Separation and determination of selenium in rocks, marine sediments and plankton by direct evolution with the bromide-condensed phosphoric acid reagent

A new method is presented for the quantitative separation and determination of selenium by direct evolution with the bromide-condensed phosphoric acid reagent (Br(-)-CPA) from rocks, marine sediments and plankton. In the reaction with the Br(-1)-CPA, selenium(IV) and (VI) in the solid samples are evolved as selenium tetrabromide, and can be collected in an absorbing solution of 0.3M hydrochloric acid and 06M perchloric add (1:1), and then determined spectrophotometrically with 4-substituted o-phenylenediamines followed by the extraction of the resulting 5-substituted piazselenol into toluene. Elemental selenium and selenide do not react with the Br(-)-CPA, but can be determined after oxidation to selenite with potassium iodate. Therefore, successive distillations, the first with Br(-)-CPA and the second with IO(3)(-)-Br(-)-CPA, give a satisfactory means of diflerential determination of selenium(IV) and (VI), and elemental selenium and selenide. This method can be successfully applied for the separation of selenium in the neutron-activation analysis of standard rock samples, marine sediments and plankton, giving good and reliable results.     

A neutron activation analysis of selenium,arsenic and antimony in rocks and sediments by simultaneous evolution with bromide-strong phosphoric acid reagent

A rapid and sensitive method for the neutron activation analysis of selenium, arsenic, and antimony is described. These elements and their compounds present in rocks and sediments were simultaneously evolved as their gaseous bromides from sodium bromide-strong phosphoric acid medium only by heating the irradiated samples in the medium. The evolved gas was absorbed in an appropriate absorption solution and then each element was finally recovered as metals for selenium and arsenic, and as sulphide for antimony. The preferable conditions for the distillation and for the separation of these elements are discussed. The method thus established was applied for the activation analyses of rocks and of river sediments, and profitable data were obtained. Part of this work was performed at the Research Reactor Institute, Kyoto University.     

Neutron activation analysis of rhenium in rocks and sediments by extraction chromatography on a pyridine-Kel-F column

A simple method for the determination of rhenium in rocks and sediments has been established. After a neutron-irradiated sample was decomposed by NaOH−Na₂O₂ fusion, the alkaline solution was fed onto a column of the mixed solvent pyridine-benzene (7:3 v/v) supported on Kel-F powder. By passage through the column of 4, 5N NaOH solution which had been equilibrated with the solvent mixture, perrhenate ion remained on the column but other nuclides were eluted. Subsequently, the perrhenate ion on the column could be eluted with a small amount of distilled water, and precipitated as tetraphenylarsonium perrhenate for counting the γ-activity of¹⁸⁶Re. By the present method 0.1 ng of rhenium could be determined with a recovery of 90–95% and an error of ±10%. A part of this work was performed at the Research Reactor Institute, Kyoto University.     

Neutron activation analysis of arsenic species

Inorganic arsenic, MMA, DMA and arsenobetaine (As) were separated by the use of cation and anion exchange chromatography combined with neutron activation. Two complementary approaches were used: firstly, authentic, non-irradiated arsenic compounds, either singly or in mixtures, were separated and NAA of the fractions used as an element specific detection method. Secondly, the arsenic compounds were neutron irradiated under different conditions and for different times and the products separated and quantified. The⁷⁶As labeled species (mono-, di and trimethylated) were then additionally used to calibrate and improve the column separations. Using the separations developed, arsenic species in samples of shrimps and the standard reference material DORM-1 were determined, after an extraction step, using ion exchange chromatography followed by INAA of the fractions collected.     

Neutron activation analysis of rhenium in rocks

A method for neutron activation determination of rhenium in rocks has been developed. Fusion with potassium hydroxide containing 15% water in a Teflon beaker was used in decomposition of irradiated samples. The purification procedure is given. Rhenium in the rocks is in the range of 1-10 ng/g.     

