BUNSEKI KAGAKU Abstracts

A brown complex or refractory organic materials, which are often called humic substances and kerogen, are ubiquitous in aquatic and terrestrial environments. They play an important role in carbon and material cycles in the environment. Although a clear understanding of their molecular nature is essential, some knowledge of their chemical structure and the mechanism by which they form and change in time on Earth is still limited. The molecular characterization of these materials is difficult due to their insolubility and complex macromolecular nature. From this review, we highlight the following three types of chemical degradation techniques, which are becoming popular in the molecular characterization of these organic materials: i.e. pyrolysis gas chromatography-mass spectrometry (py-GCMS), pyrolysis in the presence of tetramethylammonium hydroxide coupled to gas chromatography-mass spectrometry (py-TMAH-GCMS), and gas chromatography-mass spectrometry after bond-selective chemical degradation (chemical degradation-GCMS). Both py-GCMS and py-TMAH-GCMS are often used as small-scale analytical methods. py-GCMS is commonly suitable for materials (e.g. kerogen in rocks) that produce non-polar or less-polar materials (e.g. hydrocarbons) on pyrolysis, while this technique may not be suitable for young humic substances, because they tend to produce polar materials by a thermal reaction of heteroatomic (such as oxygen, nitrogen) functional groups. py-TMAH-GCMS overcomes some of the weak points of py-GCMS. Since this technique is based on the cleavage of labile C-O bonds, such as ester, amide and ether bonds with simultaneous methylation (thermochemolysis), it can be applied for characterizing macromolecular organic matter, which is on the way of change from biomacromolecules (e.g. lignin, proteins, carbohydrates and lipids). Modern sequential chemical degradation-GCMS techniques involving the successive cleavage of different types of bonds (S-C bond, ether bond, double bonds and sub-units linked to aromatic moieties etc.) in refractory organic materials are described.

An analytical method of precipitates/inclusions existing a few μm from the surface in steel sheets has been established. Less than 0.1 g of a steel surface was electrolyzed, and the extracted precipitates/inclusions were decomposed with 2-step microwave digestion (1st step with H₂SO₄ and 2nd step with HF-HNO₃). Al, Ti, Mn, Cu, Nb, V and Mo in the sample solution was determined by ICP-MS. The lower limits of detection in the surface of the steel sample were less than 1 μg g^-1 for all elements that formed precipitates/inclusions. Furthermore, the concentration of the chelating agent (acetylacetone) in the electrolyte was reduced to 0.2%, which enabled us to quantitatively extract precipitates/inclusions that were unstable in the conventional 10% AA electrolyte. The procedure was applied to steel samples before and after annealing, and depth profiles of the precipitates/inclusions were obtained.

The photocatalytic degradation of crystal violet (CV) was investigated with titanium dioxide particles (ST-01) or titanium dioxide supported on silica gel (hybrid-photocatalyst, HQC51). A CV solution was decolorized by each photocatalyst under UV irradiation. A hypsochromic shift from 590 nm to 562 nm occurred with increasing the UV irradiation time in the presence of a photocatalyst. The shift was probably caused by a stepwise release methyl groups from CV. Some photocatalytic degradation products by ST-01 were identified by using HPLC/MS and MS/MS techniques. It was proved that six methyl groups were stepwisely released from CV under photodegradation, and also dimethylamine was detected as a degradation product. In addition, ammonium ion and nitrate in sample solutions were also determined by flow injection analysis with an indophenol blue method and by using a nitrate ion selective electrode.

A new method to analyze conversion vs. depth (depth profile of conversion) in a thick-layer of UV curable resin non-destructively, using a laser micro-Raman spectrometer, has been investigated. A few methods exist to analyze the depth profiles of the curing state in a thick-layer of UV curable resins, but these methods are destructive. On one hand, laser micro-Raman spectrometry can be applied to non-destructive analysis inside a thick-layered film, but the polymerization of a sample by the irradiation of strong laser light was of concern, when it was applied to a measurement of the conversion of UV curable resin. Furthermore, if a long-wavelength laser is used in order to avoid polymerization of sample, Raman scattering at a deep part of the sample might be too weak to analyze the conversion. In this study, by confirming the influences of these issues, laser micro-Raman spectrometry was investigated as a depth-profiling method. We selected 780 nm as the long wavelength of the laser, and it was determined that the irradiation of a urethane methacrylic UV curable resin for 216 s did not promote polymerization of the sample. Then, a 1.86 mm thick cured sample of the UV curable resin was tested using the laser micro-Raman spectrometer through laser irradiation for 60 s. The Raman spectra at several depths in the cured sample were recorded. Because the spectrum of the deepest part was as clear as the others, it was determined that all of the spectra throughout the depth were acceptable to measurements of the conversions. From areas of the peaks on the spectra at 1635 cm^-1 of C=C stretching vibration in the methacrylic group, the value of the conversion at each depth in the cured sample was calculated, and the depth profile was obtained. This study showed that laser micro-Raman spectrometry can be applied to the non-destructive analysis of the depth profile of conversion in a thick-layer of UV curable resins.

