Capillary zone electrophoresis determination of fluoride in seawater using transient isotachophoresis.

We developed capillary zone electrophoresis (CZE) with indirect UV detection for the determination of fluoride (F-) in seawater using transient isotachophoresis (tITP) as an on-line concentration procedure. A method of correcting sample salinity effects was also proposed so that F- concentrations were obtained using a calibration graph. The proposed method is simple: it requires no sample pretreatment aside from dilution. The following optimum conditions were established: background electrolyte (BGE), 5 mM 2,6-pyridinedicarboxylic acid (PDC) adjusted to pH 3.5 containing 0.03% m/v hydroxypropyl methylcellulose (HPMC); detection wavelength, 200 nm; vacuum (50 kPa) injection period of sample, 5 s (254 nL); and applied voltage, 23 kV with the sample inlet side as the cathode. The limit of detection (LOD, S/N = 3) and limit of quantification (LOQ, S/N = 10) for F- reached 0.024 and 0.070 mg/L, respectively. The respective values of the relative standard deviation (RSD) of the peak area, peak height, and migration time for F- were 2.5, 3.4, and 0.30%. The proposed method was applied for the determination of F- in seawater samples collected from coastal waters of western Japan during August 26-28, 2014. Both results obtained using standard addition method and a calibration graph agreed with those obtained using a conventional spectrophotometric method.

CZE determination of submicromolar level of phenol in seawater using improved dynamic pH junction.

Using an improved dynamic pH junction as an on-line concentration procedure, we developed CZE for determining submicromolar phenol in seawater for chloride to phenol concentration ratios of 1 000 000. To enhance the effect of conventional dynamic pH junction, a saturated fatty acid solution was injected into the capillary after sample injection. We named the procedure an improved dynamic pH junction. The method requires no sample pretreatment. The following optimum conditions were established: BGE, 40 mM sodium tetraborate decahydrate adjusted to pH 9.8 containing 0.001% m/v hexadimethrine bromide; 190 nm detection wavelength; 18 s (370 nL) vacuum injection period of sample; a saturated fatty acid solution, 30 mM sodium n-hexanoate; 20 s (420 nL) vacuum injection period of the sodium n-hexanoate; and 15 kV applied voltage with the sample inlet side as the cathode. The LOD for phenol was 5.9 µg/L at S/N of 3. The respective values of the RSD (intraday) of the peak area, peak height, and migration time for phenol were 1.9, 2.9, and 0.46%. The recoveries of phenol (25-100 µg/L) spiked into the natural seawater sample obtained using the peak areas were 92-110%. The proposed method was applied to simple biodegradation experiments using natural seawater samples containing phenol.

Highly sensitive tITP-CZE determination of l-histidine and creatinine in human blood plasma using field-amplified sample injection with mobility-boost effect.

2D computer simulation revealed that amino acids and weak electrolytes were cationized because of the migration of counter-ion from a BGE zone to a sample zone, which encouraged electrokinetic injection (EKI) of these analytes (by the mobility-boost (MB) effect). To investigate the effects of kinds and concentrations of counter-ions on the MB effect and the analyte amount injected into the capillary, experiments, and 1D computer simulations were performed. When acetate was used as the counter-ion, the LODs (S/N = 3) of l-histidine and creatinine, respectively, reached 0.10 and 0.25 nM because of the concentration effect by transient ITP (tITP). The concentrations of l-histidine and creatinine in human blood plasma obtained using the proposed method were agreed with those obtained using the conventional methods. The proposed method can be applied to the analysis of amino acids and weak bases that have similar pI and pKa to l-histidine and creatinine.

Degradation of triphenylborane-pyridine antifouling agent in water by copper ions.

