Audrius Padarauskas

Simultaneous separation of inorganic anions and cations by capillary zone electrophoresis

Abstract A new capillary electrophoretic approach for simultaneous separation of fast anions and cations is demonstrated. Indirect UV detection at 214 nm in conjunction with electromigration sampling from both ends of the capillary was developed. Two electrolyte systems based on imidazole-nitrate and copper(II)-ethylenediamine-nitrate were investigated for the simultaneous separation of chloride, sulphate, hydrocarbonate, potassium, ammonium, calcium, sodium and magnesium ions. Experimental parameters that were evaluated included a nature of UV chromophore, pH of electrolyte, a nature of complexing agent. The method permits the excellent separation of three anions and five cations in only 4 min using electrolyte system containing 2.5 mmol l −1 Cu(NO 3 ) 2 , 5 mmol l −1 ethylenediamine and 1 mmol l −1 fumaric acid at pH 8.5 adjusted with tetraethylammonium hydroxide.

Ionic liquids in microextraction techniques

AbstractThe tremendous potential of room temperature ionic liquids as an alternative to environmentally harmful ordinary organic solvents is well recognized. Due to their unique properties, such as low volatility, tunable viscosity and miscibility, and electrolytic conductivity, ionic liquids have attracted extensive attention and gained popularity in many areas of analytical chemistry including modern sample preparation techniques.In this review the advantages and limitations of application of ionic liquids as solvents/sorbents for microextraction are critically discussed. Topics covered include solid-phase microextraction, single drop microextraction, dispersive liquid-liquid microextraction and hollow-fiber liquid-phase microextraction. The compatibility of the ionic liquid-based microextraction with different analytical techniques such as gas chromatography, high-performance liquid chromatography, electrothermal or flame atomic absorption spectrometry and some others is also discussed. Finally, the main practical applications on this topic are summarized.

Capillary electrophoresis in metal analysis: Investigations of multi-elemental separation of metal chelates with aminopolycarboxylic acids

Abstract Capillary zone electrophoresis was applied to the separation of Co(III), Bi(III), Fe(III), Cr(III), V(IV), Pb(II), Hg(II), Co(II), Cu(II) and Ni(II) metal ions complexed with common aminopolycarboxylic acids. Ethylenediaminetetraacetic (EDTA), cyclohexane-1,2-diaminetetraacetic (CDTA) and diethylenetriaminepentaacetic (DTPA) acids were investigated and compared in order to optimize the separation resolution. The influence of carrier electrolyte parameters such as electrolyte nature, pH and concentration upon the electrophoretic behaviour of chelates was investigated and discussed. Two migration modes – counterelectroosmotic and coelectroosmotic – were compared. Better resolution was achieved using counterelectroosmotic conditions (25 kV) with 5 mmol/l DTPA electrolyte at pH 8.5 and direct UV detection at 214 nm. The separation time was less than 8 min, but the resolution of Co(II), Cu(II) and Ni(II) chelates was poor. For all metals studied the calibration graphs were linear over at least two orders of magnitude of concentration. The detection limits were in the range 2·10−6–8·10−6 mol/l. A possibility of simultaneous determination of metal ions with different oxidation states such as V(IV)/V(V) and Cr(III)/Cr(VI) is demonstrated. Examples of electropherograms are presented for different samples. Application of the method to the analysis of metal ions in electroplating bath and waste water samples is also demonstrated.

Capillary electrophoretic determination of sulfite using the zone-passing technique of in-capillary derivatization.

A new capillary electrophoretic (CE) method was developed for the simple and selective determination of sulfite. The proposed method is based on the in-capillary derivatization of sulfite with iodine using the zone-passing technique and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying concentration of iodine, electrolyte pH and applied voltage. The optimised separations were carried out in 20 mmol l(-1) Tris-HCl electrolyte (pH 8.5) using direct UV detection at 214 nm. Experimental results showed that the injection of the iodine zone from anodic end of the capillary gives significantly better precision. Common UV absorbing anions such as Br-, l-, S2O3(2-), NO3-, NO2-, SCN- did not give any interferences. Valid calibration (r2=0.998) is demonstrated in the range 1 x 10(-5) - 8 x 10(-4) mol l(-1) of sulfite. The detection limit (SIN=3) was 2 x 10(-6) mol l(-1). The proposed system was applied to the determination of free sulfite in wines. The recovery tests established for wine samples were within the range 92-103%. The CE results were compared with those obtained by iodometric titration technique.

On-line preconcentration and determination of chromium(VI) in waters by high-performance liquid chromatography using pre-column complexation with 1,5-diphenylcarbazide

A method for on-line chromatographic preconcentration and determination of chromium(VI) traces has been developed. Chromate was preconcentrated on a C18 column (50 x 6 mm I.D.) after complexation with diphenylcarbazide (DPC). Following the preconcentration step, analysis of the sample was performed using a C18 column (100 x 6 mm I.D.) with an eluent containing 6.10(-3) mol/l sulphuric acid and 20% (v/v) acetonitrile. Direct spectrophotometric detection at 546 nm was used. Experimental parameters such as mobile phase pH, DPC concentration, preconcentration flow-rate, sample volume were optimized for preconcentration and detection of Cr(VI)-DPC complex. Under the optimum conditions, most metal ions [Cr(III), Fe(III), Cu(II), Hg(II), Mo(VI), V(V)] and inorganic anions did not interfere. A detection limit of 0.02 ng/ml Cr(VI) can be attained when a sample volume of 100 ml is used. The technique has been applied successfully to the determination of Cr(VI) traces in drinking, surface and groundwater samples and the recoveries of added chromium were in the range 94-104%.

