Determination of arsenic by galvanostatic stripping analysis and its application to steels

Arsenic can be determined by galvanostatic stripping analysis with a modified gold-film electrode, prepared by simultaneous electro-deposition of gold and arsenic on a glassy-carbon support. This initially deposited arsenic is stripped from the film before the electrode is used for the analysis, but its presence during the formation of the film apparently leads to uniformly distributed crystallization sites for the subsequent determination of arsenic, so that the precision of the determination is better than that obtained with an unmodified gold-film electrode. The pre-electrolysis is performed potentiostatically in a stirred solution of 7M hydrochloric acid, at a potential from -0.10 to -0.35 V (vs. Ag/AgCl). If the galvanostatic stripping step is performed in quiescent solution after a 6-sec rest-period, at a current of 2-12 muA, then for a 100-sec pre-electrolysis time the calibration curve is linear up to an arsenic concentration of about 2mug ml and the limit of determination is 8 ng ml . In the analysis of steel, the arsenic must first be separated by selective extraction of arsenic(III) bromide into toluene and back-extraction into the supporting electrolyte. A single extraction is virtually 100% quantitative. The relative error of the determination in steels is a few per cent and the results are in good agreement with the certified values for reference materials and with the results obtained by X-ray fluorescence analysis.     

Homogeneous enzymatic fluorescence immunoassay of serum IgG by continuous flow-injection analysis

A new technique for automated homogeneous immunoassay has been developed and applied to the determination of serum IgG. An enzyme label, horseradish peroxidase (HRP), conjugated to the antibody (anti-human IgG) was inhibited on immunochemical association. The inhibition of activity was monitored as a decrease in the laser-induced fluorescence of dichlorofluorescein, produced by the HRP-catalysed oxidation of leuco-diacetyldichlorofluorescein by hydrogen peroxide. The entire procedure was performed by flow-injection analysis at a rate of 60 samples per hour. Serum IgG concentrations from 1.4 to 25 mg/ml could be determined after a 1:700 dilution, with a within-run precision of ±9.8%.     

Molecular absorption spectrometry (MAS) by electrothermal evaporation in a graphite furnace-XIII Determination of traces of fluoride by mas of AlF after liquid-liquid extraction of fluoride with triphenylantimony(V) dihydroxide

The determination of traces of fluoride by means of the molecular absorption of AlF volatilized in graphite cuvettes is described. An extraction method for separation and preconcentration of the fluoride has been developed, to avoid matrix effects. The fluoride is extracted with 10(-3)M triphenylantimony(V) dihydroxide in M1BK, and stripped with 0.025M barium hydroxide. The method is sensitive and specific for fluoride. The detection limit is about 0.3 ng of fluoride, and the fluoride content of 6 ml of 10(-7)M solution can be determined. The determination is possible in presence of various ions, but it is estimated that usage of trace matrix separation leads to a considerable improvement in the relative detection limits (by 2-3 orders of magnitude), levels as low as 0.01 ppm being detectable in some matrices.     

Structure of H(D)TaO3 determined by powder X-ray and neutron diffraction

Pure crystalline samples of HTaO₃ and DTaO₃ have been prepared. The crystal structure has been solved using powder X-ray and neutron diffraction (at 2 K and room temperature) and has been shown to consist of Ta(O,OH)₆ octahedra sharing vertices with the oxygen atoms displaced toward the vacant perovskite A sites. The compound is isomorphous with HNbO₃, D_xWO₃, and D_xReO₃ and contains hydrogen atoms as hydroxide groups.     

Determination of thallium in lead salts by differential pulse anodic-stripping voltammetry

The determination of trace levels of thallium in lead and lead salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte without surfactant, lead at concentrations below 0.5mM does not give a peak. When the electrolyte also contains tetrabutylammonium chloride (TBAC) at 0.01 M concentration, lead can be tolerated at concentrations up to 0.05M, while the height of the thallium peak is unaffected. It is thus possible to determine 5nM T1(I) in the presence of 0.05M Pb(II), i.e., Tl at the 1 x 10(-5)% level in lead. The precision of the determination (1-4%) and the recovery are satisfactory. Neither an 800-fold excess ratio of Cu(II) to Tl(I) nor a 10(7)-fold ratio of Bi(III) interferes in the determination. Thallium has been determined in a range of lead salts of various degrees of purity.     

Decomposition of organic matter with molten alkali: determination of arsenic and antimony in organic compounds

Decomposition of organic matter with molten alkali has been examined as a method of opening out organic matrices for elemental detection and/or determination. The fusion product is readily soluble. Arsenic and antimony in organic compounds can be determined iodimetrically after mineralization by this fusion method.     

