Takashi Kaneta

Improvement of resolution in the capillary electrophoretic separation of catecholamines by complex formation with boric acid and control of electroosmosis with a cationic surfactant

Abstract In order to improve the resolution of catecholamines, the control of both the electroosmotic and the electrophoretic mobilites were carried out. The former was controlled by the addition of borate ion and a change in pH. The control of the latter was carried out by addition of a cationic surfactant. Ten catecholamines were sufficiently separated.

Hadamard transform capillary electrophoresis

This paper reports the first demonstration of a multiplex sample injection technique in capillary electrophoresis. The sample was injected into a capillary (effective length, 4 cm) as a pseudorandam Hadamard sequence by a photodegradation technique using a high-power gating laser, and the fluorescence signal, which was measured using a probe excitation beam, was decoded by an inverse Hadamard transformation. The signal-to-noise ratio was improved by a factor of 8, which was in good agreement with the theoretically predicted value of 8.02. This approach is potentially useful for the enhancement of the sensitivity by 3 orders of magnitude in high-resolution capillary electrophoresis, combined with fluorescence detection.

Effect of cetyltrimethylammonium chloride on electroosmotic and electrophoretic mobilities in capillary zone electrophoresis

Abstract The effect of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), on the electroosmotic mobility and the electrophoretic mobility of organic anions in capillary zone electrophoresis was investigated. The electroosmotic mobility showed four stepwise changes, including a reversal, with increasing CTAC concentration. The behaviour, especially the reversal of the electroosmotic mobility, was explained by assuming the formation of hemimicelles on the capillary wall. That is, CTAC first adsorbs individually by electrostatic interactions and then begins to associate into hemimicelles by Van der Waals attraction. The formation of hemimicelles changes the surface charge of the capillary wall from negative to positive and causes the reversal of the electroosmotic mobility. The effective electrophoretic mobilities of organic anions such as benzoic acid analogues were also influenced by the CTAC concentration. It was concluded that the behaviour was due to the interaction with hemimicelles on the capillary wall and also ion association with the monomer of CTAC and the interaction of micelles in bulk solution.

Effect of addition of glucose on micellar electrokinetic capillary chromatography with sodium dodecyl sulphate

Abstract Glucose was investigated as a possible additive for the improvement of resolution in micellar electrokinetic capillary chromatography. Addition of glucose to the micellar solution facilitated the complete separation of a mixture of nine nucleosides by both extending the elution range and changing the selectivity. Extension of the elution range can be attributed to an increase in the electrophoretic mobility of the micelle. It is also apparent that glucose selectively reduces the distribution coefficients for solutes containing a hydrophilic functional group. This effect was valuable in the separation of some solutes with hydrophilic functional groups and large capacity factors.

Determination of cyanine-labeled amino acid enantiomers by cyclodextrin-modified capillary gel electrophoresis combined with diode laser fluorescence detection

Enantiomeric amino acids were labeled with a cyanine derivative (Cy5) for selective determination by capillary electrophoresis combined with diode laser-induced fluorometry. Cyanine-labeled glutamic acid has a high negative charge so that it was difficult to detect by conventional capillary zone electrophoresis due to its electrophoretic mobility being greater than the electroosmotic mobility. Thus, cyclodextrin-modified capillary gel electrophoresis using replaceable poly(vinylpyrrolidone) (PVP), which effectively suppresses the electroosmotic flow, was employed to separate Cy5-labeled amino acid enantiomers. The separation of six amino acid enantiomers could be achieved by using 1% PVP solution containing 70 mM γ-cyclodextrin. It was also shown that PVP does not affect the selectivity of optical isomers.

