Keiichi Fukushi

Application of capillary electrophoresis to the analysis of inorganic ions in environmental samples

A comprehensive review is presented of the state-of-the-art of capillary electrophoresis for application to the analysis of inorganic species, mainly ions, in environmental samples. This brief review covers the developments principally in sensitivity and matrix interference for the determination of inorganic ions in the following samples: drinking, mineral, surface, and ground waters, rainwater, snow, seawater, brine and waste waters, aerosol, and others. References published mainly from 1995 to 1997 were summarized in this review.

Highly sensitive capillary zone electrophoresis with artificial seawater as the background electrolyte and transient isotachophoresis as the on-line concentration procedure for simultaneous determination of nitrite and nitrate in seawater

Transient isotachophoresis-capillary zone electrophoresis with artificial seawater as the background electrolyte (BGE) was improved to further lower the limit of detection (LOD) for determination of nitrite and nitrate in seawater. By lowering the pH of BGE, the difference between effective mobility of nitrite and that of nitrate increased, thereby permitting increased sample volumes to be tolerated and their LOD values to decrease. Artificial seawater with pH adjusted to 3.0 using phosphate buffer was adopted as the BGE. To reverse electroosmotic flow (EOF), a capillary was flushed with 0.1 mM dilauryldimethylammonium bromide for 3 min before the capillary was filled with the BGE. Limits of detection (LODs) for nitrite and nitrate were 2.7 and 3.0 microg/l (as nitrogen), respectively. The LODs were obtained at a signal-to-noise ratio of 3. Values of the relative standard deviation (RSD) of peak area for these ions were 2.0 and 0.75%, respectively, when nitrite concentration was 0.05 mg/l and that of nitrate was 0.5 mg/l. The RSDs of peak height were 4.4 and 2.3%. The RSD values of migration time for these ions were 0.19 and 0.17%. The proposed method was applied to determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS-1, distributed by the National Research Council of Canada. Results agreed with the assigned tolerance interval. This method was also applied to determination of these ions in seawater collected around Osaka Bay. Results nearly agreed with those obtained by a conventional spectrophotometric method.

Determination of bromide ions in seawater by capillary zone electrophoresis using diluted artificial seawater as the buffer solution

Abstract A novel capillary zone electrophoresis method was developed for the determination of bromide ion in seawater. A tenfold-diluted artificial seawater was adopted as the buffer solution, to prevent interference from high concentrations of chloride ion in seawater. No electroosmotic flow reverser was used to shorten the analysis time. It was found that the peak area and migration time for bromide ion were almost constant, despite differences in the salinity of sample solutions; the peak height decreased linearly with an increase in the salinity. The limit of detection for bromide ion was 0.46 mg/l ( S / N =3). The values of the relative standard deviation for peak area and migration time for bromide ion were 1.4 and 1.5%, respectively. The proposed method was applied to the determination of bromide ion in seawater samples taken from the surface and the sea-bed. The analytical results obtained by the working curve method agreed with those obtained by the standard addition method. The method may be applicable to the determination of other ions, such as nitrite and nitrate ions, in seawater

Development of a novel running buffer for the simultaneous determination of nitrate and nitrite in human serum by capillary zone electrophoresis.

In order to improve NO2- peak height and obtain a convenient buffer system for the assay of nitrogen monooxide metabolites, we developed a novel running buffer for the simultaneous determination of nitrite and nitrate in human serum by capillary electrophoresis. The addition of cetyltrimethylammonium chloride to the running buffer resulted in high-speed separation using reverse electroosmotic flow. Highly sensitive determination was also achieved using stacking with 10-fold diluted sample solutions. The samples were injected hydrodynamically for 100 s into a 50 cm x 75 microm I.D. capillary. The separation voltage was 10 kV (negative polarity). UV detection was performed at 214 nm. We obtained complete separation of nitrite and nitrate in deproteinized human serum within 6 min with optimum analytical conditions. Linear calibration curves for nitrite and nitrate for both peak height and peak area were obtained with standard addition method. The limits of detection obtained at a signal-to-noise ratio of 3 for nitrite and nitrate were 4.1 and 2.0 microM, while the values of relative standard deviation of peak height were 2.4 and 2.6%, respectively.

Determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater by capillary zone electrophoresis with artificial seawater as the background electrolyte using transient isotachophoresis

We describe a combination of selected ions as a terminating ion which is useful for transient isotachophoresis (ITP) in capillary zone electrophoresis (CZE) for the determination of nitrite and nitrate in seawater. In addition to 150 mM sulfate as the principal terminating ion, 10 mM bromate was added to a sample solution as the additional terminating ion. Artificial seawater containing 3 mM cetyltrimethylammonium chloride (CTAC) was adopted as a background electrolyte (BGE). The limits of detection (LODs) for nitrite and nitrate were 2.2 and 1.0 νg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.9 and 1.4%. The RSDs of peak height were 1.7 and 1.9%, the RSDs of migration time 0.11%. The proposed method was applied to the determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS‐1, distributed by the National Research Council of Canada (NRC). The results almost agreed with the assigned tolerance interval.

