Determination of rare-earth elements in environmental samples

A procedure is suggested of extraction-chromatographic pre-separation of REE's for the next activation determination. This method was applied for analyzing geological samples, underground and surface water, some technological materials.     

Determination of uranium, thorium and rare-earth elements in zircon samples using ICP-MS

Zircon is an accessory mineral, which occurs at low concentrations in a wide variety of rocks and is a host for hafnium, rare-earth elements (REE) and radio active elements like uranium and thorium. The presence of uranium in zircon has led to its increased use in the age determination of rocks. Zirconium is also considered as a strategic, hi-tech element because of its various applications, especially in the manufacturing, nuclear and aerospace industries. Analysis of zircon constitutes one of the tough tasks in analytical chemistry as it is a highly resistant mineral and it is extremely difficult to achieve its complete decomposition. In the present work, inductively coupled plasma mass spectrometry has been applied to the determination of hafnium, REE, uranium and thorium in zircon samples using two different sample dissolution procedures, one employing sodium peroxide fusion and another using a fusion mixture of KHF₂ and NaF in 3:1 ratio. Some selected zircon samples originating from different places on the eastern coast of India have been analysed by both the methods and values obtained by both methods were found to be in good agreement with each other. Though a number of international zircon reference materials are available, certified or even proposed values are available only for a very few elements in them. Two zircon reference materials have also been analysed by both methods and usable values have been proposed in this paper. The values obtained by both methods were found to compare well with each other and as well with those reported in literature. The % RSD for all the estimated elements varied from 1.0 to 12.0% at different concentration levels.     

Spectrophotometric determination of the total amount of rare-earth elements in agricultural samples with p-chloro-chlorophosphonazo

A simple, sensitive and accurate spectrophotometric method for determination of the total amount of rare-earth elements in agricultural samples with p-chloro-chlorophosphonazo [pCCPA, i.e., 2-(4'-chloro-2'-phosphon-benzylazo)-7-(4'-chlorophenyl)-1,8-dihydroxynaphthalene-3,6-disulphonic acid] in sulphuric acid medium has been developed. The apparent molar absorptivity of RExOy (the general formula of rare-earth oxides)-pCCPA complex is 8.17 x 10(4) 1.mole(-1) cm(-1) at 676 nm, and Beer's law is obeyed for the mixture of RExOy in the range 0-12 mug/25 ml. The proposed method has been successfully applied to the determination of the total amount of rare-earth elements in soils, herbs, vegetables, dried stems of maize, water samples and rare-earth microelement fertilizer samples with satisfactory results.     

Determination of Hf, Sc and Y in geological samples together with the rare-earth elements

 A method is described for the determination of Hf, Sc and Y simultaneously with the REE in geological materials. An earlier method for REE separation from major elements was studied with the aim to apply it also to the determination of Hf, Sc and Y. Sample decomposition was carried out by melting with LiBO₂. The method involves separation and concentration stages, using the cation-exchange resin DOWEX AG 50W-X8. Matrix elements were eluted with 2 mol/l HCl, whereas 6 mol/l HNO₃ with oxalic acid and 8 mol/l HNO₃ were used to elute the elements to be determined. Some of the matrix elements could not be completely removed. This effect as well as the recovery rates of the determined elements were investigated. The measurements were performed by ICP-AES. Spectral interferences were also tested. Received: 8 November 1995/Revised: 12 March 1996/Accepted: 14 March 1996     

Determination of rare-earth elements in rock samples by neutron activation analysis with a lithium-drifted germanium detector after chemical group-separation

A lithium-drifted germanium detector combined with chemical group-separation has been utilized for the determination of rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb and Lu) in rock samples by neutron activation. This procedure has the advantage of a low background level which cannot be attained in the non-destructive method. The combination of the Ge(Li) detector and chemical group-separation also offers a distinct simplification in the correction of contributions from other nuclides. For optimum utility of a Ge(Li) detector in neutron activation analysis, chemical group-separations are recommended.     

Activation analysis of bromine in rock samples

A simple method for the radiochemical neutron activation analysis of bromine in rock samples is described. The irradiated samples are ignited in an induction furnace in a flow of air for four minutes. The bromine expelled is collected onto activated charcoal which is measured using a Ge(Li) detector. The yield of the chemical separation is 85–100% and the detection limit is 7 ppb. The method is discussed and results for the analysis of 14 USGS standard rock samples are presented.     

Activation analysis of mercury in environmental samples

Neutron-activation analysis has been applied to the determination of mercury in a variety of environmental samples (Table 11) and so far has played an important role in the environmental research concerned with mercury pollution. The virtues of this method as its high sensitivity, applicability to various samples make the method attractive. On the other hand the high cost, limited availability of irradiation facilities, the time consumming analysis (due to irradiation and cooling) are important drawbacks and limit the use of the method, particularly in routine work. With the development of flameless atomic absorption mercury determination is more and more carried out with the aid of the latter technique. It seems, however, that activation analysis will remain a reference method and an anchorage in the cases when other methods fail.     

Activation analysis of mercury in biological samples

A method has been developed for the determination of trace quantities of mercury in biological samples, in which homogeneous irradiation was achieved by introducing a rotating irradiation disk facility in the reactor pool water, and possible loss of mercury during chemical processing was reduced by using a simple procedure. This procedure involved the destruction of the sample in a reflux system with conc. HNO₃ or fuming HNO₃+H₂O₂ and subsequent isolation of mercury by spontaneous deposition on Cu sieves from dilute HNO₃(0.5–1.5N). The possibility of using Au or Co as standards, instead of mercury which is easily volatile, was also evaluated.     

