Quantitation of Carbon Dioxide by High Performance Liquid Chromatography: The Key to Solubility Measurements in Liquefied Gas Solutions

Abstract

A technique is described whereby solubility data may be obtained for systems employing liquefied carbon dioxide as the solvent. Analysis of the solution is effected by the direct injection of an aliquot of pressurized liquid into a modern liquid chromatograph fitted with a reversed-phase C₁₈ column. Detection of the carbon dioxide is accomplished by a differential refractometer. After the appropriate calibrations are performed, data are obtained which compare favourably with the literature value of the solubility of naphthalene in liquid carbon dioxide.     

Determination of Microcystins in Cyanobacteria by Supercritical Fluid Extraction and Liquid Chromatography‐Tandem Mass Spectrometry

Abstract

A method for the detection of microcystins (microcystin LR, RR, and YR) in cyanobacteria by supercritical fluid extraction (SFE) and liquid chromatography‐mass spectrometry (LC/MS) has been developed. Supercritical fluids for the analytical extraction of nonvolatile, higher molecular weight compound, and microcystins from cyanobacteria were investigated. The microcystins included in this study are sparsely soluble in neat supercritical fluid CO₂. However, the microcystins was successfully extracted with a ternary mixture (90% CO₂, 9.5% methanol, 0.5% water) at 40°C and 250 atm. The polar carbon dioxide‐aqueous methanol fluid system gave high extraction efficiency for the extraction of the polar microcystins from cyanobacteria. The microcystins were determined by liquid chromatography‐tandem mass spectrometry (LC/MS/MS).     

Application of Supercritical fluid Extraction For Analysis of Organophosphates in Cereals

Abstract

Application of supercritical fluid extraction (SFE) utilizing pure carbon dioxide for selective isolation of organophosphates from contaminated cereals has been tested.

At the beginning of the experiments the extractability of added standards from an empty extraction vessel (thimble) and from various materials such as filter paper, sand, Celite and anhydrous sodium sulfate was tested to estimate the behavior of organophosphates. Further method development was carried out using a spiked sample of flour, which was analyzed within the proficiency testing for organophosphorus pesticides analysis (round 7) organized by Food Analysis Performance Assessment Scheme (FAPAS, MAFF-UK).

Comparison of the SFE method with a classical method currently employed for sample preparation (i.e. extraction with acetone/methanol mixture followed by gel permeation chromatographic clean up) showed advantages of the SFE technique such as simplification of the sample preparation step and thereby significant speeding up of the determination of organophosphates in cereals.     

Reversed-Phase High Performance Liquid Chromatography of Carbon Dioxide

Abstract

An investigation of the qualitative aspects of the liquid chromatography of carbon dioxide is described. It is demonstrated that although injected as a high pressure liquid, carbon dioxide dissolves in aqueous methanol mobile phases and elutes as a solution. The detector response is discussed in terms of the possible chemical interactions between the carbon dioxide molecule and the mobile phase; the effect of eluent pH upon the response is described. The variation of relative retention with mobile phase composition is detailed and the results discussed in terms of Horvath's solvophobic theory.     

Pneumatoamperometric Determination of Sulfur Dioxide in Air on ppb Level

Abstract

A simple device for the determination of sulfur dioxide at ppb concentrations in air is described. The device is composed of an enrichment unit operating continuously on the basis of gas extraction into polydisperse aerosol of a liquid transferring sulfur dioxide from liter amount of air into microliter amount of liquid. The analyte is determined pneumatoamperically from the concentrate on a gold-plated porous Teflon electrode.

The detection limit is 0.3 ppb (v), i.e. 0.87 μg/m³ of sulfur dioxide, the linear range covers several orders of magnitude. The analytical response is obtained few tenths of seconds after the gas contaminated with sulfur dioxide has entered the enrichment unit     

Electrosorption of CO and CO2 on Pt-Rh Alloy Electrodes

Abstract

The adsorption of carbon monoxide and carbon dioxide on smooth Pt-Rh alloy has been studied by potentiodynamic technique. It is shown that the main products of CO and CO² adsorption on Pt-Rh alloys (15% Rh and below) are similar to products obtained on Pt electrodes.     

Comparison of different methods of extraction for the determination of polychlorinated dibenzo-p-dioxins in soil

Summary The application of five different extraction methods including the extraction with liquid and supercritical carbon dioxide were tested on various soil samples with regard to their extraction efficiency. The carbon dioxide liquid extraction has proven to be not suitable for these applications.

