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Chemistry and Chemical Engineering
A quantitative instrumental high-performance thin-layer chromatographic (HPTLC) method has been developed for assessment of the photodegradation of bensulfuron-methyl on silica gel. The method uses automated band application on to silica gel plates with fluorescent indicator, direct development after irradiation, and scanning densitometry of fluorescence-quenched zones of samples and standards. The accuracy of the analyses was confirmed by performing recovery studies with preanalyzed samples and a blank sample fortified with the analytes. Precision was determined by analyzing samples in replicate; loaded amounts of 500–2000 ng per spot were suggested for assessing the photodegradation of the pesticides. The simplicity of sample preparation and the chromatographic techniques, high sample throughput, high reproducibility, and the strong possibility of separating the photoproducts seem to make the test on HPTLC plates highly suitable for estimation of the photodegradability of pesticides in the adsorbed state.
Homologous series of higher fatty acids, higher alcohols, and methyl esters of higher fatty acids have been separated by RPTLC. The values of R M and of the log P Rek partition coefficient from Rekker for the compounds of the homologous series could be correlated with numerical values of topological indexes based on the adjacency matrix (M, °χ, 1χ, °χν, 1χν ), and on the distance matrix (W, A, °B,1B). The most accurate prediction of the R M and log P Rek values of the compounds investigated was achieved by use of monoparametric equations containing one topological index based on the adjacency matrix.
Two-dimensional thin layer chromatography of twelve flavonoids and three phenolic acids from Betula sp. leaves has been performed in normal-phase systems. Plots showing the dependence of RM on modifier concentration in some non-aqueous systems were used to optimize the chromatographic separation. RM values were correlated for all the chromatographic systems investigated and optimum pairs of systems were then selected for use in two-dimensional TLC separations. Complete separation of the compounds investigated was achieved by use of two optimum non-aqueous mobile phases on silica plates.
The normal-phase (NP) and reversed-phase (RP) thin-layer chromatographic separations of aminoglycosides (streptomycin, kanamycin, gentamycin, and tobramycin) have been investigated on silica gel and C18 plates, respectively. The mobile phase acetone–2% sodium acetate–acetic acid–butanol, 7 + 6 + 4 + 1 (v/v) was successful for NPTLC and acetonitrile–5 mM sodium acetate buffer (pH 4.6) 4 + 18 (v/v) for RPTLC. The spots were located by use of iodine vapor. The minimum detection limits were in the range 0.4–0.6 μg. The method is a simple and direct approach for detection which does not require pre- or post-chromatographic derivatization.
Complexes of hydroxy- and alkyloxytetraphenylporphyrins with Cu (II), Zn (II), and Ni (II) have been prepared and their chromatographic behavior in adsorption and partition thin-layer chromatography has been investigated. Gutman topological indexes, Mν, and the screening effect, SE, of the hydrocarbon chains on the electron pairs of the oxygen atoms of –OR groups have been calculated for the metalloporphyrin derivatives studied. The correlation between these and chromatographic retention, expressed as RM values, has been studied.
Planar electrochromatography (PEC) is a mode of planar chromatography in which the mobile phase is driven by electroosmotic flow. The variables that affect the performance of PEC with an aqueous mobile phase on a bonded octadecylsilyl layer are discussed. These include the magnitude of the applied electric field, the concentration of the buffer salt, the pH of the mobile phase, and the concentration of acetonitrile used as the organic modifier. The effect of changing each of these variables is illustrated by model separations of a mixture of four compounds of diverse structure.
Planar chromatographic methods thin-layer chromatography (TLC) and over-pressure thin-layer chromatography (OPLC) have been developed for the determination of pigments in plant leaves. Plants with variegated leaves, which sometimes contain both anthocyanins and chlorophyll, are a reasonable material for investigation. Multicolored Coleus, Prunus cerasifera, and Rhus hirta leaves were taken for quantitative determination of anthocyanins and chlorophyll. The separation of pigments from plant leaves, which depends on compound polarity was optimized by appropriate selection of mobile and stationary phases and chromatographic conditions.
