Preparation of a high performance liquid chromatography column based on N-(3,5-dinitrobenzoyl)-aminoundecyl silica for the resolution of liquid crystal mixtures

A bonded silica stationary phase (SP 1) was prepared by connecting N-(3,5-dinitrobenzoyl) aminoundecylsilane to silica gel. The stationary phase was applied in resolving a liquid crystal mixture with a reversed phase high performance liquid chromatography (HPLC) mode and the chromatographic resolution results were compared with those on an octadecylsilane (ODS) column. From the comparison of the resolution results on SP 1 and the ODS column, we found the new stationary phase was better than the ODS column in resolving a liquid crystal mixture and the elution orders of some liquid crystal were changed. The better resolution and the change in the elution orders on the new column might be originated from additional π–π interaction between the π-acidic 3,5-dinitrobenzoyl group of the stationary phase and the π-basic aromatic group of liquid crystals.     

Spectroscopic characterization of environmentally relevant C10-chloroterpenes from a photochemically modified toxaphene standard

Twenty-five pure environmentally relevant toxaphene components have been isolated from photochemically modified technical toxaphene by means of a combination of column chromatography on silica gel and preparative high resolution liquid chromatography. These compounds are 6 chlorinated camphenes (1–3, 5, 7, and 11) and 19 chlorinated bornanes (4, 6, 8–10, 12–16, 18–24, 26, and 27 according to Table 1). Two further chlorobornanes (17 and 25) have been isolated from a highly chlorinated mixture obtained by the excess chlorination of 2-exo,10-dichlorobornane. The structural elucidation of the isolated compounds has been carried out with spectroscopical methods.     

Low-level determination of plutonium by gamma and L X-ray spectroscopy

We have developed an analytical method for detection of²³⁹Pu in aqueous samples at concentrations as low as 10^–10M. This nuclear counting technique utilizes the uranium L X-rays, which follow the alpha-decay of plutonium. Because L X-rays are specific for the element and not for the individual isotope, the isotopic composition of the plutonium sample must be known. The counting efficiency in the 11–23 keV range is determined from a plutonium standard, and the concentration of the sample is then calculated from the L X-ray count and the isotopic composition. The total L X-ray count is corrected for possible contributions from other radionuclides present as impurities by measuring the low-energy gamma-spectrum for each contaminant to establish specific photon/X-ray ratios. The ratios are important when²⁴¹Pu and²⁴²Pu are measured, because the respective decay chain members produce non-U L X-rays. This new method can replace the use of labor-intensive radiochemical separation techniques and elaborate activation methods for analysis of²³⁹Pu in aqueous samples. It is also applicable for assaying plutonium in liquid wastes that pose possible hazards to the environment.     

Capacitance of the Electrical Double Layer on Liquid Hg–Ga Alloy in Aqueous Solutions

Differential capacitance curves on an Hg–Ga electrode are obtained in aqueous solutions of various composition. An Hg–Ga electrode containing 2.1 at. % Hg to a high accuracy models electrochemical properties of a liquid Hg electrode at negative charges. This result can justify the approach according to which studying liquid In–Ga, Tl–Ga, Cd–Ga, and Pb–Ga alloys permit qualitative characterization of lyophilic properties of corresponding solid alloys.     

Rapid Chiral Separation by Flow-Through Chromatography with a Biporous Stationary Phase

Enantiomer separation is an area of increasing importance in chemistry and in the pharmaceutical industry. Although liquid chromatography is one of the most practical processes for chiral resolution, the high mass-transfer resistance of most commercially available packings makes chiral resolution time-consuming. In this work, a novel chiral stationary phase (CSP) with wide pores was prepared by coupling bovine serum albumin to a biporous resin with triazine as a linker. The rigid biporous medium was fabricated by radical suspension copolymerization with solid granules and solvents as porogenic agents. Studies by scanning electron microscopy and mercury intrusion porosimetry revealed the matrix contained two types of pore—micropores smaller than 180 nm and macropores of 500–7300 nm. Because the macropores provide convective flow channels for the mobile phase, the chromatographic process can be operated at high flow rate with low back-pressure. The biporous CSP was applied to the resolution of d, l-tryptophan (Trp). When the flow velocity was as high as 1800 cm h^–1, d, l-Trp could still be separated. By comparison of the resolution of d, l-Trp on this CSP at high flow velocities with that predicted theoretically for conventional supports we concluded that the increased flow velocity had little effect on the resolution of enantiomers with biporous packings. The results indicate that the protein biporous CSP is promising for high-speed resolution of enantiomers.Revised: 8 October 2004 and 3 January 2005     

A column packing for isothermal gas chromatographic analysis of C1−C5 paraffins and monoolefins and dimethyl ether

Summary An analytical GC method was developed which uses a single packed column consisting of three packings in series prepared with the following liquid phases: dimethyl sulfolane, propylene carbonate, and silver nitrate. This system provides satisfactory resolution of mixtures of C₁–C₅ hydrocarbons and dimethyl ether obtained when converting methanol to gasoline. Due to the high capacity of the column it is possible to inject larger sample amounts permitting trace analysis.     

