E. Kiss

Ion-exchange separation and spectrophotometric determination of boron in geological materials

Abstract Various dissolution techniques were investigated for total rocks and minerals and the best approach found was alkaline fusion. Boron in silicates was rendered chemically reactive by fusion with potassium carbonate, the fusion cake was extracted with water and borate was isolated by Amberlite XE-243 boron-selective resin. The Amberlite XE-243 resin was utilized to separate microgram amounts of boron from natural waters (fresh to hypersaline) and salt cores. Borate was eluted with 2 M hydrochloric acid and determined by spectrophotometry of the carminic acid complex at 620 nm in either 94% sulphuric acid or sulphuric/acetic acid (20:80) medium, or preferably, as the azomethine-H ion-association complex at pH 5.2 (415 nm), depending on the sensitivity required. Good precision and accuracy were obtained on several international standard rocks with an average relative standard deviation of 1.37%.

Pyridylazo-diaminobenzenes as reagents for cobalt: Spectrophotometric determination of cobalt in silicates and meteorites

Abstract Six pyridylazo-diaminobenzenes have been synthesized and assessed as chromogens for the spectrophotometric determination of traces of cobalt. Five of the reagents having chloro-, bromo- and iodo-substitutions on the heterocyclic ring show high colour stabilities and extreme sensitivities in their reactions in strongly acidic medium. The effective molar absorptivities range between 1.00 and 1.23·10 5 1 mole -1 cm -1 . Only iron and chromium(VI) interfere; the presence of fluoride and hydroxylamine makes the reactions specific. 4-(5-Bromo-2-pyridylazo)-1,3-diamino-benzene has been applied to the determination of cobalt in silicate rocks and meteorites with good precision and accuracy.

Chemical determination of some major constituents in rocks and minerals

Abstract Macro-analytical schemes are described for the determination of aluminium, total iron and iron(II), as part of the complete analysis of silicate rocks and minerals Solvent extraction eliminates interferences before titration of aluminium with DCTA Iron(III) is extracted with MIBK and determined indirectly with EDTA Iron(II) is determined by potentiometric titration under an inert atmosphere. Interferences are removed with 2,4-pentanedione and carbon tetrachloride before the determination of calcium and magnesium.

Synthesis of a sulphonated ferroin reagent for chelating iron(II) in strong acid : Spectrophotometric determination of the oxidation state of iron in silicates

Abstract The relatively easy accessibility of the ferroin chromogen 3-(4-phenyl-2-pyridyl)-5, 6-diphenyl-1,2,4-triazine (PPDT) and its diammonium disulphonate derivative (PPDT-DAS), is described via an eight-step total synthesis. PPDT-DAS shows extreme resistance to thermal and oxidative degradation and also forms the tris-chelate with iron(II) ions in molar acid concentrations. Maximal colour is formed at pH 3–8 with a molar absorptivity of 29,300 at 570 nm. Only fluoride (500 p.p.m.), EDTA, cyanide and comparable amounts of copper(I) and cobalt(II) interfere. The reagent PPDT-DAS was used for the spectrophotometric microdetermination of FeO in silicates. Any possibility of aerial oxidation was excluded by the simultaneous chelation of iron (II) in the acid decomposition step. More refractory materials were decomposed in PTFE bombs. Good precision and accuracy were obtained for the analysis of 1–5 mg samples with an average relative standard deviation of 1.33%.

Investigation of some asymmetric triazines as reagents for the spectrophotometric microdetermination of the iron oxidation state in silicates

The preparation and analytical evaluation of two asym-triazines, 3-(1-isoquinolyl)-5,6-diphenyl-1,2,4-triazine (IQDT) and 3,3′-bis(5,6-diphenyl-1,2,4-triazine (BDT), and their sulphonated derivatives (IQDT-TAS and TSBT-TAS) are described. The sulphonated ferroin chromogens formed intensely coloured tris-chelates with iron(II) in molar acid solutions and chelates were also formed with copper(I) ions. The TSBT-TAS reagent showed an exceptionally high acid tolerance in its ability to chelate iron(II) in concentrated acids. Once formed, the chelates of all four compounds possessed a high degree of stability. The IQDT and IGDT-TAS reagents formed maximal colour at pH 3–8 whereas TSBT-TAS was indifferent to pH changes in the acidic range; the molar absorptivities were 38 340 l mol−1 cm−1 at 375 nm and 27 360 at 596 nm for IQDT-TAS, and 23 500 l mol−1 cm−1 at 450 nm and 28 240 at 550 nm for TSBT-TAS. Only EDTA, cyanide and comparable amounts of copper(I) and cobalt(II) interfered. The TSBT-TAS reagents and to a lesser extent IQDT-TAS were useful for the spectrophotometric microdetermination of FeO in silicates. Aerial oxidation was prevented by the immediate chelation of iron(II) released from the silicate matrix with a decomposition acid mixture containing TSBT-TAS. More resistant minerals were decomposed in teflon bombs by prolonged heating. Good precision and accuracy were obtained for the analysis of 1–5-mg samples where the average relative standard deviation was 1.73%.

