Capillary chromatography for the separation of optical isomers was developed using an untreated poly(tetrafluoroethylene) capillary tube and a water–hydrophilic/hydrophobic organic solvent mixture as a carrier solution. The open tubular capillary was 110 cm in length (90 cm effective length) and 100 μm in inner diameter. The carrier solution was prepared with a water–acetonitrile–ethyl acetate mixture (15:3:2 volume ratio) containing 1 mM β-cyclodextrin. A model analyte solution of dansyl-DL-methionine was injected into the capillary tube by a gravity method. The analyte solution was subsequently delivered through the capillary tube with the carrier solution by a microsyringe pump; the system worked under laminar-flow conditions. The analytes were separated through the capillary tube with on-capillary detection by an absorption detector. D-Isomer and L-isomer were eluted in this order with the water-acetonitrile–ethyl acetate carrier solution including β-cyclodextrin.
Effective recognition and quantitative analysis of the prion protein are important in drug discovery and diagnosis for prion diseases, such as bovine spongiform encephalopathy and Creutzfeldt-Jakob diseases. We have developed a high-throughput method for a specific and sensitive determination of prion protein on a solid-phase membrane, based on a chemiluminescence reaction of aptamer with 3,4,5-trimethoxyphenylglyoxal. This method using aptamer is facile, inexpensive and convenient for the detection of the prion protein on a membrane, indicating a lower detection limit of ca. 4.2 pmol spot−1.
In this review, the preparation of a novel porous sheet designed for solid-phase extraction (SPE) and a comparison of the preconcentration performance of metal ions with conventional sorbents are described. A porous sheet (MAPS) with an average pore diameter, porosity, and a thickness of 1.0 μm, 75%, and 2 mm, respectively, was modified into an sorbent used for solid-phase extraction, by radiation-induced graft polymerization. Ion-exchange and chelating groups were immobilized onto polymer chains grafted to the MAPS. Also, extractants were impregnated via a hydrophobic interaction with long alkyl chains introduced into the grafted polymer chains of the MAPS. The applicability of the resultant modified MAPSs was demonstrated by adopting them to analyses of real samples.
A physical parameter for predicting the thermal stability of proteins was provided by a new approach using dynamic light scattering (DLS). The relationship between the melting point measured by differential scanning calorimetry (DSC) and the polydispersity of the hydrodynamic diameter determined by DLS analysis was examined. Calmodulin (CaM) and concanavalin A (ConA) were used as model proteins. The melting point measured by DSC, an indicator for thermal stability, increased and the polydispersity decreased on binding of the proteins to specific ligands, suggesting that the polydispersity could be used an indicator to predict thermal stability. In addition, the increase of thermal stability that resulted from forming a complex could be quantified by polydispersity analysis even when the melting point changed only slightly.
In this work, a reversible sensor to assess the total Se(IV) content in samples is described. Pre-activated glass slides were spin-coated with 100 μL of a 20-h aged sol-gel mixture of 1 mL of tetramethoxysilane, 305 μL of 50 mmol L−1 HCl and 2.0 mg of thonine. The flow-cell consisted of one of those slides as a window, and was filled with beads of a polystyrene anionic exchange resin to retain Se(IV) in the form of selenite ions. A reflectance transduction scheme at a wavelength of 596 nm was adopted. The cell was coupled to a multicommutation flow system where a programmed volume of a sample solution and 373 μL of 0.4 mmol L−1 iodide in a 1.6 mol L−1 HCl solution were sequentially inserted into the cell. The iodine produced from the reaction of retained Se(IV) with iodide bleached the blue color of thionine. Considering a sample volume of 2.30 mL, with which the preconcentration step was minimized, a linear dynamic working range between 1.5 to 20 μg mL−1 and a detection limit of 0.29 μg mL−1 were obtained. The sensor enabled us to perform approximately 200 assays, and provided results similar to those of electrothermal atomic absorption spectrometry.
A new fluorescence dye, N-amino-4-(2-hydroxyethylamino)-1,8-naphthalimide (AHN), based on 4-bromo-1,8-naphthalic anhydride was synthesized as a fluorescence probe for determining water content in organic solvents. Changing from a non-polar to a polar solvent increases the solvent interaction with excitation spectrum and emission spectrum shifts to longer wavelengths. The fluorescence intensity of the probe decreased with the increasing concentration of water. In the range of 0.00 – 4.00% (v/v), the AHN fluorescence intensity changed as a linear function of water content. The detection limits were 0.019, 0.038, and 0.060% for dioxane, acetonitrile and ethanol, respectively.
