TLC separation of some inorganic ions on diethylenetriamine impregnated layers

Summary A suitable TLC method for the separation of Co, Zn, Ni, As, Pb, Cd, Hg, Ag, Th, Se, Sn(IV), Fe(II), U, V, Cu, Ti, Zr and Sb on silica gel impregnated with diethylenetriamine and using ethanol-acetone-acetic acid (70∶50∶20) or (40∶50∶20) as solvent systems and employing 1% K₄Fe(CN)₆ or 0.5% dithizone as visualisation reagents has been developed.     

Batch (one- and two-stage) production of biodiesel fuel from rapeseed oil

Biodiesel fuel is an alternative and renewable energy source, which may help to reduce air pollution, as well as our dependence on petroleum for energy. Several processes have already been developed for the production of biodiesel. Alkali-catalyzed transesterification with short-chain alcohols, for example, generates high yields of methyl esters in short reaction times. In this study, we have evaluated the efficacy of batch (one- and two-stage) transesterification of rapeseed oil in the production of rapeseed methyl ester. The conversion of rapeseed oil exhibited similar reaction patterns and yields in 30- and 1-L reaction systems. Approximately 98% of the rapeseed oil was converted at 400 rpm within 20 min, under the following conditions: 1% (w/w) KOH, 1∶10 methanol molar ratio, and at 60°C. In the 30-L, two-stage transesterification process, approx 98.5% of the rapeseed oil was converted at a 1∶4.5 molar ratio and 1% (w/w) KOH at 60°C for 30 min (first reaction condition), and at a 1∶1 molar ratio and 0.2% (w/w) KOH at 60°C for 30 min (second reaction condition).     

Optimization of enzymatic production of biodiesel from castor oil in organic solvent medium

We studied the production of fatty acid ethyl esters from castor oil using n-hexane as solvent and two commercial lipases, Novozym 435 and Lipozyme IM, as catalysts. For this purpose, a Taguchi experimental design was adopted considering the following variables: temperature (35–65°C), water (0–10 wt/wt%), and enzyme (5–20 wt/wt%) concentrations and oil-to-ethanol molar ratio (1∶3 to 1∶10). An empirical model was then built so as to assess the main and cross-variable effects on the reaction conversion and also to maximize biodiesel production for each enzyme. For the system containing Novozym 435 as tatalyst the maximum conversion obtained was 81.4% at 65°C, enzyme concentration of 20 wt/wt%, water concentration of 0 wt/wt%, and oil-to-ethanol molar ratio of 1∶10. When the catalyst was Lipozyme IM, a conversion as high as 98% was obtained at 65°C, enzyme concentration of 20 wt/wt%, water concentration of 0 wt/wt%, and oil-to-ethanol molar ratio of 1∶3.     

Separation of fat-soluble vitamins by thin-layer chromatography

Summary This paper is dealing with the evaluation of the method for qualitative analyses of fat soluble vitamins by thin-layer chromatography on impregnated starch, cellulose and talc thin layers. Impregnation was carried out with paraffin oil. Complete analyses could be obtained on two plates with two different solvents. Vitamins K₃, K₄ and K₅ were separated with solvent I (water-dioxane-acetone-formaldehyde (85∶20∶15∶25)) whereas the other remain on the start position. Vitamins A-acetate, A-palmitate, K₁, DL-alpha-tocopherol, DL-alpha-tocopherol-acetate, D₂, D₃ were separated with solvent II (acetone-concentrated acetic acid (30∶20)) while K₃, K₄ and K₅ migrate with front. Quick and simple procedures for the preparation of the plates with an impregnated thin layer is given.     

TLC resolution of enantiomeric mixtures of amino acids

Summary Resolution of enantiomeric mixtures of DL-amino acids (Nine) using silica gel layers impregnated with (-)-bruncine is reported. The solvent system used was Butanol: Acetic acid: Chloroform (3∶1∶4). The diastereomers were formed and hydrolysed, by dilute HCl spray, on the chromatogram only and the amino acids thus resolved were located by ninhydrin spray. The cross resolution possibilities of enantiomers were also calculated.     

