Karel Štulík

Microelectrodes. definitions, characterization, and applications: (Technical report)

Theory, preparation,and applications of microelectrodes and microelectrode arrays are critically reviewed, and future trends in the field are outlined. An operational definition of a microelectrode is also recommended.

Methacrylate monolithic columns of 320 μm I.D. for capillary liquid chromatography

Monolithic capillary columns (320 microm I.D.) were prepared for capillary liquid chromatography (CLC) by radical polymerization of butylmethacrylate (BMA) and ethylenedimethacrylate (EDMA) in the presence of a porogen solvent containing propan-1-ol, butane-1,4-diol and water. The influence of the contents of the porogen solvent and EDMA in the polymerization mixture on the monolith porosity and column efficiency was investigated. The composition of the polymerization mixture was optimized to attain a minimum HETP of the order of tens of microm for test compounds with various polarities. The separation performance and selectivity of the most efficient monolithic column prepared was characterized by van Deemter curves, peak asymmetry factors and Walters hydrophobicity and silanol indices. It was demonstrated that the 320-microm I.D. monolithic column exhibited CLC separation performance similar to that observed for 100- and 150-microm I.D. monolithic columns reported in the literature; moreover, the 320-microm I.D. column was easier to operate in CLC and exhibited a higher sample loadability.

Reliability of Carotenoid Analyses: A Review

This review critically discusses the most important properties of techniques applied to analyses for carotenoids and their impact on the reliability of the analytical results. The emphasis is placed on modern methods and the most recent references. Examples of analytical procedures illustrate the characteristics of experimental approaches to carotenoid analyses but no systematic survey of applications is given. Carotenoids are characterized chemically and their occurrence and functions in organisms are outlined. The principal implications of the (bio)chemical properties of carotenoids for the selection of an appropriate analytical procedure and for optimisation of the experimental conditions are dealt with. Various aspects of pre- treatment and preconcentration of analytical samples are discussed, emphasizing modern approaches, such as microwave-assisted extraction or supercritical fluid extraction; the problems connected with chromatographic purification of carotenoids and with the obtaining of reliable standard materials are also dealt with. The approaches to determination of carotenoids involving high-performance separations are evaluated, emphasizing the importance of high performance liquid chromatography (HPLC) and capillary electrochromatography (CEC); of the detection techniques, spectrophotometry in ultraviolet and visible region (UV/VIS spectrophotometry), electrochemistry, thermal lens spectrometry (TLC), mass spectrometry (MS), nuclear magnetic resonance (NMR), and some aspects of vibrational spectrometry are primarily discussed.

Electrochemical sensors with solid polymer electrolytes

Electrochemical sensors with an electrode system formed on a solid polymer electrolyte (spe) enable detection of substances in poorly conductive liquids and in gases and can be constructed either with a liquid phase as a part of the sensor system, or as solid-state sensors. The basic properties of spe, especially Nafion, are discussed as are the methods of preparation of electrodes on the spe surface. The effects of the geometry, preparation procedure and the character of the spe/electrode boundary on the sensor properties are examined. Principal sensor designs are described and discussed and selected applications are surveyed in the tables.

High-performance separations in the determination of triazine herbicides and their residues

The present state of analysis for triazine herbicides and their residues is critically surveyed. After a brief introduction, summarizing the properties of triazines and the history of the determination of the parent compounds and their residues, attention is primarily paid to preconcentration techniques for water and soil samples, such as liquid-liquid, supercritical-fluid and solid-phase extraction, and modern separation methods employed for the actual determination, e.g., gas and liquid chromatography, especially in combination with selective detection, capillary electrophoresis and, to a lesser extent, thin-layer chromatography. Important immunoanalytical procedures are also briefly discussed.

Capillary electrophoresis of inorganic cations

The capillary electrophoresis (CE) methods of determination of inorganic cations are critically surveyed, with emphasis on the most recent works. The metal ion complexation is treated in detail, as well as the detection techniques. The advantages and drawbacks of CE compared to HPLC are briefly considered and typical examples of application to various matrices are given in a table.

High-performance liquid chromatographic determination of some anthraquinone and naphthoquinone dyes occurring in historical textiles.

A reversed-phase HPLC method has been developed for identification and quantitation of nine natural quinone dyes and applied to historical textile fibres. A Purospher RP18e column was used with a convex gradient of methanol in a mobile phase of 0.1 M aqueous citrate buffer (pH 2.5) and spectrophotometric diode-array detection at 270 nm. For identification of alizarin, purpurin and xanthopurpurin, occurring together in the madder plant, an isocratic method was used with a methanol-0.2 M acetate buffer (pH 4.3) (75:25) as the mobile phase. After an acid extraction of textile fibres and the analysis of the extracts, alizarin and purpurin were identified and quantitated in three fibres.

Electrochemical detection techniques in high-performance liquid chromatography

Abstract The field of electrochemical HPLC detectors is critically reviewed. The principal requirements for detectors and the conditions for the use of electrochemical detection techniques are summarized and important electrochemical detectors are described, with emphasis on voltammetric and coulometric detectors. The operational parameters of electrochemical detectors are evaluated and compared with the most common optical detectors. Typical applications of electrochemical detectors are listed in Table 6.

High-performance liquid chromatography of s-triazines and their degradation products using ultraviolet photometric and amperometric detection

The chromatographic behaviour of eighteen s-triazine derivatives has been studied in a reversed-phase system with a Separon SIC 18 stationary phase and a mobile phase of aqueous sodium dihydrogenphosphate and methanol. The dependences of the capacity factors on the methanol content, the pH and the ionic strength have been obtained. Ultraviolet photometric detection can generally be used whereas amperometric detection with a carbon-fibre array electrode is useful for selective detection of s-triazine hydroxy derivatives, but with a sensitivity poorer than that of photometric detection. The method has been applied to a study of the photolysis of s-triazines and the effect of the substituents and the pH on the photolysis rate.

Some potentialities and drawbacks of contemporary size-exclusion chromatography.

The present state of the chromatographic techniques based on differentiation of solutes according to their molecular sizes is briefly surveyed. Attention is centred on high-performance techniques applied to purification and characterization of natural macromolecules, and on discussion of the chromatographic approaches to the determination of the molecular masses and molecular mass distributions of both natural and synthetic polymers. The basic requirements on the selection of the separation system and the experimental conditions are summarized, demonstrated on a few examples and critically evaluated.