Simultaneous ion-exclusion/cation-exchange chromatography of anions and cations in acid rain waters on a weakly acidic cation-exchange resin by elution with sulfosalicylic acid

A simple, selective, and sensitive method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was developed using ion-exclusion/ cation-exchange chromatography with conductimetric detection. A weakly acidic cation-exchange resin column (Tosho TSKgel OA-PAK-A) and a sulfosalicylic acid-methanol-water eluent was used. With a mobile phase comprising 1.25 mM sulfosalicylic acid in methanol-water (7.5:92.5) at 1.2 ml/min, simultaneous separation and detection of the above anions and cations was achieved in about 30 min. Linear calibration plots of peak area versus concentration were obtained over the concentration ranges 0-1.0 mM for anions (R=0.9991) and 0-0.5 mM for cations (R=0.9994). Detection limits calculated at S/N=3 ranged from 4.2 to 14.8 ppb for the anions and from 2.4 to 12.1 ppb for the cations. The reproducibility of retention times was 0.14-0.15% relative standard deviation (RSD) for anions and 0.18-0.31% for cations, and reproducibility of chromatographic peak areas was 1.22-1.75% RSD for anions and 1.81-2.10% for cations. The method was applied successfully to the simultaneous determination of anions and cations in aerosols transported from mainland China to central Japan, as determined by a meteorological satellite data analyzer.     

Bildung siliciumorganischer Verbindungen. 73. Reaktionen C-chlorierter 1,3-Disilapropane mit CH3MgCl

Formation of Organosilicon Compounds. 73. Reactions of C-chlorinated 1,3-Disilapropanes with CH₃MgCl (Cl₃Si)₂CCl₂ reacts with an excess of meMgCl (me = CH₃) in Et₂O (diethylether) forming (me₃Si)₂₂C?CH₂ mainly besides Si-methylated 1,3-disilapropanes with CmeCl, CHCl, CH₂ groups [6]. For investigating the mechanism of formation of the methylidengroup reactions were carried out with differently Si-methylated and Si-chlorinated 2-methyl-1-2-chloro-1,3-disilapropanes and 2,2-dichloro-1,3-disilapropanes. Whereas (me₃Si)₂CmeCl reacts neither with meMgCl nor with Lime. it forms (me₃Si)₂C?CH₂ and (me₃Si)₂CmeH with Li or Mg resp. The reaction starts with the metallation to (me₃Si)₂CmeLi and (me₃Si)₂Cme(MgCl) resp., followed by elimination of LiH and HMgCl resp. with formation of (me₃Si)₂C?CH₂. LiH and HMgCl resp. reduces (me₃Si)₂CmeCl to (me₃Si)₂CmeH. This mechanism is supported by the reactions of (me₃Si)₂CCl(CD₃). The Si-chlorination increases the reactivity of the CmeCl group and the created C?CH₂ group favours Si-methylation. The CCl₂ group is more reactive than the CmeCl group; (me₃Si)₂CCl₂ already forms the methyliden group with meMgCl in Et₂O via the not isolated intermediate (me₃Si)₂CCl(MgCl). which prefers the methylation to (me₃Si)₂Cme(MgCl). The n.m.r. data of the investigated compounds are given.     

Photochemistry of 3-Substituted 1-Iminopyridinium Ylides. Regiospecific versus non-regiospecific photoisomerization patterns [1]

3-Substituted 1-iminopyridinium ylides 1 undergo photo-induced ring enlargement to 1H-1,2-diazepines. With strongly electron-withdrawing substituents the ring expansion process is regiospecific and leads exclusively to 4-substituted 1 H-1, 2-diazepines. Weak electron-donating substituents, like a methyl group and halogen atoms, do not have any directing effect since both 4- and 6-substituted 1 H -1,2-diazepines are obtained. With strong electron-donating substituents no diazepines are formed; instead one observes photo-induced isomerization to the 2-aminopyridine derivatives, the process being non-regiospecific. Regiospecific photo-induced ring expansion processes are explained in terms of a simple HMO model.     

