Separations in Thin Layer and High Performance Liquid Chromatography Using Alkyl Silica Gel Bonded Phases

Abstract

Separations in thin layer (TLC) and high performance liquid chromatography (HPLC) using alkyl bonded phases were carried out under optimum solvent conditions for each of three phases, RP-2, RP-8 and RP-18. The phases were tested for their efficiency and resolving power using three groups of compounds in three binary organic-water mobile phases. The organic solvents were acetonitrile, methanol and tetrahydrofuran, which are widely used as solvent modifiers in reversed phase liquid chromatography.

The results showed that, unlike HPLC, TLC using RP-18 plates was the most, and RP-2 plates the least, efficient. A naphthalene and biphenyl mixture which was resolved by HPLC using any of the three solvents and columns was not resolved by TLC using any plate or solvent combination, unless the plate was prewashed with an organic modifier. The addition of NaCl (1–2% wt/vol) to the solvent for TLC speeded development unless an alcohol was used, but did not greatly affect the separation.     

Solid-liquid extraction strategy on the basis of solvent characterization

Summary Different solvents used for extraction are characterized on the basis of the Snyder theory. The individual solvent strength (s_i) and selectivity values (s_v) of the solvents are used to formulate an extraction strategy by use of selected solvents, in a manner similar to that used for the computer-aided HPLC and TLC “PRISMA” mobile phase optimization procedures. After a pre-assay using the nine proposed solvents, twelve measurements are necessary to obtain the global optimum. The new method allows successful solid-liquid extraction of compounds from biological matrices such as medicinal and aromatic plants. Data obtained from furocoumarin isomers and flavonoid glycosides extracted from different medicinal and aromatic plants are used to demonstrate the validity of the method. The structures and properties of the compounds to be extracted do not have to be known for the procedure to be used. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Separation of Alkaloids from Datura Metel. and Sophora Flavescens Ait by High-Speed Countercurrent Chromatography

Abstract

High-speed countercurrent chromatography was successfully applied to the separation of alkaloids from two medicinal herbs. Matrine and oxymatrine were isolated from the root of Sophora flavescens Ait with a two-phase solvent system composed of chloroform-0.07 M sodium phosphate (pH 6.4), while atropine and scopolamine were purified from the flowers of Datura mete L. with a similar solvent system by modifying the phosphate buffer pH at 6.5. Identification of each alkaloid was made by either TLC or paper partition chromatography using authentic pure compounds.     

Pressurized liquid extraction and anticholinesterase activity-based thin-layer chromatography with bioautography of Amaryllidaceae alkaloids

Modern extraction technique-pressurized liquid extraction (PLE) was optimised for extraction of lycorine and galanthamine (Amaryllidaceae alkaloids) from Narcissus jonquilla ‘Pipit’. Crude extracts were purified on Oasis MCX cartridges, and the alkaloids eluted with 80-100% recoveries using methanol-10% ammonia solution (3:1, v/v). Quantitative results were obtained by both HPTLC-densitometry on silica gel plates and RP-HPLC with diode array (DAD) on XTerra C₁₈ stationary phase. Both methods were fully validated in terms of specificity, precision (including intra- and inter-day measurements), LOD and LOQ values, correlation of UV spectra and linearity of calibration curves. The methods were also well correlated each other with correlation coefficients (r) 0.98823 and 0.99081, respectively, for the mean values of galanthamine and lycorine.Among the investigated solvents methanol and 1% tartaric acid methanolic solution at default conditions (120 °C, p = 60 bar, time: 10 min, one static cycle) permit the highest yields of the total sum of the alkaloids, whereas for toluene the lowest amounts were measured. Lycorine to galanthamine mean ratios were dependant on the type of solvent used, and in toluene galanthamine and related alkaloids were preferably extracted.In temperature experiments for galanthamine, the levels of this compound increased from the temperature of 20 till 150 °C in the investigated solvent systems, then decreased with slight increase from the temperature of 175 to 200 °C in 1% tartaric acid methanolic solution. When lycorine was analysed, similar trends were observed, however the maximum of the concentration was measured at a temperature about 125 °C. The ratios of the mean values of these two compounds differed in temperature-dependant experiments in both solvent systems.Further more, two TLC with bioautography approaches were used in screening for anticholinesterese properties of the extracts. No qualitative differences were found among the different solvent extracts, and AChE inhibition was correlated with galanthamine and related compounds.In conclusion, optimised PLE was much more effective than previously applied hot-solvent extraction, microwave-assisted extraction (MAE) or ultrasound-assisted extraction (USAE).     

