Determination of chemical composition of solid inorganic substances and materials using the principles of stoichiography and voltammetry

The state of the art in determination of the phase composition of complex inorganic solids by chemical and electrochemical methods is discussed. The theoretical and practical essentials of stoichiography and the new stoichiographic method of differential dissolution (DD) are reported. The unique feature of this method is that reference samples of the analyzed solid phases are not necessary. The development of this stoichiographic method was strongly affected by voltammetry. The application of the DD method for determining the chemical composition of various substances and materials is presented. The complementary use of voltammetry and DD for the detection, identification, and quantitative determination of inhomogeneity of the chemical composition of high-temperature superconductors was shown to be efficient.     

Stoichiography and present-day analytical chemistry of solid inorganic substances and materials

The article covers factors that determine fundamental difficulties of chemical phase analysis of a mixture of solid phases of inorganic compounds. Stoichiographic principles and methods, novel for analytical chemistry and leading to the efficient solution of the problems of phase analysis, are discussed. Conditions of the selective separation of mixtures of multiphase multielement solid compounds and principles of the new method, fan-like separation, ensuring the extraction of individual phases from unseparated mixtures, are considered. An idea of a complex method of solving analytical problems by stoichiography methods in proposed. The problem of the multiplicity of objects of analysis is discussed and general principles of the efficient solution of problems of the detection and identification of components of complex mixtures of unknown chemical composition are considered.     

Specific features of the dynamic mode of differential dissolution as of a method of phase analysis

The author considers the specific features of the separation properties of the stoichiographic method of differential dissolution (DD) and the role of thermodynamic and kinetic factors in the processes of the separation of solid mixtures. It is shown that the separation properties of DD should be characterized by selectivity and efficiency, as it is accepted in chromatography. The separation possibilities of DD are considered in characterizing uniformity, stoichiometry-nonstoichiometry of the elemental composition of phases, and also of their macro- and microstructures. The comparison of the principles and characteristics of DD, voltammetry, titrimetry, mass spectroscopy, and chromatography has led to the conclusion that the place of DD among the other methods is determined, primarily, by its unique property, namely, its standardless nature.     

The study of the lipophilicity of alpha-(4-phenylpiperazin-1-yl)-gamma-phthalimidobutyramides using chromatographic and computational methods

The lipophilicity of the series of alpha-(4-phenylpiperazin-1-yl)-gamma-phthalimido-butyramides (1-8) has been investigated. Several methods, like reversed-phase thin-layer chromatography and high-performance liquid chromatography using reversed-phase RP18 and IAM.DD2 columns, were applied to determine RMO, log k0 and log k(0IAM) factors. The RP-TLC investigations were performed in mixtures of acetone-water and acetonitrile-water. For RP-HPLC method mixtures of acetonitrile, water and 0.01% TFA were used as the mobile phases while for IAM.DD2 investigations mixtures of acetonitrile and water were applied. The partition coefficients of compounds (1-8) were also calculated with the Pallas and CAChe programs. All the obtained data, both from experimental methods and computational calculations, were compared and a suitable conclusion was reached.     

Cyclische Thiophosphate,Produkte der Umsetzung von elementarem Phosphor mit Alkylammoniumpolysulfiden

Cyclic Thiophosphates, Products from the Reaction of Elemental Phosphorus with Alkylammonium Polysulfides White Phosphorus reacts very rapidly above its melting point with alkylammonium polysulfide solutions in chloroform or dimethylformamide. The reaction products are mixtures of thiophosphates, which contain compounds with phosphorus in different oxidation states. The composition of these mixtures may be changed by varying the amounts of applied polysulfidic sulfur and alkylamine. Several cyclic thiophosphates have been isolated from the mixtures in good yields; some contain P? P bonds.     

Analytical Chemistry of Phases of Variable Composition and the Principles of Stoichiographic Determination of Such Phases in Multielement Multiphase Samples

The general problems of determining the stoichiometry and content of solid phases of variable composition in multielement multiphase substances are discussed. The possibilities and conditions of application of a reference-free stoichiographic method based on the differential dissolution (DD) of components for the analysis of samples containing spatially homogeneous and inhomogeneous phases are considered. The results of mathematical modeling of the DD process for a mixture of phases of constant and variable composition are presented. These data substantiate the use of the stoichiogram affinity criterion for the identification of spatially inhomogeneous phases of variable composition. Examples of applying the DD method to the phase analysis of various substances containing phases of variable composition are given.     

