Imrich Zelenský

Determination of inorganic anions in river water by column-coupling capillary isotachophoresis

Abstract Optimal operating conditions for the simultaneous determination of Cl−, NO−3, SO2−4, NO−2, F− and PO3−4 in river water by column-coupling capillary isotachophoresis were found. The time for the complete analysis was ca. 25 min and no sample pre-treatment was needed. Detection limits for constituents that are present in river water at lower concentrations (NO−2, F− and PO3−4) were in the range 30–60 pmoles. Decomposition of NO−2 during the separation was observed and a possible mechanism is proposed.

Role of the charge number of the counter-ionic constituent in the separation of anions by isotachophoresis

Abstract The influence of the different charge numbers of the ionic forms of the buffering counter-ionic constituents on the effective mobilities of anions at pH 6.0 was investigated. It is shown that a proper choice of the charge number of the counter-ionic constituent can be used as an effective tool in optimization of the operating conditions in the separation of anions by isotachophoresis. The successful separation of a group of anions at pH 6.0 using 1,3-bis[tris(hydroxymethyl)methylamino]propane as the buffering counter constituent in the leading electrolyte (which could not be performed at this pH when other constituents were used for this purpose) illustrates the practical possibilities of this approach. Ca 2+ (a complex-forming cation) and doubly protonated diaminopropane (a non-complexing cation) were used as co-counterions in the leading electrolytes to show the different natures of their interactions with the same group of anions.

Isotachophoretic separation of alkali and alkaline earth metal cations in water—polyethylene glycol mixtures

Abstract The influence of polyethylene glycol (PEG) on the effective mobilities of alkali and alkaline earth metal cations was investigated. It is shown that appropriate proportions of water and PEG in the leading electrolyte enable a complete separation of this group of cations to be achieved by capillary isotachophoresis (ITP). The high dynamic concentration ranges of the ITP determinations achieved in the operational systems based on water—PEG mixtures are illustrated by practical examples (water samples, urine, aqueous extract of apple flesh).

Photometric detection at 405 nm in trace analysis by capillary isotachophoresis

The possibilities of photometric detection at 405 nm were investigated for trace isotachophoretic analysis of various ionic constituents. Increased selectivity of the detection enabled, for example, the detection and determination of nitrophenols at 10(-8) M in a 25-microliter sample. 5-Nitrofurylacrylic acid, a wine stabilizer, could be detected with confidence at ca. 0.1 ppm in wine without any sample pretreatment. Approximately 250-fmol amounts of amino acids, labelled with 2,4-dinitrophenyl, were detectable with the technique employed. This is almost three decades lower in comparison to what is achievable with an high resolution universal detector. The adsorption of the analytes in the sample handling devices as well as in the separation compartment were problems in the analysis at this concentration level. The detection limit given above was achieved when these phenomena were suppressed by the addition of naphthalene-1,3,6-trisulphonate or pyrophosphate to the sample solution.

Isotachophoretic determination of chromium(VI) at low parts per billion concentrations.

Factors important in the isotachophoretic determination of CrVI at low ppb concentrations were studied. To increase the selectivity of the analysis, the use of photometric detection at a 405 wavelength was preferred. Losses of CrVI due to adsorption were found to be the main potential source of analytical errors at the concentration levels of interest. The presence of sulphate in the sample solution at ca. 10(-4) M concentration eliminated the losses due to adsorption on the walls of the sample handling glassware. In analysis with a low pH of the leading electrolyte, adsorption of CrVI on the walls of the separation compartment also played a role; addition of naphthalene-1,3,6-trisulphonate to the sample solution considerably reduced this disturbance. When the precautions concerning adsorption were taken, the detection limits for CrVI were in the range 4-5 ppb (depending on the pH of the leading electrolyte) for a 30-microliters sample volume. The calibration graphs were linear over the concentration range 10(-7)-5 X 10(-6) M with good correlation coefficients. The reproducibilities of the determinations within this concentration range were 2-3% or better. The practical utility of capillary isotachophoresis in the trace determination of CrVI in drinking water and wastewater samples seems promising.

Photometric detection of amino-containing compounds in capillary isotachophoresis based on reaction with copper(II) ions

Abstract Some basic aspects of the photometric detection of amines, amino acids and peptides via their complexes (chelates) formed with Cu 2+ ions in capillary isotachophoresis (ITP) were studied. Experiments performed in this feasibility study were focused on the complexes of separands formed on the addition of Cu 2+ ions to the sample solution and the cationic mode of migration. The results suggest that only the compounds that form chelates with more than one ring are detectable photometrically as probably only this type of chelate did not bleed during the separation (migration). Detection limits for these ITP separands were in the range 10 −7 –10 −6 mol/l (30-μl sample volumes) when detection was carried out at 580 nm. ITP runs with various sample matrices indicate a high analytical selectivity of this mode of detection.