Neutron activation analysis of some volcanic rocks

INNA has been adopted for multielemental study of an acidic rock (OH-121) and three basic rocks (EH-121, WH-121 and SI-121) collected from Al-Madina in the Western Region of the Kingdom of Saudi Arbia. The basic rocks have higher concentrations of the transition elements Ti, V, Cr, Mn and Co, as compared to the acidic rock.     

Neutron activation analysis of Japanese standard rocks

Neutron activation analyses were performed for the newly issued reference rocks, GSJ JA-1 and JB-2, and also for the widely distributed GSJ JG-1 and JB-1. The contents of fourteen elements could be newly determined for the former two rocks and those of eleven elements were re-determined for the latter rocks.     

Trace element determination in rocks and sediments by neutron activation analysis

Neutron activation analysis (NAA) is one of the most used analytical techniques for trace element determination in rocks, because time consuming operations are avoided. We have analyzed different types of USGS reference materials (G-2, GSP-1, BHVO-1, STM-1, GXR-3, GXR-4, GXR-5), using both thermal (TNAA) and epithermal neutrons (ENAA). ENAA has been used to reduce interferences due to Sc-46 and to other high activities. The following elements have shown an improvement when analyzed by ENAA: Ba, Cs, Gd, Rb, Sb, Sr, Ta, Tb, Th, Tm, U, Yb, Zr; better results were found for Ce, Co, Cr, Eu, Fe, Hf, La, Lu, Na, Nd, Sc, Zn with TNAA. The accuracy of both methods has been tested comparing our results with some published values. The agreement is in general very good. The precision also is satisfactory, being for many elements better than 10%. After these tests, a study on some rock samples from the basaltic plateau of Kenya, east of Gregory Rift, has been performed by ENAA. Among the elements determined in this work, the rare earch elements (REE) can give significant petrogenetic information, by means of their distribution and fractionation in the rocks. The main parameters investigated are the degree of fractionation of light (La to Eu) relative to heavy (Gd to Lu) REE and the occurence of Eu anomalies, when the REE concentrations are compared to chondritic values. The evaluation of detection limits by TNAA has been performed for REE in sediment samples from Thyrrenian Sea (Central Italy).     

Neutron activation analysis of rhenium in rocks after preliminary extraction with acetone

A preconcentrating neutron activation method for determination of rhenium in rocks is described. The preconcentration is based on a preliminary extraction separation with acetone. The chemical recovery is determined by an isotope tracer technique using¹⁸⁶Re. The method has been applied to the determination of rhenium in rock samples and extended to more complex systems. Rhenium content is in the range of 110 ppb.     

Determination of uranium in phosphoric acid using neutron activation analysis

Phosphoric acid is generally obtained from an aqueous process starting with the reaction between phosphate rock and sulphuric acid. Due to their chemical similarity, uranium is usually associated with phosphate rock which during chemical processing is partitioned to phosphoric acid. Uranium determination in this matrix is a very important task because of its ingestion it could lead to radiological impact on the population. Therefore, a procedure was developed using an initial precipitation with calcium hydroxide and evaporation, followed by instrumental neutron activation analysis (INAA). The procedure was applied to analyse fourteen uranium enriched phosphoric acid samples.     

氢化物发生原子荧光光谱法测定磷酸中的砷

采用HCl处理H3PO4试样，氢化物发生原于荧光光谱法测定As，对仪器条件、HCl酸度、预还原剂用量、还原剂用量、共存干扰进行了试验，方法的检出限为0．18ng／mL，测定精密度1．9％-3．0％，回收率为96．0％-98．0％。     

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 determination of rheumium in rocks and ores after preliminary extraction with pyridine

A simple neutron-activation method for the determination of rhenium based on a preliminary extractive separation of the latter from molybdenum and tungsten is described. The sample is decomposed with sodium peroxide, a small amount of water is added and the resulting pulp is extracted with pyridine. The extract is evaporated to dryness, the residue is dissolved in water and the solution is passed through a column packed with Dowex 50WX8 in H⁺ form to eliminate the metal impurities. The HReO₄ passed, after neutralization with ammonia, is evaporated to dryness in penals, which then are irradiated with thermal neutrons.     