“Stat” methods in continuous flow analysis : Determination of Copper,Iron, Iodide and Hydrochloric Acid

A continuous flow “stat” method is described in which a certain arbitrarily imposed state in the flowing stream is automatically maintained by regulating the rate of flow of one of the components. The electronic system is regulated by measuring a physical phenomenon in the flowing solution. The method is illustrated by the examples of a continuous flow absorptiostat [Fe(III)/S₂O₃^2-/Cu(II)]for determinations of copper(II) (1–10 μg ml^-1), iron(III) (25–250 or 12.5–125 μg ml^-1), as well as for determination of iodide (12.8–128 μg ml^-1). A continuous flow conductostat [HCl/NaOH] for determination of 1–2.5 × 10^-4 M HCl is also described. This analytical technique is intended for automatic continuous monitoring of sample streams.     

Buchbesprechungen

Ohne Zusammenfassung     

Acidic properties of TiO2?SiO2 catalysts

The acidic properties of a series of TiO₂–SiO₂ catalysts with different Ti/Si mole ratios have been studied. In order to determine the amount of acid centers and the acid strength distribution, the Benesi method of discontinuous titration has been used. Thermogravimetric measurements were also carried out.

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TiO₂–SiO₂ Ti/Si. , - . .

     

Bildung siliciumorganischer Verbindungen. XXXIX. Teilchlorierte Carbosilane

1. Photochlorination in CCl₄ of the Si-chlorinated carbosilanes (Cl₃Si? CH₂)₂SiCl₂ and (Cl₂Si? CH₂)₃ leads to totally chlorinated compounds, e. g. (Cl₃Si? CCl₂)₂SiCl₂. After chlorination has started at one CH₂ group, formation of a CCl₂ group is preferred before another CH₂ group is involved into the reaction. Thus preparation of compounds a, b, c is possible. Cl₃Si? CCl₂? SiCl₂? CH₂? SiCl₃ (a) for (b) and (c) (see “Inhaltsübersicht”). SO₂Cl₂ (benzoyl peroxide) as chlorinating agent reacts more slowly, and opens an access to carbosilanes containing CHCl groups such as (d), Cl₃Si-CHCl? SiCl₂? CH₂? SiCl₃ (e). Reactions of compounds (a) to (d) with LiAlH₄ yields carbosilanes with SiH groups, and partially chlorinated C atoms. 2. By the high reactivity of Si? CCl₂? Si groups an exchange of Cl atoms of CCl groups in perchlorinated carbosilanes is possible for H atoms of Si? H groups in perhydrogenated carbosilanes, thus allowing the preparation of compounds containing CHCl and SiHCl groups, e. g. according to Gl.(1) (Inhaltsübersicht). Further reactions, formulated as the last equations in Inhaltsübersicht, are reported as well as the rearrangement of H₃Si? CHCl? SiH₃.     

Sign of nuclear electric quadrupole coupling constants in solids fromγ-ray anisotropy measurements after capture of polarized neutrons

An experimental method is presented which allows the determination of the sign of nuclear electric quadrupole interactions in solids. Activated target nuclei with a purely dipolar spin polarization are produced by capture of polarized thermal neutrons. The quadrupole coupling of the nuclei to the electric field gradient tensor in the target crystal converts this (dipolar) polarization partly into a (quadrupolar) alignment, which can be measured by the anisotropy of the-ray emission in a succeeding nuclear transition. The sign of the alignment created in this reorientation process depends on the sign of the electric quadrupole interaction. The reorientation effect can be enhanced by selective induction of nuclear magnetic resonance transitions. The method has been applied to measure the sign of the crystal electric field gradient (efg) in tetragonal MgF₂. Further, the sign of an efg in cubic CaF₂ originating from a¹⁹F interstitial adjacent to the activated²⁰F probe nucleus has been determined. The method is in principle applicable to a considerable number of nuclides.