which a modifier is located directly after the noun. This particular word order raises some challenging questions, which can be answered only through an accurate analysis of Latin instances and their Hebrew patterns. Discontinuous phrases can be best
Enantioselective hydrogenation over heterogeneous catalysts in the presence of a mixture of two chiral catalyst modifiers [ 1 – 7 ] often results in values of enantiomeric excess which do not follow a linear
of modifiers in the form of CaO, MgO, Fe 2 O 3 , and MnO 2 were explained on the basis of crystallochemical factors connected with the strength of the chemical bonds between the oxygen atoms and framework-forming components and modifiers. Authors
A general equation is presented for modeling retention, using the organic modifier content of the mobile phase. The equation is based on the Box-Cox transform of modifier concentration. Both the semilogarithmic relationship (Soczewiński-Wachtmeister equation) and logarithmic relationship (Snyder-Soczewiński equation) are special cases of the proposed equation. The equation can be fitted easily with free software and an additional coefficient can be interpreted as closeness to the previous models. Even with strong closeness to log-log dependence, the equation still enables extrapolation to zero modifier content. A case study on nine drug-like substances is also discussed, with comparison of 14 previously proposed retention equations found in the literature.
Authors:Qasimullah, Ali Mohammad, and Rizwana Mobin
The works reported in the literature (1994–2015) on the use of surfactants as separation modifiers of organic and inorganic compounds by thin-layer chromatography (TLC) is discussed. A number of adsorbents such as silica gel (plain and modified with surfactants and other compounds), stannous silicate, aminoplast, soil, urea-formaldehyde polymer with cellulose binder, and bismuth silicate have been used as layer materials. Surfactants used for the modification of the mobile and stationary phases in TLC have opened new opportunities for realizing novel separations of analytical importance. The salient features of TLC systems used in the analysis of organic and inorganic mixtures of substances have been provided in the tabular form.
Authors:Grażyna Janowska, Teresa Mikołajczyk, and Magdalena Olejnik
The effects of montmorillonite (MMT) content (1, 3, 5%) and the type of its modifiers on the thermal properties and flammability
of PIA nanocomposite fibers have been assessed. Sodium montmorrilonite was modified with aminododecane acid and octadecylamine.
Samples of PIA nanocomposite containing commercial MMT: Nanomer PGW from Nanocor were also included in the comparative analysis.
It has been found that the glass transition temperature (Tg) of the fibers under investigation depends on the type of MMT’s modifier. On the other hand this parameter does not affect
the thermal stability of fibers defined with T5 and T50 indicators since the thermal decomposition of modifiers takes place at lower temperatures.
The results of testing the flammability of PIA nanocomposite fibers containing 3% of variously modified MMT allow one to include
them among flame-retardant fibers.
Authors:Tatjana Djaković-Sekulić, Nada Perišić-Janjić, and Slobodan Petrović
The chromatographic behavior of
-substituted amides of
-phenylacetic, benzoic, propanoic, and 2,2-dimethylpropanoic acid has been studied in reversed-phase thin-layer chromatography on silica gel impregnated with paraffin oil. Mobile phases used were acetone-water, methanol-water, and dioxane-water.
values were calculated by linear extrapolation of retention to 0% organic modifier for each mobile phase. The relationships between
values obtained with different organic modifiers in the mobile phases are discussed.
values were obtained from the slopes and intercepts of linear relationships between retention and volume fraction of modifier. Correlation between partition coefficient, log
and between log
was examined. Results show that
is a better measure of the lipophilicity of the amides than
Authors:Tatjana Djaković-Sekulić, Nada Perišić-Janjić, Costel Sârbu, and Zagorka Lozanov-Crvenković
Reversed-phase (RP) HPTLC with aqueous ammonia-organic modifier (acetonitrile, dioxane, acetone) mobile phases has been used to study the effect on retention of the chromatographic system and the physicochemical properties of twelve 2,4-dioxotetrahydro-1,3-thiazoles. A multivariate approach to the retention behavior of these 1,3-thiazoles with three quite different organic solvents was used to explain the interactions between the analytes and the mobile phases. Principal-component analysis (PCA) and partial least-squares (PLS) regression were used to determine the molecular properties with the greatest effect on retention for each modifier. Good correlation was obtained between experimental and calculated retention data.
In addition to the fifty pesticides investigated in the first three parts of this study, in this paper plots of
against modifier concentration,
, are reported for chromatography of thirty-one moderately polar pesticides in systems of the type silica-heptane + modifier (ethyl acetate, tetrahydrofuran, and dioxane).