We have developed a simple fabrication method of a highly sensitive direct electron transfer-type electrochemical biosensor for hydrogen peroxide by use of cup-stacked carbon nanotubes (CSCNTs). The CSCNTs, formed by stacking of cup-shaped carbon units, has larger internal space and more hydrophilic edges, thanks to the presence of functional groups containing oxygen (e.g., –COOH, –OH), than multi-walled carbon nanotubes (MWCNTs). When the CSCNTs suspension was cast, the CSCNTs were dispersed homogeneously onto a glassy carbon (GC) electrode, and horseradish peroxidase (HRP) was immobilized firmly by physical adsorption without any chemical reactions. The flow injection analysis (FIA) system with the HRP/CSCNTs/GC electrode has superior sensitivity and stability to the HRP/MWCNTs/GC electrode. The detection limit was 0.75 nM (S/N = 3) and the activity was maintained over 85% for 21 days. Further, when the glutamate oxidase (GlOD)-immobilized reactor was set into the proposed FIA system, L-glutamate could be detected repeatedly with a detection limit of 1.2 nM (S/N = 3).
New electrochemical technique with a Pt-Ag twin electrode is proposed for the determining the contents of iron sulfides (FeS and FeS2) in a suspension. After electrolytic oxidation with a Pt electrode, Fe2+ was measured by linear sweep voltammetry. From relations of the charge amount from the baseline to the peak in the voltammogram of Fe2+ with the content of FeS or FeS2, linear calibration curves (a) and (b) were prepared, respectively. After measurements of Fe2+, Fe2+ and S0 were reduced with a Pt electrode to remove Fe2+ and to produce S2−. With an Ag electrode, Ag2S was deposited on Ag. A linear curve (c) was prepared from a relation between the charge amount of the Ag2S peak part and the FeS content. However, in the suspension of FeS2, Ag2S can not be detected. When this method is applied to a mixed suspension of FeS and FeS2, the content of FeS can be determined with curve (c), whereas curves (a) and (b) were not effective in the mixed suspension.
Novel packed-capillary columns for gas chromatography were developed with a thin-wall stainless-steel capillary of 1.0 mm i.d.; and rapid temperature-programmed separations have been carried out after a basic evaluation concerning the compatibility of these columns to the temperature program. With a numerical integration method, the retention of several test analytes during temperature-programmed elution was successfully estimated. In order to confirm the suitability of the packed-capillary columns to relatively fast temperature programming up to 40°C/min, theoretically predicted retention data were compared with that actually measured. The results suggested a good separation performance of the newly developed packed-capillary columns as a particle-packed column conventionally used. Also, the compatibility to a rapid temperature-programmed operation was quite satisfactory for almost all of the separations currently done in typical analytical laboratories.
Simultaneous determinations of 20 antidepressants were carried out by non-aqueous capillary electrophoresis using a background electrolyte consisting of an organic solvent. A bubble cell fused silica capillary (112.5 cm × 50 μm i.d., 150 μm i.d. bubble) was used as an electrophoresis tube. The determination was carried out at 215 nm, while the detection wavelength between 190 and 500 nm was selected for qualitative analysis. When an acetonitrile solution alone was used as the background electrolyte, good separation was observed, but it was not sufficient to separate all tested analytes. It was found that better separation was acquired by adding a few other solvents into acetonitrile, such as water and methanol; the best separation was achieved with a mixture of acetonitrile containing 60 mM ammonium acetate and 1 M acetic acid/water/methanol (100:1:0.5, v/v/v). As for the plasma sample, liquid–liquid extraction and solid-phase extraction (SPE) were considered; as a result, SPE with Oasis HLB was found to be most suitable. The present method is very useful as regards to plasma samples.
