Differential pulse voltammetric determination of arsenic(III,V) and antimony (III,V) in glasses

Summary Analytical methods based on differential pulse voltammetry (DPV) have been described for the determination of total As, As(III), As(V), total Sb and Sb(III) as trace to minor constituents in complex glasses. For total As, the sample is decomposed with HF-H₂SO₄-KMnO₄. The As(V) is chemically reduced to As (III) by hypophosphite and a DPV scan is carried out at the dropping mercury electrode from –0.2 to –0.7 Vvs. SCE (E _p –0.41V). As(V) is determined by decomposing the sample in HF-H₂SO₄ and volatilizing the As(III) as AsF₃. The chemical reduction of As(V) and the DPV scan are then applied. If the glass can be decomposed with cold HF, the As(III) present in the glass can be determined by applying the DPV scan after cold sample-dissolution. For Sb(III), the sample is decomposed with HF-H₂SO₄, diluted, and adjusted to 1M in HCl. A DPV scan is conducted from –0.03 to –0.5 V (E _p –0.15 V). Sb(V) is not reduced in the 1M HCl supporting electrolyte. Total Sb is determined by using an aliquot of the sample solution adjusted to 6M in HCl. The DPV sweep is carried out from –0.5 to –0.1 V [E _p for Sb(V) and Sb(III) is –0.30 V]. The methods have been applied to a wide range of glass compositions and the results compared with values obtained by spectrophotometry and coulometric titration.

---

Bestimmung von Arsen(III, V) und Antimon(III, V) in Gläsern mit Hilfe der Differential-Puls-Voltammetrie

Zusammenfassung Analytische Methoden auf der Grundlage der Differential-Puls-Voltammetrie (DPV) für die Bestimmung des gesamten Arsens, As(III), As(V), des gesamten Antimons und Sb(III) als Spuren in komplexen Gläsern wurden beschrieben. Zwecks Bestimmung des Gesamt-As wird die Probe mit Flußsäure +Schwefelsäure + Permanganat aufgeschlossen. As(V) wird mit Hypophosphit reduziert und die DPV wird an einer Quecksilber-Tropfelektrode zwischen –0,2 und –0,7V gegen eine ges. Kalomelelektrode (E _p =–0,41V) durchgeführt. Zur Bestimmung von As(V) wird die Probe mit HF-H₂SO₄ unter Verflüchtigung des As(III) als AsF₃ aufgeschlossen. Dann erfolgt die Reduktion des As(V) und die DPV. Wenn sich das Glas mit kalter HF lösen läßt, wird anwesendes As(III) mittels DPV in dieser Lösung bestimmt. Zur Bestimmung des Sb(III) wird die Probe mit HF-H₂SO₄ zersetzt, verdünnt und bis zur 1-Molarität mit HCl versetzt. Dann wird mit DPV zwischen –0,03 und –0,5V gemessen (E _p =–0,15V). Sb(V) wird in 1M salzsaurer Lösung nicht reduziert. Das Gesamt-Sb wird in einem Aliquot der Probelösung bestimmt, das dazu mit HCl bis zur 6fachen Molarität versetzt wird. Der DPV-Bereich wird von –0,5 bis –0,1 V ausgenützt (E _p f:ur Sb(V) und Sb(III) ist –0,30 V). Das Verfahren wurde für Gläser verschiedenster Zusammensetzung angewendet. Die Ergebnisse wurden mit den Resultaten der Spektrophotometrie und der coulometrischen Titration verglichen.

---

---

Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Titrimetric determination of silver,chloride and bromide in glasses

Titrimetric methods are described for the determination of total silver, free silver or free halide (Cl, Br and I), and bromide (or iodide) in glasses. Total silver is titrated potentiometrically with standard bromide solution after hydrofluoric—sulfuric acid sample decomposition followed by sodium hydrogensulfate fusion for volatilizing hydrogen halide. Free silver is determined similarly on a separate sample without the fusion step. For glasses containing excess of halide, free halide is titrated potentiometrically with standard silver(I) solution after dissolution of the sample in ice-cold hydrofluoric—nitric acid. Total bromide (or iodide) is determined by iodometric titration after oxidation to bromate (or iodate) with hypochlorite solution. The methods have been applied to a wide range of complex glass compositions and results are compared with values obtained by controlled-potential coulometry and x-ray fluorescence analysis.     

Synthesis and novel reactivity of halomethyldimethylsulfonium salts

Iodomethyl-, chloromethyl-, and fluoromethyldimethylsulfonium salts, 4b-d, have been synthesized and are observed to be highly reactive molecules that exhibit extraordinary diversity with respect to the nature of their reactivity, undergoing facile direct substitution (S(N)2) reactions, but also being highly susceptible to electron-transfer reactions. Cyclic voltametry experiments indicated that the iodomethyldimethylsulfonium compound, 4b, is a potent electron acceptor, even surpassing the reactivity of perfluoro-n-alkyl iodides in that capacity. The iodo- and chloromethyldimethylsulfonium salts, 4b,c, as well as the analogous iodomethyltrimethylammonium salt, 3a, are shown to be reactive SET acceptors.     