X-ray fluorescence spectrometric determination of germanium after extraction with polyurethane foam

Germanium is extracted onto polyurethane foam as molybdogermanate, and determined by X-ray fluorescence spectrometry in the dried foam. The extraction is effective between pH 0.5 and 3.7 and as little as 7 μg of germanium can be detected in 100 ml of aqueous solution.     

Multiparametric curve fitting-VII Determination of the number of complex species by factor analysis of potentiometric data

The number of complex species in solution may be determined by a computer-assisted factor analysis of a set of potentiometric titration curves, by finding the rank of the normalized data matrix. An application of the program SPECIES is demonstrated for some examples of titration data. The method is limited in that it can discriminate only between species with differing degrees of polymerization.     

Determination of the total iron content of used lubricating oils by atomic-absorption with use of emulsions

A new method is proposed for the determination of the total iron content of used lubricating oils. It is based on treatment of the samples with a mixture of hydrofluoric and nitric acids (without destruction of the organic matter) and emulsification, followed by atomic-absorption measurement. This allows the use of aqueous standards and provides a simple, rapid, inexpensive and accurate method, that is not affected by the particle size of the solids in the oil.     

Determination of nickel in the serum of occupationally exposed workers, by means of flame atomic-absorption spectroscopy

A flame atomic-absorption spectroscopy method for determination of nickel in the serum of occupationally exposed subjects has been developed. Trichloroacetic add is utilized for precipitating proteins and freeing bound nickel; sodium diethyldithiocarbamate is used as complexing agent and isopropyl acetate as the solvent for extraction. The method is characterized by good accuracy, precision and sensitivity, over a concentration range up to about 20 ng/ml. Calcium, which is present in serum in great excess with respect to typical nickel concentrations, does not interfere in the determination of the latter.     

Determination of Hg from Cu concentrates by X-ray fluorescence through preconcentration on polyurethane foam

A methodology was developed for the separation and determination of microamounts of mercury from copper concentrate samples by wavelength dispersive X-ray fluorescence (WDXRF) after solid-phase extraction of mercury from iodide medium using polyurethane foam (PUF). The best sorption conditions for the Hg-KI-PUF system were settled using X-ray fluorescence technique after collection of ground PUF on a filter paper by vacuum filtration and direct measurement of the intensity signal of the sorbed mercury on PUF. The main parameters of sorption such as iodide concentration, pH, shaking time and sample dilution effect were studied. The system shows rapid kinetic sorption and maximum X-ray intensity signal was achieved after shaking for 2 min a 0.01 mol l⁻¹ iodide solution containing microamounts of mercury in the pH range from 1.0 to 9.0. Effective sorption up to a volume of 0.9 l allows preconcentration of mercury. A linear fit up to 50 μg mercury was obtained by the plot of the initial mercury mass in the bulk solution (0.5 l) vs. its respective XRF intensity signal measurement on ground PUF after the sorption process. The calibration sensitivity, quantification and detection limits found were 9.09 CPS μg⁻¹, 9.0 and 2.7 μg, respectively. The sorption of many elements was also evaluated under the best conditions. High concentrations of Cu(II) and Fe(III) interfere seriously. Mercury-selective separation could be achieved using citrate or EDTA as masking agent; no interference due to copper matrix samples was observed in citrate medium. This methodology was evaluated by recovery for mercury determination in copper concentrate ore samples supplied by a mining industry and copper sulfate salts; the results were between 98% and 106%.     

Direct determination of gallium on polyurethane foam by X-ray fluorescence

Gallium chloride is easily extracted from 6M HCl by comminuted polyether-type polyurethane foam. After the extraction step, the gallium absorbed by the PU foam can be quantitatively determined by X-ray fluorescence. A procedure for the direct determination of gallium absorbed by PU foam by XRFS is thus described. Gallium is determined at levels as low as 60 ng/ml (C(L)), with a calibration sensitivity of 424 cps ml/mug, within a linear range 0.1-2.30 mug/ml. The procedure investigated was successfully applied to determination of gallium in aluminum alloys, bauxite and industrial residue samples.     

Determination of arsenic and zinc in tin oxide by X-ray fluorescence

Summary An XRF method to determine arsenic and zinc in high-purity tin oxide in the range of 10–1,000 ppm is described. The sample is pressed as a double-layer pellet and the analysis is carried out by using Philips PW-1220 X-ray spectrometer. Limits of detection are 13 ppm (As) and 8 ppm (Zn). Accuracy is better than 10% at a level of 50ppm; standard deviations are 8 and 9 % at this level.

