Phosphorus-containing podands. 9. Synthesis of oligoethylene glycol bis(diphenylphosphinylethyl) esters and their complexing properties with respect to alkali metal cations in a low-polarity solvent

The complexing ability of phosphoryl-containing monopodands with the general formula Ph₂P(O)CH₂CH₂O(CH₂CH₂O)_nCH₂CH₂P(O)Ph₂ (n=0–5, 6.4, 8.7, 13.2) with respect to alkali metal cations was investigated conductometrically in tetrahydrofuran:chloroform mixed solvent (4:1, vol.) at 25°C. It was found that ligands of this type are efficient complexing agents relative to all alkali metal cations, and the monopodand with n=0 also exhibits elevated Li/Na and Li/K selectivity. The effect of the structure, particularly the "rigidity" of the terminal fragments of the monopodands, on their complexing capacity was discussed. The method of synthesis of this type of ligand was described.See [1] for preceding communication.Institute of Physiologically Active Substances, Russian Academy of Sciences, 142432 Chernogolovka. Scientific-Research Institute of Chemical Reagents and Special-Purity Chemicals, Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1161–1167, May, 1992.     

Approaches to optimisation of precision in capillary electrophoresis

Summary A study has been performed to obtain insight into the relative importance of critical factors affecting the repeatability of hydrodynamic injections in CE. Precision was measured for repeated analysis of a test mixture containing two acidic compounds.The use of an internal standard was clearly shown to improve precision especially when peak area precision was poor. It is suggested that precision is maximised by employing a combination of a constant temperature, an appropriate electrolyte system, an internal standard, long injection times, and high sample concentrations. Other factors are discussed, but are classified as having only a minor impact.     

Prediction of precision from signal and noise measurement in liquid chromatography: Mathematical relationship between integration domain and precision

Summary The precision of integration over noisy instrumental output for quantitative analysis is studied. A probability theory is developed to predict the relative standard deviation (RSD) of integration results over an integration domain from one-point integration (peak height measurement) to entire area integration in HPLC. Common integration modes of horizontal zero line and oblique zero line are taken into account, but no peak overlap is assumed. The question of the analytical superiority of peak height measurement or integration for quantitation is answered. In the HPLC apparatus used, the minimum RSD of measurements is found in the integration domain of ca. ±0.5 σ for analytes [peaks are approximated by the Gaussian signal of width, σ (standard deviation)]. The RSD of integration measurements is also shown to depend on the stochastic properties of background noise (uncorrelated noise and correlated 1/f type noise). The theoretical conclusion is verified by Monte Carlo simulation and HPLC experiments for some aromatic compounds. Second Part of series cited as Ref. [1].     

Application of the reference-element technique for fast sequential flame atomic-absorption spectrometry

Fast sequential flame atomic-absorption spectrometry (FS-FAAS) is able to measure a sequence of analyte wavelengths in one monochromator scan and so achieves or exceeds the analysis speed of sequential ICP–OES. The requirements and implementation of an FS-FAAS instrument are presented in detail. FS-FAAS is a sequential multi element technique which retains the advantages of conventional FAAS, for example ease of use. While the FS-FAAS technique is an ideal tool for routine determination of elements in the mg L^–1 concentration range, it is still subject to common sources of error such as transport problems and long-term drift. The reference-element technique can be used to correct for these types of common interference; other advantages include correction of some errors which are induced during sample preparation, and improved analytical accuracy and precision. The reference-element technique when utilizing the FS- FAAS technique is described in detail and benefits of the technique will be demonstrated by comparing performance for selected applications, for example a mineral sample and a scrap wood digest.     

Physicochemical Properties of Ampicillin and Amoxicillin as Biologically Active Ligands with Some Alkali Earth,Transition Metal,and Lanthanide Ions in Aqueous and Mixed Solvents at 20, 30, and 40<Superscript>∘</Superscript>C

The acid-base equilibria of ampicillin and amoxicillin were investigated in pure water and different solvent + water mixtures (solvent = methanol, ethanol, acetone, dimethylformamide, and dimethyl sulfoxide) at a constant ionic strength (I = 0.1 mol-dm^–3 KNO₃) and organic solvent volume fractions of 10, 20, and 30%. The effect of temperature on these equilibria was studied at 20, 30, and 40C. Thermodynamic functions of these ligands were calculated and discussed in terms of G, H, and S. The number of ionizable protons was determined using conductometric titrations. The formation constant of the complexes, which form by reaction of the ligands with Mg(II), Ca(II), Zn(II), Cu(II), Ni(II), Co(II), Ce(III), Pr(III), Eu(III), Gd(III), Ho(III), Er(III), and Yb(III), are determined. The relative stability of the alkali earth, transition, and lanthanide elements are compared with each other and discussed in terms of the ionic radius and the electronic structure of the outer shell of that ion. The results obtained are discussed in terms of macroscopic properties of the mixed solvents and the possible variation in microheterogenity of the solvation shells around the solute.     

Estimation of the Cholesky decomposition in a conditional independent normal model with missing data

We investigate the problem of estimating the Cholesky decomposition in a conditional independent normal model with missing data. Explicit expressions for the maximum likelihood estimators and unbiased estimators are derived. By introducing a special group, we obtain the best equivariant estimators.     

高效毛细管电泳-电导分析仪的组装及其在碱金属离子及氨基酸分离与测定中的应用

本文叙述了制作微型电导池的一种方法。用微型电导池、直流高压发生器、电导仪、记录仪等组装了一套高效毛细管电泳－电导检测装置。HPCE－CD装置已被用于天然矿泉水中碱金属离子及人发中氨基酸的测定。获得的结果是令人满意的。在最佳实验条件下，对Li-Na-、K-的检测限分别为5．0×108mol／L。     

Studies on the interaction of poly(4-vinylpyridiniumchloride) with poly(sodiumphosphate) in an aqueous solution by conductometry

A reaction between poly(4-vinylpyridiniumchloride) and poly(sodiumphosphate) in the presence and absence of NaCl and NaBr salts was studied in aqueous solution by conductometry. The interaction of polycation and polyanion gave insoluble polyelectrolyte complex which contained polycation and polyanion in unit mole ratio in a salt-free solution. A deviation from stoichiometry was observed at high polyion concentration and in the presence of NaCl and NaBr salts. The resultant complex showed swelling property in different solvent mixtures. A maximum degree of swelling was obtained in the solvent mixture of NaBr + water and NaBr + water + acetone. Furthermore, polyelectrolyte complex sorbed salts from aqueous electrolyte solutions. The sorption of salts increased with increasing salt concentration. © 1996 John Wiley & Sons, Inc.     

Stability constants and thermodynamic data for complexes of 12-crown-4 with alkali metal and alkaline-earth cations in methanol solutions

The formation of 1:1- and 2:1-complexes of the crown ether 12C4 with mono- and bivalent cations was studied in methanol solutions by calorimetric, potentiometric and conductometric titrations. It is shown that not all donor atoms of the ligand 12C4 take part in complex formation. The accuracy of the three experimental methods are checked by comparing the results for the complexation of alkali ions with crown ether 18C6.     

高压下氮气在正庚烷-正辛烷混合溶剂中的溶解度研究

Solubilities of nitrogen in binary mixtures of n-octane and n-heptane have been measured at temperatures from 20 to 70 ℃ and pressures up to 130 atm using a precision gas-liquid solubility apparatus. Experimental results can be expressed by the following equation Inx_(N_2)=A+BP_(N_2)+CP_(N_2)~2+DInP From the results obtained, the partial molar volume of dissolved nitrogen and the Henry's Law constants have also been calculated.