Authors:Virginia Coman, Ștefan Kreibik, Miuța Filip, Mihaela Vlassa and Ioana Perhaița
Thin-layer chromatography (TLC) is a frequently used technique for the separation of polar and non-polar compounds, with a rich literature in this field. The aim of this paper is to show the TLC adsorbent quality of the Nevşehir volcanic tuff from Turkey that is compared with the Mirșid volcanic tuff from Romania. Our experimental investigations have shown that it is possible to achieve TLC plates coated with Nevşehir volcanic tuff, in natural occurrence, excepting grinding and sieving processes, which can be used for the separation of polar compounds, such as amino acids or food dyes. In the present article, modern techniques for characterizing the volcanic tuff powders, namely, X-ray diffraction, inductively coupled plasma–optical emission spectrometry, scanning electron microscopy, specific surface area and porosity measurements, and infrared spectroscopy, were used in addition to the chromatographic testing. TLC plates coated with Nevşehir tuff were prepared and tested at the separation of some amino acids, obtaining good results. Also, the impregnation of Nevşehir tuff with NaOH and NaCl, respectively, allowed the separation of some hydrophilic dyes. The obtained results have contributed to understand the chromatographic properties of the Nevşehir volcanic tuff. The TLC capability of the Nevşehir tuff can enlarge the pallete of inexpensive adsorbents with possible applications in the field of layer chromatographic separations.
Authors:Virginia Coman, Ştefan Kreibik, Mihaela Vlassa, Florina Copaciu, Ioana Perhaiţa and Miuţa Filip
In our previous papers, we defined layer (planar) dielectrochromatography and we presented its fundamentals (theoretical aspects) such as the displacement of dielectric liquids under nonuniform external alternating electric fields (dielectroosmotic flow [DEOF] effect), the displacement of solute particles or polarized granules (dielectrophoresis [DEP] effect) in electric fields generated by armatures, the theoretical evaluation of the electric intensity generated in the stratified dielectrics, etc. Ready-to-use plates of alumina, silica gel, and cellulose were used for experiments. The obtained results have encouraged us to create our own TLC plates based on alumina enriched with compounds of high dielectric constants like barium sulfate, barium titanate, and titanium dioxide. In this paper, we present the preparation of seven plates containing increasing amounts (1, 2, 3, 4, 6, 8, 10) g of barium titanate in 35 g alumina, the methodology used in their characterization, as well as the obtained results and the perspectives of using this ingredient.
Authors:Olivia Măruţoiu, Cristian Tigae, Constantin Măruţoiu, Irina Kacso, Ioan Bratu and Ioana Perhaiţa
Diatomaceous earth from Filia and silica gel RH were chemically modified with trimethoxyethylphenylsilane. The as-obtained compounds have been characterized using covering density, Fourier transform infrared (FTIR) spectroscopy, thermal analysis, and thin layer chromatography. Coverage degree (a) of chemically modified silica gel and of diatomaceous earth are in agreement with literature data. FTIR data have shown the chemical modifications of these two stationary phases. TG-DTA-DTG investigation of chemically modified stationary phases indicates that the exothermic effects can be assigned to the removal of phenyl moiety and also to the water removal from the residual silanols. The analysis of the chromatographic data demonstrates that the separations on ethyl-phenylmodified adsorbents are similar with the ones performed on C8 Merck plates.