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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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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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Thin-layer chromatography (TLC) is a simple, cost-effective, and robust analytical technique, very useful in various different application fields like, e.g., fast screening and quality control of pharmaceuticals, phytochemicals, and alimentary products. Its versatility to a large extent owes to the seminal works of the late Professor Edward Soczewiński and, in the first instance, to the rationale implemented to liquid chromatography by the Soczewiński—Wachtmeister and the Snyder—Soczewiński equations. Among the most challenging applications of TLC, one can name the enantioresolution of the racemic and scalemic mixtures and a statement that the chiral TLC in this particular respect outperforms the instrumentally more advanced chromatographic techniques is far from being an exaggeration. In the course of the past ca. 12 years, the authors of this paper have extensively investigated — mostly by means of chiral TLC — the enantioresolution of the low molecular weight carboxylic acids, to discover by sheer luck that all of them spontaneously undergo an oscillatory process, i.e., chiral conversion. Later, they collected abundant experimental evidence that the oscillatory chiral conversion is accompanied by the oscillatory condensation. Herewith, we highlight applications of the chiral TLC to demonstrate the dynamic phenomenon of the spontaneous oscillatory chiral conversion with the low molecular weight carboxylic acids.

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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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JPC - Journal of Planar Chromatography - Modern TLC
Authors:
Agnieszka Pieniak
,
Mieczysław Sajewicz
,
Krzysztof Kaczmarski
, and
Teresa Kowalska

The aim of the work discussed in this paper was to re-investigate the initial stage of the retention process in TLC, namely the moment of first contact between the analyte deposited at the origin and the mobile phase employed. It was our intention to assess the impact of dissolution of the analyte by the mobile phase on the overall mobility of the analyte in the chromatographic system. To accomplish this goal parallel experiments were performed with analyte samples applied to the stationary phase and chromatographed with and without drying (i.e. with and without evaporation of the solvent used to dissolve the analyte). As test analytes we selected two compounds (5-phenylpentanol and 2-phenylbutyric acid) able to participate in lateral interactions by hydrogen bonding and another four compounds (anthracene, phenanthrene, perylene, and tetralin) totally unable to self-associate. The results obtained are presented in two different ways, i.e. as the dependence of densitometrically measured concentration profiles and of retardation factors ( R F ) on the amount of analyte and on the mode of application (dry or wet) to the stationary phase layer. It was discovered that for both types of analyte (i.e. participating and not participating in lateral interactions) the process of dissolution at the origin is time-consuming and thus contributes to the overall retardation of migration of the analytes.

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The present research is focused on identification of volatile components of different commercial products containing raw herbs of Cistus incanus L. The dried herbal material was hydrodistilled, and the obtained essential oils were analyzed by means of gas chromatography with mass spectrometric detection. Alternatively, the headspace analysis of the volatile sample components was also performed. It was found out that the investigated samples of the C. incanus L. species show a wide variation in terms of quality and quantity of the respective essential oils, which might result in their variable biological activity also. In conclusion, a postulate for standardization of chemical composition of the raw plant material used in therapeutic preparations is formulated.

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Recently, a growing interest has been observed in preventive and “anti-ageing” medicine, accompanied by a dynamic growth of the cosmetic industry worldwide. Different companies compete in introducing the best performing antioxidants to cosmetic preparations and to diet supplements, and in the course of recent years, great attention has been drawn by trans-resveratrol. For economic reasons, the main sources of trans-resveratrol for the cosmetic industry are plants and plant extracts, and the most popular plant is common grape vine (Vitis vinifera L.). The novelty of this study was the development of a simple thin-layer chromatographic method in the reversed-phase (RP) mode with densitometric detection in the fluorescence mode (the irradiation wavelength λ = 340 nm), enabling quantification of trans-resveratrol in selected cosmetic raw materials of natural origin. Cosmetic raw materials considered were red, white, and fruit wines (employed in “wine spas”), commercial extracts of red wines and other fruits, and commercial extracts of grape skins and seeds, making twenty different samples altogether. Prior to thin-layer chromatographic analysis, trans-resveratrol was isolated from the investigated raw materials by means of solid-phase extraction (SPE). The polyphenols fraction adsorbed on SPE cartridges was eluted, and the eluates containing trans-resveratrol (along with other stilbene derivatives) were developed by means of TLC. The chromatograms were densitometrically scanned and trans-resveratrol extracted from raw materials was quantified, based on the calibration curve obtained for the trans-resveratrol standard. The limit of detection (LOD) and limit of quantification (LOQ) values of the developed method were determined as equal to 1.88 and 5.69 ng, respectively. The presence of trans-resveratrol in the analyzed samples was additionally confirmed by visualizing the chromatograms with anisaldehyde as a selective visualizing reagent.

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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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In recent TLC and polarimetric studies we showed, for the first time, the tendency of profen drugs to undergo spontaneous oscillatory chiral inversion in vitro. Because profen drugs are chiral propionic acid derivatives, we sought other chiral compounds with similar chemical structures and hence a similar tendency to spontaneously change their steric configuration. We have previously demonstrated that l -α-phenylalanine and l -tyrosine also undergo oscillatory in-vitro chiral inversion. We also demonstrated the effect of temperature and mixing on the process, and proposed a detailed model of the oscillator, providing the basis for mechanistic understanding of the oscillatory chiral inversion of these compounds. In this study we focused our attention on l -alanine, another amino acid with a chemical structure formally derived from propionic acid, and, again, by use of TLC and polarimetry, investigated the tendency of l -alanine to undergo oscillatory in-vitro chiral inversion when dissolved in neutral, acidic, and basic solvents. We also studied the effect of temperature and sample mixing. It was confirmed that l -alanine also undergoes chiral inversion. The dynamics of the process are specific to each compound.

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