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Vergleich verschiedener Extraktionsverfahren zur Bestimmung von polychlorierten Dibenzo-p-dioxinen in Böden

     

Continuous Flow Determination of Carbon Dioxide in Water by Membrane Separation-Chemiluminescent Detection

Abstract

Carbon dioxide has been found to enhance the chemiluminescence of a luminol system. A determination method for carbon dioxide in water was developed by applying this reaction to a continuous flow membrane-separation system. Concentrations of carbon dioxide as low as 0.04 μ g C /mL were determined. Membrane-separation effectively eliminates interferences from Co(II), Cr(III), Fe(III), and other ions which also enhance chemiluminescence. The relative standard deviation for this method was 2.8% (n=5) for 4.0 μ g C /mL and the time required for the analysis of one sample was 3.0 min.     

Stripping Analysis of Trace Metals at a Flow-Through Reticulated Vitreous Carbon Electrode after the Preconcentration by Supported Liquid Membrane Technique

Abstract

The performance of a flow-through mercury coated reticulated vitreous carbon (RVC) electrode in the potentiometric stripping analysis (PSA) of trace metals has been examined. A wall-jet glassy carbon cell was used for the comparative experiments. Experimental parameters influencing the stripping signals have been optimised in order to use the stripping analysis after the preconcentration and matrix isolation by supported liquid membrane (SLM) technique. The SLM with di-2-ethylhexyl-phosphoric acid (DEHPA) as the extractant in the membrane liquid for proton driven transport of trace metals across the membrane has been chosen. Results presented for lead determination in river water demonstrate the analytical advantages of coupled technique SLM-PSA.     

The Uses of Organo Phosphorus Compounds in Liquid-Liquid Extraction of Metal Ions

Abstract

A survey of the uses of organo phosphorus compounds in liquid-liquid extraction processes is presented. Some modern aspects of solvent extraction including the development of new extractants, the development of the liquid membrane technique, the design of more selective organophophorus extractants and the use of organo phosphorus compounds as extraction catalysts, are discussed.     

Flotation/ultrasound‐assisted microextraction followed by HPLC for determination of fat‐soluble vitamins in multivitamin pharmaceutical preparations

Dissolved carbon dioxide flotation–emulsification microextraction technique coupled with high‐performance liquid chromatography was developed for separation and determination of fat‐soluble vitamins (A, D₃, E, and K₃) in multivitamin pharmaceutical preparations. Dissolved carbon dioxide flotation was used to break up the emulsion of extraction solvent in water and to collect the extraction solvent on the surface of aqueous sample in narrowed capillary part of extraction cell. Carbon dioxide bubbles were generated in situ through the addition of 300 μL of concentrated hydrochloric acid into the alkaline sample solution at pH = 11.5 (1% w/v sodium carbonate), which was sonicated to intensify the carbon dioxide bubble generation. Several factors affecting the extraction process were optimized. Under the optimal conditions, the limits of detection were 0.11, 0.47, 0.20 and 0.35 μg/L for A, E, D₃, and K₃ vitamins in water samples, respectively. The inter‐day and intra‐day precision of the proposed method were evaluated in terms of the relative standard deviation and were <10.5%.     

Determination of the Concentration of Gases by Measurement of Pressure

Abstract

For the determination of the concentration of gases by means of pressure measurement, a precise equation of state is given by which analysis can be carried out within an accuracy of 10 ppm. The parameters of the equation of state are explicitely reported for carbon dioxide, argon, and helium.     

Preparation and Evaluation of Propranolol-Imprinted Monolithic Stationary Phase by In Situ Technique and Application in Analysis of Propranolol in Biological Samples

Abstract

A propranolol molecule-imprinted monolithic stationary phase (MIMSP) was synthesized by in situ technique. The recognition mechanism of the polymers and the influences of some chromatographic conditions were examined by high-performance liquid chromatography (HPLC). The imprinted polymers showed much higher selectivity for β-blockers than the nonimprinted polymers (NIPs) did, which proves the successful preparation of propranolol-imprinted polymers by using an in situ technique. Then, this technique was used to prepare a molecularly imprinted polymer solid-phase extraction column to concentrate propranolol from biological samples. The results showed that the imprinted solid-phase extraction column could selectively enrich and purify propranolol from biological samples, such as plasma.     

High-Pressure Liquid Chromatographic Assay of Azlocillin and Mezlocillin with an Anion-Exchange Extraction Technique

Abstract

An anion-exchange column deproteination technique has been employed with the high-pressure liquid chromatographic (LC) assay for azlocillin and mezlocillin. The anionexchange extraction gave excellent (97%-99%) drug recovery. Quantitation of antibiotics using the LC method compares favorably to the traditional biological assay technique with correlation coefficients for azlocillin = 0.998 and mezlocillin = 0.988. The anion-exchange extraction provides an interference-free chromatogram which aids in the LC assay of these drugs.     