Rapid potentiometric determination of the iron oxidation state in silicates

Abstract The rapid potentiometric determination of the oxidation state of iron in a wide range of silicates is described. A platinum/platinum—rhodium (20%) bimetallic electrode with a small constant applied current is used for end-point detection. Samples are decomposed in 10–60 min by boiling with hydrofluoric—sulphuric acid in special PTFE decomposition—titration vessels in an atmosphere of nitrogen. Total iron is reduced with mercury-treated zinc or nickel reductors. Sulphides or other constituents do not interfere significantly and the procedures are relatively insensitive to aerial oxidation. The average standard deviation is 0.35% for iron(II) and 0.22% for total iron. The accuracy compares well to the available data for international standard rocks.

Determination of silica in geological materials by atomic absorption spectrometry

Abstract A simple rapid method for the routine determination of silica by atomic absorption spectrometry (a.a.s.) in a wide range of geological materials is described. Samples are decomposed by heating with hydrofluoric acid in closed containers and diluted gravimetrically. Large concentrations of free hydrofluoric acid are tolerated and the resulting solutions show excellent stability. No chemical interference was identified in the atomic absorption measurements. The technique was extended to the micro-determination of silica in samples of milligram size as well as trace-level silicon in waters. The average standard deviation is ⩽1% by the recommended method, 2.6% by the micro-method and 2–6% at trace level (20–0.5 ppm Si), respectively. The procedure described complements the a.a.s. scheme in current use for some 25 major and trace elements.

Micro-fusion and spectrophotometric determination of iron(II) and iron(III) in chrome spinels and other refractories

Abstract Spectrophotometric determination of FeO in milligram samples of chrome spinels and related refractory minerals after high-frequency micro-fusion with lithium tetraborate in an inert atmosphere is described. Anomalous responses (apparent reduction or oxidation of FeO depending on the ferroin-type reagent)_rendered the procedure highly unreliable. All the fluxes containing structural oxygen, as well as phosphoric acid, acted as oxidants even when atmospheric oxidation was rigorously excluded. However, the method is suitable for micro-determination of total iron in spinels. Spectrophotometric measurements gave an average relative standard deviation of 0.73%.

Integrated scheme for micro-determination of iron oxidation states in silicates and refractory minerals

Abstract A mirco-analytical scheme incorporating four methods is described for the determination of iron(II) and iron(III) in both hydrofluoric acid-soluble and refractory minerals. The acid-soluble minerals are analyzed for FeO by direct constant-current potentiometric titration with potassium dichromate, and a separate solution is titrated similarly after Zn/Hg reduction to give total iron. The micro-determination of FeO in chromite and other refractory minerals involves dissolution in a cerium(IV)/phosphoric acid mixture and constant-current potentiometric and indirect titration of excess of cerium(IV) (phosphatocerate) with iron(II). Lithium tetraborate micro-fusion is required for measurement of total iron by atomic absorption spectrometry or spectrophotmetry. The average relative standard deviation ranged between 0.73 and 1.08%.

Elimination of major molecular chlorine interference in the iodimetric determination of sulphur in saline sediments

Abstract Free chlorine evolved during the high-frequency induction furnace combustion of saline sediments at >1500°C interfered very seriously in the iodimetric titration of liberated sulphur dioxide. Remedies based on absorption of chlorine on copper, antimony and other traps were only partly successful; copper was the most efficient but the loss of titratable sulphur was still very large. Sample desalination with refluxing anhydrous methanol in a Soxhlet extractor was the only method found to give satisfactory performance. This procedure was successful for a broad range of salinity values (reference sample mixed with sodium chloride in ratios of 0.09–1.6) without affecting the sulphur minerals present. The procedure showed excellent precision and good agreement with the “best” values available for the USGS MAG-1 Marine Mud (0.40% S) with a relative standard deviation of 1.29%. Iodimetric determination of sulphur in salt core samples (with the sediment in minor proportions) would also be possible.