Vol. 57 No. 2
Several in-capillary preconcentration methods for capillary electrophoresis have been reported for lowering the concentration detection limits. Firstly, a new kind of stacking method that makes use of a fracture on the wall of a capillary is considered. Secondly, a preconcentration method making use of a short piece of hollow fiber with an internal diameter of 140 μm, which was coaxially connected to the inlet end of a capillary, is discussed. A three-order improvement of the concentration detection sensitivity could be easily realized with only a 1 min preconcentration in this method. Thirdly, a preconcentration method with a small porous wall located near the inlet end is presented. Fourthly, an in-capillary isoelectric focusing sample-injection method is discussed. Proteins were isoelectricly focused on a neutralization reaction boundary and separated by following CE. Fifthly, in-capillary solid phase extraction preconcentration methods for CE are discussed. About 1〜3 mm SPE absorbents were filled in the inlet end of a capillary, after SPE concentration and injecting a short plug of methanol as a desorption solvent, a separation voltage was applied across the two ends of the capillary to conduct conventional CE. Especially, with a capillary opened with a hole of 30 μmm, an improved in-capillary SPE-CE method that does not suffer from an adsorption problem of adsorbing species in complex samples is proposed. The method could lower the detection limits of chloro-phenols by more than 16000-fold. Furthermore, the method was successfully applied to detect 2,4-dichlorophenol at a level of 25 pg/mL in river water.
A contact vapor-phase oxidation method for the rapid perfect combustion of a flame-resisting organic compound was designed and incorporated into a new combustion tube method. The accuracy of the amounts of detected combustion constituent was examined. A contact vapor-phase oxidation method involves the capacity of the oxidation part in the combustion tube, which is expanded to about five-times the conventional value. The combustion system, used the oxidation catalyst functions together with this. A crucible with a volume of about 20 mL was attached to the effective heating section in the combustion tube, and an introduced tube, which leads a sample capsule to the crucible, was fixed at the center of the crucible. The space between the outside wall of the introduction tube and the inside wall of the crucible was filled with platinum cylinders. Combustion of the sample fills the oxidation part with oxygen gas, the sample capsule is inserted from the introduced tube and it burns three times. Complete combustion is completed as the imperfect combustion constituent generated here, back flowing in the platinum cylinder. Thus, by incorporating contact vapor phase oxidation into the new combustion tube method, the difference in combustion between a flammable sample and a flame-resisting sample was eliminated, in the range of the sample, and the accuracy of the amount of detected carbon in thiourea was improved approximately tenfold.
Solid-phase extraction using a polyamino-polycarboxylic acid-type chelating resin was examined in order to separate lead from biological samples for an isotopic analysis of blood and teeth by inductively coupled plasma mass spectrometry. The recovery of lead from a digest of a bone certified reference material (CRM) (NIST SRM 1486 Bone Meal) was 94±6％, and ＞99.9％ of the calcium matrix was removed. The average blank level was 0.5±0.1 ng (less than 3％ of the total lead amount of the samples). The recovery of lead from whole blood reference material (89±4％) was somewhat lower than that of bone CRM, presumably because of the presence of undigested organic matter in the digest. The use of a chelating resin with a divinylbenzene/methacrylate base was more suitable than that with a methacrylate base for whole blood. The isotopic ratios of bone CRM after a lead separation were 207Pb/206Pb＝0.8201±0.0035, and 208Pb/206Pb＝2.041±0.006, showing good agreement with the information value from NIST. The isotopic ratios of lead in blood samples from 3 children and those in 4 adult bone samples were analyzed with this procedure. We found that the values were clearly different between blood and bone, indicating different sources of lead in these two types of tissues through they were taken from contemporary Japanese.
An immunochromatography assay system was evaluated as a screening method for cadmium in brown rice. Cadmium concentrations of 209 samples were measured by immunochromatography, atomic-absorption spectroscopy and ICP-AES. Concentration estimates by immunochromatography and ICP-AES were highly correlated, with a correlation coefficient of 0.92±0.03. The screening performance of both immunochromatography and atomic-absorption spectroscopy were evaluated using ICP-AES estimates as the gold standard. A comparison of these results using ROC (receiver-operating characteristic) plots showed that both immunochromatography and atomic-absorption spectroscopy are capable of providing useful screening information. In the case that the regulatory concentration of cadmium was set at 0.4 mg kg−1, the most suitable cutoff concentration for the immunochromatography for screening was shown to be at 0.3 mg kg−1, with false negative and false positive rates of zero and 4.7 percent, respectively.