A convenient TLC schedule for differential separation and quantification of prostaglandins,thromboxanes, and hydroxy fatty acids formed from [1-14C]arachidonic acid in human blood platelets

Eleven TLC solvent systems were evaluated for the separation of prostaglandins F_2α, E₂ and D₂, thromboxane B₂, 12-OH-5,8,10-heptadecatrienoic acid (HHT), 12-OH-5,8,10,14-eicosatetraenoic acid (HETE), and arachidonic acid (AA) from each other. A three-solvent development TLC procedure, which can conveniently be used for routine resolution of mixtures of these metabolites on a single TLC plate, is reported. The method was used for quantification of the metabolites formed from ¹⁴C-labeled AA by washed human platelets.     

Catalytic hydrogenation of crotonaldehyde in the liquid phase using Pt and Ru/SnO<Subscript>2</Subscript> catalysts

Effects of the precursor of active metal and of the reduction temperature upon activity and selectivity in selective hydrogenation of crotonaldehyde by Pt/SnO₂ and Ru/SnO₂ catalysts were studied. Experiments were performed in the liquid phase with a group of solvents tested: propan-2-ol, toluene, hexane and tetrahydrofuran. The best results were achieved with catalysts from ex-nitrate precursors/Pt(NH₃)₄(NO₃)₂ and Ru(NO)(NO₃)₂/reduced at 150° C. Propan-2-ol was evaluated as the most appropriate solvent to gain high yields of crotylalcohol in this study. A new hydrogenation product, 2-methylprop-2-en-1-ol (methallylalcohol), was observed.     

Pt/WO3/ZrO2 催化甘油选择性脱羟基制 1,3-丙二醇反应的溶剂效应

 考察了不同溶剂中 Pt/WO3/ZrO2 催化剂催化甘油加氢制 1,3-丙二醇的反应性能. 结果表明, 质子溶剂乙醇和水有利于甘油转化为 1,3-丙二醇. 含有乙醇或水的二元混合溶剂表现出明显的溶剂组分协同效应, 使用混合溶剂时 1,3-丙二醇选择性超过使用单一溶剂, 而且混合溶剂的组成对反应性能影响很大.     

“PRISMA” Model for Computer-Aided HPLC Mobile Phase Optimization Based on an Automatic Peak Identification Approach

Abstract

The tripartite “PRISMA” optimization model, as part of the “PRISMA” system, includes all possible solvent combinations between 1–4 solvents, with a possible fifth one as modifier. The solvent composition is characterized by the solvent strength (S_T) and the selectivity points (P_S).

At a constant S_T the correlation between the P_S and the retention data (horizontal function) can be described by a quadratic function. For constant P_S the solvent strengths and retention data correlate (vertical function) with a logarithmic function. These correlations are used to formulate a mathematical model for the dependence of retention times (capacity factor) on the mobile phase composition. Unknown compounds are estimated in the mathematical model from a sequence of standard chromatograms after having identified individual peaks by an automatic procedure. Only retention times, relative peak areas, and information about the mobile phase compositions are required as input for the identification approach. The approach involves a combination of statistical methods which exploit both the basic properties of retention data and the mathematical relation between retention data, selectivity points, and solvent strength as derived from the “PRISMA” model. Diagnostic information for checking the identification is generated as a by-product. The mathematical model completed by the estimated constants predicts the expected retention times for each possible mobile phase combination. Peak start and peak end times are predicted in a way similar to the retention times, once the identification has been performed. The most important aspects of a chromatogram can thus be predicted for arbitrary mobile phases.

The separation quality of predicted chromatograms is assessed by the chromatographic response function (CRF). The optimal mobile phase combination is that which theoretically generates the chromatogram with the maximal CRF value. This optimal composition is found by a simple mathematical procedure, which maximises the CRF in dependence upon the mobile phase combination. The optimum found is a local one if the starting set of chromatograms contains no variation of the solvent strength, and a global one if, in the set of starting chromatograms, the solvent strength is varied in a suitable way. Recommendations for the starting position are given.

Twelve measurements are necessary for a local optimum, and 15 for the global one. To increase the accuracy, six measurements at three different solvent strength levels are proposed. Generally the highest and the lowest solvent strength level differ by ±(5)% from the middle level.

This strategy is also relevant when modifiers are used in constant amounts. The chromatographic behavior of substances to be separated can be predicted with 1% accuracy from correlations of k' values and selectivity points. Based on these relationships, an automatical mobile phase optimization strategy for isocratic separations is suggested with the “PRISMA” model.     

