BUNSEKI KAGAKU Abstracts

The reduction of nitrate to nitrite by using a filter disk (pore size 0.45 μm ; φ25 mm) loaded with 0.5 g of zinc powder was investigated. When a 20 mL of sample, to which 0.1 g of ammonium sulfate and 0.2 mL of 1 g/L EDTA solution were added, was filtrated with filter disk at 15 mL/min, nitrate was reduced to nitrite with ca. 93％ efficiency. Nitrite in the filtrate was determined by naphthylethylenediamine spectrometry. The precision of repeated tests (n＝10) was ca.1％ on the nitrate standard solution (0.15 μgN/mL). Good results were obtained in recovery tests using sea water treated with potassium peroxydisulfate.

The abuse of drugs is increasing and causing serious social problems world wide. The development and application of analytical methods of drugs of abuse are very important for the prediction of and protection from the risk to human health. On the other hand, analyses of biological samples, such as blood and urine are requisite to elucidate the use of drugs. Among the biological matrices, hair is valuable and includes intake information of the drug for a long period. Because the history of hair analysis is relatively new, along with the development of analytical instruments, practical and valuable methods for analysis of drugs of abuse have been developed. Now, these methods have been utilized in such fields as forensic science and clinical chemistry. In this review, the history and significance of hair analysis are discussed, and recently reported application cases are introduced.

Pulsed-laser irradiation of thiol-passivated gold nanoparticles in cyclohexane resulted in a rapid agglomeration and fusion of gold nanoparticles due to a partial desorption of immobilized thiol molecules. At the same time, a patterned deposition of gold nanoparticle corresponding to the shape of the laser spot was found on the surface of a substrate that was immersed into a colloidal solution. In order to extend this phenomenon to practical and analytical applications, some basic investigations, spectroscopic studies for elucidating the deposition mechanism and the effects of a surface modification of the glass plate were carried out. It was found that the quantity and size of the deposited gold nanoparticles were dramatically changed only by a partial replacement of the immobilized dodecanethiol with 1,6-hexanedithiol, and were also dependent on the wavelength and the power of the laser light. Independently, laser-induced patterned deposition was carried out onto a glass plate and a membrane filter, and subsequent electroless copper plating catalyzed by the deposited gold nanoparticles, and applications to surface plasmon resonance sensing and surface-enhanced vibrational spectrometry have been successful.

A determination of the mixing ratio of two or more compounds in each sample was carried out using the principal component score. The determination method of the mixture by the principal component analysis method has already been applied to principal component regression analysis (PCR). In PCR, principal component analysis is carried out using 4 or 5 known samples of clear mixing ratio and the unknown samples. However, in this method, the mixing ratio of an unknown sample is determined using the principal component score of the last principal component of the obtained known sample. The mixing ratio of ethyl acetate, acetonitrile, and ethanol in an organic solvent was determined by this method. Regarding the result, this method was able to determine the mixing ratio in an unknown sample with comparable high precision.

In order to elucidate the applicable range and accuracy of absorption spectrophotometry in the micro-region using a confocal laser scanning microscope (CLSM), micro-silica gel beads (2) immobilizing a given molar concentration (C₁^m) of dihydroxo(tetraphenylporphyrinato)- antimony(V) bromide (1) were prepared. The measurable area on the beads was determined to be a circle of 2.14 μm diameter by magnifications of an objective lens, the diameter of fiber core, and the diameter of a pinhole. Moreover, the range of the diameter of the beads and the spectral range were decided to be 4 μm〜350 μm and 488〜775 nm, respectively. Using a halogen lamp as a light source on CLSM, the molar concentrations (C₂) of 1 in 2 were determined by absorption spectrophotometry. The value of C₂ showed good agreement with C₁^m with 0.11〜0.73 of the standard deviation. Thus, absorption spectrophotometry in the micro-region will be a powerful tool for the quantitative analysis of transparent materials of micron-order.

Accompanied by the introduction of new regulations in environment and foodstuffs fields, various kinds of mixed standard solutions of organic substances are on the market in Japan for the convenience of analysts. However, since these standard solutions are not certified, it is necessary to evaluate their reliability. In the present study, in order to evaluate the validity of the concentrations of the standard solution on the market, 3 mixed solutions (10 μg/mL) were examined ; these contained 68 pesticides each. They were diluted with hexane to prepare 1 μg/mL each, and were measured by an internal-standard method using GC/MS. The measurement values of 68 the pesticides between the 3 mixed standards were analyzed by one-way layout analysis and by multiple comparisons. As a result, the values of 30 out of the 68 pesticides were significantly different from each other, which indicates that the analytical results obtained using these standards are deemed to be significantly different. From these results, it was confirmed that an improvement in the reliability of the concentrations in standard solutions and disclosure of the preparing process of standard solutions is strongly required.

Azo-type disperse dyes are considered to be one of the causative agents of the allergic contact dermatitis caused by textile products. It was difficult to identify disperse dyes dyed in textile products, because of a large variety of them. We measured the mass spectra of disperse dyes known to be allergenic. In addition, we developed a method for determining the chemical structures of azo-type disperse dyes that have specific chemical structures for dyeing and coloring by the mass spectra. The developed method was applied to eight cases of textile products causing allergic contact dermatitis. The dyed disperse dyes were purified by high-performance liquid chromatography (HPLC), and the mass spectra were obtained using a direct probe. These results showed that dyes unrecognized as sensitizing disperse dyes develop allergic contact dermatitis. Our study suggests that this method is effective to identify those disperse dyes that cause allergic contact dermatitis.

Capillary liquid chromatography (LC) saves energy and waste, and possesses several advantages over conventional LC ; nevertheless it has not been very much popularized since its appearance due to the fact that the column efficiency of the capillary at this moment is not dramatically higher than that of conventional LC. The present research focused on developing versatile capillary LC systems using commercially available low dead-volume micro unions and valves, allowing simple postcolumn-controlled stepwise-gradient elution, on-line sample enrichment (on- and precolumn enrichments) and recycle separation with relatively superior efficiency and tolerable band broadening. The on-column enrichment gave a 50-fold improvement in sample injection, while the precolumn allowed injection of up to 5000-fold, which is so far the highest enrichment factor that has been reported. These systems were successfully applied to the analysis of environmental as well as drinking water samples. Alternatively, an alternate-pumping recycle chromatography system was newly-designed using two monolithic silica capillary columns, and baseline separation of benzene and deuterated benzene was achieved after 5 cycles when the system attained 160000 theoretical plates. Additionally, the development of a novel glass-bead-based immobilized-enzyme micro column for simple and swift on-line protein digestion and its peptide separation by reversed-phase HPLC was also described.