Triphenylborane-pyridine (TPBP) is an antifouling compound used in Asian countries, including Japan, and its residue has not been detected in aquatic environments to date. There are limited data on its fate for environmental management. The purpose of this study was to evaluate whether TPBP is degraded by metal ions in aquatic environments. TPBP with metal ions in 20 mM sodium acetate buffer at pH 8.0 was placed at 25 degrees C in the dark for 24 h. The concentrations of TPBP and its degradation products, such as diphenylboronic acid, phenylboronic acid (MPB), phenol, benzene, biphenyl, and boron were determined. The presence of copper ions (50 mg/l), but not zinc or manganese ions, resulted in complete degradation of TPBP in 24 h. The TPBP degradation was much faster than the boron production in the initial reaction (0-1 h) with copper salts, depending on the copper salts tested. TPBP was degraded by copper ions (5 mg/l) in 24 h, producing phenol, MPB, biphenyl, and borate. Cu2+ as copper(II) chloride or copper(II) acetate led to complete degradation of TPBP, and thylenediaminetetraacetic acid disodium salt addition suppressed the TPBP degradation. Cu+ as copper(I) acetate also completely degraded TPBP, and bathocuproine addition suppressed the TPBP degradation. This suggests that copper ions existing in natural environments might degrade TPBP released from antifouling paint into water, and this could be one of the important mechanisms to dissipate TPBP residues in aquatic environments.

Effects of metal pyrithione antifoulants on freshwater macrophyte Lemna gibba G3 determined by image analysis.

Copper pyrithione (CuPT(2)) and zinc pyrithione (ZnPT(2)) are two popular antifouling agents that prevent biofouling. Research into the environmental effects of metal pyrithiones has mainly focused on aquatic animal species such as fish and crustaceans, and little attention has been paid to primary producers. There have been few reports on residues in environmental matrices because of the high photolabile characteristics of the agents. Residue analyses and ecological effects of the metabolites and metal pyrithiones are not yet fully understood. This study was undertaken to assess the effects of CuPT(2), ZnPT(2), and six metabolites (PT(2): 2,2'-dithio-bispyridine N-oxide, PS(2): 2,2'-dithio-bispyridine, PSA: pyridine-2-sulfonic acid, HPT: 2-mercaptopyridine N-oxide, HPS: 2-mercaptopyridine, and PO: pyridine N-oxide) on a freshwater macrophyte. A 7-day static bioassay using axenic duckweed Lemna gibba G3 was performed under laboratory conditions. Toxic effects of test compounds were assessed by biomass reduction and morphological changes were determined in image analysis. Concentrations of ZnPT(2) and CuPT(2) and those of PT(2) and HPT in the medium were determined by derivatizing 2,2'-dithio-bispyridine mono-N-oxide with pyridine disulfide/ethylene diamine tetra-acetic acid reagent that was equimolar with pyrithione. The toxic intensity of the compounds was calculated from the measured concentrations after 7-day exposure. ZnPT(2), CuPT(2), PT(2), and HPT inhibited the growth of L. gibba with EC(50) ranging from 77 to 140 µg/l as calculated from the total frond number as the conventional index, whereas the other four metabolites had less effect even at 10 mg/l. The presence of the former four toxic derivatives resulted in abnormally shaped and unhealthily colored fronds, whose size was about 20% of the control fronds. EC(50), calculated from the healthy frond area determined in image analysis, ranged from 10 to 53 µg/l. Thus, image analysis as part of a duckweed bioassay can detect the toxic effects of pyrithione derivatives with 3-10 times higher sensitivity than the traditional index.

A novel hybrid mode of sample injection to enhance CZE sensitivity for simultaneous determination of a pyridine-triphenylborane anti-fouling agent and its degradation products.

We developed a novel hybrid sample injection mode (HSIM) that presents the combination of electrokinetic injection and vacuum injection to enhance detection sensitivity in CZE. Samples were introduced using both vacuum and electrokinetic injections simultaneously, with a water plug injected into the capillary prior to sample introduction (i.e. similarly to field-amplified sample injection, FASI). Using a sample mixture containing an anti-fouling agent applied to ship hulls, pyridine-triphenylborane and its degradation products (diphenylborinic acid, phenylboronic acid, and phenol) dissolved in ACN, the length of water plug, time, and voltage for sample introduction were optimized. The signal intensity (peak height) was found to be up to a 30-fold increased using HSIM by applying 4 kV for 4 s at the inlet end of the capillary as the cathode with supplementary vacuum in comparison with only vacuum injection for 4 s. The LODs (at a S/N of 3) for pyridine-triphenylborane, diphenylborinic acid, phenylboronic acid, and phenol were 0.88, 1.0, 21, and 23 µg/L, respectively. At the level of 0.04 mg/L, the RSDs (n=4, intra-day) for the above analytes were in the ranges of 1.9-11, 4.3-9.2, and 0.34-0.66% for peak area, peak height, and migration time, respectively. The HSIM is a simple and promising procedure useful for enhancing the sensitivity for both low-and high-mobility ions in CZE.

