Marja-Liisa Riekkola

Non-aqueous capillary electrophoresis

The benefits of non-aqueous capillary electrophoresis have been described in a number of recent publications. The wide selection of organic solvents, with their very different physicochemical properties, broadens our scope to manipulate separation selectivity. The lower currents present in non-aqueous solvents allow the use of high electric field strengths and wide bore capillaries, the latter in turn allowing larger sample load. In many cases detection sensitivity can also be enhanced. The potential of non-aqueous capillary electrophoresis is discussed throughout the paper, and the feasibility of capillary electrophoresis under non-aqueous media is demonstrated with reference to several applications.

Study on liposomes by capillary electrophoresis.

Liposomes made of mixtures of zwitterionic and anionic lipids were investigated by means of capillary electrophoresis and dynamic light scattering. The influence of the molar lipid ratio and of the buffers, used in the running electrolyte solution, on the physical characteristics of the liposomes were investigated. Data on effective electrophoretic mobilities, total charges as well as sizes of the liposomes are given. In addition, examples on the use of liposomes as carriers in electrokinetic capillary electrophoresis for the separation of benzene derivatives, steroids, and phenols are shown.

Extraction of polychlorinated biphenyls with water under subcritical conditions

Abstract Supercritical fluid extraction is a fast and efficient method to extract all manner of organic compounds from a wide variety of solid sample matrices. Due to the marked change in its polarity with temperature, water is an interesting alternative to carbon dioxide as the extraction fluid. By merely adjusting the temperature, selectivity can be achieved for inorganic or organic compounds and for polar or non-polar organic compounds. Many organic compounds are sufficiently soluble to be extracted under subcritical conditions and, in this way, instrumental and other problems, such as the high corrosiveness of supercritical water, can be avoided. Instrumentation for sub- and supercritical water extraction was developed and modified in several ways with the aim of simplifying the procedure while maintaingng good recoveries. Good recoveries of polychlorinated biphenyls (PCBs) spiked into sea sand and of native PCBs in a real soil sample were achieved with liquid collection. Relative to Soxhlet extraction, recoveries were higher or similar when solid-phase and liquid collection were combined. With a solid-phase trap packed with Tenax, the recovery was usually more than 85% for spiked PCBs.

On-line coupled liquid chromatography–gas chromatography

On-line coupled liquid chromatography-gas chromatography (LC-GC) is a powerful technique that combines the best features of LC and GC and is ideal for the analysis of complex samples. This review describes the unique features of on-line coupled LC-GC. The different interfaces and evaporation techniques are presented, along with their advantages and disadvantages. Guidelines are given for selecting a suitable LC-GC technique and representative applications are noted.

Pressurised hot water extraction–microporous membrane liquid–liquid extraction coupled on-line with gas chromatography–mass spectrometry in the analysis of pesticides in grapes

Pressurised hot water extraction-microporous membrane liquid-liquid extraction was coupled on-line with gas chromatography-mass spectrometry (PHWE-MMLLE-GC-MS) for the analysis of pesticides in grapes. MMLLE serves as a trapping step after PHWE. Water from PHWE is directed to the donor side of the membrane unit and the analytes are extracted to the acceptor solution on the other side. The role of MMLLE is to clean and concentrate the extract before on-line transfer to the GC via a sample loop and an on-column interface using partially concurrent solvent evaporation. The extraction conditions were investigated, and then the quantitative features such as linearity, limit of quantification (LOQ), extraction yield and enrichment factors. LOQs in the range 0.3-1.8 microg kg(-1) were achieved. Procymidone and tetradifon were found in the skins of the grapes. The results were in good agreement with those obtained by liquid-solid and ultrasonic extractions.

Capillary electrophoresis with wide-bore capillaries and non-aqueous media

Abstract A major drawback of capillary electrophoresis is that its use for semi-preparative purposes is problematic. To overcome the problems associated with wide-bore capillaries, non-aqueous background electrolyte instead of aqueous buffers was used. The effect of the capillary diameter on capillary electrophoretic separation was investigated in ethanol–acetonitrile–acetic acid (50:49:1, v/v) containing 20 m M ammonium acetate. This buffer allowed the use of wider capillaries and higher electric field strength than the corresponding buffer containing water in place of ethanol and acetonitrile. Increasing the internal diameter of the capillary from 50 to 200 μm allowed a 16-fold increase in the sample load at the same ratio of injected volume to total volume. In wide-bore capillaries the difference between the inlet and outlet buffer level leads to siphoning, which has a marked effect on the apparent electroosmotic velocity and the efficiency of the separation. The effect of the physical properties of the solvent on siphoning is discussed. Our results indicate that non-aqueous media may have a major role in semi-preparative capillary electrophoresis.

Capillary electrophoresis of diuretics

The review surveys the application of capillary electrophoresis to the screening, identification and determination of diuretics and probenecid. The number of publications is still limited, but the studies already published clearly show that capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography are excellent alternatives for the investigation of diuretics. High accuracy identifications of diuretics and probenecid, even in urine samples, can be obtained when CZE is used with the marker techniques. This review paper has been written from the viewpoint of practical use and some hints are given for future CE studies on diuretics.

Stability of polycyclic aromatic hydrocarbons in pressurised hot water

The stability of seven polycyclic aromatic hydrocarbons (PAHs) were studied in aqueous solutions at 100-350 degrees C. The aqueous solution of one PAH compound at a time was sealed in a stainless steel bomb-type reaction vessel in an argon atmosphere and heated for 10 to 240 min in an oven. The contents of the vessel were analysed by GC-MS. At 300 degrees C, degradation was observed even with the shortest heating time, 10 min. The degradation products were typically different oxidation products such as ketones and quinones. In addition to the heating time and temperature, the concentration of the analyte and the inner surface of the vessel affected the results.

Capillary electrophoresis of methyl-substituted phenols in acetonitrile

The separation of mono- and dimethylphenols by capillary electrophoresis in pure acetonitrile was investigated. In acetonitrile, uncharged phenols interact with background electrolyte anions forming negatively charged complexes, which can be separated from each other by capillary electrophoresis. The background electrolyte anions tested were acetate, bromide and chloride. The calculated formation constants for phenol-anion complexes were highest with acetate and smallest with bromide. Complex formation was found to be sensitive to traces of water in the background electrolyte. The separation of methylphenols was also carried out in acetonitrile at high pH using background electrolytes prepared from diprotic acids and tetrabutylammonium hydroxide. At high pH the phenols were partly dissociated, providing an additional mechanism for the separation. All methylphenols were separated with the use of malonate background electrolyte. However, this approach was prone to interference from methanol resulting from the tetrabutylammonium hydroxide solution.

Continuous two-dimensional field-flow fractionation: a novel technique for continuous separation and collection of macromolecules and particles

Instrumental techniques to analyse macromolecular and particulate materials have undergone rapid development in response to the need for high resolution, precise identification and characterization, and enrichment and collection for further analysis. Continuous two-dimensional field-flow fractionation (2D-FFF), which is described in this article, is a novel technique for separation and collection of macromolecules and particles. 2D-FFF is based on the conventional field-flow fractionation principle but with carrier flow in two-dimensions. This overview discusses the principle of the technique, describes the instrumentation and suggests potential applications and further extensions. An overview of the basic field-flow fractionation principle is presented.