Human liver dihydrodiol dehydrogenase 1-catalyzed reaction generating 9alpha,11beta-prostaglandin F2 from prostaglandin D2 followed by micellar electrokinetic chromatography

An enzyme reaction converting prostaglandin D2 (PGD2) into 9alpha,11beta-prostaglandin F2 (9alpha,11beta-PGF2) by a human liver-originated recombinant dihydrodiol dehydrogenase 1 (DD1) has been studied using CE. Four prostaglandins, viz. PGD2, 9alpha,11beta-PGF2, PGE2, and PGF2a (see Fig. 1, the latter two major PGs are possibly coexisting compounds in the assay mixtures), were completely separated by using SDS or PEG as buffer additives. Because analysis times in the SDS system were shorter than in the PEG system, SDS was employed in measurements of the enzyme activity of DD1. The pH dependence and the reaction temperature dependence of enzyme activity have been studied. The present method enabled us to detect all of the participants in the enzyme reaction: PGD2, 9alpha,11beta-PGF2, nicotinamide adenine dinucleotide phosphate (NADPH), and NADP+. Thus, direct, comprehensive, and reliable analysis of the enzyme reaction becomes possible. Enzyme activity has hitherto been estimated indirectly from the decrease of fluorescence derived from NADPH as an index of progress of the enzyme reactions in batch methods employed in conventional studies. In addition, the low sample consumption characteristic of CE should be a significant advantage of the present method in characterization of less commonly available enzymes such as the recombinant species used in this work.     

UV spectroscopic quantitative determination of methanofullerene derivatives with a different degree of substitution

A spectroscopic method for the analysis of compounds belonging to methanofullerenes with different functionalization and a number of substituents is developed. In order to determine the composition of mixtures of these compounds the standard spectrophotometric procedure along with derivative spectroscopy are applied. Acceptable reproducubility and sensitivity of the methods used are demonstrated on model mixtures of fullerene derivatives. The reaction mass obtained in the interaction of fullerene with diallyl ester of malonic acid is analyzed.     

Stability-indicating methods for determination of pyritinol dihydrochloride in the presence of its precursor and degradation product by derivative spectrophotometry

A first-derivative spectrophotometric (1D) method and a derivative-ratio zero-crossing spectrophotometric (1DD) method were used to determine pyritinol dihydrochloride (I) in the presence of its precursor (II) and its degradation product (III) with 0.1N hydrochloric acid as a solvent. Linear relationships were obtained in the ranges of 6-22 microg/mL for the (1D) method and 6-20 microg/mL for the (1DD) method. By applying the proposed methods, it was possible to determine pyritinol dihydrochloride in its pure powdered form with an accuracy of 100.36 +/- 1.497% (n = 9) for the (1D) method and an accuracy of 99.92 +/- 1.172% (n = 8) for the (1DD) method. Laboratory-prepared mixtures containing different ratios of (I), (II), and (III) were analyzed, and the proposed methods were valid for concentrations of < or = 10% (II) and < or = 50% (III). The proposed methods were validated and found to be suitable as stability-indicating assay methods for pyritinol in pharmaceutical formulations.     

Characterisation of quaternary mixtures by the apparent content curves method: identification of tocopherols in vegetable oils

A procedure for identification of the compounds in quaternary mixtures has been developed. The proposed procedure is based on the apparent content curves method. From these curves and using the Q parameter, work conditions are selected and quaternary mixtures treated as "pseudoternary" mixtures.A simple strategy to test matrix effects at working wavelengths has been developed, identification limits established and following the identification table quaternary mixtures were easily characterised. The procedure has been applied to the identification of phenols in mixtures by UV-visible spectrophotometry and tocopherols in edible oils by fluorimetry. Results obtained for edible oils are in agreement with the composition obtained by use of the reference method.     

Photochemical reactions of substituted cyclobutadieneiron tricarbonyl complexes with acetylenes

When mixtures of monosubstituted cyclobutadieneiron tricarbonyl complexes and propyne are irradiated, substituted toluenes are obtained. The composition of the isomeric mixture is influenced by the nature of the substituent in the metal complex. Electron-withdrawing groups produce mixtures containing a very large percent of the ortho isomer while electron-releasing groups yield mixtures rich in the para isomer. Complex mixtures of isomeric benzene compounds are obtained when substituted acetylenes are allowed to react with methyl- or isopropylcyclobutadieneiron tricarbonyl.     

