The titrimetric determination of calcium and magnesium in silicate rocks

A cation-exchange scheme is described for the separation of calcium and magnesium from interfering elements in rapid silicate analysis. Interfering elements can be eluted from the ammonium form of Zeo-Karb 225 with a solution of the ammonium salt of ethylenediaminetetraacetic acid at pH 4.5. Calcium and magnesium are not eluted with this reagent but can be eluted consecutively with ammonium chloride solution and titrated photometrically with EDTA. Calcium and magnesium can be separated quantitatively from Al, Fe, Ti, Mn, Bi, Cd, Cr, Co, Cu, Pb, Mo, Ni, U, V, rare earths, and Zn.     

Elimination of anionic interference in flame photometric determination of calcium in the presence of phosphate and sulphate

Studies on the interference of phosphate and sulphate in the flame emission of calcium as calcium chloride have shown that there is a fall of intensity corresponding initially to the quantity of the interfering anion, the emission intensity reaching a constant value at a certain ratio of PO₄^-3 or SO₄^-2 to Ca⁺².On addition of appropriate quantities of lanthanum (or iron) to the sample, the intensity of the calcium emission lines is restored to the value it had when the interfering anions were absent.It is postulated that lanthanum replaces calcium in a phosphate- or sulphate-containing compound, that without lanthanum does not form calcium ions even at high temperature.     

Elimination of phosphate interference in flame photometric determination of strontium and barium

The interference of phosphate in the flame emission of calcium, strontium and barium was studied. The emission intensity decreases proportionally to the amount of interfering anion up to a maximum depression for equimolar amounts of phosphate to metal. A thermostable phosphate is formed before the cation enters the flame. Appropriate addition of lanthanum restores the three alkaline earth lines to their intensities in absence of phosphate, the lanthanum displacing, the alkaline earths from their phosphates before the hot region of the flame is reached.     

Indirect flame photometric determination of sulphate ions

In this paper the possibilities have been studied of determining sulphate ions by indirect flame photometry by difference. Barium and Strontium in constant concentration were used as background elements. By means of the methods proposed sulphate ions can be determinined in the concentration range 0 to 70 p.p.m. with barium and 0 to 110 p.p.m. with strontium. The determinations can be carried out in dilute solutions of alkali metal sulphates and sulphate ions can also be estimated in the presence of macroquantities of other compounds. This may prove useful for the quantitative estimation of sulphate as an impurity in Chemical reagents. Some examples are given of the determination of the degree of purity of substances containing sulphate as impurities.     

The use of lanthanum chloride to prevent interferences in the flame photometric determination of exchangeable calcium in soils

An examination of the interferences of aluminium, bicarbonate, phosphate, sulphate and silicate in the flame photometric determination of calcium in ammonium chloride solutions has shown that, with the exception of bicarbonate, all cause serious interference. Addition of lanthanum to the solution can satisfactorily prevent each of these interferences Provided the lanthanum to aluminium ratio is at least 12.5 I by weight all interference from aluminium can be prevented The use of lanthanum chloride to prevent such interferences in the determination of calcium in ammonium chloride lcachates of soils is discussed and a simple flame photometric method for the determination of exchangeable calcium in soils is proposed.     

Photometric determination of arsenic in silicate rocks

Summary The method described consists in decomposing the silicate rock sample by fusion with sodium hydroxide or sodium hydroxide-peroxide, leaching the melt with water, evolving arsine from the filtrate, and finally determining arsenic by photometric evaluation of molybdenum blue. Satisfactory accuracy has been demonstrated for the range 0.0 to 20 p. p. m. As, for which the method is particularly intended.

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Zusammenfassung Zur Bestimmung des Arsengehaltes in Silikatgesteinen wird die Probe durch Schmelzen mit Natriumhydroxyd und gegebenenfalls Natriumperoxyd aufgeschlossen. Aus dem Filtrat der wäßrigen Lösung dieser Schmelze wird Arsenwasserstoff entwickelt und in natriumhydrogenkarbonathältiger Jodlösung aufgefangen. Das hierbei entstehende Arsenat wird nach Zugabe von Molybdatreagens und Bisulfit photometrisch bestimmt. Für Arsengehalte unter 0,02% werden nach dieser Methode Resultate von zufriedenstellender Genauigkeit erhalten.

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Résumé La méthode décrite consiste en la décomposition de l'échantillon de roche silicatée par fusion avec la soude ou le peroxyde de sodium, reprenant la partie fondue par l'eau, libérant l'hydrogène arsénié du filtrat et finalement dosant l'arsenic par colorimétrie du bleu de molybdène. Une précision suffisante a été mise en évidence dans le domaine de 0,0 à 20 p. p. m. d'arsenic pour lequel la méthode convient particulièrement bien.

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Fulbright Scholar.     

Photometric determination of phosphorus in silicate rocks

Phosphorus in silicate rocks may bedeterminedaccurately by the photometric molybdovanadophosphoric acid method following decomposition of the sample with nitric-hydrofluoric acid.     

