Neutron activation analysis for determination of cerium trace impurity in high purity lanthanum oxide

Cerium trace impurity in high purity lanthanum oxide (99.99%) has been determined by NAA after pre-separation of La matrix. In this method, the sample was dissolved in conc. nitric acid and diluted with water. The final concentration of solution is about 0.1M of nitric acid. It was passed through a MnO₂ column. Under these conditions cerium is retained on the column quantitatively without retaining lathanum. Cerium is eluted with 4M nitric acid. The recoveries of Ce were checked with tracers and by standard addition to lanthanum oxide matrices. Results obtained on a high purity lanthanum oxide are reported here.     

Determination of praseodymium in lanthanum compounds by neutron activation and ion exchange separation

Summary A procedure was developed to determine small amounts of praseodymium in lanthanum compounds by neutron activation analysis. After irradiation of the sample in a reactor praseodymium is separated from lanthanum by anion exchange and Pr-142 is measured by a gamma-ray spectrometer. From the high decontamination factor of 110⁸ a detection limit of 5ppb praseodymium in lanthanum may be calculated. Because of the strong activation of lanthanum, the handling of samples with activities of about 1 Ci La-140 would be required. For the analyses carried out here with respect of sample weights, neutron flux and irradiation time a detection limit of 2.4ppm was obtained.

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Bestimmung von Praseodym in Lanthanverbindungen durch Neutronenaktivierung und Ionenaustausch

Zusammenfassung Zur Bestimmung von geringen Mengen Praseodym in Lanthanverbindungen wurde ein auf Neutronenaktivierungsanalyse basierendes Verfahren entwickelt. Nach Bestrahlung der Probe im Reaktor wird Praseodym mit einem Anionenaustauscher von Lanthan getrennt und Pr-142 mit einem Gamma-Spektrometer gemessen. Der mit der Trennung erreichte Reinigungsfaktor von 110⁸ würde eine Nachweisgrenze von etwa 5ppb Praseodym in Lanthan erlauben. Wegen der starken Aktivierung des Lanthans würde das aber den Umgang mit Proben von ca. 1 Ci La-140 erfordern. Mit den hier gewählten Probenmengen, Neutronenflüssen und Bestrahlungszeiten wurde eine Nachweisgrenze von 2,4ppm erreicht.

Presented at the Ulmer Symposium Analytische Chemie — Elementanalyse mit chromatographischen Methoden, Sept. 19–21, 1979, D-7900 Ulm     

Neutron activation determination of impurities in germanium

A neutron activation (NA) method for the determination of 24 microimpurities in germanium has been developed. The method is based on the separation of the matrix and isotopes genetically connected by extraction chromatography.     

Removal of disturbances in carbon determination by activation analysis for lowering the detection limit

A sensitive method of carbon determination in silicon by activation with deuterons and³He particles followed by chemical separation of the measured nuclides¹³N and¹¹C has been developed. Aside from the etch removal after irradiation, it is essential for a low detection limit to avoid too much thermal exposure of the target surface during the irradiation process, or else microflaw formation and diffusion on the surface have to be anticipated. The ion current must have an optimal rather than a maximum value.     

Ultratrace determination of europium in high-purity lanthanum, praseodymium and dysprosium oxides by luminescence spectrometry

A luminescence spectrometric method was developed for the determination of ultra trace amounts of europium (down to 1 x 10(-13) M) in high purity lanthanum, praseodymium and dysprosium oxides. This is based on the enhanced luminescence of europium-thenoyltrifluoroacetone (TTA)-dibenzo-18-crown-6 (DBC)-Triton X-100 in the presence of terbium. The fluorescence intensity is linear with europium concentration in the range 1 x 10(-11) - 1 x 10(-6) M under the recommended conditions. The optimized procedure is successfully utilized for the determination of ultratrace amounts of europium in lanthanium, praseodymium and dysprosium oxides.     

A technique for improved detection limit in indirect neutron activation determination of boron

Using vanadium as the activable element, an indirect cyclic neutron activation technique for determination of boron in aqueous solutions has been developed. Experimental arrangement consisted of a 5 Ci Pu?Be based neutron irradiator and a 7.5 cm × 7.5 cm NaI/Tl/ detector. Recycling of vanadium between the irradiation source and the detector produced improved detection limit and sensitivity.     

Trace determination of lanthanum,cerium, and praseodymium based on adsorptive stripping voltammetry

A sensitive stripping procedure is described for quantifying lanthanum, cerium and praseodymium ions, based on the controlled adsorptive accumulation of the lanthanide/o- cresolphthalexon complex onto the static mercury drop electrode. The effect of various operational parameters on the stripping response is discussed. A 20-min accumulation period coupled with differential pulse measurement of the current resulting from the adsorbed complex permits quantitation down to the 1 × 10^?10 M level. For concentrations ranging from 2.5 × 10^?8 M to 2.5 × 10^?9 M, a 0.5- to 4-min accumulation period is sufficient. The relative standard deviation ar the 7 × 10^?8 M level ranges from 1 to 6%.     

