K. Šlais

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.

Electrochemical cell with effective volume less than 1 nl for liquid chromatography

Abstract The design and the application of an electrochemical detector with volume less than 1 nl is described. The detection limit is less than 0.1 pg. The application of the detector in combination with capillary columns in liquid chromatography yields good separation efficiencies within relatively short analysis times.

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.

Minimization of extra-column effects with microbore columns using electrochemical detection

Abstract The characteristics of a simple two-electrode electrochemical detector (cell volume 20 nl) for microbore columns are described. An injection valve is connected to the microbore columns so as to provide low sample dispersion during injection. The applications described show that the equipment fully exploits the advantageous features of short columns down to 50 × 0.5 mm. The minimum detectable quantity when using small columns is 3 pg of pyrocatechol, the linear dynamic response range exceeding three orders of magnitude.

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.

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.

Sample-induced internal gradient and ionic strength in ion-exclusion microcolum liquid chromatography

Abstract A simple method for the generation of a variable gradient of decreasing ionic strength is described. The principle permits the gradient elution of organic ions under the conditons of ion-exclusion chromatography, i.e ., with the signs of the solute and sorbent charges being the same. The method allows the gradient to be induced simultaneously with sample introduction on to the separation column. Such conditions are useful for trace analysis based on on-column preconcentration from a large sample volume and subsequent gradient elution. The method was applied to the separation of UV-absorbing organic anions on a microcolumn packed with a reversed-phase sorbent with fixed anionic groups.

Enrichment techniques and trace analysis with microbore columns in liquid chromatography

The advantages of microbore columns for trace analysis by liquid chromatography are identified, with reference to on-column enrichment techniques performed on analytical micro-columns. The selectivity and high sensitivity of the amperometric detector are utilized in combination with a microbore column for a number of pharmaceutical and bioanalytical analyses, including phenothiazines, parabens, sulphonamides, catecholamines, tetracyclines, vitamins, amino acids and dipeptides.

Simultaneous conductivity and amperometric detector with a single cell for microbore liquid chromatography

Abstract A detector for microbore liquid chromatography is described, which can monitor column eluents by both electrical conductivity and electrode reaction. The volume of the single detector cell is 15 nl. The noise of the conductivity detection is equivalent to 1/20 000 of the background electrolyte conductivity. The noise of the amperometric detection is 7 pA. The mutual independence of both detection modes is discussed. The detector performance is demonstrated by the detection of inorganic anions and urea derivatives separated on a microbore column.