Determination of bromate in highly saline samples using CZE with on-line transient ITP.

We developed CZE with direct UV detection for the determination of bromate in highly saline samples such as seawater and salts using transient ITP as an on-line concentration procedure. The following optimum conditions were established: BGE, artificial seawater containing no bromide adjusted to pH 3.0; detection wavelength, 210 nm; vacuum injection period of sample, 18 s (378 nL); terminating ion solution, 600 mM sodium acetate; vacuum injection period of the terminating ion solution, 7 s (147 nL) for seawater and 12 s (252 nL) for salts; applied voltage, 7 kV with the sample inlet side as the cathode. The LOD for bromate was 30 microg/L (BrO(3) (-)-Br) with S/N of 3. The respective values of the RSD of the peak area, peak height, and migration time for bromate were 6.4, 1.5, and 0.51%. Seawater and salt samples, with bromate added, were analyzed using this method. The recovery of bromate in seawater samples was 85-105%. Linear regression equations relating area and height responses to concentration for bromate were obtained using the salt samples.

Capillary zone electrophoresis determination of aniline and pyridine in sewage samples using transient isotachophoresis with a system-induced terminator.

Transient isotachophoresis (tITP) with a system-induced terminator (SIT) was developed for capillary zone electrophoresis (CZE) determination of aniline (An+) and pyridine (Py+) in sewage samples. After sample injection, a water vial was set at the sample-inlet side. Then voltage was applied to generate a system-induced terminator (H+). Experiments and simulations revealed a concentration effect by tITP with an SIT: background electrolyte (BGE) - 100mM acetic acid (AcOH) and 50mM NaOH (pH 4.6); detection wavelength - 200nm for An+ and 254nm for Py+; vacuum injection period - 15s (190nL); SIT generation - 10kV applied for 80s with the sample inlet side anode; separation voltage - 20kV with the sample inlet side anode. The limits of detection (LODs, S/N=3) of An+ and Py+ respectively reached 10 and 42µg/L, with good repeatability (peak area RSDs≤6.9%) and calibration graph linearity (R2=0.9997). The proposed method was applied for determination of An+ and Py+ in sewage samples. Recoveries of An+ (0.50mg/L) and Py+ (2.0mg/L) in spiked sewage samples were 94-104%.

Distribution of perfluoroalkyl compounds in Osaka Bay and coastal waters of Western Japan.

Perfluoroalkyl acids (PFAAs) including perfluoroalkyl sulfonates (PFSAs) and perfluoroalkyl carboxylates (PFCAs) were analyzed in sediment samples taken from Ajifu Waterway in Osaka city, from Osaka Bay, and from Kagoshima Bay, as well as in fifteen seawater samples collected from Osaka Bay and coastal waters of Western Japan. In all sediment samples, only PFCAs were detected, and the highest concentration was determined in Ajifu Waterway, where ΣPFAA was 58990 ng kg-1 dry weight. The total concentrations of PFAAs in sea water samples ranged between the limit of quantification and 53.4 ng L-1, and perfluorohexanoic acid was the most prevalent and had the highest concentration of 37 ng L-1. The changes in the patterns and concentrations of PFAAs in Osaka Bay and coastal waters of Western Japan indicate that the PFAAs in surface waters are influenced by sources from Keihanshin Metropolitan Area, mainly the Yodo River basin, and the dilution effect which naturally occurs during their transport to the Pacific Ocean.

Determination of ammonium in river water and sewage samples by capillary zone electrophoresis with direct UV detection.

We developed capillary zone electrophoresis (CZE) with direct UV detection for determination of ammonium in environmental water samples. Ammonium in the samples was partly converted into ammonia in the alkaline background electrolyte (BGE) during migration and was detected by molecular absorption of ammonia at 190 nm in approximately 7 min. The limit of detection (LOD) for ammonium was 0.24 mg/l (as nitrogen) at a signal-to-noise ratio of three. The respective values of the relative standard deviation (RSD) of peak area, peak height, and migration time for ammonium were 2.1, 1.8, and 0.46%. Major alkali and alkaline earth metal ions coexisting in the samples did not interfere with ammonium determination by the proposed method. The proposed method determined ammonium in surface water and sewage samples. The results were compared to those obtained using ion chromatography (IC).

High-throughput nitric oxide assay in biological fluids using microchip capillary electrophoresis.