Neutron activation determination of impurities in high purity tin

A method of neutron activation determination of more than 20 impurities in high purity tin with an extraction separation of the matrix has been developed. The detection limits of impurities in the flux of 5·10¹² n·cm^?2s^?1 are on the level of 10^?5–10^?7%. Possibilities of instrumental determination of 11 elements are discussed.     

Neutron activation analysis of rare earth impurities in europium oxide

A neutron activation analysis method for determining Yb, Dy, Ho, Sm and La impurities in europium oxide with sensitivities of 10^?5 to 10^?7% is described. The method is based on a preliminary concentration of the rare earth elements by reducing europium(III) with zinc to europium(II), and separating the trivalent rare earth elements by extraction chromatography. After neutron irradiation, the individual radioisotopes of the rare earth elements are separated by using KU-2 cation exchange resin and ammonium α-hydroxyisobutyrate solution as the eluant.     

Neutron activation analysis of deep sea sediments from the regions near Japan

Eighteen trace elements, including seven rare earth elements (REEs), and major and minor elements in the sediment samples from the Japan Sea and the northwestern Pacific near Japan were determined with instrumental neutron activation analysis (INAA). Most REE patterns (chondrite-nomalized) of the sediments were nearly identical to the patterns of terrigenous materials without cerium anomaly whereas the La/Yb ratio varied with the site locations. The variation of the La/Yb ratio of the sediments may indicate the regional variation of the mixing proportion of the terrigenous materials from the continent to the materials from the volcanic island arcs including the Japanese islands. The Th/Sc ratio of the sediments tended to increase with distance from the island-arc volcanism. Regional variation of the Th/Sc ratio may indicate variation of amount of the continental terrigenous materials supplied to the sediments.     

Neutron activation method for nitrogen determination in biological specimens

For the determination of the nitrogen content in plants, 14 MeV neutron activation analysis was used based on the determination of the elemental concentration by measuring the area of the gamma-radiation of the radionuclide¹³N as a result of¹⁴N(n, 2n)¹³N reaction. Three methods were tested in order to obtain quantitative results: comparator method, method for absolute determination of the neutron flux and monitor method. Using the monitor method, results for nitrogen content in plant species were obtained-for beans 74.8% and for maize 1.8%. The precision of determination is ±10%. The possible sources of errors are analyzed. The efficiency of the Ge(Li) detector has been determined using a combined -source in the energy interval 120–1400 keV with precision of 4.5%. The sensitivity achieved was 4 mg or 47 imp/mg per min.     

Determination of concentration distribution of trace elements near the detection limit

The results of a numerical simulation, performed to check the validity of a method developed for reconstruction of concentration distributions truncated by the detection limit, are reported in the context of trace element analysis in biomedical samples by total-reflection X-ray fluorescence. This method, by correcting a distribution over the whole range of concentrations in a population of samples, restores a number of measurements reporting results below the detection limit. We show by Monte Carlo simulations, assuming lognormal distributions to describe both the concentrations measured as well as the detection limits in the biomedical samples, that the method developed is accurate to within 5% for most typical situations. Moreover, we demonstrate that the factor limiting the accuracy of the correction is the number of measurements, not the correction procedure itself. We have found in simulations that the reconstruction of a concentration distribution, for a typical population size of N=100, is possible when the concentrations are measured only in 20–30% of samples. On the other hand, we show that by ignoring the truncation of a concentration distribution by the detection limit, the results can be systematically biased by as much as 50%. The method developed is applied to the analysis of trace elements in human breast tissue samples by total-reflection X-ray fluorescence (TXRF). The results are also discussed in terms of the size of the population studied.     

Neutron activation analysis for the determination of contaminants in food contact materials

A neutron activation method has been developed for the analysis of high density polyethylene, low density polyethylene, polypropylene, polyethylene terephthalate and polystyrene. Samples weighing 2–5 g were irradiated in a thermal neutron flux of 10¹⁶ neutrons m^–2 s^–1 and measured with gamma ray spectrometry for 64 elements. With the method developed here over 50 elements can be detected at concentrations below 1 mg/kg. Correction factors were applied for neutron flux variation and counting geometry.The method was validated using reference material citrus leaves (NIST) for Na, Mg, Al, K, Ca, Mn, Cu, Sr and I, and a suite of in house standards doped with Al, Cr, Co, Mg, Zn and Sb confirmed repeatability of the method. The method was used to measure inorganic contaminants in the raw polymers and retail samples of plastic packaging used in contact with food.     