A method for the determination of several tricyclic antidepressants (imipramine, desipramine, amitriptyline, nortriptyline, clomipramine, norclomipramine, doxepine and nordoxepine) in breast milk has been developed. This assay consists of a common extraction process in an organic phase, which is evaporated until dried and finally reconstituted in the appropriate buffer for injection in a capillary electrophoresis system. The capillary electrophoresis method used is an “acetonitrile stacking” method previously reported for determining these drugs in serum samples. The method developed was applied to the analysis of these compounds in human breast milk at different concentration levels (50, 100 and 200 ppb of the TCAs hydrochlorides). An interference study of some ansiolitic drugs such as lorazepam and alprazolam was made.
In this study, a microemulsion electrokinetic chromatography (MEEKC) was used to analyze ten non-steroidal anti-inflammatory drugs (NSAIDs) in water samples. The type and ratio of organic modifiers were found to be the predominant influences on the NSAIDs separation. Subsequently, field-amplified sample injection was coupled with this MEEKC method in order to enhance the detection sensitivity. When both the acid plug (3 s) and water plug (5 s) were placed at the front of the capillary, and the acetonitrile (ACN) solvent was added to the water plug (10% ACN) and the sample matrix (15% ACN), the separation time was shortened to 15 min, as well as the limit of detection (LOD) of these NSAIDs was reduced to the range of 0.03 to 0.3 μg/L, which provided about a 1400-fold to 6100-fold enhancement in LOD. Finally, the proposed on-line concentration MEEKC method also successfully determined the NSAIDs residues in water samples after solid-phase extraction.
The open-cell titration of seawater was studied for alkalinity measurements by colorimetry. 1) The colorimetric pH of free hydrogen ion concentration, pHF(ind), was calculated from the ratio of the absorbances at 436 and 590 nm (R = 590nmA/436nmA), along with the molar absorption coefficient ratios (e1, e2 and e3/e2) and a tentative acid dissociation constant value (pKa2). 2) The perturbation of hydrogen ion was evaluated from the change in titration mass (Δm). The total hydrogen ion concentration at m + Δm, pHT(at m+Δm), was calculated using pHF(ind) for a mass m and constants for sulfate (ST) and fluoride (FT). 3) The alkalinity (AT) was computed from the titrant mass (m + Δm) and the corresponding pHT(at m+Δm) through a non-linear least-squares approach using the pKa2 value as a variable parameter. Seawater sample at 2000 m depth from the West Pacific was analyzed. The resulting AT (2420.92 ± 3.35 μmol kg−1) was in good agreement with the AT measured by potentiometric electric force (2420.46 ± 1.54 μmol kg−1). The resulting pKa2 was 3.7037, in close proximity to that reported by King et al. (pKa2 = 3.695).
The effects of an on-line ion suppressor device on alkali metal ion adduct formations of the model compound tacrolimus were investigated. The base peak ion in the positive ion ESI-MS spectrum of tacrolimus was a sodium ion adduct, [M+Na]+. On the other hand, an ammonium ion adduct, [M+NH4]+, was the base peak ion in the full-scan mass spectrum of tacrolimus with a cation-exchange suppressor resin, and both [M+Na]+ and [M+K]+ were eliminated. These results indicate that the combination of an on-line ion suppressor with ESI-MS is a simple and effective technique that eliminates undesirable alkali metal ion adduct formations in the positive-ion mode.
A portable spectrofluorometer device comprising an ultraviolet LED (380 nm) as a light source, an LED driver, a microsyringe as a cell, an optical fiber cable, a CCD spectrometer and a personal computer was used on-site. The device works on a battery for 3 h without the need to re-charge. The consumptions of reagents and sample solution can be reduced by using the device. Using fluorescein solution as a standard, the performance of this device was compared with that of a bench-top spectrofluorometer. The device applicability was demonstrated by the determination of selenium content in river water as a model of hazardous elements in the environment. Selenium reacted with 2,3-diaminonaphthalene to form piazselenol, which was then extracted with cyclohexane. The determination was carried out with both the portable device and the spectrofluorometer. The entire process was completed in approximately 15 min. The recovery of selenium in a river-water sample ranged from 104 – 112% and the detection limit was 0.5 μg L−1.
The influence of seawater salts as salting out agents on the purge-and-trap gas chromatography (PT-GC) determination of trihalomethanes (THMs) was studied. This is particularly important since seawater is chlorinated when used as a cooling agent in coastal nuclear power stations. The chlorination produces unwanted THMs as by-products. A PT-GC apparatus was used to determine the Henry’s Law constant of each THM, with seawater as the sample matrix.