A comparative test of differential scanning calorimeters

The Dutch Society for Thermal Analysis has developed tests to measure the resolution and the sensitivity of Differential Scanning Calorimeters. For this test the substance 4,4-azoxyanisole is used. This substance shows two transitions: a solid to liquid crystal transition at about 117°C (H120 J g^–1) and a liquid crystal to isotropic liquid transition at about 134°C (H2 J g^–1). The resolution test is performed using an amount of 5 mg substance and a high heating rate of 20°C min^–1. The resolution is evaluated by measuring how well the two peaks are separated. An amount of 0.25 mg substance and a low heating rate of 0.1 °C min^–1 is used for the sensitivity test. The sensitivity is evaluated as the ratio of the peak height of the LC-transition and the top-top noise level.Members of the TAWN were asked to participate in the test. Each participant was provided with an amount of sample and a test procedure. 47 Contributions were received and these results are presented.All members of the TAWN who participated in the tests are thanked for their contributions.     

Anwendung der Hochdruck-Flüssigkeits-Chromatographie zur Analyse von Penicillinen und Cephalosporinen

Zusammenfassung Es wird eine Methode zur Analyse einiger Penicilline und Cephalosporine mit eng verwandter Struktur mittels reversed-phase Flüssigkeits-Chromatographie beschrieben. Der Einfluß des pH-Wertes sowie der Natriumchlorid-Konzentration der mobilen Phase auf die Auflösung des Ampicillins und Epicillins wird diskutiert. Das Verfahren kann zur selektiven Analyse synthetisch hergestellter Antibiotika sowie den entsprechenden pharmazeutischen Zubereitungen verwendet werden. Wegen der hohen Empfindlichkeit (10^–1 g cm^–3) kann die Methode auch zur Analyse von Penicillinen in physiologischen Flüssigkeiten verwendet werden.

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Application of high-pressure liquid chromatography to the analysis of penicillins and cephalosporins

Summary A reversed phase liquid chromatography method for the analysis of some penicillins and cephalosporins of closely related structure is described. The influence of eluent pH and sodium chloride concentration on the resolution of ampicillin and epicillin is discussed. The methodology can be applied to the selective analysis of synthetically produced antibiotics and also to their pharmaceutical preparations. Because of its high sensitivity (10^–7 g cm^–3) the method can also be used for the analysis of penicillins in physiological fluids.

     

Synthesis and electrochemical study of Li-Mn-Ni-O cathodes for lithium battery applications

Cathode powders of the Li–Mn–Ni–O system have been prepared at a Mn/(Mn+Ni) ratio varying from 0 to 1. The solid state reaction method was used to obtain the cathode materials by mixing MnO₂, LiCO₃ and NiO. A 20% excess of lithium was used in the precursors. The materials produced were examined by X-rays to identify their structure. Batteries were assembled by using these materials as cathode with a liquid electrolyte consisting of EC/DC 1:1, 1 LiPF₆ and Li anode. Their capacity, cycle fading and charge-discharge conditions were evaluated.Presented at the 3rd International Meeting "Advanced Batteries and Accumulators", June 16th–June 20th 2002, Brno, Czech Republic     

Low level determination of thallium in biological and environmental reference materials by RNAA using several counting methods

A new RNAA procedure was developed capable of low level determination of thallium in biological and environmental samples. After high fluence neutron irradiation in a nuclear reactor, wet ashing of samples and T1(I) separation by solvent extraction with sodium diethyldithiocarbamate at pH 13, several types of counting were employed to compare their detection limits and to utilize the self-validation principle of NAA. The following measurement modes were used: High efficiency counting of -rays of²⁰²T1 and Hg X-rays produced on decay of²⁰⁴T1 using a well-type HPGe detector, combined ^– ray and ^–-counting of²⁰⁴T1 with the aid of a HPGe planar detector, and liquid scintillation counting and counting of Cerenkov radiation of ^–-particles of²⁰⁴T1. The lowest detection limit of 0.034 ng of T1 was achieved on liquid scintillation counting of²⁰⁴T1. The method was applied for the analysis of biological NIST SRMs 1515, 1573a, 1577b and environmental NIST SRM 1633a. Good agreement was found between the thallium certified value in SRM 1633a and values determined in this work by all counting modes. For SRM 1573a, results in agreement were obtained by two counting modes, while counting of Hg X-rays of²⁰⁴T1 was only used for SRMs 1515 and 1577b.     

