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  • Author or Editor: Mieczysław Sajewicz x
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The steadily increasing consumption of popular drugs (e.g. common anti-bacterial, anti-convulsant, anti-hallucinatory, anti-inflammatory, and analgesic formulations) prescribed both in human and veterinary medicine (and sometimes available even without medical prescription) results in growing contamination of the environment by these substances and their metabolites. This contamination is naturally directed through the rivers to the seas and oceans and tends to accumulate in these terminal reservoirs.It was the aim of the work discussed in this paper (i) to establish a simple yet efficient solid-phase extraction (SPE) method for isolation of the drugs josamycin, sulfamethoxazole, carbamazepine, diclofenac, and iopromide from aqueous matrices; (ii) to quantify these compounds by use of densitometric TLC; and (iii) to test the method by applying it to environmental samples (river water from South Poland). The results obtained clearly demonstrate that SPE combined with densitometric TLC is highly suited to this analytical task.

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Tea is one of the most popular beverages in the world. The exact composition of tea depends on the manufacturing process. Our goal was to optimize the chromatographic conditions for separation of tea extract and to apply the optimized method for determination of gallic acid in oolong, black, and pu-erh tea. Chromatographic separation was performed on silica gel 60 F 254 TLC plates with chloroform-ethyl acetate-formic acid, 5 + 4 + 1 ( v/v ), as mobile phase. Densitometric measurement was performed in the ultraviolet region at λ = 280 nm. Quantification of gallic acid in pu-erh tea was also performed by a spectrophotometric method based on the coupled redox complexation reaction occurring in the system Fe(III)-gallic acid-2,2′-dipyridyl ( λ max = 522 nm).

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In our earlier papers we provided indirect experimental evidence strongly in support of our long-established hypothesis that aliphatic ligands on chemically bonded TLC-type stationary phases (i.e. RP-18, RP-8, CN, and Diol) are partially aromatized relatively easily at considerably elevated temperatures (i.e. much higher than 100°C). The first indication of such a possibility was apparent from Raman spectra obtained from these phases by use of a high-power laser-light source emitting in the NIR range. Irradiation of samples of the adsorbents with the NIR light caused their evident heating and the consequent appearance of a predominant Raman band in the so-called aromatic region of the spectra. Later this unexpected, and in some ways disturbing, phenomenon was utilized positively in a new method for Raman spectroscopic evaluation of the density of coverage of the silica matrix with octadecyl ligands.In this paper we report results from an experiment designed to provide more convincing and direct evidence in support of our hypothesis about this partial aromatization. To collect such evidence we had to re-design the procedure used to heat the samples of stationary phase, and to find the most efficient means of extracting and separating the aromatization products. It became obvious that to obtain readily measurable quantities of such products the samples should be heated in a closed system (e.g. in a sealed glass ampoule or in the stainless steel tube which forms part of the apparatus for accelerated solvent extraction, ASE) which prevents the compounds from escaping from the reaction system at high temperatures. We then used two advanced methods of solvent extraction — ultrasonic extraction and ASE — to separate the expected aromatization products from the solid matrix of the adsorbents investigated. Finally, analysis of the extracts obtained was performed by HPLC with diode-array detection. Our results furnish convincing evidence of an efficient aromatization process occurring equally with TLC-type octadecyl and octyl ligands heated at 170°C.

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Chiral separations by gas and liquid chromatography (thin-layer chromatography included) remain an analytical challenge, hence even moderate success in this field is very likely to be regarded as a valuable separation achievement. There has been only one literature report of chiral separation of S -(+)- and R -(−)-ibuprofen by TLC. The original procedure was performed with laboratory-coated glass plates and resolution of the two enantiomers in one-dimensional mode was incomplete. In an attempt to enhance the resolution the authors made use of less convenient and considerably more time-consuming two-dimensional TLC and the final result was not very impressive (Δ R F = 0.03). These chromatograms were visualized by exposure of the developed plates to iodine vapor and no direct confirmation of the identity of the two chromatographic bands was produced.The goals of this study were: (i) to adapt the experimental conditions used for this separation to commercial chromatographic glass plates; (ii) to enhance the resolution of the two antipodes; and (iii) to produce up-to-date UV spectroscopic evidence of successful separation.

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We have previously discussed in detail thin-layer chromatographic studies of the retention of the 2-arylpropionic acids (2-APA) S -(+)-and S , R -(±)-ibuprofen, S -(+)-naproxen, and S , R -(±)-2-phenylpropionic acid. Chiral TLC was performed on commercial silica gel layers impregnated with l -arginine in the cationic form as chiral ion-pairing reagent. Retention and separation of the species was checked by densitometry.In this paper we report the striking skewed migration of these chiral APA in these TLC systems. Scanning of the chromatographic plates at 1-mm intervals revealed that the tracks of the S -(+) and the R -(−) APA can deviate markedly from the vertical in mutually opposite directions. This striking effect in the two-dimensional separation of the enantiomers is most probably caused by stereospecific intermolecular interactions which occur during ion-pair formation between l -arginine in the cationic form, deposited on the silica gel layer as chiral selector, and each individual 2-APA in the anionic form.

