Dušan Kaniansky

Capillary electrophoresis of inorganic anions

This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE.

Isotachophoresis and isotachophoresis : zone electrophoresis separations of inorganic anions present in water samples on a planar chip with column-coupling separation channels and conductivity detection

The use of a poly(methylmethacrylate) chip, provided with two separation channels in the column-coupling (CC) arrangement and on-column conductivity detection sensors, to electrophoretic separations of a group of inorganic anions (chloride, nitrate, sulfate, nitrite, fluoride and phosphate) that need to be monitored in various environmental matrices was studied. The electrophoretic methods employed in this study included isotachophoresis (ITP) and capillary zone electrophoresis (CZE) with on-line coupled ITP sample pretreatment (ITP-CZE). Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the CC chip were suppressed and electrophoresis was a dominant transport process in the separations performed by these methods. ITP separations on the chip provided rapid resolutions of sub-nmol amounts of the complete group of the studied anions and made possible rapid separations and reproducible quantitations of macroconstituents currently present in water samples (chloride, nitrate and sulfate). However, concentration limits of detection attainable under the employed ITP separating conditions (2-3 x 10(-5) mol/l) were not sufficient for the detection of typical anionic microconstituents in water samples (nitrite, fluoride and phosphate). On the other hand, these anions could be detected at 5-7 x 10(-7) mol/l concentrations by the conductivity detector in the CZE stage of the ITP-CZE combination on the CC chip. A sample clean-up performed in the ITP stage of the combination effectively complemented such a detection sensitivity and nitrite, fluoride and phosphate could be reproducibly quantified also in samples containing the macroconstituents at 10(4) higher concentrations. ITP-CZE analyses of tap, mineral and river water samples showed that the CC chip offers means for rapid and reproducible procedures to the determination of these anions in water (4-6 min analysis times under our working conditions). Here, the ITP sample pretreatment concentrated the analytes and removed nanomol amounts of the macroconstituents from the separation compartment of the chip within 3-4 min. Both the ITP and ITP-CZE procedures required no or only minimum manipulations with water samples before their analyses on the chip. For example, tap water samples were analyzed directly while a short degassing of mineral water (to prevent bubble formation during the separation) and filtration of river water samples (to remove particulates and colloids) were the only operations needed in this respect.

Capillary zone electrophoresis separations of enantiomers present in complex ionic matrices with on-line isotachophoretic sample pretreatment.

Analytical capabilities of capillary zone electrophoresis (CZE) with on-line coupled capillary isotachophoresis (ITP) sample pretreatment in the column-coupling capillary electrophoresis equipment to separate and determine enantiomers present in multicomponent ionic matrices were studied. Tryptophan was used as a model analyte in the ITP-capillary zone electrophoresis experiments performed in this context while a 90-component model mixture of UV-light absorbing organic anions and urine served as multicomponent sample matrices. Various working modes in which the on-line coupled capillary isotachophoresis-capillary zone electrophoresis combination in the column-coupling separation system can operate were employed in the anionic regime of the separation with direct injections of the samples. Advantages and limitations of these working modes in the separations of enantiomers present in model and urine matrices were assessed. Experiments with model mixtures of tryptophan enantiomers revealed that the two were resolved in the capillary zone electrophoresis stage with the aid of alpha-cyclodextrin also when their concentration ratio in the sample was 1:200 while the concentration of L(-)-tryptophan was 25 nmol/l. The limits of detection for the enantiomers were at approximately 10 nmol/l (approximately 1.5 ng/ml) concentrations for a 220 nm detection wavelength of the UV detector employed in the capillary zone electrophoresis stage and for a 30 microliters sample load. A high sample load capacity of the on-line coupled capillary isotachophoresis stage was effective in separating the samples corresponding to 3-6 microliters volumes of undiluted urine. The results from the runs with urine samples showed that only the capillary isotachophoresis-capillary zone electrophoresis combination with a post-column on-line coupled capillary isotachophoresis sample clean-up (responsible for a removal of more than 99% of the sample anionic constituents migrating in the on-line coupled capillary isotachophoresis stack and detectable in the capillary zone electrophoresis stage) provided a universal alternative for the detection and quantitation of the model analyte (L(-)-tryptophan).