Simultaneous determination of ibuprofen and paracetamol using derivatives of the ratio spectra method

Simple, rapid and accurate new method is described for the simultaneous determination of ibuprofen (IB) and paracetamol (PA) in two components mixture and Cetofen tablets. The method depends on the derivative of the ratio spectra DD by measurement of the amplitude of ¹DD at 225.6 nm and the amplitude of ²DD at 238.9 nm for IB and PA. Calibration graphs are linear in the range 2–32 (LOD 0.53) and 2–24 (LOD 0.57) μg/ml IB and PA, respectively. The proposed method is successfully applied for simultaneous determining IB and PA in authentic mixtures and Cetofen tablets.     

Equilibrium phase diagrams of aqueous mixtures of malonic acid and sulfate/ammonium salts

Tropospheric aerosols are usually complex mixtures of inorganic and organic components. Although the thermodynamic properties of inorganic aerosols have been widely studied, the effect of organics on such properties is still under discussion. In this study, solubility in water, water activity (a(w)) of aqueous solutions, deliquescence relative humidity (DRH), eutonic composition, and eutonic DRH were determined for bulk mixtures of malonic acid (MA) with ammonium sulfate (AS) and ammonium bisulfate (ABS) at 25 degrees C over the full range of composition (from 0 wt % to the solubility limit of the mixture components). The data were used to construct equilibrium phase diagrams, which show the phase of the mixtures as a function of total composition, dry mixture composition, water content, and ambient relative humidity (RH). This work complements previous reports on the thermodynamic properties of AS/MA mixtures because the range of concentrations investigated is larger than in any other published single study. On the other hand, this is the first report on the a(w), deliquescence, and water absorption of ABS/MA mixtures. The eutonic composition for AS/MA mixtures was found to be 66.8 MA dry wt % (MA dry wt % = MA mass x 100/(AS mass + MA mass) with a DRH of 0.437. The eutonic composition for the ABS/MA mixtures was lower than for the AS/MA mixtures: 20.9 MA dry wt % with a DRH of 0.327. Measured a(w) of liquid AS/MA and ABS/MA solutions is compared with an extended Zdanovskii-Stokes-Robinson expression, obtaining a good agreement (error < 5-6%). The expression was used to predict water uptake of mixtures and might be useful to interpret particle hygroscopic growth experiments. Comparison of the AS/MA and ABS/MA systems indicates that ABS reduces the DRH and enhances water uptake, relative to mixtures with AS. The results confirm that ambient particles containing sulfate and water-soluble organic compounds can remain liquid or partially liquid at very low ambient RH conditions, especially if the sulfate is not completely neutralized.     

The chemical composition of mixed wastes: Analysis of the photolysis products of organic ligands

A survey of the literature regarding the composition of mixed wastes originating from the clean ups of spills of radioactive solutions shows that (1) the mixtures obtained in studies of the X-ray and -ray radiolysis, and of the UV-photolysis of organics in aqueous solutions have very similar composition provided the photolysis is carried out with UV beams with wavelengths below 242 nm; (2) the composition of the organic fraction of mixed wastes containing initially EDTA, NTA, and/or citric acid is complex. The mass recoveries are between 20 and 60%; and (3) the UV-photolysis of complexing agents gives much more complex mixtures at high pH than at low pH, because carbonyl compounds are formed, and these compounds undergo complex series of reactions in strongly alkaline solutions. The mixed wastes considered have a high pH due to the necessity of complexing strongly the heavy metals involved in spills. These results are confirmed by an investigation of the properties of the products of the UV-irradiation of EDTA, citric acid and some of their binary mixtures. The products of the esterification by BF₃/BuOH are only partly soluble in methylene chloride. Much better yields are obtained by using BF₃/BuOH as the reagent.¹³C NMR illustrates the composition of the mixture, without requiring a separation and is useful to follow the fate of compounds during their methylene chloride extraction after esterification.     