Determination of copper in glasses by flame atomic absorption and plasma emission spectrometry

Summary Ground samples (150m, 0.5 g) are decomposed in a mixture of HF and HNO₃ acids followed by evaporation to dryness, dissolution of the residue in dilute HNO₃ acid, and dilution to 50 ml. Spectral interferences of 14 tested elements are negligible for AAS but in some cases (Nb, Ti, Zr) minor spectral corrections must be made for plasma techniques depending on the level of interferent and analyte. Nonspectral (matrix) interferences at the 1000g/ml interferent level are all less than 3.5% relative for AAS and less than 5% relative for ICP (except for Ca, Li, and Na where the effects are depressions of 7 to 10% relative). Matrix effects for DCP at the same interferent level are generally more pronounced and amount to enhancements of 5 to 15% relative for 11 of the 14 elements tested. Plasma matrix effects, especially alkali effects, can be compensated by the use of an alkali-aluminum buffer medium (1000g Na/ml plus 500g Al/ml as used in this study), a procedure which is most useful for the DCP approach. Copper can be determined down to 10 ppm in the original sample. A comparison of results shows AAS and ICP to be in good agreement with the DCP being slightly less accurate, although the differences in results may be of little practical significance. In terms of freedom from spectral and non-spectral interference, AAS was judged to have a slight advantage for copper.

---

Bestimmung von Kupfer in Gläsern durch Flammen-Atomabsorption und Plasma-Emissions-Spektrometrie

Zusammenfassung Gemahlene Proben (150m, 0,5 g) werden in einem Gemisch aus HF und HNO₃ aufgeschlossen, zur Trockne verdampft, in verd. HNO₃ gelöst und auf 50 ml verdünnt. Spektrale Interferenzen 14 geprüfter Elemente sind bei der AAS ohne Belang, aber in manchen Fällen (Nb, Ti, Zr) sind je nach der Größenordnung der Störfaktoren geringe spektrale Korrekturen erforderlich. Nichtspektrale (der Matrix zuzuschreibende) Störfaktoren in der Größenordnung von 1000g/ml bewirken weniger als 3,5% rel. Abweichung bei der AAS und weniger als 5% rel. bei ICP (inductively coupled plasma) (ausgenommen Ca, Li und Na, die eine Minderung der Werte um 7–10% bewirken). Matrixeffekte bei DCP (direct coupled plasma) bei gleicher Größenordnung des Störfaktors sind im allgemeinen stärker ausgeprägt und bewirken bei 11 von 14 geprüften Elementen Steigerungen um 5–15% rel. Plasma-Matrix-Effekte, besonders Alkali-Effekte lassen sich mit Hilfe eines Puffermediums (1000g Na/ml+500g Al/ml) kompensieren, was sich vor allem bei DCP bewährt hat. Cu kann bis zu 10 ppm in der ursprünglichen Probe bestimmt werden. Die Ergebnisse von AAS und ICP stimmen gut überein mit denen von DCP, die etwas weniger genau sind; diese Differenzen dürften aber praktisch nur wenig bedeuten. Abgesehen von spektralen Störungen erwies sich AAS für Cu etwas vorteilhafter.

---

---

Presented at the 9th International Symposium on Microchemical Techniques, Amsterdam, August 28–September 2, 1983.     

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

Spectrophotometric titration of zirconium in siliceous materials

An accurate and selective complexometric titration procedure based upon a spectrophotometrically detected end-point has been developed for the determination of zirconium in glasses, glass-ceramics and refractories. A p-bromomandelic acid separation step for zirconium imparts excellent selectivity to the procedure. The method is particularly important for the 1–5% concentration range where a simple, accurate and selective method for the determination of zirconium has been lacking.     

Compleximetric titration of aluminum and zirconium in siliceous materials after alkali fusion of samples

Rapid methods for the determination of zirconium and aluminum in siliceous materials are described. Samples are decomposed by sodium carbonate—sodium borate fusion and dissolved in perchloric acid. The zirconium is titrated directly with standard EDTA solution at 90–95 ° C in 1 M perchloric acid solution with xylenol orange as the indicator. Aluminum is then complexed by boiling with an excess of EDTA and the free EDTA is back-titrated potentiometrically with standard zinc solution. Interference of titanium in the aluminum determination is prevented by lactic acid masking. The methods have been applied successfully to a wide variety of glass-ceramics, refractories and NBS minerals.     

On <Emphasis Type="Italic">g</Emphasis>-functions for Laguerre function expansions of Hermite type

We examine weighted L ^p boundedness of g-functions based on semigroups related to multi-dimensional Laguerre function expansions of Hermite type. A technique of vector-valued Calderón–Zygmund operators is used.