Determination of fluorine in silicate and phosphate rocks,micas and stony meteorites

By making certain modifications to a published procedure for fluorine in rocks, it has been possible to improve stability and extend the range of the method. The modified method has been successfully applied to silicate and phosphate rocks, micas, glass and stony meteorites, containing from 60 p.p.m. to 8% fluorine. Some precautions are recommended for reliable determination of chlorine.     

Atomic absorption spectrometric determination of copper in calcium carbonate scale and carbonate rocks by direct atomization of solid samples

Powdered samples (1 mg) are mixed with 1 mg of powdered graphite and copper is determined by atomic absorption spectrometry in a miniature graphite cup placed in a graphite crucible. Optimum conditions were drying at 200 °C (30 s), ashing at 900 °C (30 s), atomizing at 2700 °C (15 s) and cleaning at 2800 °C (10 s). Samples were powdered to 1–10 μm particle size. Magnesium, manganese and iron did not interfere. The effect of calcium carbonate was eliminated by the graphite addition. Results for copper (0.5–5 μg g^?1) in the scale and rocks agreed well with values obtained for dissolved samples. Relative standard deviations (n=10) were 4.9% for 1.2 μg g^?1 copper and 14.8% for 0.577 μg g^?1.     

The flame photometric determination of alkali metals, alkaline earths and copper in nuclear grade uranium

Summary A method, which involves prior chemical separation of uranium from impurities by tributylphosphate extraction, is described for the determination of alkali metals, alkaline earths and copper in nuclear grade uranium. The characteristic emission lines, excited in hydrogen-oxygen flame, are isolated by a small monochromator and recorded photoelectrically.Using 3 g samples 0.005 ppm of Li, 0.001 ppm of Na, 0.05 ppm of K, 1 ppm of Mg, 1.5 ppm of Ba and 2 ppm of Cu can be determined in uranium, with reproducibilities better than ± 3%.Some interelemental interferences are discussed, and the possibilities of their elimination are described.The method can be used without modification for the analysis of uranium containing up to 100ppm of impurities.

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Zusammenfassung Es wird ein Verfahren zur flammenphotometrischen Bestimmung von Alkalien, Erdalkalien und Kupfer in Uran von nuklearem Reinheitsgrad beschrieben, das eine vorherige Extraktion des Urans mit Tributylphosphat verwendet. Die charakteristischen Emissionslinien werden durch eine Wasserstoff-Sauerstoff-Flamme angeregt, durch einen kleinen Monochromator isoliert und photoelektrisch registriert. Mit einer Probe von 3 g können noch 0,005 ppm Li, 0,001 ppm Na, 0,05 ppm K, 1 ppm Mg, 1,5 ppm Ba und 2 ppm Cu mit einer Reproduzierbarkeit von <± 3% bestimmt werden. Störungen durch andere Elemente sowie Möglichkeiten zu ihrer Ausschaltung werden diskutiert. Das Verfahren kann bis zu einem Gehalt von 100 ppm an Verunreinigungen in Uran angewendet werden.

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On leave to the IAEA Vienna, Austria.     

Non-aqueous fluorimetric determination of scandium in silicate rocks

A method for the fluorimetric determination of scandium with 1,2,7-trihydroxyanthraquinone in dimethylformamide medium is described. The calibration graphs obtained by the normal, synchronous, and synchronous first and second derivative techniques are linear between 12 and 225 ng/ml, and the detection limit is 2 ng/ml. The method is applied to the determination of Sc(III) in two simulated and two naturally occurring rocks.     

The determination of trace amounts of zirconium,hafnium, thorium and cerium in silicate rocks

A method is described for the determination of traces of zirconium, hafnium, cerium and thorium in rocks. After the sample has been opened up, these elements are separated from the major component elements by extraction from 10 N nitric acid with a 40% solution of tri-n-butyl phosphate, cerium being oxidised with bro-mate. After back-extraction the elements are separated from each other and from other extracted elements by cation exchange. Zirconium is determined photometrically with quinalizarin sulphonic acid which gives about twice the sensitivity of alizarin red S. Thorium is determined photometrically with thorin, and cerium by utilizing its bleaching action on iron(II) phenanthroline. Hf is determined spectro-graphically.     

Determination of sulphur in silicate and carbonate rocks by wavelength dispersive XRF

Summary A method has been developed for the determination of sulphur in geological materials within the concentration range 0.003–3%. For samples with differing matrices such as geological materials, the fusion method should be employed for X-ray fluorescence flux mixture analysis. The sample is heated with the Li₂B₄O₇ and LiNO₃ (15) in a Pt-Au crucible to 750° C. It has been experimentally verified that the slow heating of the sample in an electric furnace and the presence of an oxidizing agent allows a quantitative binding of all sulphur so that it does not evaporate during subsequent melting of the sample. The glass disc prepared in this way serves not only for the determination of sulphur but also for that of the other major elements. The relative standard deviation of the newly developed method of 4% and the limit of detection 0.003% suffice for the reliable analysis of sulphur in geological materials.