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Bestimmung von Arsen und Zink in Zinnoxid mit Hilfe der Röntgenfluorescenz

Zusammenfassung Das beschriebene Verfahren eignet sich zur As- und Zn-Bestimmung im Bereich von 10 ppm–1000 ppm in Zinnoxid. Die Probe wird zu einer Doppelschichttablette gepreßt und die Analyse mit Hilfe eines Philips PW-1220 Röntgenspektrometers durchgeführt. Die Erfassungsgrenzen sind 13 ppm (As) bzw. 8 ppm (Zn). Die Genauigkeit ist besser als 10 % (50 ppm-Bereich); die Standardabweichung in diesem Bereich beträgt 8 bzw. 9 %.

     

Separation and determination of aluminium by single-column ion-chromatography

A quick, reliable method for the determination of Al(III) in the presence of other metal ions is presented. A Chromatographic system consisting of a low-capacity cation-exchange column, an eluent of diprotonated p-phenylenediamine, and a conductivity detector was used to measure the retention times for various cations. During the course of this work, it was found that Al(III) was eluted later than most bivalent metal ions but earlier than other tervalent metal ions. Therefore the concentration of eluent was adjusted so that an early sharp peak was obtained for Al(III) and the bivalent metal ions were eluted as a group. Through analysis of an NBS standard, as well as of solutions containing Al(III) and other metal ions, the method was shown to be precise, accurate and rapid for determination of Al(III) without interference from common bivalent metal ions.     

Preconcentration of some transition and rare-earth elements by Donnan dialysis

A method using Donnan dialysis for the preconcentration of some transition and rare-earth elements is described. Enrichment factors of about 20 are obtained in 1 hr. Calibration curves that are linear over 2 orders of magnitude are obtained with a relative precision of about 3% when Co(II) is used as an internal standard. The effect of aluminium in the receiver electrolyte on the interference caused by phosphate in the sample solution is discussed.     

Catalytic titration of iodide, bromide and thiocyanate by use of the silver catalysed phloxin-persulphate reaction

A method for the catalytic titrimetric determination of iodide, bromide and thiocyanate is described, based on the inhibitory effect of these anions on the silver-catalysed oxidation of phloxin by persulphate in the presence of 2,2'-bipyridyl. The end-point is determined photometrically by measuring the absorbance at 537 nm. Amounts of iodide, bromide and thiocyanate in the 0.01-7.94, 0.11-4.73 and 0.12-3.59mg ranges, respectively, are titrated with a relative error of about 1%.     

Studies on determination of fluoride in zinc and lead concentrates by using a fluoride ion-selective electrode

A modification of the potentiometric determination of fluoride has been developed, which allows use of aqueous fluoride standards in analysis of lead or zinc concentrates, instead of the need to use matrix-matching or standard additions.     

The molecular structure of gaseous methyl vinyl ether at room temperature, studied by molecular orbital constrained electron diffraction and microwave spectroscopy

The gas phase molecular structure of methyl vinyl ether at room temperature has been studied by joint analysis of electron diffraction and microwave data. Constraints on geometrical and thermal parameters were derived from the geometry and force field of the s-cis form, obtained by ab-initio calculations (4–21 G basis set) after complete geometry relaxation. A range of models was investigated that fits all available data (infrared, microwave and electron diffraction). The following r_g/r-parameters were obtained: C=C: 1.337 Å, C(sp²)---O: 1.359 Å, C(sp³)---O: 1.427 Å, : 1.102 Å C=C---O : 127.3° and COC: 116.8°. Experimental r_g---r_e (ab initio) corrections are given for C=C, C(sp²)---O and Csp³)---O.

This investigation demonstrates that molecular orbital constrained electron diffraction is sufficiently reliable and in such a manner that it can be applied to more complicated problems.     

Coulometric titration by a controlled-potential pulsed-charge potentiometric technique-II Acid-base, precipitation and homogeneous redox systems

An unconventional coulometric method, based on electrolysis at controlled potential by means of discrete charge-pulses, with end-point detection obtained by mathematical linearization of potentiometric data, has been applied to various systems. The results appear very satisfactory: very weak acids can be determined with high accuracy; in the case of precipitation reactions the selectivity is high enough to allow titration of the components of halide mixtures; for homogeneous redox systems some problems caused by irreversibility at the indicator electrode are overcome.     

Direct X-ray fluorescence detection of mercury on polyurethane foam sorbents

An improved method for conducting a sorption X-ray fluorescence analysis of mercury (II) in water with static and dynamic preconcentrations in the form of iodide complexes on polyurethane foam sorbents based on ethers has been proposed. It was shown that optimizing the conditions of measuring analytical signals enabled a significant (one order of magnitude or more) increase in the sensitivity of the detection of X-ray fluorescence and widening of the linear range of graduation dependence.