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  • Author or Editor: Tadeusz Henryk Dzido x
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Coccidiostats are a group of drugs used for the treatment of coccidiosis. This disease is common among animals for slaughter. Residues of the mentioned drugs can be potentially harmful for human health, so there is a constant need for cheap and quick method for their determination. A novel sample preparation technique, solvent front position extraction (SFPE), for liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for such a purpose. In the SFPE procedure, the adsorbent layer of a chromatographic plate is used for purification and separation of substances of interest from matrix components. After applying the SFPE technique, solutes and the internal standard are not only separated from unwanted components, but also focused and evenly distributed in the zone located at the solvent front position. From such a zone, the substances can be directly transferred from thin-layer chromatography (TLC) plate to LC-MS instrument using the TLC-MS Interface. Focusing the substances of interest in a narrow zone improves the sensitivity of an assay, while the homogeneity of these zones guarantees their accurate quantification, even if only a part of the substance zone undergoes extraction using a TLC-MS Interface. The SFPE procedure is especially recommended for samples with high viscosity or/and with large amounts of contaminants and enables cleaning a final sample solution from matrix components, showing lower and stronger retention than the solutes of interest. In this work, the application of SFPE procedure for separation of the substances of interest from two biological matrices (bovine serum and animal feed) is presented. The results are promising and allow their application for further research of these compounds.

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Our article presents the comparison of two methods: high-performance thin-layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC), implemented for the separation of a test mixture of purine derivatives. The two methods were compared in terms of separation selectivity and separation time. Our results show that PPEC enables the separation of the mixture (azathioprine, caffeine, theobromine, theophylline and acyclovir) which could not be efficiently separated in the HPTLC system, due to the different selectivities of separation. PPEC also enables to obtain a much faster separation, performed on the longer distance, in comparison to HPTLC. This makes PPEC a technique which can be useful in the analysis of purine derivatives and other drugs.

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JPC - Journal of Planar Chromatography - Modern TLC
Authors: Radosław Łukasz Gwarda, Wojciech Szwerc, Monika Aletańska-Kozak, Anna Klimek-Turek, Andrzej Torbicz, Adam Chomicki, Ryszard Kocjan, Dariusz Matosiuk and Tadeusz Henryk Dzido

In our previous papers, we have mentioned some specific disruption of peptide zones shape and chromatogram distortion, when using mobile phase containing ion-pairing acids. This problem is investigated here. It concerns not only some specific separation conditions but also various separation systems with silica-based adsorbents and water—alcohol mobile phases. We show that the problem results from significant amount of metallic impurities present in the adsorbents investigated. Our results prove that these impurities strongly affect the activity of free silanol groups and thus the retention of basic or amphoteric compounds and the quality of the results obtained. The standard method of washing adsorbent layer with methanol is not effective against the impurities. Washing chromatographic plates with a solution containing an acid significantly reduces the amount of metallic impurities in the adsorbent, resulting in the reduction/elimination of these adverse effects. However, it also leads to the increase of heterogeneity of acidic groups activity and deterioration of separation system efficiency. Therefore, removing metal ions from the adsorbent may not always be advantageous. Avoiding of use of strong ion-pairing acids is also problematic and not always possible. Thus, the production of high-purity silica of homogenous activity seems to be the best and the most reliable solution of the problem described.

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