The preparation and characterization of the cross-linked spherical, cylindrical, and vesicular micelles of poly(styrene-b-isoprene) diblock copolymers

PI cores of the micelles of poly(styrene-b-isoprene) (PS-b-PI) diblock copolymers, in PS selective solvents, were cross-linked with sulfur monochloride (S2Cl2). The cross-linked micellar structure was maintained after dialysis in THF (neutral solvent) and did not change during heating. Cross-linking brought about the opportunity for TEM images in a solution state; otherwise, the micellar structure would be destroyed (or changed) during the evaporation of the solvent on a carbon-coated copper grid. The Flory interaction parameter, chi, between the PI block and the solvent was controlled by mixing two selective solvents (DMP/toluene, DMP/DEP and DEP/DBP) which have different degrees of selectivity for the PS block, as well as heating the solutions. Two block copolymers, PS(7.2K)-b-PI(7.8K) and PS(5.5K)-b-PI(18.8K), were studied in order to clarify the effects of the relative chain length of each block on the micelle structure in the selective solvents. PS(7.2K)-b-PI(7.8K), which is nearly symmetric, showed only spherical micelles in the DMP/toluene mixture. The basic spherical micellar shape of PS(7.2K)-b-PI(7.8K) did not change with chi, while the size and aggregation number of the micelles increased as chi increased until 2.05 and then were saturated after that. PS(5.5K)-b-PI(18.8K), which is asymmetric, showed a structural change from spherical to cylindrical to vesicular micelles with an increase in the selectivity of the DMP/DEP and DEP/DBP mixtures (which was also confirmed by TEM and SAXS studies). Giant vesicular micelles with a diameter of approximately 2.5 microm were observed in high-selectivity solvents. The size of the vesicular micelle seemed to decrease as selectivity decreased. The systematic changes of the micellar structures of PS(5.5K)-b-PI(18.8K), via changes in solvent selectivity, could be demonstrated through TEM images, which were prepared by evaporating the solvent of the cross-linked micellar solution onto the carbon-coated grid after dialysis.     

Preparative Isolation of Pyrrolizidine Alkaloids Derived from Senecio Vulgaris

Abstract

A large scale method for the isolation of pyrrolizidine alkaloids has been adapted from a previously published analytical method. This method is a reverse phase high pressure liquid chromatography technique, utilizing a .005 M KH₂ PO₄ (pH 6.3) — methanol solvent system. The pyrrolizidine alkaloids derived from Senecio vulgaris (common groundsel) have been utilized in this system.     

The effect of chromatographic conditions on the separation of selected alkaloids on CN-silica layers

ABSTRACT

Selected alkaloids were chromatographed on cyanopropyl-silica thin layers using nonaqueous and aqueous eluents containing various free silanol blocker agents. Because of the strong retention of these basic compounds, nonaqueous eluents containing medium polar diluents, strongly polar modifiers, or aqueous eluents containing organic modifier, water, and silanol blockers (ammonia, diethylamine, and ionic liquid) were required for analysis. Mobile phases containing addition of acids were also tested for separation of investigated alkaloids. The most selective and efficient systems were used in two-dimensional separations of isoquinoline alkaloids’ mixture and plant extracts.     

Proton Magnetic Resonance Studies of Binary Aqueous Solvent - Dowex 50W Systems

Abstract

Pmr is used to evaluate solvent selectivity and to furnish an indication of water structure in binary aqueous solvent - ion exchange resin systems. The hydrogen form of Dowex 50W-X8 equilibrated with binary aqueous solvents exhibits pmr peaks for internal water which are shifted downfield relative to the water - ion exchanger system. The greater the mole fraction of organic solvent in the system, the greater the downfield shift.     

The Identification of Drugs of Abuse in Urine Using Reverse Phase High Pressure Liquid Chromatography

Abstract

A rapid, isocratic HPLC procedure for the identification of drugs of abuse in urine is described. The procedure utilizes a reverse phase μC₁₈ column, a methanol/water mobile phase, buffered to pH 7.5, and a UV detector operating at 254 nm. Using indole as an external standard, 13 common drugs of abuse can be differentiated in less than 15 minutes. Nine different drugs of abuse were identified in actual drug screen urine samples, confirming TLC results. Reproducibility and quantitative capabilities of this method were also demonstrated. Due to apparent interferences from drug metabolites this method must at present be used in conjunction with another established method such as TLC or GC for positive drug identification.     