Comparison of various detection limit estimates for volatile sulphur compounds by gas chromatography with pulsed flame photometric detection

This paper addresses the variations that presently exist regarding the definition, determination, and reporting of detection limits for volatile sulphur compounds by gas chromatography with pulsed flame photometric detection (GC-PFPD). Gas standards containing hydrogen sulphide (H(2)S), carbonyl sulphide (COS), sulphur dioxide (SO(2)), methyl mercaptan (CH(3)SH), dimethyl sulphide (DMS), carbon disulphide (CS(2)), and dimethyl disulphide (DMDS) in concentrations varying from 0.36ppb (v/v) up to 1.5ppm (v/v) in nitrogen were prepared with permeation tubes and introduced in the gas chromatograph using a 0.25-ml gas sampling loop. After measuring the PFPD response versus concentration, the method detection limit (MDL), the Hubaux-Vos detection limit (x(D)), the absolute instrument sensitivity (AIS), and the sulphur detectivity (D(s)) were determined for each sulphur compound. The results show that the MDL determined by the US Environmental Protection Agency procedure consistently underestimates the minimum concentrations of volatile sulphur compounds that can be practically distinguished from the background noise with the PFPD. The Hubaux-Vos detection limits and the AIS values are several times higher than the MDL, and provide more conservative estimates of the lowest concentrations that can be reliably detected. Sulphur detectivities are well correlated with AIS values but only poorly correlated with MDL values. The AIS is recommended as a reliable and cost-effective measure of detection limit for volatile sulphur compounds by GC-PFPD, since the AIS is easier and faster to determine than the MDL and the Hubaux-Vos detection limit. In addition, this study confirmed that the PFPD response is nearly quadratic with respect to concentration for all volatile sulphur compounds.     

Neutron activation determination of the oxygen factor for high temperature superconducting materials

Due to its precision and sensitivity, activation analysis can be applied in investigating the composition of high temperature superconducting materials (HTSC) including determination of the oxygen factor. When activation is ensured with fast neutrons, it is expedient that the oxygen factor be determined by the ratio of oxygen to one of the elements of the matrix. In case of yttrium-based ceramics the analytical parameter is chosen in the form of a ratio of activities due to oxygen and yttrium. Other types of HTSCs were analyzed in terms of O/Cu ratio. The relative standard deviation rangea from 0.3 to 0.5% for O/Y and O/Cu ratios for 10 replicate analyses of the same sample.     

Rare earth impurities in high purity lanthanum oxide determined by neutron activation analysis

Individual rare earth impurities in high purity La₂O₃ (99.9%) have been determined by NAA after pre-separation of the matrix (La). The separation is carried out on an anion exchanger (Dowex 1×8) using different mixtures of methanol/nitric acid as eluants. The rare earth elements from Dy to Lu are eluted quantitatively using a 10% 1M HNO₃-90% methanol mixture, while the light rare earths from Ce to Gd are eluted quantitatively using a 10% 0.05M HNO₃-90% methanol mixture. La, which is retained on the column, is eluted using 0.1M HNO₃. The recoveries of the various rare earth elements have been checked using radiotracers and also by spiking the sample with known amount of elements, and the recoveries are found to be quantitative. Results obtained on a typical high purity lanthanum oxide are reported here.     

X-ray fluorescence determination of lanthanum,cerium, praseodymium,and neodymium in technological solutions after preconcentration on DETATA cellulose filters

Sorption of some rare earth elements on filters with immobilized diethylenetriaminetetraacetate (DETATA) groups was studied. It was shown that the elements are quantitatively extracted from solutions with volume of 20–500 mL at pH values ranging between 3.5 and 5.5 and a flow rate from 1 to 8 mL/min. It was proposed to use masking agents such as sulfosalicylic acid and 1,10-phenanthroline for extracting elements from iron-containing solutions. The elements were determined directly on filters by X-ray fluorescence spectroscopy. The calibration dependences were shown to be linear in the concentration range from 2 to 100 μg of rare earth element per filter. The limits of detection of La, Ce, Pr, and Nd calculated on the basis of the 3s criterion in the case of extraction from 100 mL solutions were 0.03, 0.03, 0.01 and 0.01 μg/mL, respectively.     

Neutron activation as a routine method for the determination of trace elements in water

By freeze-drying the following elements can be determined in natural water except sea water: Au, Ba, Br, Ca, Ce, Co, Cr, Eu, Fe, K, La, Mo, Na, Sb, Sc, Se, U, Zn. Some problems may arise with respect to As and Hg. Cu, Cd and Ni can only be determined if present in high concentrations. Separation by adsorption on charcoal in presence of complexing agents gives yields between 75 and 100% for the following elements in sea water: Ag, Au, Cd, Ce, Co, Cr, Eu, Fe, Hg, La, Mo, Sc, Se, U, Zn (As 67%, Sb 56%). Activation or use of labelled ions and study of exchange give information about mobility of trace elements in suspended matter.     

Neutron activation analysis of steel for sub ppm amounts of lanthanum and gold without determining the chemical yield

Résumé On a mis au point une méthode d'analyse par activation neutronique du lanthane et de l'or en quantités inférieures au ppm dans l'acier, sans détermination du rendement chimique. La méthode consiste à isoler quantitativement les activités de La et d' Au par des procédés d'échange d'ions et à faire ensuite une spectrométrie NaI(T1). La limite de détection est abaissée jusqu'à 10 et 5 ppb pour La et Au respectivement. Il n'y a pratiquement pas d'interférence avec les autres éléments habituellement présent dans l'acier.