BUNSEKI KAGAKU Abstracts

The total design of novel metal fluorescent probes for capillary electrophoresis-laser-induced fluorescence detection (CE-LIF), and along with a systematic study for high resolution by combination of various chemical parameters, including fluorometric properties, thermodynamics, and kinetics, were conducted. In these studies, sub-ppt sensitivity levels, high resolution among metal probe complexes, and robust applications to real samples were successfully obtained. In probe design, the quenching effect by heavy and paramagnetic metal ions was effectively controlled by adjusting the distance between the fluorophore and chelating moiety. Chelating moieties suitable to yield kinetic inertness were investigated amongst acyclic or macrocyclic hexa- or octadentates. In addition to the probe design, two new separation modes were developed, including : (i) a dynamic ternary complexing separation mode, in which the charge of an inert mother metal-probe complex is controlled by adding auxiliary ligands to form a ternary complex ; (ii) an ion association complex separation mode, in which the addition of a polycation gives different sizes or shapes of polycation-probe association complexes, which, in turn, lead to different mobilities. Furthermore, a chemical suppression technique of metal-ion contaminants was developed, since the problem of contamination is of great importance for ultratrace detection. The contamination suppression system was achieved by integrating kinetics, and thermodynamics of the probe and the suppression reagent complexes with metal ions. This system successfully provided a contamination-free and -stable system for ppt level detection.

A method for the on-line absorptiometric determination of trace amounts of boron in natural water samples was improved using a commercially available 1-cm anion-exchange column presorbed with chromotropic acid. On-line reaction and separation were achieved by controlling the pH in order to accelerate complex formation in the column by 3, and to stabilize the complex at pH 8 for selective elution of the 1 : 2 complex and its detection at 350 nm. The analytical time for a 3.2 cm³ water sample was 12 min, and the detection limit was 0.06 μg dm⁻³. The method was applied to the boron analysis of natural water samples on Iriomote Is., the Ryukyus. The boric acid concentrations of rain and two river water samples were ranged from 3.1 to 40.8, 20.3 to 28.5 and 14.7 to 20.9 μg dm⁻³, respectively. In each case, the fraction of non-sea salt origin was estimated to be high, probably suggesting that the nss-B had been transported a long distance from the Asian Continent.

The electronic cigarette, introduced recently to the marketplace, is a battery-powered device that provides tobacco-like smoke by heating a chemical solution into a vapor. There is, however, little information available regarding the safety of the electronic cigarette, because analysis of the smoke produced is very difficult due to the nature of the chemical components, e.g. acrolein and other carbonyls. Recently, an effective method for the determination of acrolein and other carbonyls using a dual-cartridge system has been developed. Each cartridge consists of reagent-impregnated silica particles ; the first contains hydroquinone (HQ) for the inhibition of acrolein polymerization, while the second contains 2,4-dinitrophenylhydrazine (DNPH) for the derivatization of carbonyls. Samples were drawn through the cartridge, first through the HQ-impregnated silica and then the DNPH-impregnated silica. During extraction, excess DNPH was washed into the HQ bed, where it reacted with acrolein and other trapped carbonyls to form the corresponding hydrazone derivatives. All of the hydrazones derived from airborne carbonyls were completely separated and measured using HPLC. In this study, we analyzed carbonyl compounds generated by the electronic cigarette using the HQ-DNPH technique. Results showed that formaldehyde, acetaldehyde, acrolein, glyoxal and methyl glyoxal were contained in the electronic cigarette smoke. The maximum concentration of formaldehyde was 260 mg/m³. Depending on the brand, cartridges usually contain humectants to produce the vapor (e.g. ethylene glycol, propylene glycol or glycerol) and flavors (e.g. tobacco, mint, fruit and chocolate). Therefore, a simple electronic cigarette was made, comprising a coiled Nichrom wire and glycols ; a voltage of 1.5〜7.5 V was applied to the Nichrom wire. It was found that when the voltage exceeded 3 V, a mist containing carbonyl compounds was generated. From the results, it was elucidated that ethylene glycol was oxidized to formaldehyde and glyoxal ; propylene glycol was oxidized to formaldehyde, acetaldehyde and methylglyoxal ; and glycerol was oxidized to formaldehyde, acrolein, glyoxal and methylglyoxal.

