M. Krejčí

Vacant peaks in liquid chromatography

Abstract The origin and properties of vacant chromatographic peaks that occur most often when a two-component mobile phase is used and that do not belong to any component of the mixture under analysis are described.

Flow characteristics and technology of capillary columns with inner diameters less than 15 μm in liquid chromatography

Abstract The flow characteristics of capillary columns at flow-rates up to 10 −5 μl/sec have been studied experimentally as a function of the column diameter and of the pressure drop. Theoretical conclusions based on the Poiseuille equation and band broadening for unsorbed solutes have been tested. The preparation of glass capillary columns is described, and the role of the glass melting temperature is discussed. The inner diameters (5–34 μm) of the columns were measured both by microscopy and hydrodynamically. The maximum difference between the two measurements was 2.8 μm, but in most cases it did not exceed 1.5 μm. The modified flame-ionization detector was used.

Trace analysis by peak compression sampling of a large sample volume on microbore columns in liquid chromatography

Abstract Theoretical analyses and practical examples have shown the advantages of microbore columns when injecting solutes dissolved in a non-cluting solvent. In the determination of polynuclear aromatic hydrocarbons and chlorinated phenols, reversed-phase chromatography with amperometric detection yielded detection limits from 20 to 280 ng 1-1 in the sample. The method works with a small amount of sample (1 ml), with simple injection and without a pump for flushing the injection loop.

Open tubular columns in liquid chromatography

Abstract Capillary liquid chromatography was studied in liquid-solid and liquid-liquid systems. It was proved that selectivity data obtained with an analytical column are the same as those obtained with a capillary column having a layer of adsorbent on its wall. In the liquid-liquid system, up to 1,250,000 theoretical plates were obtained for an unretained solute with an effectiveness of 50 theoretical plates per second. Possibilities of applying commercial pumps and detectors to the work with capillary columns were demonstrated.

New principle of sample introduction integrated with mobile phase delivery for micro-column liquid chromatography

Abstract The possibilities and limitations of a liquid micro-chromatograph with integrated sample introduction and mobile phase delivery systems are considered. Basic values of chromatographic constants such as capacity ratio and number of theoretical plates are expressed as a function of a defined and limited retention volume. A new type of the liquid micro-chromatograph is described. The sample introduction system is integrated with a mobile phase delivery system in one instrumental section. A gradient of the mobile phase can be generated in the device. The new principle is applicable as a portable, fully automated analyser. Volumes of 0.01–500 μl can be injected. A controlled sample introduction velocity makes it possible to generate extremely small dispersions. A column efficiency of near to theoretical levels can be achieved with an amperometric detector. Both trace analyses and rapid chromatographic separations are demonstrated.

Experimental comparison of some detectors used in high-efficiency liquid chromatography

Abstract The properties of the detectors that are most often used in high-efficiency liquid chromatography were studied under identical conditions. Sensitivities and contributions to the height equivalent to a theoretical plate were determined for a differential refractometer, a capacitance detector, a UV spectrophotometer and two types of detector with effluent transporter.

Generation of electricity in low-conductivity liquid as a detection principle in liquid chromatography

Abstract A detection principle is described that is based on the measurement of streaming curreng. Relationships are presented that described the generation of electricity in low-conductivity liquid during their flow through a capillary or a porous bed. By virtue of the theory of an electrical double layer, the dependence of the magnitude of the electrical current transported by the liquid on the composition of the mobile phase and the nature of the phae interface is derived. The response i.e, the electrical current, has the character of a mass-sensitive response. The detection principle is non-selective and non-destructive.

Measurement of exclusion volumes of packed columns by means of electrokinetic detection

Abstract A method is described for the measurement of the exclusion volumes of packed chromatographic columns by means of electrokinetic detection in liquid chromatography.

Analysis of non-ionic surfactants of the alkylphenol type in the presence of mineral oil by means of liquid chromatography

Abstract A method has been developed for the determination of trace amounts of non-ionic surfactants of the alkylphenol type and mineral oil in waste waters. The separation of different Arkopals, p-C9H19·C6H4·O·(CH2·CH2O)nH, according to the number of ethylene oxide units by liquid—liquid chromatography is described. The procedures were elaborated for the discrimination of oil and surfactant components in the sample. Selective detection of both components in the UV region (254 and 285 nm) was used. UV and IR spectra of the surfactants are shown. An enrichment procedure using a pre-column packed with Porapak Q was tested. Water, in which trace amounts of Arkopal and oil were to be determined, functioned as a very weak mobile phase in the pre-column. After completion of the enrichment procedure, n-hexane was used as a strong mobile phase with simultaneous pre-column heating. Enrichment factors of up to 106 were determined, which enabled the components at concentrations down to the parts per million level to be determined. The error of the determinations was calculated.

Wire detector with an alkali flame ionization sensing element for liquid chromatography

Abstract A detector with a wire mass transfer was modified for the analysis of thermally labile halogen derivatives of tetrahydrofurans. The wire and eluate enter a combustion oven directly and the combustion products are carried by a tream of air into a double-burner alkali flame ionization sensing element.