In order to develop a high-throughput screening method for the nitrogen monoxide metabolites, nitrite and nitrate, in biological fluids, we have investigated the simultaneous determination of these metabolites using microchip capillary electrophoresis (MCE). In this study, the control of applied voltage to obtain higher sensitivity by increasing the sample injection volume was investigated. Also, the improvement of reproducibility by correcting the injection volume using the internal standard was investigated. By increasing the sample volume, the limits of detection achieved for nitrite and nitrate were 24 and 12 microM, respectively. Because we used a 10-fold diluted sample when detecting nitrite and nitrate in human serum, it was necessary to increase the sensitivity by a factor of 10-50. The run-to-run and day-to-day relative standard deviations achieved were improved to less than 10% by using an internal standard to correct the injection volume. Moreover, we obtained successful separation of nitrite and nitrate in spiked human serum within 6.5 s under optimum analytical conditions. As a result, although it is necessary to obtain greater sensitivity, it was concluded that determination of the amount of NO metabolites in biological fluids using MCE is possible.

Determination of ammonium cations and alkali and alkaline earth metal cations in jellyfish by capillary zone electrophoresis.

We developed a capillary zone electrophoresis method with indirect UV detection for determination of ammonium cations and alkali and alkaline earth metal cations in jellyfish. As the background electrolyte, a mixture of N-methylbenzylamine, citrate, and 18-crown-6 was used for the complete separation of all analyte cations. The limits of detection were 0.13 - 0.34 mg l(-1) at a signal-to-noise ratio of three. The values of the relative standard deviation of peak area were 3.2 - 4.9%. The proposed method successfully determined the above analyte cations in jellyfish for approximately 4 min.

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.

Simultaneous determination of iodide and iodate in seawater by transient isotachophoresis-capillary zone electrophoresis with artificial seawater as the background electrolyte.

We developed capillary zone electrophoresis with transient isotachophoresis (ITP) as an on-line concentration procedure for simultaneous determination of iodide and iodate in seawater. The effective mobility of iodide was decreased by addition of 20 mM cetyltrimethylammonium chloride to an artificial seawater background electrolyte so that transient ITP functioned for both iodide and iodate. Limits of detection for iodide and iodate were 4.0 and 5.0 microg/l (as iodine) at a signal-to-noise ratio of 3. Values of the relative standard deviation of peak area, peak height, and migration times for iodide and iodate were 2.9, 1.3, 1.0 and 2.3, 2.1, 1.0%, respectively. The proposed method was applied to simultaneous determination of iodide and iodate in seawater collected at a pond at our university.

Simultaneous separation and on-line concentration of amitrole and benzimidazole pesticides by capillary electrophoresis with a volatile migration buffer applicable to mass spectrometric detection.

This study used capillary electrophoresis (CE) to investigate the simultaneous separation and on-line concentration of five pesticides: amitrole (AMT), carbendazim (MBC), 2-aminobenzimidazole (ABI), thiabendazole (TBZ) and 1,2-diaminobenzene (DAB). A volatile migration buffer was used for the investigation because of the applicability to mass spectrometric (MS) detection. They were separated completely at pH 4.0 as a result of changing pH using formic acid-ammonium formate buffer. Values of the dissociation constant for MBC and DAB estimated from the changes in the mobility with pH showed good agreement with values in the literature. Dissociation constants for AMT and TBZ were estimated. Limits of detection (LODs) for the analytes were on the ppm level with UV detection under the optimized separation condition. On-line concentration by simple stacking mode was not effective except to 2-aminobenzimidazole because of the peak tailing. The addition of formic acid to sample matrix improved the peak shapes. That improvement may be attributed to transient isotachophoretic effect. The concentration factors obtained from the comparison of the LODs were in the range of 7.6-27-fold. This concentration method was applied preliminarily to CE with MS detection.

Simultaneous determination of nitrate and nitrite in biological fluids by capillary electrophoresis and preliminary study on their determination by microchip capillary electrophoresis.

