Gradient separation of pharmaceuticals employing supercritical CO2 and modifiers

Sub- and Supercritical Fluid Chromatography (SFC) were used to separate seven purine and pyrimidine-based drugs. A two-pump system was used, where one pump delivered the carbon dioxide, and the other pump delivered modifier. The modifiers used in this work were methanol, and methanol containing 0.001 M tetrabutylammonium hydroxide. Two of the compounds studied were hydrochloride salts. These compounds were analyzed by a Supercritical Fluid Extraction (SFE)/SFC method.     

Matrix independent supercritical fluid extraction of polycyclic aromatic hydrocarbons by employing binary modifiers

A universal extraction method has been developed for polycyclic aromatic hydrocarbons using supercritical fluids. The method is nearly matrix-independent and therefore applicable to different kinds of matrices with only minor changes. New binary modifiers, containing small amounts (1%) of active additives in organic solvents have been used. In contrast to extractions with neat CO₂ or CO₂ modified with neat co-solvents, the use of binary modifiers has resulted in significantly higher extraction efficiencies for different kinds of matrices. The applicability of the new modifier-solutions has been shown for three different matrices, a fly ash, a sediment and a sewage sludge.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

Retention prediction and computer-assisted optimization for the separation of PTH-amino acids in isocratic reversed-phase liquid chromatography

Summary Retention prediction of phenythiohydantoin amino acid derivatives in isocratic reversed-phase liquid chromatography was investigated. The predicted retention data of all derivatives were evaluated by comparing them with actually measured retention data. Excellent agreements between these data were found. The optimized conditions to separate overlapping components can also be predicted using the developed computer-assisted optimization system with the concept of retention prediction.     

Formation of porous flat membrane by phase separation with supercritical CO2

Microporous polystyrene membranes were prepared by the phase separation process using the supercritical CO₂ as a nonsolvent for the polymer solution. The thin polymer solution in a laboratory dish was located inside a cell and the supercritical CO₂ was introduced to induce the phase separation. The dry flat microporous membranes were obtained without collapse of the structure after the CO₂ pressure was diminished. Effects of the experimental conditions such as the CO₂ pressure, the polymer concentration and the temperature on the average pore size and membrane porosity were investigated.     

Lattice Monte Carlo simulations of phase separation and micellization in supercritical CO2/surfactant systems: effect of CO2 density

Lattice Monte Carlo simulations are used to study the effect of nonionic surfactant concentration and CO2 density on the micellization and phase equilibria of supercritical CO2/surfactant systems. The interaction parameter for carbon dioxide is obtained by matching the critical temperature of the model fluid with the experimental critical temperature. Various properties such as the critical micelle concentration and the size, shape, and structure ofmicelles are calculated, and the phase diagram in the surfactant concentration-CO2 density space is constructed. On increasing the CO2 density, we find an increase in the critical micelle concentration and a decrease in the micellar size; this is consistent with existing experimental results. The variation of the micellar shape and structure with CO2 density shows that the micelles are spherical and that the extension of the micellar core increases with increasing micellar size, while the extension of the micellar corona increases with increasing CO2 density. The predicted phase diagram is in qualitative agreement with experimental phase diagrams for nonionic surfactants in carbon dioxide.     

Organic modifiers for the separation of organic acids and bases by liquid chromatography

A straight-chain alcohol or diol additive in the mobile phase was used to modify and improve the HPLC separation of organic acids and bases. Incorporation of 2% 1-butanol, 1% 1,2-hexanediol, or 0.25% 1,2-octanediol into an aqueous mobile phase greatly improved the separation of alkane carboxylic acids on a silica C18 column, both in terms of separation time and peak shape. When 1.5% 1-hexanol, 0.09% 1-decanol or 0.01% 1-dodecanol was added to an acetonitrile-water (30:70) mobile phase, much sharper peaks and better resolution were obtained for aromatic bases separated on an underivatized polystyrene-divinylbenzene column. The mobile phase additive is believed to coat the stationary phase surface by a dynamic equilibrium. The coated surface is more hydrophilic and facilitates the efficient partitioning of analytes between the mobile and stationary phases.     

Fluorinated surfactants in supercritical CO2

Liquid or supercritical carbon dioxide has important environmental and economic advantages over petrochemical solvents currently used for industrial processes. However, low solubility in CO₂, particularly of polar compounds, is a hurdle to its implementation as an acceptable alternative. These solubility problems have been overcome by employing specialised fluorinated surfactants to stabilise water nano-droplets as water-in-supercritical/liquid CO₂ microemulsions. Such novel microemulsions can now facilitate innovative ‘green-and-clean’ applications of carbon dioxide technology.     

Phase separation of ploy(ethylene glycol) + n-butanol mixture induced by supercritical CO_2

The phase behavior of supercritical (SC) CO2 PEG 1000 (PEG with average molecular weight of 1000 g/mol) n-butanol system was studied. It was demonstrated that SC CO2 could induce phase separation of PEG 1000 n-butanol system under suitable conditions. This hints that SC CO2 has potential applications in the separation of mixtures of PEG organic compound.     

