The preparation of a cabbage reference material for environmental monitoring and food analysis

 Cabbage is frequently used in environmental monitoring and food control, and, hence, cabbage reference materials (RMs) are required for ensuring quality assurance. A cabbage RM was prepared in view of certification of specific elements from the "black list" of high toxicological interest and nutritive importance. All tasks of the RM production (production of the plant material, cutting and freeze-drying, determination of the residual water content, preparation of the RM, homogeneity testing, stability testing, certification measurements) are described in detail. Received: 12 November 1999 / Accepted: 29 January 2000     

Synthesis,Characterization, and Crystal Structure of Thallium(I) Complex containing Monodeprotonated 2,6‐Pyridinedicarboxylic Acid

The reaction of an ethanolic solution 2,6‐pyridinedicarboxylic acid ( 1 , LH₂) with TlNO₃ in the presence of triethylamine led to the coordination polymer [Tl(LH)]_n ( 2 ). The complex was characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction. Crystal data for 2 at –80 °C: monoclinic, space group I2/a, a = 696.1(1), b = 1190.6(2), c = 931.0(2) pm, β = 103.28(1)°, Z = 4, R₁ = 0.0256.     

Arene Complexes of Univalent Gallium,Indium, and Thallium

Arene complexes of main-group metals were, until recently, rare species—in contrast to the now classical, analogous complexes of transition metals. In systematic investigations, it has been possible to prepare and structurally characterize arene complexes of the univalent elements gallium, indium, and thallium, which directly follow the d-block elements in the periodic table. This new type of compound is characterized by centric (η⁶) coordination of the metal to the arene; both mono- and bis(arene) complexes are known. The interaction can be explained by the perfect agreement between the HOMO/LUMO symmetry of the arene and of the low-valent metal. The electronic states of the nd¹⁰(n + 1)s² configuration, which are partially modified by relativistic effects, play a particularly important role. The relationship to the few known complexes of the neighboring elements (Sn^II, Pb^II) becomes plausible via the isoelectronic principle. The arene/Ga^I, In^I, Tl^I systems are of potential significance as homogeneous reducing agents and as agents for the activation of aromatic compounds, the purification of metals, and the separation of metals from nonaqueous media.     

Characteristics of Subtractive Anodic Stripping Voltammetry of Lead,Cadmium and Thallium at Silver‐Gold Alloy Electrodes

Silver‐gold alloy electrodes have been studied for the purpose of the quantitative determination of heavy metals by subtractive anodic stripping voltammetry, (SASV). The results have been compared with those obtained with the silver and gold electrodes. The 50/50 a/o Ag/Au alloy electrode is the most suitable for quantifying thallium in the presence of lead and cadmium. The separation of its peak from those of lead and cadmium is 200 mV, which is about twice the separation obtained on the pure metal electrodes and is also better than on mercury. The silver electrode is suitable for the simultaneous determination of thallium, lead and cadmium. The peaks of lead and cadmium overlap on the 50/50 alloy. Pure silver or pure gold can be used for simultaneous quantification of these two metals. The use of gold for quantifying lead and cadmium is more limited because the peak potential of cadmium is shifted in the negative direction as its concentration increases and at [Cd²⁺]>200 nM, the two peaks merge. SASV enables correction for background currents and is of utmost importance for obtaining well‐defined peaks. The peaks of lead, cadmium and thallium appear over a relatively narrow potential range (ca. 200 mV) on all the electrodes presented in this work. For this reason, the quantifying of a peak is based on the derivative at the inflection point of only one of its branches (ascending or descending). All SASV measurements were carried out without removal of oxygen.     

Zur Kenntnis von BaTiVO4 und SrTiVO4

On BaTiVO₄ and SrTiVO₄ BaTiVO₄ and SrTiVO₄ were prepared in closed systems by solid state reactions. They crystallize with orthorhombic symmetry (BaTiVO₄: space group D-Pmnb; a = 5.889; b = 7.889; c ?10.397 Å; Z = 4; SrTiVO₄: space group D-P2¹,2¹,2¹,2¹; a = 5.855; b = 7.572; c = 10.012 Å; Z = 4) and belong to β-K₂SO₄-type. The ordered occupation of point positions by Ba²⁺ and Tl⁺ as well as the decrease in symmetry of SrTiVO₄ are discussed.     

Spectrographic estimation of Ga, In and Tl in semiconductor grade selenium

Summary An emission spectrographic method for the estimation of Ga, In and Tl in semiconductor grade selenium at less than a ppm concentration has been developed. The impurities were separated from 1 g of selenium by volatilizing it from its solution in nitric acid and sulphuric acid. The residue containing the impurities was dissolved in small amounts of 6 M HCl and was loaded along with the washings on 10 mg mixture containing graphite (90%) and sodium chloride carrier (10%) in the electrode crater. The spectra were excited in a d.c. arc carrying 13 A current. The detection limits lie in the range of 0.0025–0.005 ppm. The precision of the method ranges from 7–12% for these elements. The recoveries of impurities from selenium were confirmed using radioactive tracers.