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Summary

In many publications on the thin-layer chromatographic analysis of the medicinal plant extracts, striking skewness of the separated chromatographic bands with many phytochemicals can be seen, although no attention has ever been paid to this odd mass transfer effect. In our earlier studies on the thin-layer chromatographic enantioseparation of certain low molecular weight carboxylic acids, lateral relocation thereof (i.e., the side-wise deviation of their migration route from linearity) was registered. Then we found out that lateral relocation was observed with these analytes only, which structurally resembled molecular rotors. In this study, we investigate the role played by the thin-layer chromatographic stationary phases in lateral relocation of botanically relevant molecular rotors. Thus, three carboxylic acids were selected as the test analytes, all of them resembling molecular rotors and abundantly present in the medicinal plant extracts. We selected two most popular thin-layer chromatographic stationary phases also, i.e., silica gel (characterizing with microcrystalline chirality) and alumina (achiral). Lateral relocation of the test analytes was observed on the silica gel stationary phase only. A conclusion was drawn that the chiral stationary phase makes a complementary contribution to lateral relocation (along with the propeller-like molecular structure of the analytes). In our view, specially devised thin-layer chromatographic systems can prove a convenient nano-platform for future investigation of the drug transport patterns, advantageous in the pharmacokinetic studies.

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JPC - Journal of Planar Chromatography - Modern TLC
Authors: Agnieszka Godziek, Anna Maciejowska, Ewa Talik, Mieczysław Sajewicz, and Teresa Kowalska

Spontaneous oscillatory chiral conversion and condensation of low-molecular-weight chiral carboxylic acids have been investigated by our research group for almost 10 years now. However, dynamics of these oscillatory processes substantially differ from one compound to another, moreover, spontaneous chiral conversion and condensation of sulfur-containing amino acids have not been investigated so far. To this effect, we present in this paper the results of our current investigations on spontaneous oscillatory chiral conversion and condensation of l-cysteine (l-Cys), a biologically important sulfur-containing semiessential amino acid. In our thin-layer chromatographic experiments, we employ the Mn(II) and Zn(II) cations to facilitate the enantioseparation of l-Cys from the spontaneously formed d-Cys, to prevent chiral conversion of the L form, and to highlight rapid consumption of Cys in the course of condensation. Spontaneous peptidization of Cys is confirmed with use of thin-layer chromatography-mass spectrometry (TLC-MS). Additionally, we emphasize the oscillatory nature of the investigated process with use of high-performance liquid chromatography-evaporative light scattering detection (HPLC-ELSD) and provide a complementary insight in the chemical structure of the spontaneously formed Cys-derived oligopeptides with use of HPLC-MS.

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Our earlier thin-layer chromatographic and polarimetric investigations enabled discovery of the spontaneous in-vitro oscillatory chiral inversion of the profen drugs S -(+)-ibuprofen, S -(+)-naproxen, and S -(+) and R -(−)-flurbiprofen, etc., and then of the α-amino acids l -phenylalanine, l -alanine, and l -tyrosine. In those investigations, thin-layer chromatography convincingly demonstrated its potential as a flexible and handy tool in the service of physical organic chemistry in general and investigation of organic reaction mechanisms in particular. Later — largely on the basis of thin-layer chromatographic evidence — we proposed a reaction-diffusion model that may provide the core of a mechanistic understanding of the spontaneous oscillatory in-vitro chiral inversion of profens and α-amino acids. In this study, we present thin-layer chromatographic and polarimetric evidence of the analogous process of the oscillatory chiral in-vitro inversion of S -(+)-ketoprofen, which is meant to expand an already existing database, mostly originating from our laboratory and documenting the universal nature of this process with α-substituted chiral propionic acid derivatives (in the first instance, profen drugs and α-amino acids).

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JPC - Journal of Planar Chromatography - Modern TLC
Authors: Jaroslaw Polanski, Mieczysław Sajewicz, Magdalena Knas, Monika Gontarska, and Teresa Kowalska

In our earlier studies on the retention fundamentals in thin-layer chromatography (TLC), we have focused our attention on the important issue which was the deviation from linearity (i.e., handedness) of the chiral analytes’ migration tracks. Presently, this issue is revisited and referred to as lateral relocation of the analytes. We provide new experimental evidence of this striking phenomenon, and as a test mixture, we use (±)-2-phenylpropionic acid. Moreover, we employ three different chromatographic systems, i.e., those based on the bare silica gel layers, and the silica gel layers impregnated with l-arginine and dl-arginine. The observed lateral relocation of the 2-phenylpropionic acid enantiomers is interpreted as a non-linear motion, resembling that of the propeller-like chiral rotors. More general comments are made on lateral relocation and skewed retention of the structurally fit analytes in certain chromatographic systems.

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