The chromatographic behavior of fullerene C60 has been studied on silica gel layers impregnated with solutions of glucose, sucrose, fructose, and dextrans of MW 20, 40, and 110 kDa, and with hexane as mobile phase. It was found that the RF of fullerene decreases as the concentration of impregnating solution is increased. The retention of fullerene C60 changes to a smaller extent when dextran solutions are used.
The solid-phase interaction of fullerene with the carbohydrates sucrose and dextran was studied by use of differential scanning calorimetry (DSC) and by NMR and UV-vis spectroscopy. The interaction with sucrose is greater than that with the dextrans.
Correlation was observed between the chromatographic behavior of C60 fullerene and the solid-phase interaction of the compound with carbohydrates.
Carbohydrates have been examined by TLC on layers modified with metal ions, in the form of salts, by dipping commercial plates in methanolic solutions or by use of mobile phase additives; the mobile phases were mixtures of acetonitrile, propan-2-ol, or acetone with water or aqueous solutions of the metal salts. The effect on spot shape and retention of the identities and concentrations of the metal ions used for impregnation are discussed, and the selectivity of the different systems investigated are compared. The chromatographic properties of the adsorbents used were compared by consideration of the relationships between RM values measured on the different layers.
In normal TLC practice, migration of the mobile phase through the layer is controlled by capillary forces. Under these conditions the velocity at which the solvent front moves is a function of the distance of the front from the solvent entry position, and this velocity declines as the distance increases. In this work we have proved that the velocity and migration distance of the mobile-phase front in porous media can be increased by application of an external electric field. We have called this displacement effect on liquids ‘dielectroosmotic flow’ (DEOF), because of its similarity with electrokinetic phenomena. Capillary tubes were used to enable understanding of the flow phenomena which occur in porous media.
A stand-alone argentation TLC (Ag-TLC) procedure has been established for rapid estimation of the authenticity and densitometric quantitation of fatty acid groups in milk fats. The applicability of methyl (ME) and isopropyl (IPE) ester derivatives for accurate short-chain fatty acid analysis by Ag-TLC and GLC was compared and a correction coefficient compensating for loss of C4–C10 saturated fatty acids has been proposed. To check its accuracy and reproducibility the method was applied to model mixtures and to real margarine and butter samples. Low levels of trans fatty acids can be unequivocally detected and amounts down to 0.2% can be measured precisely. The method gives a good estimate of the diversity of isomeric fatty acids in the samples and when precautions are taken to avoid overloading, it provides reliable results with good accuracy.
A simple and reliable HPTLC method has been developed and validated for the determination of dexamethasone (as the sodium phosphate salt) and xylometazoline (as the chloride). Assay of the compounds was performed on silica gel HPTLC plates with spherical particles by development with the mobile phase ethyl acetate–acetonitrile–diethylamine–water, 3 + 3 + 1 + 1 (v/v). A TLC scanner set at λ = 240 nm was used for direct evaluation of chromatograms in reflectance/absorbance mode. The validation data linearity (R > 0.996), precision (RSD = 1.67–2.77%), accuracy (recovery = 95.95–100.69%) and LOD and LOQ (ng levels) were determined and found to be satisfactory.
Assay of dexamethasone and xylometazoline in nasal drops was performed simultaneously with assay of preservatives such as methyl para-hydroxybenzoate. The effect of the most commonly used preservative, benzalkonium chloride on the concentrations of active substances was investigated; it was found that this compound led to a significant reduction of the dexamethasone sodium phosphate content of nasal drops.
A method developed for quantitative determination of the total amount of polyaromatic hydrocarbons (PAH) in human hair has been applied to the analysis of smokers’ hair. The procedure involves washing the hair with dichloromethane, acid decomposition of the hair matrix, micro-liquid extraction, and HPTLC determination of total PAH concentrations in the whole extract. The concentrations of PAH in human hair were in the range 0.005–0.3 μg g–1 hair.
High-performance thin-layer chromatography (HPTLC) on silica plates, with two successive mobile phases, has been used for analysis of seven amine azo dye isomers prohibited under a German ban. Dichloromethane was used for the first development, to a distance of 4.5 cm. After drying, the second development was performed with toluene–tetrahydrofuran, 10 + 1 (v/v), to a distance of 8.5 cm. Spots were visualized at λ = 254 nm. Eighteen amines have been studied by use of the method. The limit of determination (X) and the correlation coefficient in the range X to 5X are reported for each amine. To increase the sensitivity of detection, the UV spectrum was acquired for each amine and the wavelength of maximum absorbance (λmax) was used to establish the limit of determination. Synthetic mixtures and dye samples have been resolved and quantified.