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Spektrographische Bestimmung von Gallium, Indium und Thallium in Halbleiterselen

Zusammenfassung Eine 1 g-Probe wird in Salpeter- und Schwefelsäure gelöst und die Verunreinigungen durch Verflüchtigung des Selens isoliert. Sie werden in 6 M HCl gelöst und zusammen mit einem Graphit/NaCl-Gemisch (91) in die Elektrode eingebracht. Zur Anregung dient ein Gleichstrombogen (13 A). Die Nachweisgrenzen liegen im Bereich von 0.0025–0.005 ppm, der Variationskoeffizient bei 7–12%. Die Wiedergewinnung der Verunreinigungen wurde mit Hilfe von Radioindicatoren geprüft.

     

Polarographic determination of Pb, Tl, Bi and Sb in ethylenediamine in presence of mannitol

Summary Pb, Tl, Bi and Sb yield well defined polarograms in 1 M ethylenediamine in presence of 3% mannitol, with half-wave potentials at – 0.71 V, – 0.51 V, – 0.60 V and – 1.10 V, respectively. Only Pb and Tl develop maxima which can be suppressed by 0.02% gelatin. Presence of mannitol prevents the precipitation of Pb, Bi, and Sb in the alkaline solution. Simultaneous determinations of Pb/Tl, Bi/Sb, and Pb/Sb can be carried out.

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Polarographische Bestimmung von Pb, Tl, Bi und Sb in Äthylendiamin in Gegenwart von Mannit

Zusammenfassung Gut ausgebildete Polarogramme kann man von diesen Elementen in 1 M Äthylendiamin in Gegenwart von 3% Mannit erhalten. Die Halbstufenpotentiale liegen bei – 0,71 V (Pb), – 0,51 V (Tl), – 0,60 V (Bi) und – 1,10 V (Sb). Maxima, die im Falle von Pb und Tl gebildet werden, können durch 0,02% Gelatine unterdrückt werden. Durch Mannit wird die Fällung von Pb, Bi, und Sb in der alkalischen Lösung verhindert. Simultanbestimmungen von Pb/Tl, Bi/Sb und Pb/Sb sind möglich.

Our sincere thanks are due to Dr. G. B. Singh, Professor and Head, Department of Chemistry, B.H.U. for providing the necessary facilities.     

The Oxidation of Heterogeneous Tl/Ni/P‐Alloys — Preparation and Crystal Structures of the Thallium Nickel Phosphates TlNi4(PO4)3, Tl4Ni7(PO4)6, and Tl2Ni4(P2O7)(PO4)2

Single crystals of the first anhydrous thallium nickel phosphates were prepared by reaction of heterogeneous Tl/Ni/P alloys with oxygen. TlNi₄(PO₄)₃ (pale‐yellow, orthorhombic, space group Cmc2₁, a = 6.441(2)Å, b = 16.410(4)Å, c = 9.624(2)Å, Z = 4) crystallizes with a structure closely related to that of NaNi₄(PO₄)₃. Tl₄Ni₇(PO₄)₆ (yellow‐brown, monoclinic, space group Cm, a = 10.711(1)Å, b = 14.275(2)Å, c = 6.688(2)Å, β = 103.50(2)°, Z = 8) is isotypic with Na₄Ni₇(PO₄)₆, and Tl₂Ni₄(P₂O₇)(PO₄)₂ (brown, monoclinic, space group C2/c, a = 10.389(2)Å, b = 13.888(16)Å, c = 18.198(3)Å, β = 103.1(2)°, Z = 8) adopts the K₂Ni₄(P₂O₇)(PO₄)₂ structure. Tl₂Ni₄(P₂O₇)(PO₄)₂ could also be prepared in nearly single phase form by reaction of Tl₂CO₃, NiO, and (NH₄)₂HPO₄.     

Syntheses and structural characterization of New Tl + and K + complexes of 3,5-dinitrobenzoic acid (HDNB), [Tl(μ-DNB)] n and [K(μ-DNB)(μ-HDNB)] n

Two new Tl⁺ and K⁺ complexes of 3,5-dinitrobenzoic acid (HDNB), [Tl(μ-DNB)] _n and [K(μ-DNB)(μ-HDNB)] _n have been synthesized and characterized by elemental analysis, IR, ¹H NMR and ¹³C NMR spectroscopy. Determination of the structure of the [K(μ-DNB)(μ-HDNB)] _n and [Tl(μ-DNB)] _n by X-ray crystallography shows that there are nine coordinate K atoms (KO₉) and eight coordinate Tl atoms (TlO₈). The [Tl(μ-DNB)] _n and [K(μ-DNB)(μ-HDNB)] _n complexes are 2D and 3D coordination polymers, respectively.     

Studies of Anion Transport Through Supported Liquid Membrane

Abstract

Transport studies of anions were investigated through cellulose triacetate supported liquid membrane. The experimental variables explored were concentration of anions, sodium hydroxide, and stirring speed. The two-channel membrane system has been explored for the transport of carbonate ions from source to receiving phases. Carbonate ions are selectively transported through the cellulose triacetate supported liquid membrane in comparison with that of nitrate and sulfate. Sulfate and nitrate anions are strongly held in the cellulose triacetate membrane, and then stripped out later. Carbonate ions are loosely bound to the cellulose triacetate membrane and stripped out earlier.