A method of determination of the position of tautomeric keto-enol equilibrium from IR spectral data using the Meyer equation

Conclusions A method of determining the equilibrium position of tautomers having two forms in the equilibrium, of which only one appears in the spectrum, is described.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1620–1621, July, 1969.     

A method for determining the position of tautomeric equilibrium solely from infrared and ultraviolet spectral data

Conclusions A method was described for determining the position of equilibrium in tautomeric systems, using only data from IR and UV spectra.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1887–1888, August, 1968     

A simple method for a determination

The a term is a primary parameter that is used to indicate the deviation of the epithermal neutron distribution in the k ₀-standardization method of neutron activation analysis, k ₀-NAA. The calculation of a using a mathematical procedure is a challenge for some researchers. The calculation of a by the "bare-triple monitor" method is possible using the dedicated commercial software KAYZERO^®/SOLCOI^®. However, when this software is not available in the laboratory it is possible to carry out the calculation of a applying a simple iterative linear regression using any spreadsheets. This approach is described in this paper. The experimental data used in the example were obtained by the irradiation of a set of suitable monitors in the NAA #1 irradiation channel of the HANARO research reactor (KAERI, Korea). The results obtained by this iterative linear regression method agree well with the results calculated by the validated mathematical method.     

Synthesis and spectral examination of the position of tautomeric equilibrium in 2-thioxo-4-quinazolone

2-Thioxo-4-quinazolone and its derivatives mono- and dimethylated at ring atoms N₍₁₎ and N₍₃₎ and the exocyclic sulfur have been synthesized. Using model compounds, UV spectroscopy has been used to show that 2-thioxo-4-quinazolone exists in the thioketo-form, no appreciable amounts of the thiol or enol isomers being present.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1236–1238, September, 1986.     

A simple spectrophotometric method for the determination of minoxidil

A simple and sensitive method for the determination of minoxidil using 3-methyl-2-benzothiazolinone hydrazone (MBTH) and Fe(III) as the coloring agent is described. The method is sensitive to permit the determination of 0.5–4.5 μg ml⁻¹ of minoxidil at 500 nm. The accuracy and precision of the method were checked by high-performance liquid chromatography.     

A simple colorimetric method for the determination of ammonia in seawater

A method is proposed for the determination of trace amounts of ammonia in seawater. After calcium and magnesium have been chelated with CDTA, the blue colour obtained with hypochlorite and thymol-acetone is measured at 630 nm. The sensitivity is 1.3 ng NH₄⁺-N/cm².     

Graphical method for the determination of the complex NMR shift and equilibrium constant for a hetero-association accompanying self-associations

We describe a novel graphical method which, in conjunction with the previously proposed graphical determination of monomer shift, dimer shift, and dimerization constant for self-association, allows us to determine the complex shift and equilibrium constant for a hetero-association, A + B ⇌ AB, accompanying self-associations, A + A ⇌ A₂, and B + B ⇌ B₂. The merit of the new method includes the removal of the restrictions imposed on the conventional Benesi-Hildebrand (B-H) plot: (1) that the concentration of one component must be much less than that of the other; (2) that there be no accompanying self-association. The simultaneous equilibrium of the self-association of 2-pyrrolidone (A) and that of 4-methyl-α-pyrrolidone (B) and the hetero-association between A and B in acetonitrile-d₃ at 25‡C is studied. The inappropriateness of the B-H plot in dealing with this case is also pointed out.     

A new method for the determination of thermodynamic equilibrium constants in separation processes

A new approach to the determination of thermodynamic equilibrium constants in ion-exchange and solvent extraction processes is described. A plot of the logarithm of the distributing species activity in the aqueous phase as a function of its concentration in the non-aqueous phase has an inflection point. The ordinate of the inflection point gives directly the logarithm of the thermodynamic equilibrium constant of the reaction considered. This was made possible by finding that the ratio between n power of the free extractant molecule (or free site) activity and the activity of the distributing species-extractant complex is unity as this point.     

A simple HPLC method for the determination of apigenin in mouse tissues

The flavone apigenin occurs in many leafy vegetables and fruits. It has been reported to have cancer chemopreventive efficacy in rodents. An HPLC method described previously for the determination of tricin, the dimethoxy cogener of apigenin, was modified and validated for measurement of apigenin in mouse tissues. Separation was carried out on a Hypersil-BDS C(18) column (4.6 x 250 mm) with an isocratic mobile phase of 55% methanol in 0.1 m ammonium acetate, pH 5.10, containing 0.27 mm disodium ethylenediamine tetraacetic acid. UV detection was at 336 nm, without interference from endogenous tissue compounds. The assay was linear in the range 25-400 ng/mL, 0.25-4 microg/mL and 2.5-40 microg/mL, with r(2) > 0.99 in all cases, for mouse plasma, liver and intestinal mucosa, respectively. Apigenin in mouse plasma, liver and intestinal mucosa was efficiently extracted with 0.1 m acetic acid in acetone. The assay recovery at low, medium and high concentrations was between 94.6 and 131.7% for all biomatrices, with a relative standard deviation of <10%. The lower limit of quantification for plasma was 25 ng/mL with a relative standard deviation of <15%. The method was used to measure the steady-phase apigenin levels in tissues of mice receiving apigenin in their diet.     

A simple visual method for the determination of phosphorus in environmental waters

Summary The visual method proposed here for the determination of phosphate ion in environmental water samples does not need any instrument. The highly sensitive method is based on the observation of the blue color produced as the result of ion association of phosphomolybdate and malachite green in acidic medium. Down to 10 ppb of phosphate-phosphorus can be determined by addition of 1 ml of reagent solution to 4 ml of sample in a test tube. The method has been effectively used for the determination of phosphate ion which is a nutrient for phytoplakton in brackish lakes and rivers.

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Einfaches visuelles Verfahren zur Phosphorbestimmung in Umwelt-Gewässern

     

A simple approach to determine the equilibrium shape and position of sandwiched polymer droplets

The thermodynamic shape and position of a polymer drop sandwiched between two polymer melt plates were predicted by simulating the change of the interfacial energy according to various shapes and position of the drop. The calculation results were in a precise coincidence with the experimental results exhibiting lens, spreading, and encapsulation. The simple formula and easy concept of the calculation can be useful to predict the morphology of immiscible ternary blends with the information of the interfacial tensions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2729–2738, 2007