Dye-binding methods based on protein error for determining human serum albumin are classified into two methodologies via measurements of the absorbance increase under an acidic condition (absorbance increase method) and the absorbance decrease in a pH region near the neutral condition (absorbance decrease method). The color development of protein in the absorbance increase method is known to be affected by the pH, and the concentrations of dye, buffer and coexisting anions in the samples. However, the effect of coexisting anions on color development in the absorbance decrease method is unclear. In the present work, the effect of an inorganic salt on color development in the absorbance decrease method was investigated by a calculation based on the chemical equilibrium of the protein error and an experiment, and was compared with the results of the absorbance increase method. By adding an inorganic salt, the absorbance was decreased. The degree of its decrease was smaller in the absorbance decrease method than in the absorbance increase method, and differed according to the kind of inorganic salt. The experimental results agreed well with those obtained by a calculation.

The detection performance of a portable corona discharge ionization-type ion mobility spectrometer (LCD 3.2E, Smiths Detection) was investigated using nerve gases, blister agents, blood agents and related compounds. The vapors of sarin, soman and tabun were recognized as "G" after about several seconds of sampling; the detection limits were around 0.2 mg/m³. The vapors of mustard gas, lewisite 1, hydrogen cyanide and chloropicrin were recognized as "H" after several seconds of sampling, and the detection limits were around 10 mg/m³. The vapors of cyanogen chloride were also recognized as "H", but the detection limit was around 500 mg/m³. The vapors of trimethylphosphate, triethylphosphate, n-propanol, diethylamine, triethylamine, formaldehyde, and N,N-dimethylformamide were recognized as "G", and the vapors of 1,4-thioxane, 2-mercaptoethanol, diethylether and acetic acid were recognized as "H".

Acetyl-L-carnitine (L-AC) has an effect of cerebral metabolism improvement. However, the enantiomer, acetyl-D-carnitine (D-AC), does not show this effect. Several methods for the determination of D-AC in L-AC have been developed, but they were not sufficient for quality control. The author has developed an indirect HPLC enantioseparation method and a direct one for the determination of D-AC in L-AC and NMR enantioseparation methods with chiral shift reagents. 1) AC and C could be separated with an ODS column by reversed-phase HPLC after derivatization with L-alanine-β-naphthylamide. 2) AC could be separated directly by reversed-phase chiral HPLC using SUMICHIRAL OA-6100 with a mobile phase of 2 mmol/L aqueous CuSO₄ solution containing 500 mmol/L NaClO₄. 3) The NMR method with (+)-(R)-18-crown-6 tetracarboxylic acid as a chiral shift reagent was successfully applied for determining of the enantiomeric purity of L-alanine-β-naphthylamide. 4) Enantiomer signal separation of AC was obtained on the NMR analysis by diastereomeric interaction with Pr[hfc]₃ as a chiral lanthanide shift reagent. These four methods were found to be applicable as practical quality control methods for the enantiomeric excess determination.

Capillary electrophoresis (CE) is a powerful method for drug analysis. However, even now, CE is still not used routinely as a quality control (QC) method. The present study focused on developing the CE method for practical use. First, the enantiomer separation of drugs by CE, employing various compounds as chiral selectors (CSs), was studied. In the case of 2,6-di-O-methyl-β-cyclodextrin and sulfated cyclodextrins, the purity of the CS, i.e., degree of substitution (DS), strongly affected enantiorecognition of the drug. It was found that controlling the DS of these selectors is essential for practical use. In the case of carboxymethyl (CM) polysaccharides, the introduction of an ionic group (i.e., CM) enhanced the enantioselectivity, compared with the natural polysaccharides. 18-Crown-6 tetracarboxylic acid was useful for the enantioselectivity of amino acids (AAs). Employing chrysoidine as a chromophore additive, indirect enantiomer separation of free AAs was successful. Next, the developed CE methods were applied to actual formulation analysis. Purity testing, content uniformity and assays of the ingredients of commercial pharmaceutical formulations were successfully performed. Finally, micellar electrokinetic chromatography was applied for the identification and assay of marker substances of Chinese natural medicines. The results mentioned above demonstrated that the CE method can be used practically as a routine QC analysis.