This paper reports a recently developed technique, coupling of optimum-performance laminar chromatography (OPLC) with online radioactivity detection (OPLC–RD). Sample preparation for purification of urinary metabolites of a 14C-labeled drug candidate was performed on octadecyl-modified silica solid-phase extraction columns. Optimum-performance laminar chromatography was conducted on aluminum-backed silica gel layers with butanol– acetic acid–water as mobile phase. Eluate radioactivity was detected by use of a flow-cell radioactivity detector equipped with solid scintillator, and eluate fractions containing radioactivity were collected. Strongly retained radioactive components were detected off-line after development by use of digital autoradiography (DAR).
The isolated fractions containing metabolites were further purified by reversed-phase high-performance liquid chromatography coupled with radioactivity detection; this provided a second dimension for additional selectivity. Purified metabolite fractions were submitted to structure elucidation by spectroscopic methods.
The novel on-line optimum-performance layer chromatography with radioactivity detection, combined with high-performance liquid chromatography with radioactivity detection and digital autoradiography techniques, the advantages and disadvantages of which are discussed in detail in this paper, provides a rapid, effective, and economic tool which can be applied to advantage in metabolism research.
In this paper we report our most recent experimental results relating to the thermal instability of selected alkyl chemically bonded stationary phases. The phenomenon of the thermal instability of such phases, as a result of their irradiation with a high-power neodymium laser, the light source of a Raman spectrometer, has been demonstrated in a series of our earlier publications. We even established a novel method of estimating the density of coverage of the silica matrix with alkyl ligands by utilizing the thermal instability of the phases discussed. The mechanism of the thermal transformation of alkyl chemically bonded ligands remained rather obscure, however, vague speculations only were made about the possible aromatization of these ligands.
In this paper we provide additional experimental evidence in support of our earlier hypothesis about possible aromatization of alkyl ligands on the surface of the acidic/basic silica matrix under the influence of high temperature. This evidence was obtained by use of instrumental techniques such as Raman spectroscopy, differential scanning calorimetry (DSC), and UV absorption spectroscopy. Although all these techniques supply indirect evidence only, the results reported furnish a convincing confirmation of our earlier intuitions.
The effect of cold-stress (2°C, 7 days cold-hardening) on the level of polyamines in different varieties of wheat and genetically modified wheat samples (chromosome substitution lines, deletion lines, recombinant lines) has been investigated. Biogenic amines (spermine, spermidine, putrescine, and agmatine) were determined as the dansyl derivatives by stepwise gradient elution with the Personal OPLC BS 50 Chromatograph. Short-term cold-hardening caused characteristic changes in free polyamine content of wheat genotypes. The total free polyamine content was significantly lower in the cold-hardened samples than in the control samples. It seems that accumulation of spermine and agmatine might be good markers of cold sensitivity.
A quantitative thin layer chromatographic (TLC) method on silica gel, with ethyl acetate–acetone–alcohol, 62 + 40 + 3 (v/v) as mobile phase, has been developed for the determination of olaquindox at ppm levels in animal feed. Preliminary purification consists of extraction with water, adsorption on XAD-4, washing, and elution with acetonitrile. Before the elution step acetylolaquindox is added as internal standard. The residue obtained after evaporation of acetonitrile is dissolved in a small volume of methanol. Quantitation is performed by densitometry at λ = 360 nm.