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Schwefelbestimmung in Silicat- und Carbonatgesteinen mit Hilfe der wellenlängendispersiven Röntgenfluorescenzanalyse

Zusammenfassung Das Verfahren zur Schwefelbestimmung in geologischen Materialien wurde für einen Bereich von 0,003 bis 3% ausgearbeitet. Angesichts der verschiedenartigen Matrix wird ein Aufschlußverfahren empfohlen, bei dem die Probe mit einem Gemisch von Li₂B₄O₇ und LiNO₃ (15) in einem Pt/Au-Tiegel bei 750° C erhitzt wird. Durch langsames Aufheizen und durch die Gegenwart eines Oxidationsmittels wird der Schwefel quantitativ gebunden, so daß er während des Schmelzvorganges nicht verdampfen kann. Die so hergestellte Schmelztablette dient neben der Schwefelbestimmung auch zur Bestimmung der übrigen Hauptbestandteile. Die Standardabweichung der Methode beträgt 4%, die Nachweisgrenze liegt bei 0,003%.

     

Use of lanthanum and sulphuric acid to suppress interferences in the flame photometric determination of calcium m soil extracts

Interference by iron, aluminium and phosphate in the flame photometric determination of calcium in soil extracts is not fully suppressed by lanthanum unless dilute sulphuric acid is also present. The investigation was restricted to the oxy-acetylene flame.     

Anion-exchange separation and spectrophotometric determination of vanadium in silicate rocks

A combined anion-exchange-spectrophotometric method has been developed for the determination of vanadium in silicate rocks. A rock sample weighing about 0.1 g is decomposed with a mixture of sulphuric and hydrofluoric acids and after removal of HF the residue is taken up with dilute sulphuric acid. This solution is adjusted to be 0.05M in sulphuric acid and contain 0.3% hydrogen peroxide, and is passed through a column of Amberlite CG 400 (sulphate form). The sorbed vanadium is eluted with 30 ml of 1M hydrochloric acid. The effluent is evaporated to dryness, made 0.1M in hydrochloric acid and 3% in hydrogen peroxide content, and passed through a column of Amberlite CG 400 (chloride form) to get rid of accompanying thorium and zirconium. Vanadium is stripped by elution with 20 ml of 1M hydrochloric acid and subsequently determined spectrophotometrically with 4-(2-pyridylazo)resorcinol. The detection limit is 0.4 ppm.     

Compleximetric determination of calcium in impure calcium carbonate and limestone

Calcium is determined in impure calcium carbonate and limestone samples by titrating with 0.01 M disodium EGTA at pH 12 in the presence of at least 0.6 mg of magnesium and a maximum of 500 μg of iron(III), using a pH 12.5 sodium hydroxide-potassium cyanide-sodium sulfide buffer and Calcon indicator. The results of such titrations are compared with those obtained by titrating at pH 10 the calcium perchlorate solutions derived from calcium oxalate, and with those of a modified LEWIS AND MELNICK method. The results for magnesium (% MgO) obtained by difference are in fair agreement. Magnesium can be titrated compleximetrically as magnesium perchlorate, but the reagent blank must be determined.     

The flame photometric determination of Fe,Ni, Co,Cu, Mn,Cr, and Al in waters

Summary A method for the flame photometric determination of Fe, Ni, Co, Cu, Mn, Al, and Cr in various waters is described. Samples can be analysed directly after removal of interfering anions or after separation (and concentration) of the elements to be determined from any interfering cations. Fe, Ni, Co, and Cu are extracted as carbamates, Al as cupferronate, and Cr as the ion-association complex HCrO₃Cl. The extractant used for all is hexone.The elimination of the interference of Mg with Fe is discussed. The variation of the relative error of the emission measurement with the concentration of the elements was investigated.

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Zusammenfassung Eine Methode zur flammenphotometrischen Bestimmung von Fe, Ni, Co, Cu, Mn, Al und Cr in Wässern wurde beschrieben. Nach Entfernung der störenden Anionen oder nach Abtrennung (und Anreicherung) der zu bestimmenden Elemente von etwa störenden Kationen können die Proben direkt analysiert werden. Fe, Ni, Co und Cu werden als Carbamate extrahiert, Al als Cupferronat und Cr in Form des Ionen-Assotiationskomplexes HCrO₃Cl. Als Extraktionsmittel dient in allen Fällen Hexon.Die Beseitigung des störenden Einflusses von Magnesium bei der Eisenbestimmung wurde diskutiert. Die Variation des relativen Fehlers der Emissionsmessung mit der Konzentration der Elemente wurde untersucht.

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Résumé On décrit une méthode pour le dosage par photométrie de flamme du Fe, Ni, Co, Cu, Mn, Al et Cr dans des eaux variées. On peut faire l'analyse directe après élimination des anions qui interfèrent ou après séparation (et concentration) des éléments à doser d'avec les cations gênants. On extrait Fe, Ni, Co et Cu sous forme de carbamates, Al en cupferronate, et Cr à l'état de complexe par association ionique, HCrO₃Cl. Dans tous les cas, on utilise l'hexone comme agent d'extraction.On discute l'élimination de l'interférence du Mg par le Fe. On a suivi la variation de l'erreur relative dans la mesure de l'émission en fonction de la concentration des éléments.

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Paper presented at the Symposium on Analytical Chemistry, Graz, 29th September–1st October 1965.