Analysis of highly saline samples by capillary zone electrophoresis: enhanced direct UV detection of inorganic anions using on-capillary preconcentration and clean-up techniques

The ability to analyze samples with disparate levels of analyte and matrix ions is among the important benefits defining the practical utility of modern capillary electrophoresis. To compensate for the sensitivity limitations regarding trace-level inorganic anions, a number of on-line approaches that should offer an improved S/N ratio in direct UV detection were examined. The novel use of reversed pre-electrophoresis (at the applied voltage opposite to the separation voltage) made it possible to efficiently remove the most part of high chloride levels from the sample and hence to lower the background signal and to inject increased quantities of fast analyte anions. Specifically, by taking these advantages the sensitivity response of iodide was improved by a factor of 5 over normal CE mode. Using isotachophoretic sample stacking, a two-fold increase in detectability was obtained for moderately mobile anions, nitrate and nitrite, that corresponds to the minimum detectable concentrations close to their natural occurrences in seawater. Furthermore, field-amplified sample injection at increased electrolyte-to-sample matrix concentration ratios enabled the maximum S/N enhancement, with detection limits at the level of 10(-6) M and lower in the presence of > or = 5 x 10(4)-fold molar excess of chloride.

Improvement of capillary zone electrophoresis sensitivity with artificial seawater as the background electrolyte utilizing transient isotachophoresis for the determination of nitrite and nitrate ions in seawater

We describe capillary zone electrophoresis (CZE) with transient isotachophoresis (ITP) for the determination of low concentrations of nitrite and nitrate ions in seawater. Bromide‐free artificial seawater was adopted as background electrolyte (BGE) to eliminate the interference of high concentrations of salts in seawater. To reverse the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the BGE. High concentrations of chlorate were added to sample solutions as the terminating ion to generate the ITP process before the CZE separation. In general, the stacking effect increased with increasing amounts of chlorate injected into the capillary. The limits of detection (LODs) for nitrite and nitrate were 0.063 and 0.033 mg/L when the chlorate concentration was 600 and 200 mM, respectively; these were half of those obtained by CZE without the transient ITP. The LODs were obtained at a signal to noise ratio (S/N) of 3. The relative standard deviations (RSD, n = 10) of the peak areas for these ions were 3.2 and 2.9%. The RSDs of peak heights for these ions were 1.6 and 2.1%. The RSDs of migration times for these ions were 0.67 and 0.46%.

Use of cyclodextrins in the isotachophoretic determination of various inorganic anions

Abstract The effects of α-, β- and γ-cyclodextrins on the effective mobilities of various inorganic anions in capillary isotachophoresis were studied. The effective mobilities of several anions decreased when the concentration of cyclodextrins in an ordinary leading electrolyte was increased up to 50 mM, whereas the effective mobilities of a few anions remained almost constant. Hence by use of α-cyclodextrin, nitrite and nitrate ions, cyanate, thiocyanate and selenocyanate ions and chlorate and perchlorate ions were completely separated and could be determined. The effective mobilities of iodide, periodate and tetrathionate ions also decreased with increasing concentration of α-, β- or γ-cyclodextrin.

Simultaneous determination of nitrate and nitrite ions in seawater by capillary zone electrophoresis using artificial seawater as the carrier solution

We are proposing a novel capillary zone electrophoresis for the simultaneous determination of nitrate and nitrite ions in seawater. An artificial seawater was adopted as the carrier solution to eliminate the interference of high concentrations of chloride ion etc., in seawater. For the purpose of reversing the electroosmotic flow, 3 mM cetyltrimethylammonium chloride was added to the carrier solution. A 100 μm I.D. capillary was used to extend the optical path length. Regardless of the salinity of sample solutions, the peak areas and migration times for nitrate and nitrite ions were within ±3%, while the peak heights for these ions decreased linearly with increasing salinity of sample solutions. The limits of detection for nitrate and nitrite ions were 0.04 and 0.07 mg/l (S/N=3, based on three-times the baseline noise), respectively. The values of the relative standard deviation (RSD) of peak areas for these ions were 1.5 and 2.4%. The RSDs of migration time for these ions were 0.85 and 0.78%. The proposed method was applied to the determination of nitrate and nitrite ions in seawater samples taken from the surface and the seabed. The recovery of nitrate and nitrite ions was 97-114%.

Determination of ascorbic acid in vegetables by capillary zone electrophoresis

Capillary zone electrophoresis (CZE) was used for the determination of ascorbic acid (AsA) in vegetables. AsA was extracted from vegetables by homogenizing with 2% thiourea–10 mM hydrochloric acid and determined directly by CZE with a borate buffer. The limit of detection (LOD) for AsA was 0.35 mg/l (S/N=3). Relative standard deviations of peak area and migration time for AsA in vegetables were 8.7 and 0.3%, respectively. Recovery of AsA was 97–112%. AsA concentrations in various vegetables were determined by the method. The method was also used for the determination of AsA in vegetables that had been cultivated by using fermented blue mussels, to examine their usefulness as a fertilizer for vegetables.