Capillary zone electrophoresis of complex ionic mixtures with on-line isotachophoretic sample pretreatment

Separation modes provided by the column-coupling configuration of the separation unit in an on-line combination of capillary isotachophoresis (ITP) with capillary zone electrophoresis (CZE) were studied from the point of view of their potential in the (trace) determination of ions present in complex ionic matrices. Urine was arbitrarily chosen as such a matrix while sulphanilate and 3,5-dinitrosalicylate (currently not present in urine) served as model analytes. In one of these modes, ITP was employed to remove only the most abundant sample constituent (chloride) and concentrate the rest of those migrating between the leading and terminating zones for injection into the ZE stage. In the other mode, ITP was employed for maximum sample clean-up. Here, only the analyte(s) with a minimum of the matrix constituents was transferred for a final separation in the ZE stage. The fraction to be transferred was defined via a pair of discrete spacers added to the sample. Although a highly efficient sample clean-up was typical in this instance, the use of identical migration regimes in both stages (the separations according to ionic mobilities) did not prove the resolution of one of the analytes (sulphanilate) from the matrix constituent(s) in the ZE stage. A considerable improvement in this respect was achieved easily when the ITP clean-up was based on the separation according to pK values while the constituents present in the transferred fraction were finally separated via differences in their ionic mobilities. This two-dimensional approach provided a way to achieve a 150 ppb (10−6 mol 1−1) concentration detection limit for sulphanilate in a 1-μl volume of urine taken for the electrophoretic run.

Isotachophoresis and isotachophoresis‐zone electrophoresis of food additives on a chip with column‐coupling separation channels

The use of a poly(methylmethacrylate) chip, provided with two separation channels in the column-coupling (CC) arrangement and on-column conductivity detection sensors, to isotachophoresis (ITP) and ITP-ZE separation and determination of food additives was studied. A group of preservatives and taste intensifying components examined in this study included benzoate, sorbate, p-hydroxybenzoic acid esters (parabens), and glutamate, while various food products and cosmetics represented different matrices (proteins, fat, organic acids, carbohydrates, salts). ITP on the CC chip was found suitable for the determination of glutamate in the food products with only a minimum sample preparation (dilution, filtration). It also provided a rapid and simple procedure for the determination of parabens in cosmetics. On the other hand, ITP experiments with benzoate and sorbate revealed that sample preparations providing high analyte/matrix concentration ratios are essential when these food preservatives are to be determined by ITP on the chip. ITP-ZE combination on the same chip provided a solution to this problem by integrating an efficient ITP sample preparation (concentration of the preservatives and removal of the main part of the matrix), capable of processing μL sample volumes, with a final ZE separation and sensitive detection (low μmol/L limits of detection) of the preservatives. In both ITP and ITP-ZE separations on the CC chip no interference from food matrices was found.

Determination of organic acids and inorganic anions in wine by isotachophoresis on a planar chip.

Isotachophoretic (ITP) separation and determination of a group of 13 organic and inorganic acids, currently present in wines, on a poly(methyl methacrylate) chip provided with on-column conductivity detection was a subject of a detailed study performed in this work. Experiments with the ITP electrolyte systems proposed to the separation of anionic constituents present in wine revealed that their separation at a low pH (2.9) provides the best results in terms of the resolution. Using a 94 mm long separation channel of the chip, the acids could be resolved within 10-15 min also in instances when their concentrations corresponded to those at which they typically occur in wines. A procedure suitable to the ITP determination of organic acids responsible for some important organoleptic characteristics of wines (tartaric, lactic, malic and citric acids) was developed. Concentrations of 2-10 mg/l of these acids represented their limits of quantitation for a 0.9 microl volume sample loop on the chip. A maximum sample load on the chip, under the preferred separating conditions, was set by the resolution of malate and citrate. A complete resolution of these constituents in wine samples was reached when their molar concentration ratio was 20:1 or less. ITP analyses of a large series of model and wine samples on the chip showed that qualitative indices [RSH (relative step height) values] of the acids, based on the response of the conductivity detector, reproduced with RSD better than 2% while reproducibilities of the determination of the acids of our interest characterized RSD values better than 3.5%.

Determination of bromate in drinking water by zone electrophoresis-isotachophoresis on a column-coupling chip with conductivity detection.