Abstract
A modified QuEChERS method using a GC-ECD to determine the multiple residues of pyraclostrobin, difenoconazole, dimethomorph and azoxystrobin and to indirectly determine the total residues of maneb, mancozeb and propineb by a GC-FPD (with an S filter) was established and validated. Meanwhile, field trials were conducted in accordance with good agricultural practice (GAP) to study their characteristics of residue degradation under the agricultural climate and cropping system of Guangxi Province. The separation effect of each target peak was good with a linearity range of 0.01–5 mg L−1, a limit of detection (LOD) of 0.003–0.015 mg kg−1 and a limit of quantification (LOQ) of 0.01–0.05 mg kg−1. The average recovery ranges of vegetable tomatoes and cherry tomatoes were 70.5–120.0% and 70.8–119.8%, respectively, with relative standard deviations (RSDs) of less than 7.1%. Field trials of seven fungicides in vegetable and cherry tomatoes showed that the half-lives (t 1/2 ) of the dithiocarbamate fungicides (metiram, mancozeb, and propineb, defined as total residues determined as CS2), pyraclostrobin, difenoconazole, dimethomorph, and azoxystrobin were in the ranges of 5.2, 12.7–17.8, 7.6–7.9, 6.6–6.9, and 6.3–6.6 d in vegetable tomatoes, respectively. The cherry tomatoes presented ranges of 4.3–4.5, 10.8–11.8, 6.7–7.0, 5.4–5.5, and 5.9–6.2 d, respectively. Combined with the final residue and market monitoring results, the results show that cherry tomatoes have significantly higher terminal residues, initial deposits, and maximum residues of seven fungicides than vegetable tomatoes, and these seven pesticides can be detected in cherry tomatoes purchased from three markets. Therefore, cherry tomatoes may be regarded as representative varieties of tomatoes in realizing residual extrapolation for the establishment of the maximum residue limit (MRL) value of fungicides in tomatoes and for conducting market monitoring.
The chromatographic behavior of six macrocyclic antibiotics (erythromycin, troleandomycin, tylosin, vancomycin, rifamycin B, and rifampicin) has been examined on Polyamide 11F254 TLC plates as stationary phase with five binary solvent mixtures (methanol–water, ethanol–water, propanol–water, acetonitrile–water, and tetrahydrofuran–water) as mobile phases in which the concentration of the organic modifier was from 0 to 100% (v/v). Chromatographic retention data and a possible retention mechanism are discussed.
The retention behavior of twenty-four alkaloids has been investigated in normal-phase systems on thin layers of aminopropylsilica and bare silica developed with a variety of binary mobile phases prepared from n-hexane and polar modifiers – 2-propanol, ethyl acetate, methyl ethyl ketone, tetrahydrofuran, dioxane – in different concentrations. The retention factors obtained were fitted to the logarithmic Snyder–Soczewiński equation; the results are presented as the equation parameters and the statistical coefficients which prove the goodness of fit of the results with the displacement theory of retention.
The retention behavior of the alkaloids was also investigated in reversed-phase systems with buffered aqueous–acetonitrile mobile phases (pH 9.15) and the cyanopropyl- and octadecylsilica as stationary phases. Retention factors obtained for use of different concentrations of acetonitrile in the mobile phase were fitted to the semi-logarithmic equation or to quadratic polynomial equation selected for RP systems and are also presented as equation parameters and statistical coefficients which prove the goodness of fit of the results obtained with the theories derived for RP systems.
Separation selectivity was presented as the RF spectrum for the aminopropyl phase, comparing the separation selectivity obtained by use of different mobile phases, and as RF1 vs RF2 correlation diagrams for different systems, enabling selection of the most selective systems for separation of particular pairs or groups of alkaloids. Such correlation diagrams are presented for the aminopropyl phase and silica with four non-aqueous mobile phases and also for CN-silica and C18 phases, and for CN-silica and diol phases with aqueous mobile phases.
The thin-layer chromatography of eighteen anions has been performed on silica layers with mixed aqueous–organic mobile phases. Binary mobile phases consisting of distilled water and acetone or acetonitrile were found suitable for resolving hexacyanoferrate(II) from hexacyanoferrate(III) or thiocyanate whereas ternary solvent systems consisting of distilled water, carbon tetrachloride, and acetonitrile was found most suitable for separating ternary mixtures of hexacyanoferrate(II), hexacyanoferrate(III), and thiocyanate. Distilled water–acetonitrile–carbon tetrachloride, 10 + 80 + 5, was the best mobile phase for separation of three-component mixtures of these anions in the presence of heavy metal cations and amino acids. The proposed method works well for the separation of Fe(CN)6 4–, Fe(CN)6 3–, and SCN– from industrial waste water, saline water, hard water and fixer and bleach samples.