Synthesis of ditopic ligands for the selective extraction of copper(II) nitrate and crystal structures of their Cu(II) complexes

We have synthesized two ditopic ligands for selective extraction of copper(II) nitrate. We also synthesized one cation-only binding analog for comparison. All three ligands were characterized by conventional techniques. Competitive two-phase metal ion solvent extraction experiments were performed at 25 °C over a period of 24 h. These ligands showed significant selectivity for Cu(II) ions, having the ditopic ligands extract 81 and 73% of the Cu(II) ions in a solution of different metal ions {Ni(II), Co(II), Cu(II), Zn(II), Cd(II), Pb(II)} at pH 5.09. Competitive transport experiments (water/chloroform/water) were undertaken employing each ligand separately as the ionophore in the membrane (chloroform) phase. No metal ion transport was observed, but a large concentration of Cu(II) was present in the membrane phase. Competitive anion extraction and transport were carried out with the ditopic ligands, yielding selective extraction and transport of nitrate. Furthermore, a pH isotherm of the best ditopic ligand (H₂L²) with Cu(II) was determined from pH 1.0 to 6.0, producing a pH_½ value of approximately 2.6. Finally, crystal structures of the ditopic ligands complexed with Cu(II) were determined and refined. The coordination geometry around the metal centers are distorted square planar and the Cu(II)-donor bond lengths fall within the normal range.     

Effect of binary block‐selective solvents on self‐assembly of ABA triblock copolymer in dilute solution

We have studied the self‐assembly of the ABA triblock copolymer (P4VP‐b‐PS‐b‐P4VP) in dilute solution by using binary block‐selective solvents, that is, water and methanol. The triblock copolymer was first dissolved in dioxane to form a homogeneous solution. Subsequently, a given volume of selective solvent was added slowly to the solution to induce self‐assembly of the copolymer. It was found that the copolymer (P4VP₄₃‐b‐PS₃₆₆‐b‐P4VP₄₃) tended to form spherical aggregate or bilayer structure when we used methanol or water as the single selective solvent, respectively. However, the aggregates with various nanostructures were obtained by using mixtures of water and methanol as the block‐selective solvents. The aggregate structure changed from sphere to rod, vesicle, and then to bilayer by changing water content in the block‐selective solvent from 0 to 100%. Moreover, it was found that the vesicle size could be well controlled by changing the copolymer content in the solution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1536–1545, 2008     

A Comparison of Polymer Separation Efficiency and Resolution by Gradient LC,GPC and TLC

Abstract

The specific resolution of gradient LC and reversed phase TLC methods for the separation of different molecular weight standards of poly(isoprene), poly(ethylene glycol), poly(ethylene oxide), poly(styrene) and poly(α-methylstyrene) were determined. It was found that gradient LC has an order of magnitude greater resolving power (for high polymers) than gel permeation chromatography (GPC) while TLC had from two to five times the resolving power of GPC in the molecular weight range investigated. This is a direct result of the greater selectivity of gradient LC and TLC techniques. The specific resolution is also dependent on the type of gradient used to achieve fractionation for the LC technique.     

Heterogenic catalytic hydrolysis and analysis of natural pyrethrins in subcritical water coupled with solid phase microextraction (SPME) and GC-MS

The methodology for the detection of picogram quantities of nucleotides directly from TLC plates without the use of radioactive labeling has been developed. The method couples thin-layer chromatography (TLC) separation with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) detection. The TLC/MALDI coupling protocol was studied and optimized for the separation and detection of deoxyribonucleotides. Several ammonia based solvents were examined as potential extraction solvents for the TLC/MALDI coupling protocol. It was found that in order to obtain maximum MALDI signal intensity and minimal analyte spreading, the extraction solvent should produce R_f-values for the analytes in the range of 0.3–0.4. R_f-values above this range led to extensive analyte spreading and those below this range resulted in poor extraction. Various MALDI matrices and co-matrices were investigated, the best results were obtained using 2′,4′,6′-trihydroxyacetophenone (THA) as a matrix. The extraction solvent chosen was an ammonium hydroxide/methanol (100 mM/30%, R_f = 0.28–0.38) solvent system which was found to provide the best sensitivity, minimal lateral spreading and excellent matrix transfer. Using the optimized coupling protocol, the detection limits for the deoxyribonucleotide monophosphates were established at or better than 10 picograms. Received: 27 May 1998 / Revised: 18 June 1999 / Accepted: 22 June 1999     

A green epoxidation system with poly(4‐vinylpyridine) microsphere‐supported molybdenum catalyst

The immobilization of molybdenum (Mo) compounds on poly(4‐vinylpyridine) (P4VP) microspheres for catalytic epoxidation was reported. P4VP‐supported Mo compounds were highly efficient and selective for the epoxidation of cis‐cyclooctene using hydrogen peroxide (H₂O₂) as oxygen source. When ethanol was used as solvents, outstanding catalytic activity and selectivity were observed for Mo‐containing catalysts in the epoxidation of cis‐cyclooctene. A completely green epoxidation system based on H₂O₂ and cleaner solvent has been achieved, and the heterogenized Mo catalyst can be recovered for five times without loss of its activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 558–562, 2010