In order to develop a highly sensitive and high-throughput screening method for nitrogen monoxide metabolites in biological fluids, we have investigated the simultaneous determination of nitrite and nitrate, using capillary electrophoresis and microchip capillary electrophoresis. In capillary zone electrophoresis, a running buffer based on human serum components with high ionic strength has been developed for the determination of nitrite and nitrate in human serum and human saliva. We obtained successful separation of nitrite and nitrate in the serum and the saliva within 7 min under optimum analytical conditions. Linear calibration curves for nitrite and nitrate for both peak height and area were obtained by a standard addition method. The limits of detection obtained at a signal-to-noise ratio (S/N) of 3 for nitrite and nitrate in the serum were 2.6 and 1.5 microM, respectively. The values of the relative standard deviation of peak height for the serum with 9.2 microM nitrite and 20.9 microM nitrate were 5.7 and 4.1%, respectively. For on-site analysis with high-throughput screening, a microchip capillary electrophoresis method using a microchip made of quartz with a UV detector was developed. In this high-throughput format, using a running buffer with an electroosmotic flow modifier, the peaks of nitrite and nitrate in an artificial serum sample were obtained within 8 s. In high-resolution mode, using the buffer without electroosmotic flow modifier, the separation of nitrite and nitrate was obtained within 15 s. In high-resolution mode, using an artificial serum sample with 50 microM NO2- and 50 microM NO3-, the limits of detection (S/N = 3) of 41 microM for NO2- and 26 microM for NO3- were obtained. The method was applied to human serum and saliva. We obtained peaks due to nitrite and nitrate in 10-fold diluted saliva.

Separation and on-line concentration of bisphenol A and alkylphenols by micellar electrokinetic chromatography with anionic surfactant.

Separation and on-line concentration of bisphenol A and three alkylphenols were investigated by micellar electrokinetic chromatography with the anionic surfactant, sodium dodecyl sulfate. The separation conditions were optimized by the simultaneous addition of the organic solvent and cyclodextrin to the running solution. The separation of hydrophobic analytes and 4-nonylphenol isomers was improved by the addition of 10% methanol and 5 mM beta-cyclodextrin to the running solution. When the sweeping with the running solution was used as the on-line concentration procedure, 69-, 48-, 55- and 41-fold increases in detection sensitivity were obtained for bisphenol A, 4-tert.-butylphenol and 4-(1,1,3,3-tetramethylbutyl)phenol, and the second peak of 4-nonylphenol isomers, respectively. The detection limits were 0.0071, 0.0065, 0.021 and 0.055 mg/l, respectively. These results were better than those with the cationic surfactant, tetradecyltrimethylammonium bromide.

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.

Separation and on-line concentration of bisphenol A and alkylphenols by micellar electrokinetic chromatography with cationic surfactant.

The separation and on-line concentration of bisphenol A and three alkylphenols were investigated by micellar electrokinetic chromatography with cationic surfactant. Tetradecyltrimethylammonium bromide was used as surfactant and the separation conditions were optimized by the addition of the organic solvents and cyclodextrins to the running solution. The separation of hydrophobic analytes and 4-nonylphenol isomers was improved by the addition of 20% acetonitrile and 20 mM beta-cyclodextrin to the running solution. When the sweeping with the running solution used as the on-line concentration procedure, 56-, 67- and 29-fold increase in detection sensitivity of bisphenol A, 4-tert.-butylphenol and 4-(1,1,3,3-tetramethylbutyl)phenol, respectively. The detection limits were 0.030, 0.098 and 0.159 mg/l, respectively.

Role of counter-ions in background electrolyte for the analysis of cationgenic weak electrolytes and amino acids in neutral aqueous solutions by capillary electrophoresis with electrokinetic injection.

We elucidated theoretically and experimentally that counter-ions in background electrolyte (BGE) play a role of booster for electrokinetic injection (EKI) for the determination of cationgenic weak electrolytes and amino acids in neutral aqueous solutions using capillary electrophoresis (CE). The pH change in the sample solution caused by the migration of counter-ions resulted in the increase of analyte mobility and hence the increase of the amount of analyte injected into the capillary. This type of EKI was named as counter-ion boosted EKI. Using the counter-ion boosted EKI-capillary zone electrophoresis (CZE), the limit of detections (LODs, S/N=3) for creatinine (4.8nM) and l-histidine (9.0nM) were lowest ever achieved by CE with UV detection. The RSDs (n=3) of the migration time for creatinine and l-histidine were obtained as 0.35% and 0.34%, for peak areas of 13% and 12%, and for peak heights of 12% and 8.5%, respectively. The concentrations of creatinine and l-histidine in a urine sample obtained by the proposed method were within those reported with a good recovery.