Preparation of ketones by direct reaction of grignard reagents with acid chlorides in tetrahydrofuran

Grignard reagents react with acid chlorides in tetrahydrofuran at low temperature to produce ketones in excellent yields. The results reported here strongly indicate the importance of the solvent in Grignard reagent chemistry.     

The determination of arsenic in rocks,sediments and minerals by arsine generation and atomic absorption spectrometry

An arsine generation-atomic absorption method for the rapid and precise determination of 0.04–4000 p.p.m. arsenic in geological materials is described. The siliceous sample is decomposed with perchloric, nitric and hydrofluoric acids and potassium permanganate solution, and the residue is dissolved in dilute hydrochloric acid. Arsine is generated with potassium iodide, tin(II) chloride and zinc powder, and introduced to an argon—hydrogen flame. The method is applied to various standard rocks, NBS mineral standards, and geochemical exploration samples. The relative standard deviation is 4–14 %.     

Extraction and analysis of arsenic in soils and sediments

The ability to extract arsenic (As) from soils and sediments, and analyze it with accuracy and precision, is of paramount importance, given the high risk that As, even in relatively low concentrations, poses to pore waters and biota. A large number of methods exist for extracting and analyzing total As, and As associated with a variety of operationally defined phase associations, in soils and sediments. We give an overview of methods used at present, and consider potential problems. We strongly recommend adoption of universal standard techniques and certified reference materials, especially for sequential extraction schemes.     

Neutron activation analysis in geochemical characterization of Jurassic–Cretaceous sedimentary rocks from the Nordvik Peninsula

As a part of geophysical, stratigraphical and paleontological study aimed at precise correlation of the Jurassic–Cretaceous (J/K) boundary interval in the Tethyan and Boreal Realms, detailed magnetostratigraphic and biostratigraphic profiles with well-calibrated J/K boundary have been selected from several localities for geochemical characterization. Instrumental and radiochemical neutron activation analyses (INAA and RNAA, respectively) were employed in the characterization of a vertical profile around the supposed J/K boundary in the Boreal Realm situated on the Nordvik Peninsula, Northern coast of Middle Siberia (Laptev Sea), Russia, for which an iridium anomaly has been reported in literature. INAA enabled determination of about forty major and trace elements. An RNAA procedure for assaying platinum group elements (PGE) has been tested consisting in sample decomposition by alkaline–oxidative fusion, reduction of PGE, and precipitation of their sulphides. Despite several difficulties, the procedure enabled to found Pt and Ir at ppb and sub-ppb levels, respectively, in several samples, namely in pyrite aggregates originated probably in diagenetic reductive processes following decomposition of burried organic matter. However, the existence of a pronounced PGE spike reported previously for the J/K boundary on the Nordvik Peninsula has not been confirmed.     

Separation and determination of ruthenium by evolution with chromium(VI)-condensed phosphoric acid reagent

Ruthenium in various chemical forms can be evolved as the tetroxide from insoluble matrix materials by heating the sample with chromium(VI)-condensed phosphoric acid reagent (abbreviated as Cr(VI)-CPA). Because of its excellent decomposing power for various solid samples, condensed phosphoric acid is very useful in the chemical analysis of various insoluble materials, and when an oxidizing agent such as potassium dichromate is added in the CPA medium, drastic oxidation proceeds on heating. This method is now extended to the separation of ruthenium from marine sediments. During the reaction with Cr(VI)-CPA ruthenium tetroxide is evolved and collected in an absorbent solution of 6M hydrochloric acid and ethanol (1:1), and the ruthenium is then determined spectrophotometrically with thiourea or radiometrically by counting the beta or gamma-activity. Osmium, which can be evolved as the tetroxide by the same treatment, can be eliminated beforehand by heating the sample with Ce(IV)-CPA, which removes osmium but not ruthenium. The successive distillations by means of Ce(IV)-CPA and Cr(VI)-CPA give satisfactory results for the separation between osmium and ruthenium. This method might be useful for the separation of ruthenium in geochemical or neutron-activation analysis.