Combined technology for the synthesis, separation, screening, and analysis of combinatorial libraries is described. The technique enables a rapid route from synthesis to the testing of chemical compounds. Chemistry can be rapidly optimized and vital information obtained by testing by-products and reagents simultaneously if desired. Screening can be performed without need for reaction work-up and without the need for undesired chemical manipulation, or further handling. Emphasis has been given to bioautographical/agar overlay screening methods for the testing of antimicrobial agents.
Abstract
There has been a lively interest on macrocyclic polyamine alkaloids due to their remarkable pharmacological activities such as anti-tumor, anti-inflammatory, anti-Alzheimer's disease and anti-parasitic. Tripterygium wilfordii is a widely used traditional Chinese medicine, which is abundant in alkaloids including macrocyclic polyamine alkaloids. However, there are rarely studies on macrocyclic spermidine alkaloids of T. wilfordii so far. In this article, we use three known macrocyclic spermidine alkaloids celafurine, celabenzine and celacinnine, and successfully develop a simple and sensitive HPLC method for simultaneous quantification of macrocyclic spermidine alkaloids in root, stem and leaf of T. wilfordii.
Abstract
β-sitosterol (BS) and lupeol (LU) exhibit a number of biological activities and are the important bioactive marker compounds in pharmaceutical science. In the present study, a simple, precise, accurate and validated high performance thin layer chromatographic (HPTLC) method was developed for simultaneous quantification of these two compounds in leaves, stem and roots of Uraria picta, a critically endangered medicinal plant and one of the important constituents of ten plants ayurvedic formulation called Dashmoola. Standards and test samples were applied on TLC aluminum plate precoated with 0.2 mm layer of silica gel 60F254. The plate was run in a twin glass chamber comprising toluene: methanol: chloroform (8:1:1, v/v/v) as a mobile phase. The plates were immersed in anisaldehyde-sulfuric reagent and then heated at 105 °C for 5 min in CAMAG TLC plate heater for appearance of bands. Densitometric scanning was performed at λ max = 525 nm using tungsten light source in CAMAG TLC Scanner4 armed with WinCATS software. R F values of BS and LU standards and those of test samples were found to be 0.53 ± 0.01 and 0.63 ± 0.01 respectively. The method was further validated by following the International Conference of Harmonization (ICH) guidelines. For BS and LU, the linear regression data for the calibration plots revealed a satisfactory linear association with r 2 = 0.995 and 0.998, respectively. Linear range for both BS and LU was 200–600 ng/band. Accuracy of the method was evaluated by performing recovery study at three different levels by standard addition methods with an average recovery of 99.86% and 101.07%. The results revealed that the leaf samples of U. picta contained highest concentration of BS (0.150 ± 0.02%) while its root samples confined the highest concentration of LU (0.149 ± 0.01%). The developed method can be applied for routine and quality control analysis in different herbal formulations containing U. picta species.
A new simple, precise, rapid, and selective high–performance thin-layer chromatography (HPTLC) method has been developed for the analysis of finasteride in pharmaceutical formulations. The method uses loratadine as an internal standard. The stationary phase was silica gel 60F254 prewashed with methanol; chloroform–ethyl acetate, 6 + 4 (v/v) was used as mobile phase. Detection and quantification were performed densitometrically at λ = 228 nm. The linear range of the analysis was 0.2–2.0 μg and the percentage recovery was 101.8%.
A high-performance thin-layer chromatographic method with densitometric detection has been used to determine the convallatoxine content of extracts from the various parts (flowers, leaves, and underground parts such as the rhizomes and buds on the rhizomes) of the plant. Plant extracts were separated on thin layers of silica gel Si 60F254 by multiple gradient development. The convallatoxine content was determined by densitometry and the results were evaluated statistically.
This review covers the use of topological indexes based on the adjacency and distance matrixes to predict the R F and R M values, and the physicochemical properties, of a variety of groups of organic compounds investigated by TLC. This review indicates that further investigations on the application of the topological indexes in TLC are justifiable.