A new technique to separate lead (Pb) from geochemical samples using a highly selective resin for Pb (MetaSEP Analig® Pb-02) was developed. The technique was applied to determining precise lead isotope ratios using multi-collector ICP-MS (MC-ICP-MS). To evaluate the performance of this technique, Pb isotopes in eleven kinds of Geochemical Reference Samples supplied from Geological Survey of Japan (GSJ-GRS) were investigated using this technique. The obtained Pb isotopic compositions in the GSJ-GRSs agreed very well with the reported values. Employing this technique, Pb isotope ratios of ten kinds of GSJ-GRSs, for which Pb isotope ratios are not reported, were determined. The uncertainties the of measurement were approximately 0.02％ and 0.005％ (2SE) in each 208Pb/204Pb and 207Pb/206Pb isotope ratio measurements, respectively. Our new technique and the new data for the GSJ-GRSs will be useful tools for the Pb isotopic analysis of geochemical samples.
Bisform-8-quinolinols linked at the 2- and 2'-positions by using three kinds of spacer groups have been synthesized according to the Knoevenagel reaction. The acid-dissociation constants (pKa1) of the ligands and their formation constants (log kf) with several metal ions were measured in 50％ v/v aqueous dioxane by UV-vis spectroscopy. In the case of the ligand having an ethane spacer group, two pKa1 values were observed, which suggests that it may adopt a gauche conformation in acidic solutions, and can form 1 : 1 intramolecular complexes with Cu2＋ or Zn2＋. The logkf of Cu2＋, Zn2＋,Ga3＋ and In3＋ are found to be higher than the corresponding values for 8-quinolinol. In these metal ions, Ga3＋ forms the most stable complex at the lower pH values, and the molecular structure roughly determined by X-ray analysis is considered to be 2 : 2 Ga-bisquinolinol chelates bridged by a twisted Ga-O-Ga. In addition, the Ga3＋ complexes exhibited advantageous emission intensity over the Zn2＋ complex. The bisform-8-quinolinols adopting a gauche comformation act as a tetradentate ligand and strongly coordinate with some metal cations.
The oxidation reaction from sulfite ion to sulfate ion with hydrogen peroxide is an autocatalytic reaction, in which a proton (H＋) acts not only as the reaction product, but also as the reactant. This reaction provides the characteristic S-shape pH vs. time curve, which contains the inflection time and the dynamic pH change at the end point. The threshold of the concentration of hydrogen peroxide exists in the presence of the progress of this reaction, and the value of the threshold is determined by the ratio of the concentration for several concentrations of a sulfite ion. Furthermore, the pH change at the end point can be visualized using a pH indicator, such as bromothymol blue. Based on these findings, using this reaction for the microplate, the visual determination of hydrogen peroxide by counting the discoloring color number has been developed. By the proposed method, 2.5×10−3〜1.0 mol dm−3 of hydrogen peroxide could be visibly determined. Moreover, the influence of the temperature was examined. As a result, the analytical method was able to be used within a wide range of temperatures.
A portable total reflection X-ray fluorescence spectrometer was applied to the analysis of trace elements contained in commercial bottled oolong tea, water in a pool on unpaved ground, and a leaching solution of a plastic toy coated with a metallic foil in order to discuss the possibility of applying to analyses of soft drinks, environmental water, and leaching solutions of products for daily use by using this spectrometer. Sulfur, potassium, and manganese were detected in the oolong tea. Sulfur, potassium, calcium, and iron were detected in the water. Manganese was detected in the leaching solution. These elements were quantified by an internal standard method. The quantified concentrations were a few mg/L to a few hundred mg/L, which were equivalent to several tens of nanograms to several micrograms of each element in the dry residues of the samples. This portable spectrometer performed multi-elemental simultaneous quantification by the simple method, and it was possible for it to perform quantification approximately.