Aliphatic carboxylic acids as new modifiers for separation of 2,4-dinitrophenyl amino acids by micellar liquid chromatography

The possibilities of isocratic separation of 2,4-dinitrophenyl derivatives of 12 amino acids that considerably differ in hydrophobicity by micellar mobile phases with different organic modifiers have been discussed. For the first time aliphatic carboxylic acids have been used as modifiers of micellar eluent in micellar liquid chromatography with C18 columns. Elution strength of hybrid micellar phases on the basis of sodium dodecylsulfate and aliphatic carboxylic acids increases in sequence: acetic相似文献   

Sequestration of supercritical CO2 by mercury oxide

HgCO₃·2HgO (mercury oxide carbonate), along with partly unreacted reactants, was obtained by exploring the behaviour of the Hg₂Cl₂/HgO binary system in supercritical CO₂ (scCO₂) at 200°C, 22000 kPa in the presence and absence of water, using a self-made laboratory-scale system. The reaction of pure HgO with scCO₂ aimed at the synthesis of HgCO₃ (mercury carbonate), also yielded the same product. Meanwhile, with a small amount of water present in the Hg₂Cl₂/HgO-scCO₂ system, at 200°C, 22000 kPa, the mineral terlinguaite (Hg₄O₂Cl₂) was obtained instead of mercury oxide carbonate. Repeating this reaction under the same conditions, but in the absence of CO₂, again resulted in the synthesis of terlinguaite, leading to the assumption that the scCO₂ had no influence on the synthesis of terlinguaite. This study reveals a new moisture-free laboratory method and conditions for the permanent fixation of CO₂ by HgO. This method bears two benefits: 1) it can be introduced to reduce the Hg content in flue gas and fly ash emitted from coal-burning power plants and municipal waste incinerators; 2) it can contribute to CO₂ mineralisation in montroydite (HgO) geological formations as mercury oxide carbonate.     

Identification of subnanomole amounts of PTH-amino acids by high performance thin-layer chromatography

Summary High performance thin-layer chromatography (HPTLC) of PTH-amino acids on 5×5 cm silica gel plates precoated with a fluorescence marker gives 10–20 fold increase in sensitivity compared to ordinary silica gel plates. Separation of PTH-Leu from PTH-Ile is easily achieved in contrast to chromatography on polyamide sheets. Only two solvent systems are required and as many as 12 samples can be chromatographed on each plate. However, if the sample is contaminated with N-phenylthiourea a third solvent system is necessary.     

Interaction of pharmaceutical hydrates with supercritical CO2

The aim of this work was to study the solubility in supercritical CO₂ of the hydrated phase of three model drugs, namely theophylline, carbamazepine, and diclofenac sodium, in comparison with the respective anhydrous form. Possible solid-state modifications, stemming from the interaction with supercritical CO₂, were investigated by differential scanning calorimetry, thermogravimetric analysis, hot stage microscopy, Fourier Transform infrared spectroscopy and Karl-Fischer titrimetry. It was found that all three pharmaceutical hydrates exhibited higher solubility in supercritical CO₂ than the relevant anhydrous phases. In the case of theophylline monohydrate, the instability of the crystal phase at the experimental temperature adopted has been evidenced. Diclofenac sodium tetrahydrate represents a peculiar case of chemical interaction with the acid supercritical fluid, mediated by crystal water. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of modifiers in supercritical fluid chromatography

Investigations have been initiated to examine the basic elements of resolution and how they vary individually and collectively in terms of modifiers used in supercritical fluid chromatography (SFC). Capacity factors (k′) have been determined for a mixture of polynuclear aromatic hydrocarbons from SFC experiments as function of modifier identity and concentration using different stationary phases. Using carbon dioxide as the primary mobile phase, the modifiers investigated included methanol, 2-methoxy ethanol, 1-propanol, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, sulfur hexafluoride, and freon 11.     

Sorption and swelling of semicrystalline polymers in supercritical CO2

The equilibrium sorption and swelling behavior of four different polymers—poly(methyl methacrylate), poly(tetrafluoroethylene), poly(vinylidene fluoride), and the random copolymer tetrafluoroethylene–perfluoromethylvinylether–in supercritical CO₂—are studied at different temperatures (from 40 to 80 °C) and pressures (up to 200 bar). Swelling is measured by visualization, and sorption through a gravimetric technique. From these data, the behavior of amorphous and semicrystalline polymers can be compared, particularly in terms of partial molar volume of CO₂ in the polymer matrix. Both poly(methyl methacrylate) and the copolymer of tetrafluoroethylene exhibit a behavior typical of rubbery systems. On the contrary, polymers with a considerable degree of crystallinity, such as poly(tetrafluoroethylene) and poly (vinylidene fluoride), show larger values of partial molar volume. These can be related to the limited mobility of the polymer chains in a semicrystalline matrix, which causes the structure to “freeze” during the sorption process into a nonequilibrium state that can differ significantly from the actual thermodynamic equilibrium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1531–1546, 2006