HPLC separation of hydrogenated derivatives of buckminsterfullerene

Summary The effect of composition and flow rate of the mobile phase on the HPLC separation of hydrogenated buckminsterfullerene (C₆₀H_n n=2–38) was investigated on BuckySep column. Toluene was used as the basic solvent and hexane, heptane, cyclohexane, THF, acetonitrile, acetone, ethanol and 2-propanol as co-solvents. The fraction of co-solvents was varied 10–80%, and the flow rate 1–0.1 mL min⁻¹. Toluene-acetonitrile 65∶35 and toluene-acetone 50∶50 provided the best separation. Under the best conditions complete separation of C₆₀H₂ and almost complete separation of the four most abundant isomers of C₆₀H₄ were achieved. Separation of derivatives with higher hydrogen content was very poor. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997     

HPLC study of the intramolecular cyclization of a new nematogenic molecule. The gas chromatographic properties of the resulting liquid crystal

Summary The internal cyclization of a new phenyldiazene liquid crystal (called A), with an activated methylene group in theortho position to the diazo linkage, has been studied. The kinetics of cyclization were studied at different temperatures and followed by HPLC. Separations were performed on a 30 cm×0.4 cm silica column withn-heptane-tetrahydrofuran-acetonitrile, 190∶20∶5 (v/v), as mobile phase. The Van't Hoff plot (of ln reaction constantk against 1000/T) gives a mean activation energy of 101.3±2.1 kJ mol⁻¹. The analytical properties of A and the final compound B during the decomposition were investigated by gas chromatography on home-made glass capillary columns coated with A. The retention times of the solutes tested became constant when the B/A ratio reached 5, which corresponds to 83% cyclization. The nematic phase of B has interesting properties enabling the separation of the isomers of decalin, the positional isomers of diethylbenzenes and phenols, and some polyaromatic hydrocarbons and their derivatives.     

Evolution of the solvent polarity in an electrospray plume

Solvent polarity plays an important role in electrospray ionization-mass spectrometry (ESI-MS), one of the most widely used analytical methods for biochemistry. To have a comprehensive understanding of how solvent polarity affects ESI-MS measurements, we systematically investigated the polarity change in the ESI plume formed from an ethanol solution using laser-induced fluorescence (LIF) spectroscopy. Two solvatochromic dyes (i.e., dyes whose fluorescence emission is sensitive to solvent polarity), Nile red and DCM (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran), were used as probes. The peak emission wavelengths of these two dyes exhibited significant red shifts (8–12 nm) when the measuring spot was moved away from the spray tip and in radial direction in the plume, indicating a dramatic polarity change during shrinking of the droplets. The emission intensities were also measured with a polarity-insensitive dye as a reference. The results are consistent with the peak wavelength measurements. Two key mechanisms responsible for the change of solvent polarity in the plume were considered, water entrainment from the surrounding air and solvent evaporation. Furthermore, quantitative analysis of the solvent polarity change was performed by using the Lippert-Mataga polarity parameter Δf. The value of Δf reached 0.305–0.307 at the periphery of the ESI plume, which means that the solvent polarity in the smaller droplet is close to that of a mixture of 30% water and 70% ethanol (Δf = 0.307), even though the bulk solvent was ethanol containing less than 1% water as an impurity.     

Influence of injection parameters on column performance in nanoscale high-performance liquid chromatography

Summary The influence of the injection volume and the sample solvent on column efficiency has been evaluated in packed nano liquid chromatography using columns 150μ i.d. Evaluation of column performance was by means of reduced plate height (h) versus reduced velocity (v) for four polyaromatic hydrocarbon test compounds (PAHs). When compounds are dissolved in a weak solvent (such as MeCN: H₂O, 30∶70), and whatever the injection volume −60 or 200 nL-a gain in efficiency can be observed due to the well-known on-column focusing phenomenon, but keeping constant solute retention factors. Under optimized conditions (flow rate: 150 nLmin⁻¹, solvent sample MeCN: H₂O, 30∶70, injection volume 200 nL), a reduced plate height of 1.83 has been obtained for a 15 μm C₁₈ packing corresponding to 36000 plates m⁻¹, which illustrates the absence of any extracolumn band broadening under nano LC conditions.     