The solvation parameter model has been used to characterize the retention properties of a varied group of solutes in silica gel thin-layer chromatography (TLC) and in silica gel and alumina column liquid chromatography. The model was unable to describe retention on silica gel TLC plates with the R M value as the dependent variable for five single-solvent mobile phases. The results were improved by fitting the retention data to the simple competition model and separating the solute and solvent contributions (denoted S and eºA S, respectively) to the free energy of adsorption on the inorganic oxide. Separate models were then constructed to enable estimation of values of S and A S from structure. These models were successful in describing retention in column liquid chromatography on silica gel with mixtures of methyl t-butyl ether and hexane as a mobile phase. This approach proved less reliable for calculating retention in TLC, probably because of non-equilibrium in the separation system. Evidence is presented that neither the solute adsorption parameter (S) nor the solute cross-section (A S) as used in these studies is unambiguously defined. Further refinements aimed at establishing clearly defined solute and solvent adsorption terms, and possibly including selective solute–solvent interactions in the mobile phase as a secondary contribution to retention, could result in improved model performance. The approach described here should be considered preliminary and thought of as a stepping stone in the direction towards a comprehensive model for structure-driven method development in normal-phase separations, which are currently less developed than models available for reversed-phase separations.
Persilben (3,5-methoxy-2-hydroxy-E-stilbene) was satisfactorily separated on thin layers of silica gel, by use of two-step gradient elution, and quantified by densitometric techniques. The results were evaluated statistically. Eight acetone extracts from herbs and rhizomes of six taxons of Polygonum L. genus: P. lapathifolium ssp nodosum (Pers.) Dans., P. lapathifolium ssp. tomentosum (Schrank) Dans., P. hydropiper L., P. bistorta L., P. amphibium L., P. convolvulus L. (Bilderdykia convolvulus L.) were studied. Persilben was detected in the herbs of five taxons of Polygonum L. The amounts of the compound ranged between 46.3 and 174.2 μg g– 1 dry herbs.
A new horizontal sandwich chamberis described in this paper. Mobile phase can be applied to any part of the plate by use of this chamber. This has enabled a new mode of development in TLC, in which the starting position of development can be anywhere instead of at the origin; we therefore call this new mode ‘half-way development’. Compared with traditional development, the new mode can be used to develop any separated spot again. Many other modes of development can also be performed with this chamber, for example relay development on an over-length plate, programmed multiple development, gradient development, band application, concentration, and micropreparative separation. These methods are simple and convenient and give good results.
Mixtures of dyes have been used to verify above supposition with the above-mentioned methods. The results obtained are satisfactory.
A thin-layer chromatographic and densitometric method has been developed for the identification and quantitation of gliclazide and its impurities on silica gel, using chloroform–methanol, 19 + 1 (v/v), as mobile phase. UV densitometric measurements were made at λ = 226 nm. The method is characterized by high sensitivity (15 ng), linearity over a wide concentration range (0.06 to 0.30 mg mL– 1), and high recovery (100.23%). It was found that the established conditions can be also used for determination of impurities in medicines.
Molecular interactions have been evaluated in liquid adsorption chromatography with mixed mobile phases. Two equations based on different retention mechanism models were verified experimentally. The parameters of both equations were calculated and interpreted. The parameters described the association phenomenon in analyzed systems. Solvation effects were taken into account. These effects were confirmed by use of two independent theories and two independent equations. The equation parameters were calculated for test substances in four chromatographic systems in which solvation phenomenon was present or not. A linear relationship was found between parameters analyzed. Chromatographic measurements were obtained by use of thin-layer chromatography.
This report describes the TLC separation of two classes of chiral drug, including β-blocking drugs and non-steroidal anti-inflammatory drugs (NSAID) on molecularly imprinted chiral stationary phases, in the same way as has been performed by HPLC. Several molecularly imprinted polymers (MIP) were prepared using the enantiomers of either the β-blocking drugs, R-(+)-propranolol, R-(+)- or S-(–)-atenolol, or the NSAID, S-(+)-naproxen and S-(+)-ibuprofen, as print molecules. Three different functional monomers, ITA, MAA, and VPD were employed in the imprinting process. The polymers prepared in the presence of MAA or VPD could be coated as thin layers on glass supports, but not those prepared in the presence of ITA. The MIP of R-(+)-propranolol, with 5% acetic acid in acetonitrile as mobile phase, resolved the racemate of propranolol into two spots, but tailing spots were obtained. The MIP prepared from S-(+)-naproxen, with 1% acetic acid in THF–heptane, 1 + 1, as mobile phase, resolved the racemate of ketoprofen into enantiomers, with a good separation factor (α = 5.2).