Determination of rare-earth eleemnts in rock samples by neutron activation analysis

A Ge(Li) detector combined with cation exchange separation has been used for the determination of 12 rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, and Lu) in rock samples by neutron activation analysis. After purification by the conventional hydroxide-fluoride precipitation, the rare-earth elements are separated into two fractions, light (La-Tb) and heavy (Ho-Lu), by EDTA cation exchange, and the γ-activities of the two fractions are measured by a Ge(Li) detector. The heavy rare-earths, such as Ho, Er, and Tm, can be easily γ-counted without serious interference from the intense Compton background and photopeaks due to the light rare-earths such as¹⁴⁰La,¹⁵³Sm,¹⁵²Eu, and¹⁶⁰Tb. The chemical yields (60%) for the individual rare-earths are determined by a reactivation technique. The results obtained for the U.S. Geological Survey standard rocks G-1 and W-1 are compared with the previously reported data.     

Fast neutron activation analysis of rare-earth elements in monazite from Korea

The relative ans single comparator methods have been applied to determine 7 rare-earth elements and U, Th in Korean Monazites by 14.5 MeV neutron activation analysis. The (n, 2n) nuclear reactions are used for all elements except La, for which (n, p) reaction is used. Al is used as a flux monitor for the relative method and as a singlle comparator for the single comparator method. The analytical results obtained by the two methods agree well within 3% deviation except for Sm and Gd. These results are also compared with the result obtained by a single comparator method using reactor neutron.     

Determination of rare-earth elements in steels by radiochemical neutron activation analysis

For the separation of rare-earth elements from steel, with a cation exchange resin, separation experiments were performed on NIST reference materials of SRM-363 and SRM-364. Iron, Na, Cr, Mn, Co, Cu, As, Mo, Sb and W were separated in 2M hydrochloric acid, five rare-earth elements, La, Ce, Pr, Nd and Sm and three other elements, Hf, Zr and Ba were separated using 8M nitric acid. Each element was determined by a single comparator method using two monitors, gold and cobalt.     

Evaluation of spectral interferences in the atomic emission determination of some rare-earth elements and yttrium in natural samples

Spectral interferences were quantitatively estimated using two characteristics: (1)Q ₁ (gl _a ) andQ _W (gDgl _a ) defined as the ratio of sensitivities of overlapping lines or their wings to the sensitivity of the line under investigationgl _a and (2)c _L , _I quantities defined as the contribution of foreign (interfering) lines to the real detection limit at the analytical line. With the use of an automated wave scanning and computer treatment of spectra, 20 analytical lines of medium and heavy lanthanides (from Eu to Lu) and Y and also overlapping lines of 29 interfering elements were examined. An arc two-jet plasmatron with an argon flow, predominantly giving a spark spectrum of rear-earth elements, was used as a source of excitation. The data obtained can be used in the atomic-emission analysis of natural samples for selecting preferential analytical lines.     

Direct spectrographic analysis of trace elements in soil samples

Summary A direct emission Spectrographic method for the estimation of Ba, Co, Cr, Cu, Mn, Ni, Pb, V and Zn in soil samples is described. The sample, free from organic matter is thoroughly mixed with graphite-internal standard mixture and excited in UCC 1989 type electrode using 15 A d.c. A 3.4 m Jarrel-Ash grating spectrograph is employed to photograph the spectra on SA-1 photographic plates. Synthetic standards are used for establishing working curves. The precision of the method, expressed as coefficient of variation is ±11%.

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Direkte spektrographische Analyse von Elementspuren in Bodenproben

Zusammenfassung Eine direkte emissionsspektrographische Methode zur Bestimmung von Ba, Co, Cr, Cu, Mn, Ni, Pb, V und Zn in Bodenproben wird beschrieben. Die von organischen Substanzen freie Probe wird mit einem Gemisch von Graphit und innerem Standard vermischt und mit Hilfe von 15 A Gleichstrom in einer Elektrode vom Typ UCC 1989 angeregt. Die Spektren werden in einem 3,4 m Jarrel-Ash Gitterspektrograph auf SA-1 Platten aufgenommen. Zur Aufstellung der Eichkurven werden synthetische Standards verwendet. Die Genauigkeit (Variationskoeffizient) beträgt ±11%.

     

Thiocyanates of rare-earth elements with tetramethylphenanthroline

Molecular [M(NCS)₃(H₂O)(Me₄Phen)₂] · (Me₄Phen) · 0.75EtOH and anionic [H(Me₄Phen)][М(NCS)₄(Me₄Phen)₂] complexes are synthesized using thiocyanates М(NCS)₃ · 6H₂O (M = Y, Eu, Tb) and 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4Phen). The complexes are characterized by IR spectroscopy and elemental, X-ray phase, and X-ray diffraction analyses (CIF files CCDC no. 1498178–1498184). The thermoanalytical study shows that the solvate molecules Me₄Phen are localized in the internal coordination sphere of the molecular complexes at 195–250°C. The magnetic behavior of the Eu and Tb complexes is governed by the nature of the Ln ion.