Lipase-catalyzed esterification of selected phenolic acids with linolenyl alcohols in organic solvent media

Lipase-catalyzed esterification of selected phenolic acids with linolenyl alcohols was investigated in selected organic solvent media. The enzyme activity for the esterification of dihydrocaffeic acid with linolenyl alcohol in solvent mixtures of hexane/2-butanone of 75∶25 (v/v) and 65∶35 (v/v) was 0.88 and 0.47 μmol of esterified dihydrocaffeic acid/(g of solid enzyme·min), respectively, with a corresponding esterification yield of 76 and 58%, respectively. However, the esterification of ferulic acid with linolenyl alcohol in the reaction medium of hexane/2-butanone of 65∶35 (v/v) resulted in a low yield (16%). Using the reaction medium of hexane/2-butanone of 75∶25 (v/v), an increase in linolenyl alcohol concentration with a concomitant use of a constant amount of dihydrocaffeic acid resulted in an increase in esterification yield. The highest esterification yield of 99% was obtained with a ratio of dihydrocaffeic acid to linolenyl alcohol of 1∶8 after 7 d of reaction. Biosynthesis of the end product, linolenyl dihydrocaffeate, was confirmed by electrospray ionization mass spectroscopy structural analysis; the esterproduct demonstrated an antiradical activity close to that of α-tocopherol.     

A new chromatographic method for the separation of food dye mixtures on thin MgO layers

Summary A new effective TLC method has been developed for the separation of the five main watersoluble food dyes such as indige carmin, cochineal red, acid amaranth I, orange yellow S and tartrazine G. The chromatograms are developed by the ascending technique on thin MgO layers applied onto glass plates, previously activated at 130°C. A 82 mixture of 15% sodium citrate and methanol is used as the developing phase. This composition was selected on the basis of Snyder's theory and the polarity index which for this mixture is 8.3. The proposed method permits the full separation of the dye mixture from a 0.3l sample solution with concentrations of 1×10^–6 mole/liter.     

Separation of amino acids. Possibilities offered by optimized associations of low-voltage electrophoresis and chromatography on finely textured paper and on cellulose thin-layers

Summary Three optimized small-scale methods for amino acid separation are described and compared. Two dimensional separations are based on paper or cellulose thin-layer ionophoresis and chromatography with simple and inexpensive apparatus. The influence of experimental conditions on resolution and amount required for amino acids possessing almost identical mobilities, is studied. The quickest procedure based on the coupling of 200×200×0.25 mm thin-layer, low-voltage electrophoresis (20 V/cm) with chromatography, and the system: cellulose −1.04 mol dm⁻³ formic acid — tertbutanol/methanol/pyridine/formic acid/water (33∶43∶9.6∶0.4∶20), provides very reproducible results with high separating power for small samples (2–10 nmoles).     

Comprehensive separation of iridoid glycosides and triterpenoid saponins from Dipsacus asper with salt‐containing solvent by high‐speed countercurrent chromatography coupled with recycling mode

The roots of Dipsacus asper Wall as a commonly used traditional Chinese medicine are used for tonifying liver and kidney and strengthening bones and muscles. However, an effective separation strategy for comprehensive and rapid separation of the main active compounds from the roots of D. asper is nonexistent. This investigation provided an effective separation method based on AB‐8 macroporous resin column chromatography using different ratios of ethanol in water and two different modes of high‐speed countercurrent chromatography with salt‐containing solvent system for rapid enrichment and separation from the roots of D. asper. The macroporous resin column chromatography was performed on AB‐8 resin using ethanol in water ratios of 10, 30, 40, 50, and 80% as the optimized enrichment conditions for iridoid glycosides and triterpenoid saponins with different polarities. For high‐speed countercurrent chromatography separation, the conventional and recycling modes were combined together to develop a strategy for 12 compounds ( 1 – 12 ) from the enriched parts of 30, 40, and 80% ethanol, including six high‐polarity iridoid glycosides ( 1 – 6 ) using inorganic salt‐containing solvent system and six triterpenoid saponins ( 7 – 12 ). Recycling high‐speed countercurrent chromatography separation was successfully applied to separate two isomers ( 9 and 10 ) after 11 cycles.     