Simultaneous determination of iron(II) and iron(III) in water by capillary electrophoresis

Abstract Capillary zone electrophoresis (CZE) was applied for the simultaneous determination of iron(II) and iron(III) selectively complexed with 1,10-phenanthroline and CDTA. The best separation was achieved using a fused silica capillary (47 cm × 75 μ m i.d.) filled with a borate buffer (100 mmol l −1 , pH 9.0) and with direct UV detection at 254 nm. The separation time is less than 3 min. The influence of different experimental parameters such as pH, the sequence of adding and the molar ratio of the complexing agents on the iron(II)/iron(III) ratio was studied. The complexed sample mixture (pH 9.0) is stable for a few days at room temperature. The detection limits achieved are 0.06 mg l −1 for Fe(II) and 0.1 mg l −1 for Fe(III). The method was applied for the determination of both dissolved iron species in tap water and groundwater samples.

Capillary electrophoretic determination of thiosulfate, sulfide and sulfite using in-capillary derivatization with iodine

A new capillary electrophoresis (CE) method was developed for the rapid, simple and selective determination of thiosulfate, sulfide and sulfite species. The proposed method is based on the in‐capillary derivatization of separated sulfur anions by mixing their zones with the iodine zone during the electrophoretic migration and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying electrolyte pH, electrolyte counter‐ion, concentration of iodine, and applied voltage. The optimized separations were carried out in 20 mmol/L Tris‐chloride electrolyte (pH 8.5) using direct UV detection at 214 nm. All three sulfur species were well resolved in less than 4 min. The method gives repeatability comparable or even better than this obtained for sulfur anions using standard CE technique. The proposed CE system was applied to the monitoring of sulfur anions in spent fixing solutions during the electrolytic oxidation.

Matrix solid-phase dispersion extraction of carbadox and olaquindox in feed followed by hydrophilic interaction ultra-high-pressure liquid chromatographic analysis

A new method involving matrix solid-phase dispersion (MSPD) extraction and hydrophilic interaction ultra-high-pressure liquid chromatography (HILIC-UHPLC) with photodiode array detection was developed for the determination of carbadox and olaquindox in feed. Separation of carbadox and olaquindox was achieved within 1 min on the 1.7 microm Acquity UPLC BEH HILIC column by using isocratic elution with a mobile phase consisting of 10 mmol L(-1) ammonium acetate in acetonitrile-water (95:5, v/v) at a flow rate of 0.5 mL min(-1). Optimization of MSPD extraction parameters, such as type of solid sorbent and elution solvent were carried out. Optimal conditions selected for MSPD extraction were: 0.25 g of feed sample, 0.5 g of octadecylsilica as solid sorbent and 10 mL of acetonitrile-methanol (8:2, v/v) as eluting solvent. Both analytes provided average recoveries from spiked feed samples ranging from 89.1 to 98.4% with relative standard deviations less than 10%. Obtained performance characteristics are comparable to those achieved by liquid-liquid extraction-HPLC with the advantages of being simpler and significantly faster.

Simultaneous determination of inorganic anions and cations in waters by capillary electrophoresis.

The applicability of a recently proposed capillary electrophoresis technique based on the electromigrative sample introduction from both ends of the capillary was further investigated for the simultaneous determination of inorganic anions and cations in real water samples. The optimized separations were carried out in 5.0 mmol l-1 copper(II)-ethylenediaminehydroxide and 2.0 mmol l-1 triethanolamine electrolyte neutralized with chromic acid to pH 8.0, using indirect UV detection at 254 nm. Nine inorganic ions (Cl-, NO3-, SO4(2-), HCO3-, K+, NH4+, Na+, Ca2+ and Mg2+) were well separated in less than 5 min. The analytical performance of the method is discussed in terms of migration time, peak area and corrected peak area repeatability, linearity of response and detection limits. To evaluate this system, the determination of anions and cations was examined for mineral water, tap water and river water samples using Li+ as the internal standard. The comparison of the results with ion chromatography and conventional capillary electrophoresis is presented.

Capillary electrophoretic determination of thiosulfate and its oxidation products.

Capillary electrophoresis (CE) was developed for the rapid and simple determination of thiosulfate and its oxidation products such as common polythionates, sulfite and sulfate. Direct and indirect UV detection techniques were investigated. The optimized separations of UV absorbing S2O3(2-), S4O6(2-), S5O6(2-) and S6O6(2-) anions were carried out in 5 mmol l(-1) (NH4)2SO4, 5 mmol l(-1) KH2PO4 electrolyte at pH 5.0, with direct UV detection at 214 nm. All analytes were well resolved in less than 4 min. Analysis of S2O3(2-), S4O6(2-), SO4(2-) and SO3(2-) ions can be performed in 5 mmol l(-1) H2CrO4, 1 mmol l(-1) hexamethonium hydroxide electrolyte neutralized with triethanolamine to pH 8.0, using indirect UV detection at 254 nm. However, the detection sensitivity for tetrathionate was poor. Other polythionates can not be detected at all because of their high absorbance even at 254 nm. The developed CE method was applied for the monitoring of sulfur species in spent fixing solutions during the electrolytic oxidation.