The use of capillary zone electrophoresis (CZE) on‐line coupled with isotachophoresis (ITP) sample pretreatment (ITP‐CZE) on a poly(methylmethacrylate) chip, provided with two separation channels in the column‐coupling (CC) arrangement and on‐column conductivity detection sensors, to the determination of bromate in drinking water was investigated. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the ITP‐CZE separations. A high sample load capacity, linked with the use of ITP in this combination, made possible loading of the samples by a 9.2 νL sample injection channel of the chip. In addition, bromate was concentrated by a factor of 103 or more in the ITP stage of the separation and, therefore, its transfer to the CZE stage characterized negligible injection dispersion. This, along with a favorable electric conductivity of the carrier electrolyte solution, contributed to a 20 nmol/L (2.5 ppb) limit of detection for bromate in the CZE stage. Sample cleanup, integrated into the ITP stage, effectively complemented such a detection sensitivity and bromate could be quantified in drinking water matrices when its concentration was 80 nmol/L (10 ppb) or slightly less while the concentrations of anionic macroconstituent (chloride, sulfate, nitrate) in the loaded sample corresponding to a 2 mmol/L (70 ppm) concentration of chloride were still tolerable. The samples containing macroconstituents at higher concentrations required appropriate dilutions and, consequently, bromate in these samples could be directly determined only at proportionally higher concentrations.

Electroosmotic flow suppressing additives for capillary zone electrophoresis in a hydrodynamically closed separation system.

Electroosmotic flow in a hydrodynamically closed capillary zone electrophoresis (CZE) separation compartment must be minimized to achieve high efficiency CZE separations. A group of eight potential electroosmotic flow suppressors was investigated in this context for the separations in fluorinated ethylene-propylene capillary tubes. The suppressors included water soluble methylhydroxyethyl derivatives of cellulose, polyvinylalcohol, polyvinylpyrrolidones and polyethyleneglycols of different molecular masses and Triton X-100. Methylhydroxyethylcellulose derivatives and polyvinylalcohol were found to provide the highest separation efficiencies for a group of model anions when the electroosmotic flow suppressors were used as the carrier electrolyte additives. Using a methylhydroxyethylcellulose coated separation compartment very significant improvements in the separation efficiencies were achieved for polyvinylpyrrolidones and polyethyleneglycols applied in the carrier electrolyte solutions. For example, polyvinylpyrrolidone K 90 applied in this way gave for some of the model analytes the plate height values approaching those estimated in the calculations as theoretical limits for our experimental conditions (H approximately 3.5 microns). CZE experiments with albumin and gamma-globulin showed that the use of methylhydroxyethylcellulose derivative in the carrier electrolyte solution at pH = 9.2 was effective in eliminating potential disturbances in the separation efficiencies of the analytes due to adsorption of the proteins.

Separation of synthetic food colourants by capillary zone electrophoresis in a hydrodynamically closed separation compartment

Abstract Separation conditions enabling the complete resolution of eleven permitted synthetic food colourants and some of their subspecies by capillary zone electrophoresis (CZE) were determined. Those conditions involve combining a suitable pH of the carrier electrolyte (pH 6.8) with host-guest complexation effects of β-cyclodextrin. A 300 μm I.D. capillary tube made of fluorinated ethylene-propylene copolymer in a hydrodynamically closed separation compartment was used for the CZE separations. The capillary could accommodate 90-nl sample injection volumes, thus providing limits of detection for the dyes of 11–300 ppb using a photometric detector operating at a wavelength of 254 nm. R.S.D.s of 0.4–3.0% were typical for the determinations of the dyes present in samples at 16 ppm concentrations. Erythrosine, exhibiting residual adsorption, gave more-scattered results under identical working conditions (R.S.D. of ca. 9.0%). The utility of this rapid CZE procedure (migration times of the dyes were 2.5–10.5 min) is illustrated for several practical samples, including soft drink concentrate and liqueur and monitoring of the stability of aqueous solutions of indigo carmine.

Separation of alkali and alkaline earth metal and ammonium cations by capillary zone electrophoresis with indirect UV absorbance detection

Abstract Carrier electrolytes combining complexing effects of negatively charged counter ions and electroneutral 18-crown-6 were investigated in the separations of alkali and alkaline earth metal and ammonium cations by capillary zone electrophoresis with indirect UV absorption detection. The use of tartrate with 18-crown-6 at a 0.04 mol 1 −1 concentration permitted the complete resolution of these cations in one electrophoretic run. Benzimidazole served as a visualization co-ion for indirect detection at 254 nm. The separation of some alkali and alkaline earth metal and ammonium cations in rain, tap and mineral water samples illustrates the application potential of the proposed approach.