Věra Pacáková

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.

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.

Gas and high-performance liquid chromatography of phenols

SummaryGas and high-performance liquid chromatographic methods in the analysis of phenols are reviewed. Among the great number of phenolic compounds analyzed, alkylphenols, chlorophenols, dihydroxy- and trihydroxybenzenes and biphenols are chiefly considered. The advantages and drawbacks of the methods are discussed, quoting the most important work. Relationships between the structural characteristics of phenols, the stationary phase structure, the mobile phase composition and the retention data are treated. Typical examples of the conditions for GC and HPLC analysis are summarized in tables. The literature comprises over 270 references, most of them recent.

Amperometric flow detection with a copper working electrode—response mechanism and application to various compounds

The mechanism of amperometric detection with a copper electrode has been studied with four amino-acids in four different carrier liquids containing aqueous buffer and methanol. It is concluded that the response is produced by complexation of the test substances with cupric ions in the outer, porous layer of the passivating film, with formation of CuL(+) species. The increase in detector current is primarily determined by the complexation kinetics and to a lesser degree by the stability of the complex formed. The complexation rate strongly decreases with increasing amounts of organic solvent in the carrier liquid. The optimal detection conditions are discussed on the basis of the detection mechanism. Results are given for the detection of various structural types of amines and amino-alcohols.

A simple method for the trace determination of methanol, ethanol, acetone and pentane in human breath and in the ambient air by preconcentration on solid sorbents followed by gas chromatography

A simple technique has been developed for preconcentration of gaseous trace organic compounds on solid sorbents, followed by gas chromatography. The sorbent is packed in a cartridge from a syringe needle placed in the gas chromatographic injector and the analytes previously adsorbed are thermally desorbed at the injector temperature and then directly swept by the carrier gas into the column. The system has been tested for a charcoal-based adsorbent and silica gel, with pentane, methanol, ethanol and acetone as the model analytes. The procedure is rapid, the detection limits vary from a few nmol l(-1) to values below 0.1 nmol l(-1) (i.e., a few ppb), the linear dynamic range amounts to at least five concentration decades and a typical relative standard deviation is 10% at the nmol l(-1) concentrations. It has been shown that the method is readily applicable to determination of instantaneous concentrations of the analytes in natural and industrial atmosphere and to their monitoring in human breath which is important for medical and hygienic practice. In general, the procedure is applicable to low-molecular volatile organic compounds.

Comparison of enantioselective separation of N-tert.-butyloxycarbonyl amino acids and their non-blocked analogues on teicoplanin-based chiral stationary phase

Abstract A teicoplanin-based chiral stationary phase (CSP) was tested for enantioseparation of underivatized amino acids and their N - tert .-butyloxycarbonyl ( t -Boc) derivatives, important precursors in peptide synthesis. Mobile phase composition was optimized for organic modifier and triethylamine acetate buffer (TEAA) contents, and retention and enantioresolution of t -Boc-amino acids and their non-blocked analogues were compared. The importance of the amino group of amino acids in the interaction mechanism was evaluated. Native amino acids have better possibility for interaction with teicoplanin; they are more retained on the CSP and better enantioresolved than the blocked amino acids. Presence of triethylamine in the aqueous portion of the mobile phase was shown to be important for separation of enantiomers of t -Boc-amino acids; while native amino acids were almost not affected by the addition of TEAA. Results obtained for blocked amino acid on teicoplanin CSP with mobile phase composed of 1% triethylamine acetate, pH 4.1 and organic modifier were compared to those got on hydroxypropyl-β-cyclodextrin CSP. Good enantioseparation in a reasonable analysis time was obtained on the teicoplanin-based chiral stationary phase.

The application of precision gas chromatography to the identification of types of hydrocarbons

Abstract It appears that under precisely controlled conditions retention indices of apolar substances on apolar stationary phases can be reproduced to 0.03 units. This permits the accurate measurement of the temperature coefficients of the K ovats index for different classes of hydrocarbons. In this way classes of compounds having similar ΔI values ( I polar - I apolar ) may be distinguished. This is of particular importance because of the lower precision of the index data on polar stationary phases.