Heli Sirén

Determination of the carboxylic acids in acidic and basic process samples by capillary zone electrophoresis

Capillary zone electrophoresis (CZE) with indirect UV detection was used in developing a method for the simultaneous determination of inorganic anions, aliphatic and heterocyclic organic acids in various processed samples. The analytes were determined simultaneously in 10 min using an electrolyte containing 20mM 2,3-pyrazine dicarboxylic acid, 65mM tricine, 2mM BaCl(2), 0.5mM cetyltrimethylammonium bromide, and 2M urea at pH 8.06. Linear plots for the analytes were obtained in the concentration range of 2-150 mg L(-1). Relative standard deviations (RSDs) of peak areas during a 3-day analysis period varied from 5.5% for glycolate to 9.5% for oxalate. RSDs of migration times varied between 0.4% and 1.1%. The detection limit (at S/N 3) was 1 mg L(-1) for all the analytes studied. The proposed method was successfully demonstrated for the determination of carboxylic acids in eight oxygen treated samples of commercial softwood and hardwood kraft lignin and two red wine samples of Pinot Noir grapes. In the kraft lignin samples the concentrations of carboxylic acids correspond to the oxidation time. The acid concentrations of wine varied considerable.

Aqueous and non-aqueous capillary electrophoresis of polar drugs

Aqueous and non-aqueous capillary electrophoresis (CE) systems nwere employed for the separation of basic and acidic polar drugs using ncapillary zone electrophoresis (CZE) and micellar electrokinetic nchromatography (MECC) techniques. This work was performed to determine the ndifferences in selectivity, after chemical adjustment of the media, of the nseparation of closely related drugs (by measurement of separation nefficiency, resolution and detection) in aqueous and non-aqueous solvents. nVarious electrolytes were tested in aqueous and organic solvent media. The nbest separation in aqueous CZE was obtained in 25 mM phosphate solution at npH 7.3. In aqueous MECC, the best performance was obtained in pH 10.5 nbuffer containing glycine and dodecyl sulfate. Non-aqueous CE separations nwere performed in electrolyte mixtures containing nmethanol–acetonitrile, ethanol–acetonitrile and npropan-2-ol–acetonitrile (50∶49, v/v) modified by ammonium nacetate and water-free glacial acetic acid. Acetone was also used instead nof acetonitrile in the separation media. In non-aqueous CE systems, the neffect of water in the non-aqueous sample and as part of the electrolyte nsolution played a significant role in the separation of polar anionic ndrugs.

On-Line Flow Injection—Capillary Electrophoresis Instrument with Contactless Conductivity Detection for Sensitive Cation Analyses

Abstract A new system for on-line analyses of metal cations has been developed by combining flow injection sample introduction with on-line capillary electrophoresis. The on-line analysis instrument has a simple construction and it allows fast sample introduction from a flowing solution. The ends of the separation capillary and the electrodes were placed opposite to each other into tubings that were installed over them behaving as flow-through channels. The capillary temperature during the analyses was controlled by water cooling and the analyte monitoring was conducted with a contactless conductivity detector. The construction allowed compound detection of very low concentrations. The instrument was used for simultaneous determination of ammonium, potassium, calcium, magnesium, and sodium as complexes in aqueous 18-crown-6 ether – acetate electrolyte solution. Flow injection analysis of sample introduction was kept apart from the ligand modified electrolyte solution. Calibration with standard mixtures of alkali metals, alkaline earth metals, and ammonium was linear in the range from 10 ng/mL to 1 µg/mL for each analyte. The intraday reproducibility for the separations was 2% (RSD). The detection limit for the cations was 10 ng/mL. The studies showed the performance of the method to be sensitive for the monitoring of inorganic ions in water treatment.