Ljerka Bokić

Optimization of the TLC Separation of Seven Amino Acids

A ternary mobile phase for thin-layer chromatographic separation and identification of seven amino acids on microcrystalline cellulose, with ninhydrin as detection reagent, has been optimized by use of the experimental design software packages Design-Expert 6 and Statistica. When the results from each product were compared the optimum mobile phase was found to be butanol-glacial acetic acid-water 60.14:18.77:21.09. The performance of this mobile phase was confirmed experimentally.

Removal of metal-complex dyestuffs by croatian clinoptilolite

One of the most significant commercial applications of natural zeolites is the removal of metal ions from wastewater1–5. Some metal-complex dyes used for wool dyeing are copper and chromium complexes6,7. Chromium has the advantage over copper because of its greater stability to acids and alkalis. This paper deals with the possibility of eliminating of metal-ions from metal complex dyestuffs after the dyeing process by natural zeolites. The sorption properties of pre-treated and raw clinoptilolite for copper(II) and chromium(III) ions from metal complex dyes were investigated. The copper(II) complexes were prepared with two ligands: a 2-(2-pyridylmethylene-amino) phenol (PMAP) and 2-(2-quinolylmethylene-amino) phenol (QMAP)8. The chromium(III) complexes were prepared with 3-methyl-1-phenyl-5-pyrazolone (C. I. 18744) and 1-amino-2-naphtol-4-sulfonic acid (C. I. 14880). It was shown that various factors influence the Cu2+ and Cr3+ bonding capacities to natural zeolites, including chemical treatment of natural zeolite and particle size of zeolites. This study demonstrated that the pre-treated and raw clinoptilolite can be used as an effective adsorbent for the treatment of wastewater containing copper(II) and chromium(III) ions from metal compex-dyestuff.

TLC separation and identification of heavy metals present in cotton material

Optimization of the separation and identification of heavy metals present in cotton material has been performed by TLC-densitome-try after microwave digestion of cotton samples. The best separation was achieved on precoated microcrystalline cellulose layers with acetonitrile-conc. HCl-water as mobile phase. Optimization of the composition of the ternary mobile phase was achieved by use of experimental design software. Plates were visualized with quercetin-dimethylglyoxime-NH3 reagent. A highly sensitive CCD color video camera was used to capture the chromatograms under white light.

A note on the determination of the binder composition on an historic painted textile

Abstract Sophisticated modern instruments and methods can contribute to the preservation of national and cultural heritage. Modern analytical methods such as chromatography, spectrometry and densitometry are extremely useful, particularly for the analysis of rare works of art from which only very small samples are available. This study describes the identification of the binding medium from a 200-year-old fragile silk banner using thin layer chromatography and video densitometry. The method involved the separation and identification of pure amino acids, vapour-phase hydrolysis of both the reference protein materials and the sample from the banner, and thin layer separation of the components. The separation was achieved using cellulose plates and a mixture of butanol, acetic (ethanoic) acid and water as eluent. The plates were sprayed with ninhydrin solution and then recorded by a Camag video densitometer system. The chromatograms with coloured spots were recorded under white light using a highly sensitive charge-coupled device (CCD) colour video camera. Images were acquired, processed and archived with Video Store 2 version 2.30 documentation software, and analysed using the Vista Scan program. The results for the unknown protein binder were compared with those for the standards. The experimental data identified the proteinaceous binder as an animal glue.

Analysis of waxes on historical samples by thin-layer chromatography

Analysis of the composition of binders applied to different historical objects is an important analytical task. On the basis of the results from this investigation, different cleaning, conservation, and restoration steps may be applied without a danger of damaging the treated materials. Very often the binders are mixtures of natural materials such as waxes, resins, proteins, and sugars. In this work thin-layer chromatography on silica gel 60 F254 plates with petroleum ether–diethyl ether–acetic acid 90:10:1 (v/v) as mobile phase was used to identify the unknown waxes in binding media on several different historical samples. Visualization was performed under UV light at 254 nm. The waxes identified were carnauba, candelilla, and lanolin.

Kinetics of polarographic reduction of pentavalent vanadium in alkaline phosphate buffer solution

Summary The kinetics of polarographic reduction of V(V) to V(IV) in phosphate buffer at pH 9.47 was investigated. An irreversible wave, corresponding to one-electron reduction, is shifted to less negative potentials with increasing concentration and atomic number of alkali metal cations of supporting electrolyte. An evaluation of the following: charge on the reacting particle ( z =−1), electron transfer coefficient (α=0.56), and true rate constant of the electrode process at the half-wave potential ( k =7.9×10 −4 cm s −1 ), was made using Frumkins correction for the double layer effect. The rate of the electrode process was shown to decrease with increasing pH. Chronovoltammetric records suggested insolubility of the reduction product. A reaction sequence is proposed for the electrode process.