts of fluorinated acids.

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Zusammenfassung Eine Methode für die Mikrobestimmung von Sauerstoff in fluorhaltigen organischen Verbindungen wurde beschrieben. Das Untersuchungsmaterial wird mit¹⁸O-markierter Bernsteinsäure in einem evakuierten, verschlossenen, besonders gereinigten Kupferrohr pyrolysiert. Nach Gleichgewichtsemstellung bei 850° C wird dieses Rohr punktiert und die Pyrolysegase in ein Massenspektrometer geleitet. Der Vergleich des m/e-46/44-Verhältnisses (C¹⁶O¹⁸O/ C¹⁶O₂) mit dem nach Pyrolyse der¹⁸O-markierten Verbindung allein bietet die Möglichkeit, den Sauerstoffgehalt der Probe zu berechnen.Die Kupferrohre werden aus gewöhnlichem, hartem Rohrmaterial mit 1/4 Zoll äußerem Durchmesser hergestellt, mit Wasserstoff reduziert, im Vakuum erhitzt und schließlich durch Induktion verschweißt.Das Verfahren wurde erfolgreich zur Analyse verschiedener fluorhaltiger Verbindungen einschließlich Metallsalzen fluorhaltiger Säuren verwendet.

     

Separation of carrier-free 48Sc tracer and its determination by isotopic dilution

An easy method for speedy and quantitative separation of carrier-free scandium tracer formed by the (48)Ti(22)(n,p)(48)Sc(21) nuclear reaction has been developed. Separation of (48)Sc (1.83 days) from the target titanium metal was carried out by co-precipitating the tracer with calcium fluoride precipitated at pH approximately 4 from the solution of irradiated titanium in hydrofluoric acid. The freshly formed fluoride precipitate was dissolved in conc. hydrochloric acid, and the tracer extracted with tributyl phosphate and then stripped into aqueous medium. The carrier-free tracer was estimated by isotopic dilution. with calcium fluoride as non-isotopic diluent.     

Semi-automated fluorimetric determination of nanogram quantities of selenium in biological material

A semi-automated method, based on the solvent extraction and fluorescence of 4,5-benzopiazselenol, is described for the determination of selenium in biological material. Samples, in batches of up to 150, are digested in a mixture of nitric and perchloric acids in temperature-controlled aluminium blocks. Selenate formed in the perchloric acid is reduced to selenite with hydrochloric acid. Metal ion interferences, including hydroxide adsorption of selenite, are prevented by ethylenediaminetetraacetic acid. Sulphate above 50 mM precipitates the 2,3-diaminonaphthalene, so wool digests were diluted accordingly. The digests are analysed from their digestion tubes at the rate of 40 per hour by the semi-automated method. Results for blood and a variety of food samples compare favourably with those obtained by other methods including hydride/atomic absorption and instrumental neutron-activation analysis.     

The determination of selenium in urine

The selenium excreted in urine can be measured to assess the dietary status of selenium, an essential trace element in human nutrition. The objectives of this work were: 1) to develop a procedure, capable of high sample throughout, by which the major interferences can be reduced such that selenium concentrations can be measured in urine by Neutron Activation Analysis (NAA) using^77mSe (17.4 s; and 2) to apply the method to a human dietary selenium study in which several selenium monitors were compared. The method involves a pre-irradiation arsenic-coprecipitation separation of the selenium from urine in the presence of a high specific-activity⁷⁵Se tracer. The processed urine samples are analyzed using NAA. The procedure was applied to 58 urine specimens longitudinally collected from 12 subjects consuming three different levels of selenium. A dose-response relationship was observed in urine as well as a high correlations with both serum and whole blood selenium concentrations.     

Iodine determination in milk by isotope dilution analysis

Iodine is an essential trace element in the human diet. It is utilized in the synthesis of L-monoiodothyrosine, which is a precursor of the thyroid hormones, thyroxin and triiodothyronin. In this study, a method that can determine iodine concentrations in milk has been developed. The method is based on substoichiometric isotope dilution analysis (IDA). Iodine concentrations were measured in milk, which has been collected from three big cities and environment municipalities of Aegean Region. The iodine concentration ranges were within 436.8 and 896.7 μg/kg in milk samples. Mean iodine concentration was not greatly changed from season to season, between 1998 and 2002. This revised version was published online in August 2006 with corrections to the Cover Date.     

The determination of selenium status in the Australian diet using neutron activation analysis

Australia-wide samples of 50 representative foods from each of the State capitals were analysed for selenium by instrumental and radiochemical neutron activation analysis. Results were compared with State and Federal Regulations for toxic elements in foods as well as with recommendations by Australian and US authorities for safe and adequate dietary intake of this essential trace element.     

A comparison of two digestion procedures for the determination of selenium in biological material

Two digestion procedures have been tested on samples of flour, blood and urine for application in the determination of selenium by hydride-generation atomic-absorption spectrometry. The first utilizes a mixture of concentrated nitric, perchloric and sulphuric acids and the second a mixture of magnesium nitrate hexahydrate, concentrated nitric acid and 6M hydrochloric acid. The accuracy of the procedures was tested by analysis of standard reference materials and by comparison with results from neutron-activation analysis. It was found that the "magnesium method" can replace the more common procedure, which includes perchloric acid, for the sample types investigated in this paper.     

The optimal amount of isotopic spike solution for ultratrace analysis by isotope dilution mass spectrometry

 Inductively coupled plasma mass spectrometry (ICP-MS) and high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) are powerful methods of determining metallic impurities in the low- and sub-ppt level in process media such as ultra-pure water used in semiconductor and wafer manufacturing. By using mass spectrometers for analysis, an isotope dilution analysis (IDMS) is possible. The reproducibility of an IDMS is unmatched. For concentration levels near the instrument detection limit a novel method is reported to find the optimal amount of isotopic spike solution. This optimal value can be derived by the law of propagation of uncertainty combined with the Poisson statistics of the measured number of counts. Generally, an excess of isotopic spike solution should be used to provide results of lowest possible uncertainty. The results are presented in a diagram for easy practical use. Received: 14 October 1997 · Accepted: 13 February 1998     

电化学分析法测定硒的研究进展

本文综述了国内外电化学分析(极谱和溶出伏安法)测定痕量硒的研究进展,主要包括极谱催化波、吸附波以及阴极溶出伏安法,阳极溶出伏安法,并从反应体系、催化波类型、检出限和电极反应机理等方面进行归纳与评述,展望了硒分析方法的研究方向和发展前景,对进一步研究硒的电化学性质和探索测定硒的新体系有重要参考价值。