Ultrafiltration of triglyceride from biodiesel using the phase diagram of oil–FAME–MeOH

To continuously obtain biodiesel of high purity, a membrane separator integrated with liquid–liquid extraction for the oil–FAME–MeOH system is studied. The liquid–liquid phase equilibrium data for the oil–FAME–MeOH are determined experimentally and compared with the general prediction of the modified UNIFAC. The tie line test demonstrates that composition of the methanol-rich phase is free of TG at 20 °C. Using the continuous cross-flow ultrafiltration, the oil-rich phase can be rejected by the ceramic membranes while the methanol-rich phase permeates through the membranes. When the feed bulk composition is controlled within the two-phase zone, such as the oil:FAME:MeOH of 20:30:50 wt.%, the permeate is found to be free of oil while the obtained permeate flux is higher than 300 kg/m² h under the transmembrane pressure of 600 mmHg and the inlet flow rate of 300 ml/min at 20 °C. By contrast, it shows almost no separation when the inlet concentration of oil–FAME–MeOH locates on its boundary line or within the single-phase zone. The quantitative filtration tests show that the compositions in the two liquid phases and the operating parameters are also considered simultaneously to screen the origin oil and get the FAME product of high purity.     

X-Ray fluorescence analysis in the scanning electron microscope

Summary X-ray fluorescence analysis can be performed in a scanning electron microscope equipped with an energy dispersive X-ray spectrometer by means of a special attachment. For the production of primary X-rays a target is positioned in the electron beam. With this technique an improvement of the detection limits is obtained because of the small fraction of bremsstrahlung in the X-ray spectrum. As a disadvantage a loss of lateral resolution occurs. The performance features of different types of construction (transmission and massive targets) are be compared for experimental results and theoretical models.The paper has been presented at 12th Colloquium on Materials Analysis, Institute for Analytical Chemistry, Technical University in Vienna, May 13–15, 1985.     

Phase Equilibria and Nonequilibrium Structures in the Sodium Di-2-Ethylhexyl Phosphate–Decane–Water System

Phase equilibria and nonequilibrium structures in the sodium di-2-ethylhexyl phosphate (NaSDEHP)–decane–water system were studied. It was found that, at a certain component ratio, a microemulsion and a liquid crystal phase are present in the system. The phase diagram was plotted, describing two- and three-phase equilibria: NaSDEHP and water solution in decane–microemulsion, microemulsion–liquid crystals, NaSDEHP and water solution in decane–microemulsion–liquid crystals, and NaSDEHP and water solution in decane–liquid crystals. The viscosity of NaSDEHP microemulsion was measured. It was shown that the viscosity increases significantly with an increase in the ratio of sodium hydroxide and di-2-ethyhexyl phosphoric acid molar concentrations from 0.6 to 1.0. Formation of the third liquid (microemulsion) phase in the vicinity of the oil–water interface was found upon the transfer of NaSDEHP from one phase to the other.     

Liquid–liquid phase transfer of magnetite nanoparticles

The study presents first experimental results of the transfer of magnetite nanoparticles from an aqueous to a second non-miscible non-aqueous liquid phase. The transfer is based on the adsorption of macromolecular surfactants onto the particle surface at the liquid–liquid interface. For a successful direct phase transfer, it is essential to have cations, like ammonium ions, present in the aqueous phase as well as a threshold concentration of surfactant in the organic liquid phase. While penetrating the liquid–liquid interface, the particles are covered with the surfactant and therefore a partial de-agglomeration is initiated. Based on literature and experimental data a mechanism of surfactant adsorption is proposed. The competing adsorption of the surfactant molecules at the liquid–liquid interface leads to the formation of emulsions and therefore to a hindrance for particles passing the interface. Nevertheless a high efficiency of 100% yield can be reached using optimized process parameters for the phase transfer process.     