High performance liquid chromatography-electrospray lonization MS-MS analysis ofForsythia koreana fruits, leaves, and stems. Enhancement of the efficiency of extraction of arctigenin by use of supercritical-fluid extraction

Summary A method involving high-performance liquid chromatography coupled with electrospray MS-MS has been developed for the analysis of the constituents of the fruits, leaves, and stems ofForsythia koreana. Ten compounds including caffeoyl glycosides and lignans could be separated and detected with good sensitivity. The MS-MS spectra obtained provided information about their structures, for example the sugar and aglycone moieties present. Supercritical-fluid extraction was also used to improve the efficiency of extraction of arctigenin, which has the highest anti-inflammatory activity of the compounds produced by this plant. Although carbon dioxide without any modifier extracted only 66% of that obtained by extraction with methanol, an 80:20 (v/v) carbon dioxide-methanol mixture greatly enhanced the extraction yield-to 110%.     

The Assembling and Application of an Automated Segmented Flow Analyzer for the Determination of Dissolved Organic Carbon Based on UV‐Persulphate Oxidation

Abstract

A simple and reliable methodology developed on an automated segmented flow analyzer has been implemented for the determination of organic forms of carbon in aqueous solutions. Conversion of dissolved organic matter to carbon dioxide is performed by a UV‐persulphate oxidation. After oxidation, the concentration of carbon dioxide in the sample induces a change in pH that will alter the color intensity of a phenolphthalein solution. The color intensity of the solution is measured automatically by colorimetry. Caffeine and acid ascorbic were tested in order to assess the accuracy of the analytical methodology. Reproducibility tests demonstrated a very good precision for natural waters and for organic compounds. Salinity changes showed no interferences, which suggests how appropriate this methodology is for routine analysis and how useful and convenient it is for shipboard work on ocean and estuarine research.     

A MECHANISTIC STUDY OF THE FORMATION OF [Ru6C(CO)16]2− FROM [Ru6(CO)18]2−

Abstract

The kinetics of the transformation of [Ru₆(CO)₁₈]^2? into [Ru₆C(CO)₁₆]^2? in diglyme over the temperature range 130–160°C have been determined. The results are consistent with reversible loss of a carbonyl ligand from [Ru₆(CO)₁₈]^2?, followed by formation of carbon dioxide and reassociation of carbon monoxide to give the observed product. Mass spectral analysis of the evolved carbon dioxide trapped as barium carbonate supports an intramolecular pathway for the disproportionation of carbon monoxide.     

Supercritical Fluid Extraction of Bivalve Samples for Simultaneous GC-MS Determination of Polychlorobiphenyls and Polycyclic Aromatic Hydrocarbons

Abstract

A method is presented for the simultaneous determination of polychlorobiphenyls and polycyclic aromatic hydrocarbons in bivalve samples. The method implies the fortification of the freeze-dried sample with isotopically labeled internal standards; followed by extraction with supercritical carbon dioxide modified with 3% methanol, then a simple clean-up step on a silicagel packed Pasteur pipette and, finally, determination by gaschomatography-mass spectrometry. The method requires little time and labor compared to traditional methods, uses negligible amounts of solvents and produces little wastes. Sixty different PCB congeners and seven selected PAHs are analyzed. Six replicate analyses were performed on the SRM 2974 certified material and the results are discussed.     

Liquid Chromatographic Analysis for Flecainide with Use of a Microbore Column and Ultraviolet Detection

Abstract

We describe a simple, isocratic high-performance liquid chromatographic method for measuring the oral antiarrhythmic agent flecainide acetate in serum or plasma. Sample analysis involves a simple organic extraction followed by chromatography on a microbore reverse phase column with ultraviolet detection at 298 nm.     

Determination of Oxalate with Immobilized Oxalate Oxidase in an Enzyme Thermistor

Abstract

This paper describes a rapid enzymic procedure, based on calorimetry, for specific determination of oxalic acid. Oxalate is oxidized by immobilized oxalate oxidase to hydrogen peroxide and carbon dioxide. The heat generated by this reaction is measured in a calorimetric device, the enzyme thermistor. Oxalate concentrations as low as 0.02 mM can be determined. Also described is purification and immobilization of the enzyme, as well as the effect of some of its inhibitors. The urinary oxalate content of 16 persons was determined using the enzyme thermistor. For samples containing a very low concentration of oxalate (less than 0.2 mM) an extraction step with tributylphosphate can be introduced to purify and concentrate the oxalate. The oxalate content in different kinds of food was also determined.