Acid–Base Titrations Using Microfluidic Paper-Based Analytical Devices

Rapid and simple acid-base titration was accomplished using a novel microfluidic paper-based analytical device (μPAD). The μPAD was fabricated by wax printing and consisted of ten reservoirs for reaction and detection. The reaction reservoirs contained various amounts of a primary standard substance, potassium hydrogen phthalate (KHPth), whereas a constant amount of phenolphthalein was added to all the detection reservoirs. A sample solution containing NaOH was dropped onto the center of the μPAD and was allowed to spread to the reaction reservoirs where the KHPth neutralized it. When the amount of NaOH exceeded that of the KHPth in the reaction reservoirs, unneutralized hydroxide ion penetrated the detection reservoirs, resulting in a color reaction from the phenolphthalein. Therefore, the number of the detection reservoirs with no color change determined the concentration of the NaOH in the sample solution. The titration was completed within 1 min by visually determining the end point, which required neither instrumentation nor software. The volumes of the KHPth and phenolphthalein solutions added to the corresponding reservoirs were optimized to obtain reproducible and accurate results for the concentration of NaOH. The μPADs determined the concentration of NaOH at orders of magnitude ranging from 0.01 to 1 M. An acid sample, HCl, was also determined using Na2CO3 as a primary standard substance instead of KHPth. Furthermore, the μPAD was applicable to the titrations of nitric acid, sulfuric acid, acetic acid, and ammonia solutions. The μPADs were stable for more than 1 month when stored in darkness at room temperature, although this was reduced to only 5 days under daylight conditions. The analysis of acidic hot spring water was also demonstrated in the field using the μPAD, and the results agreed well with those obtained by classic acid-base titration.

Optical chromatography: Size determination by eluting particles

A new method for the determination of particle size was developed using optical chromatography. After separating polystyrene particles, the laser power was gradually reduced, permitting the elution of small to large particles. Particle size was calculated from the laser power when the particle was eluted with a medium flow. This approach is more accurate than the technique previously reported because there is no need to determine the position of the beam waist. Advantages of the new approach are discussed theoretically and experimentally. The precision in size determination was improved by a factor of 3.3, i.e. the standard deviation in the measurement was reduced from 10 to 3% for 1 mum beads by replacing optical chromatography with the present method.

Separation of polycyclic aromatic hydrocarbons by micellar electrokinetic chromatography with laser fluorescence detection

Abstract Polycyclic aromatic hydrocarbons (PAHs) were separated by micellar electrokinetic chromatography and were detected by laser fluorometry. The PAHs with large molecular weights were separated by using dimethylformamide as an organic modifier. A He-Cd laser (325 nm, 5 mW) or a blue semiconductor laser (415 nm, 50 μW) was used as an exciting light source. The detection limit ( S N = 3 ) for perylene was 1.4 × 10−7 M under He-Cd laser excitation or 3.4 × 10−7 M under semiconductor laser excitation.

Method development for the determination of arsenic by sequential injection/anodic stripping voltammetry using long-lasting gold-modified screen-printed carbon electrode

An automated method has been developed for determining the concentration of inorganic arsenic. The technique uses sequential injection/anodic stripping voltammetry with a long-lasting gold-modified screen-printed carbon electrode. The long-lasting gold electrode was electrochemically deposited onto a screen-printed carbon electrode at a potential of -0.5 V vs. Ag/AgCl in a supporting electrolyte solution of 1M hydrochloric acid. Under optimal conditions and the applied potentials, the electrode demonstrated that it can be used for a long time without a renewal process. The linear range for the determination of arsenic(III) was 1-100 μg L(-1), and the limit of detection (LOD) in standard solutions was as low as 0.03 μg L(-1) for a deposition time of 120 s and sample volume of 1 mL. This method was used to determine the concentration of arsenic(III) in water samples with satisfactory results. The LOD in real samples was found to be 0.5 μg L(-1). In addition, speciation between arsenic(III) and arsenic(V) has been achieved with the proposed method using deposition potentials of -0.5 V and -1.5 V for the determination of the arsenic(III) concentration and the total arsenic concentration, respectively; the results were acceptable. The proposed method is an automated system that offers a less expensive alternative for determining trace amounts of inorganic arsenic.

Immunoassay for human serum albumin using capillary electrophoresis–semiconductor laser-induced fluorometry

Capillary electrophoresis combined with semiconductor laser-induced fluorometry was applied to an immunoassay of human serum albumin. Human serum albumin was labeled with a fluorescent molecule (Cy5), which has an absorption maximum at 649 nm. The labeled albumin was purified by ultrafiltration in order to reduce signals, which are unreacted labeling reagent, product, and fragment products derived there from. After the purification, no signal for unreacted labeling reagent and fragment products was detectable in the electropherogram of the labeled albumin. The labeled albumin was then reacted with anti-albumin to form an immunocomplex, which was separated from the excess free albumin. The competitive immunoassay was used in the determination of human serum albumin in a controlled serum sample, using the labeled albumin. The obtained value was found to be 0.21 +/- 0.02 mg/ml, which is in good agreement with other known values.