3-羟基丁酸的气相色谱分析

采用ＢＦ３－ＣＨ３ＯＨ酯化衍生法,以正辛酸作内标,建立了３－羟基丁酸、巴豆酸、３羟基丁醛、巴豆醛等混合体系中３－羟基丁酸的气相色谱分析方法,利用标准样对照并结合质谱分析确定了化学合成３－羟基丁酸反应混合物的组成。该法线性范围为０．４０～１６０．６７ｇ／Ｌ,相关系数为ｒ＝０．９９９５。方法快速、简单、重现性好,并用于化学合成３－羟基丁酸反应混合物的分析,结果令人满意。     

New Insights into the Effects of Tetrahydrofuran and Dioxane on the Selectivity of Ternary Eluent Compositions in RP-HPLC Systems

The present paper discusses the tendencies in the retention changes of a diverse set of organic model compounds on HPLC C18 stationary phases in aqueous ternary eluent mixtures containing tetrahydrofuran or 1,4-dioxane, and one short chain aliphatic alcohol (ethanol, n-propanol or isopropanol). The set of compounds consisted of steroid and non-steroid molecules with different hydrogen bond donor and/or acceptor abilities. Every eluent mixture contained 75 V/V% water and 25 V/V% organic solvent(s). The composition of the mixture was changed in 5 V/V% steps, starting with the binary alcohol–water mixtures and finishing with the binary ether–water mixtures. The results show clearly the dependency of retention times on the eluent composition, the size of the molecules, and the occurence of the hydrogen bond donor/acceptor groups. The isopropanol–tetrahydrofurane–water mixtures resulted in selective changes in the retention times of the compounds with acidic groups or with other non-acidic OH or NH protons in the neighborhood of electron-withdrawing groups. Every compound has shown elevated retention times in the isopropanol–dioxane–water, n-propanol–tetrahydrofuran–water, or n-propanol–dioxane–water mixtures. Clear trends could not be observed in the eluents with ethanol. The probable reason for the retention enhancement is the adsorption of the organic components of the mobile phase on the surface of the stationary phase. The different effects of the alcohols may originate from the interaction of their varying aliphatic alkyl chains with the C18 chains. This phenomenon may result in different availability of the C18 chains for dioxane, tetrahydrofuran and the model compounds.     

Potential of thermodynamic tools (group contribution methods, factual data banks) for the development of chemical processes

Reliable knowledge of the thermophysical properties of pure compounds and their mixtures in the whole composition and a wide temperature and pressure range is a vital prerequisite for the computer aided synthesis, design and optimization of chemical processes. At the beginning of the development of thermodynamic models, the main interest was directed to the development of predictive g^E-models for vapor–liquid equilibria (VLE) of subcritical compounds. Today group contribution equations of state are available which can also handle supercritical compounds, very asymmetric systems and even systems with strong electrolytes. These sophisticated models together with factual data banks (e.g. the Dortmund Data Bank) are powerful software tools for the reliable development of chemical processes and other applications of industrial interest. In this paper, the status of the different approaches and important applications of industrial interest using thermodynamic information derived from factual data banks or by using sophisticated predictive thermodynamic models will be presented.     

Kinetic fluorimetric determination of histidine,histamine and their mixtures

Kinetic fluorimetric methods for the determination of histidine and histamine, both separately and in mixtures, are described; the methods are based on the accelerating effect of these compounds on the oxidation of 1,1,3-tricyano-2-amino-1-propene by hydrogen peroxide in the presence of copper. A differential rate method is used for resolution of mixtures of these compounds (10^?5 M level), in which synergic effects are taken into account. The relative standard deviations for histidine and histamine are 1.4% and 2.1%, respectively, for separate determinations but 4.0% and 3.4%, respectively, for determinations of mixtures. Histamine/histidine ratios between 1:1 and 16:1 are satisfactorily resolved.     

Extraction of wood compounds by use of subcritical fluids

Summary A study of the extraction of oak wood compounds with subcritical water-ethanol mixtures as extractants, with an ethanol content between 0 and 60%, is reported. Identification and characterization of the extracted compounds were achieved by spectrophotometry and by gas chromatography with either flame ionization or mass spectrometric detection. Extraction was performed statically by use of a single cycle or repeated cycles. All variables affecting the extraction process were studied and optimized. Extraction time and temperature were 60 min and 200°C, respectively. Comparison of the extract thus obtained with commercial extracts showed the former to be rich in compounds characteristic of the commercial extracts. The method also enables manipulation of extract composition by changing the temperature and the water/ethanol ratio used. It is faster than traditional procedures for obtaining wood extracts.