We investigated the high-performance liquid chromatographic (HPLC) separation characteristics of bromide (Br⁻), nitrate (NO₃⁻), iodide (I⁻) and thiocyanate (SCN⁻) on a Hydrosphere C18 column (150 × 4.6 mm i.d.) with 0.1% aqueous phosphoric acid-acetonitrile elution and UV detection at 210 nm. The inorganic anions were retained and well separated on the column without using ion-pairing reagents. The retention of these inorganic anions increased with increasing acetonitrile concentration or decreasing phosphoric acid concentration. According to the evaluation of the basicity at the surface of the octadecylsilica packing material of Hydrosphere C18, we concluded that the inorganic anions were retained on the column by an anion-exchange interaction. We investigated the determination of Br⁻, I⁻ and SCN⁻ with a mobile phase consisting of 0.1% phosphoric acid-acetonitrile (80 : 20, v/v) and a 10-μL injection at a flow-rate of 1.00 mL min⁻¹. The calibration curves for the inorganic anions were linear over the concentration range of 1.0 × 10⁻⁶–5.0 × 10⁻⁴ M. The detection limits (S/N = 3) for Br⁻, I⁻ and SCN⁻ were 2.5 × 10⁻⁷, 0.9 × 10⁻⁷ and 2.4 × 10⁻⁷ M, respectively. We applied this method for an investigation of inorganic anion transmission through ultrafiltration membranes.

The separation method and the determination of amorphous boron and boron carbide in carbon nanotubes (CNTs) were investigated. The boron carbide was precipitated in the CNTs when they were sintered after adding amorphous boron. The carbon nanotubes and boron carbide were not dissolved, whereas the amorphous boron could be dissolved with 7 N nitric acid. After dissolving amorphous boron in CNTs with 7 N nitric acid, residual boron carbide and CNTs were separated by filtration with a membrane filter. The separated insoluble boron carbide and CNTs on the filter were fused with molten sodium carbonate in a platinum crucible. The concentrations of boron in the filtrate and the insoluble residue were determined by inductively coupled plasma-optical emission spectrometry. It was found that the amount of the precipitated boron carbide increased along with an increase in the addition amount of boron and the rise of the temperature. The amount of unreacted amorphous boron in the CNTs was only a little.

A Schisandra chinensis and Schisandra sphenanthera were distinguished by the score plots of PC3 vs. PC1 of principal component analysis (PCA) of the near infrared (NIR) spectra. The four producing districts of Schisandra chinensis were also distinguished by the score plots of PC1 vs. PC2 of NIR data. The concentrations of Schisandrin and Schisantherin A in the Schisandra chinensis and Schisandra sphenanthera, using values measured by the HPLC method as the reference values were predicted from the NIR data by multiple linear regression (MLR) analysis. The coefficient of determination between the value of Schisandrin and Schisantherin A by HPLC method and the NIR predicted value were r² = 0.885 and r² = 0.942, respectively. This result shows that the concentration of Schisandrin and Schisantherin A could be easily, rapidly and nondestructively determined by NIR spectroscopy combined with MLR analysis.

An interlaboratory study was performed to find a method for the determination of total anthocyanin content in black rice and black soybean, based on the pH differential method. The extraction procedure of anthocyanin in milled materials of black rice and black soybean was optimized ; the recoveries determined for milled materials of rice and soybean spiked with cyanidin-3-glucoside were 98.9% and 92.1%, respectively. Duplicate determinations of total anthocyanin content performed by two technicians on five different test materials on three different days resulted in relative standard deviations of 1.6 to 2.7%. Seven collaborators in six laboratories participated, and measured the total anthocyanin content in five test materials as blind duplicates by the proposed method. A statistical treatment revealed that the relative standard deviation of the repeatability (RSD_r) and the relative standard deviation of the reproducibility (RSD_R) for the determination of total anthocyanin content were 0.9% to 4.0% and 1.5% to 6.1%, respectively. The HorRat values (RSD_R/predicted RSD_R) were 0.25 to 1.24. The present study demonstrated that the proposed method for the determination of total anthocyanin content in black rice and black soybean showed good interlaboratory reproducibility in the range from 0.50 to 2.71 mg/g. The expanded uncertainty, obtained by multiplying the standard deviation of the reproducibility (s_R) by the coverage factor (k = 2), ranged from 0.021 to 0.326 mg/g.