Solubility of Solid 2,3-Dimethylbutane and Cyclopentane in Liquid Argon and Nitrogen at the Standard Boiling Points of the Solvents

The solubilities of solid 2,3-dimethylbutane and cyclopentene in liquid argon at a temperature of 87.3 K and in liquid nitrogen at 77.4 K have been measured by the filtration method. The hydrocarbon contents in solutions were determined using gas chromatography. GC–MS was used to identify impurities in solutes. The experimental value of the mole fraction solubility of solid 2,3-dimethyl-butane in liquid argon at 87.3 K is (8.26 ± 1.60) × 10^–6 and (2.77 ± 0.94) × 10^–8 in liquid nitrogen at 77.4 K. The experimental value of the mole fraction solubility of solid cyclopentene in liquid argon at 87.3 K is (5.11 ± 0.44) × 10^–6 and (4.60 ± 0.76) × 10^–8 in liquid nitrogen at 77.4 K. The Preston–Prausnitz method was used for calculation of the solubilities of solid hydrocarbons in liquid argon in the temperature range 84.0–110.0 K and in liquid nitrogen from 64.0 to 90.0 K. The solvent–solute interaction parameters l ₁₂ were also calculated. At 90.0 K liquid argon is a better solvent for investigated solid hydrocarbons than is liquid nitrogen.     

Very-high-speed liquid column chromatography the system and selected applications

Summary Instrumentation needed to achieve very high performance (plate/s) liquid chromatography is discussed. With recently available systems using relatively short (100–125 mm) columns of conventional internal diameter (4–6 mm) and packed with 3–5 m particles, analysis in very short times (usually 1–3 min) is possible. Coupling such columns in series provide very high performance in a time still significantly less than previously encountered. Performance of such liquid chromatographic systems is illustrated with a number of practical examples including analgesic tablets, cosmetics, soft drinks, antioxidants and polyaromatic hydrocarbons.Enlarged text of a paper presented at the 32nd Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 9–13, 1981, Atlantic City, New Jersey (Paper No. 462).     

The Efficiency of Substance Separation in Countercurrent Liquid Chromatography

The effect of hydrodynamic parameters and the specific features of instrument design on the efficiency of substance separation in countercurrent liquid chromatography (CCC) was studied using a constant retention factor of the stationary phase in the column. The study was conducted with the separation of benzyl alcohol and p-cresol in a two-phase liquid system heptane–ethyl acetate–methanol–water (1.4 : 0.6 : 1 : 1) in as an example. It was shown that the peak resolution is improved with an increase in the rotational speed of the column and a decrease in the flow rate of the mobile phase. The best peak separation was attained using columns for which the ratio of the column rotation radius to the radius of column revolution was 0.615. It was shown that countercurrent chromatography allows the separation of substances with low partition constants (K < 1) in dilute solutions. The volume of the test sample may be up to 15% of the total volume of the chromatography column.     

Preparative separation of fullerene adducts by liquid chromatography on polystyrene gel

Summary The preparative separation of numerous fullerene adducts by liquid chromatography on polystyrene gel is described. These adducts can be resolved on a scale of 10–40 g/day on a 600×20 mm column. Both toluene and chloroform can be used as mobile phases; toluene offers better solubility for the adducts and chloroform better peak resolution.     

Solubility of Solid 1-Hexyne in Liquid Argon and Nitrogen at the Standard Boiling Points of the Solvents

The solubilities of solid 1-hexyne in liquid argon at 87.3 and in liquid nitrogen at 77.4 K have been measured by the filtration method. The hydrocarbon contents in solutions were determined using gas chromatography. GC–MS was used to identify impurities in 1-hexyne. The experimental value of the mole fraction solubility of solid 1-hexyne in liquid argon at 87.3 K is (0.85 ± 0.19) × 10^–7 and (1.25 ± 0.08) × 10^–8 in liquid nitrogen at 77.4 K. The Preston–Prausnitz method was used for calculation of the solubilities of solid hydrocarbon in liquid argon in the temperature range 84.0–110.0 K and in liquid nitrogen from 64.0 to 90.0 K. The solvent–solute interaction parameters l ₁₂ were also calculated. At 90.0 K liquid argon is a better solvent for solid 1-hexyne than is liquid nitrogen.     

Silicon–air batteries

A new “metal”–air battery based on silicon–oxygen couple is described. Silicon–air battery employing EMI·2.3HF·F room temperature ionic liquid (RTIL) as an electrolyte and highly-doped silicon wafers as anodes (fuels) has an undetectable self-discharge rate and high tolerance to the environment (extreme moisture/dry conditions). Such a battery yields an effectively infinite shelf life with an average working voltage of 1–1.2 V. Silicon–air battery can support relatively high current densities (up to 0.3 mA/cm²) drawn from flat polished silicon wafers anodes. Such batteries may find immediate applications, as they can provide an internal, built-in autonomous and self sustained energy source.