Gradient thin-layer chromatography and densitometry have been used for qualitative and quantitative analysis of caffeic acid in some Dipsacaceae family plants. The presence of caffeic acid was determined in complex plant extracts before and after acid hydrolysis.
By use of pH 6.0 acetate buffer a mixture of Chelidonium majus L. alkaloids has been separated, on a classical silica column, into two groups, tertiary and quaternary alkaloids. The relationships between R F and the concentration of methanol in the acetate buffer suggested it was possible, by gradient elution in which the concentration of methanol in the pH 6.0 aqueous acetate buffer was increased, to separate the quaternary alkaloids further into fractions containing 2 or 3 alkaloids. These fractions were then separated by micropreparative zonal thin-layer chromatography. Sanguinarine and chelerithrine of high purity were obtained.
A computer-driven office scanner has been modified to enable measurement of the fluorescence of aflatoxins on thin-layer chromatography (TLC) plates. The main modifications were substitution of the light tube with a black light tube and inclusion of a filter. The strategy behind this modification, and its problems, are discussed. The modified scanner can be used to determine aflatoxins at low nanogram levels, which, when used in combination with an appropriate TLC method, enables monitoring of the compounds in food and feed at the levels stipulated in European legislation.
The chromatographic behavior of calix[4]arene, 4-tert-butylcalix[4]arene tribenzoate, 4-tert-butylcalix[5]arene, and pyrene have been studied. Chromatography was performed on K-60 and RP-18 wettable with water TLC and HPTLC plates under isothermal conditions (303 K). Methanol, ethanol, and acetonitrile and their binary mixtures with water were used as mobile phases. The ranges of mobile-phase compositions in which retardation factor (R F) values were equal to zero were wider for alcohol–water mixtures than for acetonitrile–water mixtures. Plots of R M against the mole fraction of acetonitrile in water (0.19 ≤ X S ≤ 1.00) were linear for all the solutes investigated. The best separation of the calixarenes was obtained by use acetonitrile–water mobile phases and RP18W plates.
Levels of formaldehyde, formed within the cells of plants, animals, and man, are related to the physiological state of an organism. We have previously reported the possibility of determining the formaldehyde content of human teeth in some physiological states, and it was established that the level of HCHO in carietic teeth is higher than in healthy teeth. The aim of the work described in this paper was the OPLC determination of HCHO levels in teeth suffering from eight different rare pathological disorders. It was shown that significantly different levels of formaldehyde were present in teeth in different pathological states. The highest HCHO content was observed in teeth with acute inflammatory changes. The lowest level was found in teeth with no inflammatory changes.
A new TLC procedure has been developed for the purification, separation, and isolation of paclitaxel and cephalomannine from yew twigs. Preliminary purification of the taxoid fraction from non-polar ballast (chlorophylls and waxes) and highly polar components is possible by use of an alumina column and stepwise gradient elution with dichloromethane–ethyl acetate containing different proportions of methanol. The application of zonal TLC on silica with dichloromethane–dioxane–acetone–methanol as mobile phase enables enrichment of the paclitaxel- and cephalomannine-containing fraction. Isolation from the fraction containing paclitaxel and cephalomannine was achieved by TLC on silanized silica gel with methanol–water as mobile phase.
The Eurachem/Citac Guide on measurement uncertainty establishes general rules for evaluating and expressing measurement uncertainty across a broad spectrum of measurements and presents a special calculation procedure called the ‘error-budget approach’. In this work the error-budget model has been tested using the quantitative HPTLC determination of sodium glutamate in a food product as an example. The TLC procedure was divided into stages, each of which was evaluated. The cause-and-effect diagram was constructed and possible sources of uncertainty were listed. We found that the dominant sources of uncertainty were sample preparation, chromatographic separation, secondary chromatography, stability of instrumentation, inhomogeneous illumination, distribution of compound molecules in the stationary phase, and the relative position of spots and scanning slit, among others. The uncertainty estimated by means of the error-budget method was less than one fifth of the value obtained from the validation study. The contribution from sources selected and processed according to the Citac guide is so small that it can be neglected.