The electronic spectroscopy and photophysics of tropolone and its van der Waals complexes

Studies of the electronic spectroscopy of tropolone in a variety of media are reviewed. Attempts to understand the effects of the surrounding medium on tropolone in its ground and first excited singlet states by studying the spectra and dynamics of its van der Waals complexes are described. The van der Waals complexes studied to date fall into two groups. Those which are primarily dispersively bound exhibit red microscopic solvent shifts, have observable tunneling doublet splittings and have structures in which the solvent species are bound above and below the plane of the chromophore in the 1∶1 and 1∶2 clusters. Those which are primarily hydrogen-bonded exhibit blue microscopic solvent shifts and exhibit no observable tunneling doublets.     

A simplified method for the determination of fenpropathrin residues in fruits

Summary A simple and efficient method is described for the determination of fenpropathrin in oranges, pears, apples and strawberries. The procedure is based on the extraction of each homogenized fruit sample with hexane:acetone (1∶1, v/v) mixture, followed by a cleanup technique on a column packed with florisil, using a hexane:ethyl ether (7∶3, v/v) mixture, and gas chromatographic analysis with electron capture detection (ECD). The fortification levels (0.5;1.0;2.0 mg kg⁻¹) were selected according to the maximum residue limits (MRLs) established for fenpropathrin by Brazilian legislation. Mean recoveries from five replicates of fortified fruit samples ranged from 83 % to 98%, with coefficients of variation from 1.4 to 13.5 and detection limits varying from 0.1 to 0.2 mg kg⁻¹.     

HPLC separations of meropenem and selected pharmaceuticals using a polar endcapped octadecylsilane narrow bore column

Summary Stability indicating high performance liquid chromatography methods have been developed for the assay of meropenem in combination with either dopamine (A), aminophylline (B), metoclopramide (C) or ranitidine (D) in intravenous fluid mixtures. Separations B, C and D were performed on a polar endcapped ODS column (150×2 mm) with aqueous, pH 3.0—acetonitrile (89∶11, 88∶12, and 92∶8) eluent and detection at 270, 290, 317 nm respectively. Meropenem was linear over the concentration ranges 126.88–507.50, 131.25–525, and 131.25–525 gmg mL⁻¹. Aminophylline, metoclopramide and ranitidine were linear over the concentration ranges 13–52, 37.5–150, and 25–100 μg mL⁻¹. Separation A was performed on a conventional ODS column (150×2.1 mm) with aqueous, pH 3.0—acetonitrile (85∶15) eluent and detection at 280 nm. Meropenem and dopamine were linear in the 61.25–245 and 10–40 μg mL⁻¹ ranges, respectively. Accuracy and precision for all methods were 0.20–3.30% and 0.10–1.58%, respectively. Accelerated stability studies have been carried out on each drug by exposure to acid, base, H₂O₂, and heat for different time periods.     

