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Tungsten isotope composition of a sample of deep-seated rock can record the influence of core-mantle interaction of the parent magma. Samples of kimberlite, which is known as a carrier of diamond, from the deep mantle might exhibit effects of core-mantle interaction. Although tungsten isotope anomaly was reported for kimberlites from South Africa, a subsequent investigation did not verify the anomaly. The magnesium-rich and calcium-rich chemical composition of kimberlite might engender difficulty during chemical separation of tungsten for isotope analyses. This paper presents a simple, one-step anion exchange technique for precise and accurate determination of tungsten isotopes in kimberlites using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Large quantities of Ca and Mg in kimberlite samples were precipitated and removed with aqueous H(2)SO(4). Highly pure fractions of tungsten for isotopic measurements were obtained following an anion exchange chromatographic procedure involving mixed acids. That procedure enabled efficient removal of high field strength elements (HFSE), such as Hf, Zr and Ti, which are small ions that carry strong charges and develop intense electrostatic fields. The tungsten yields were 85%-95%. Advantages of this system include less time and less use of reagents. Precise and accurate isotopic measurements are possible using fractions of tungsten that are obtained using this method. The accuracy and precision of these measurements were confirmed using various silicate standard rock samples, JB-2, JB-3 and AGV-1.

Most polyols (L = alditol or carbohydrate) form dinuclear tungstate complexes according to the over-all equilibrium 2WO4(2-) + 2H+ + L equal equilibrium [W2O7L]2- + H2O. When the reaction is fast and complete, it allows the acidimetric titration of tungstate. The formation constants of the complexes of a series of polyols were determined by potentiometry. Their values were higher at low ionic strengths. Opposite structural factors govern the stabilities and the formation rates of complexes: alditols of threo configuration react with tungstate faster than those of erythro configuration, but the stability order is erythro greater than threo. Of the polyols investigated, only xylitol and D-glucitol (sorbitol) allowed a fast and accurate potentiometric titration. Using 0.02 M HCl as titrand, 0.04 mmol of tungstate was determined in a volume of 100 cm3. The interference of molybdate is discussed in detail.

An indirect method is described for the determination of tungsten as tungstate in tissue samples by atomic absorption spectrometry (AAS). Tungstate forms a stable ion-association complex [Fe(dipy)3]2+WO4(2-) (dipy = 2,2'-dipyridyl) in acidic solution, which can be extracted into chloroform with an efficiency of higher than 98%. The extract can be analysed for iron (and hence indirectly for WO4(2-] by flame AAS after stripping back into 60% perchloric acid. The calibration graph is linear up to 19 p.p.m. of WO4(2-) and the limit of detection is 0.17 p.p.m. Many foreign ions do not interfere and the method has been applied successfully to the determination of tungstate in rattus norvegicus tissue samples.