Optimization of the composition and pH of the mobile phase used for separation and determination of a series of quinolone antibacterials regulated by the European Union

Summary To ensure the safety of human food the European Union (EU) has set tolerance levels for quinolone compounds in animal products, so screening and confirmatory analytical methods are required for monitoring of these drugs. In this work, the proportion of organic modifier and the pH of acetonitrile-water mixtures used as mobile phases were optimized for separation of a group of quinolones. Linear solvation energy relationship (LSER) formalism based on the single solvent polarity parameterE _T ^N was used to predict the chromatographic behaviour of the compounds as a function of the amount of acetonitrile in the mobile phase. Correlation between retention and the pH of aqueous-organic mobile phases has also been used to optimize mobile-phase pH. The optimized mobile phase was a linear gradient starting from 18∶82 (v/v) acetonitrileacetate + formate buffer, pH 2.5. Quality data were determined and were satisfactory. The method detection limit was approximately 10 ng mL⁻¹ for most of the quinolones studied. The proposed mobile phase is compatible with mass spectrometric detection of the substances.     

Preparation of mono- and diacylglycerols by enzymatic esterification of glycerol with conjugated linoleic acid in hexane

Esterification of glycerol with conjugated linoleic acid (CLA) was carried out in hexane. Lipase from Rhizomucor miehei provided a high degree of esterification (80%) in 8 h at 50°C when used at 15% (w/w) in a system containing a 1∶2 molar ratio of glycerol to free fatty acids. Esterification levels >80% were obtained in 8 h at 40°C with 15% (w/w) lipase from Candida antarctica at the same molar ratio of reactants. The extent of esterification of CLA was >90% after 4h of reaction at 50°C with a 5% (w/w) loading of either R. miehei or C. antarctica lipase, together with a 1∶1 molar ratio of substrates. Both enzymes incorporated the original CLA as acylglycerol residues in primarily 1,3-diacylglycerol and 1-monoacylglycerol. The CLA-rich acylglycerols can be employed as emulsifiers or as substitutes for natural fats and oils.     

Determination of organophosphorus pesticides and metabolites in crops by solid-phase extraction followed by liquid chromatography/Diode array detection

Summary A multiresidue method for the analysis of 28 common organophosphorus pesticides and 3 of their main metabolites (paraoxon-ethyl, paraoxon-methyl and malaoxon) in a variety of crop samples has been developed. An aliquot of the chopped sample is homogenized with an organic solvent. The efficiency of extraction methods using methanol, acetone and acetonitrile was evaluated. The acetonitrile gives higher recoveries and minimizes co-extractives from the samples matrix. The resulting aqueous acetonitrile extract is filtered and cleaned by solid phase extraction (SPE). For SPE three different types of adsorption materials (Carbograph 1, LiChrobut-EN and Amberchrom CG-161m) were compared. The cleaned-up extract is injected into the LC system. Three different analytical columns were tested in conjunction with two mobile phase compositions of different polarity. The use of LC-DAD techniques allowed the identification of both organophosphorus pesticides and metabolites by means of standard and spectral comparison, respectively. The accuracy of the quantitative determination measured in terms of average percentage recovery of 31 compounds in crop samples was 61–96% with a relative standard deviation of 5–10%.     

Paper chromatography of metal ions in solvents containing methylamine

Summary The effect of methylamine and methylamine hydrochloride has been systematically investigated in the paper chromatography of various metal ions. It has been found that methylamine hydrochloride like EDTA helps in preventing tailing. A new separation of Fe, Mn, Ni, and Co has been developed. The R_f-values are 0.97, 0.49, 0.08, 0.79 respectively and the solvent system used is ethylacetoacetate/methylamine hydrochloride/conc. hydrochloric acid (2027). The values are equally spaced, the spots are compact and the separation is probably the best yet recorded.

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Zusammenfassung Es wird über eine systematische Untersuchung des Einflusses von Methylamin und Methylaminhydrochlorid bei der Papierchromatographie verschiedener Metallionen berichtet. Dabei ergab sich, da\ Methylaminhydrochlorid Ähnlich wie ÄDTA zur Verhinderung der Schwanzbildung benutzt werden kann. Zur Trennung von Fe, Mn, Ni und Co wird ein Lösungsmittel aus Acetessigester, Methylaminhydrochlorid und konz. SalzsÄure (2027) empfohlen (R_f-Werte: 0,97, 0,49, 0,08 bzw. 0,79), mit dem sehr gute Ergebnisse erzielt wurden.