BUNSEKI KAGAKU Abstracts

Single-drop micro extraction (SDME) that can archive extraction by contacting continuously a droplet to a sample solution by rotating a spiral extraction cell, after the sample solution has been filled in the extraction cell vertically placed, and then the extracting droplet is introduced in the cell, was examined. Fluorinated alcohols and Malachite green (MG) were used as the extraction solvent and model sample, respectively. After MG in 20% NaCl aqueous solution (2.5 μM) was filled in a glass extraction cell (2.6 mm i.d. ; 1.8 m long ; 9.3 mL of the net volume ; and 10 cm of the diameter of spiral), 3.0 μL of a droplet of 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (OFP) as the extracting solvent was introduced into the cell. After introduction, extraction was performed for four minutes by moving the droplet at a rate of 1.5 cm/s in one roundtrip by rotating the extraction cell at room temperature. In this case, an enrichment factor (the ratio of the concentrations in the droplet and the sample solution, before and after the extraction, respectively) was obtained to be 0.54 × 10³. On the contrary, when a droplet (0.96 μL) of 1H,1H-pentadecafluoro-1-octanol (PDFO) was used as the extracting media, and them similar extraction was performed at 65°C, the enrichment factor was estimated to be 1.6 × 10³. A PDFO droplet after the extraction was solidified by cooling to room temperature, therefore, it was possible to separate by filtration as a spherical particle.

A novel solid-phase extractant that will demonstrate a dispersion force was synthesized to improve the extraction efficiency for halogenated solutes, including clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), which is widely used as a herbicide. The 2,4-dibrominated phenoxy group was immobilized on the surface of a hydrophilic methacrylate resin. The solid-phase extraction properties for the halogenated solutes were evaluated by solid-phase extraction using a cartridge packed with the synthesized extractant. Clopyralid and its analogues, i.e. benzoic acid, 2,5-dichlorobenzoic acid, pyridine carboxylic acid and so on, were used as probes. This dispersion-force extractant could selectively entrap the halogenated aromatic carboxylic acids including clopyralid in every organic solvent used for the extraction of pesticide residues. The extractant was applied to the analysis of clopyralid in whole-grain samples. The extracts of the milled whole grain by water-acetone solution were passed through the extractant. Cropyralid trapped on the extractant was eluted by a methanol-water solution containing diethylamine after washing the extractant with an organic solvent ; then, the effluent was measured by the HPLC-UV method. The detection limit on the optimized method was 0.16 μg g⁻¹ for clopyralid. The recoveries of clopyralid in four kinds of whole grain were good with 88–95% in triplicate.

An atomic emission detection (AED) device with face-to-face coaxial electrodes using a helium radio-frequency plasma (RFP) for gas chromatography (GC) was prepared. The plasma generation unit was constructed by coaxcially positioning face-to-face two platinum tubular electrodes (2.0 mm o.d. and 1.0 mm o.d.). Moreover, in order to prevent contamination of the atmosphere, a structure in which the circumference of the quartz discharge tube was enclosed by helium (sheath flow structure) was adopted. The head of an optical fiber was placed on the AED device, and the end was connected to a spectrometer. The prepared AED device was set on a conventional GC for the measurement. When tert-butyl methyl ether was used as an oxygen-containing compound, the atomic emission wavelength due to oxygen was possible to be detected. When the detection wavelength, applied power, applied frequency and flow-rate of the make-up gas were set at 309.0 nm, 3 W, 250 kHz and 5 mL min⁻¹, respectively, the detection limit as the amount of oxygen was obtained to be 42 pg s⁻¹ (3 σ). It would be applied to high-sensitive measurements of oxygen-containing compounds in petroleum products and oxidized compounds.

The simultaneous and selective determination of inorganic nitrogen species (nitrite, nitrate, and ammonium ions) in seawater samples was examined by ion chromatography. Nitrite and nitrate ions were separated on a monolith type of ODS columns equilibrated with DDAB (dilauryldimethylammonium bromide) using 0.4 M potassium chloride + 5 mM phosphate buffer (pH = 5.0) as the eluent, and were detected by UV at 225 nm. Whereas, ammonium ion was detected at 710 nm as indophenol blue derivative by post-column reaction in the presence of dichloroisocyanurate and 1-naphthol. The length of the cation exchange column and the addition of sodium ethylenediaminetetraacetate in reaction solution were optimized in order to suppress interference by magnesium and calcium ions in seawater samples. Thus, this method enabled the direct determination of inorganic nitrogen species for the first time. Calibration curves of all ions in 35‰ artificial seawater showed good linearity (R² = 0.999) in the range of 0–5 mg L⁻¹. The detection limits (S/N = 3) of nitrite, nitrate, and ammonium ions were 0.8 μg L⁻¹, 1.8 μg L⁻¹, and 3.6 μg L⁻¹, respectively. Also, the repeatability (1 mg L⁻¹, n = 5) was below 0.55% (retention time), 1.80% (peak area), and 1.75% (peak height). The present method was applied to the simultaneous and selective determination of inorganic nitrogen species in seawater samples of a port area and a semi-closed area. The recovery by analysis of spiked samples was in the rage of 91–107%.

A novel, simple and highly sensitive amperometric flow-injection analysis (FIA) system with electrochemical detection for azide was developed by using hemoglobin-adsorbed carbon-felt (Hb-CF). This electrochemical FIA is based on the inhibitory effect of azide upon the Hb-CF-catalyzed electrochemical reduction of dissolved oxygen. The Hb-CF showed excellent bioelectrocatalytic activity for the reduction of oxygen, based on direct electron transfer between Hb-heme and the CF, and this activity was reversibly inhibited by azide. When air-saturated 0.1 M phosphate/citrate buffer (pH 5.0) was used as a carrier at an applied potential of –0.2 V vs. Ag/AgCl, the steady-state background current due to the Hb-CF-catalyzed O₂ reduction was reversibly inhibited by the injection of azide (200 μL), leading to peak-shape current responses. The magnitude of the inhibition peak currents (I_pⁱⁿ) changed over the concentration range from 0.3 to 100 μM, and the detection limit of azide was found to be 0.15 μM (S/N = 3). The inhibition peak currents were scarcely changed after 14 days of storage in 0.1 M phosphate/citrate buffer (pH 5.0) at 4°C.

Novel 8-quinolinol derivatives, 7-bromo-5-methoxymethyl-8-quinolinol (HBrO₁Q) and 7-iodo-5-methoxymethyl-8-quinolinol (HIO₁Q), were synthesized by halogenating 5-methoxymethyl-8- quinolinol at the 7-position. From the distribution behavior of the reagents between carbon tetrachloride and water, an increase in hydrophobicity and acidity by the halogenation was confirmed. Furthermore, a remarkable increase in the extractability of the Cu(II) ion was found. It was shown that HIO₁Q had the extraction constant of Cu(II) which is the highest in 8-quinolinols reported so far.

Synthetic cannabinoids and synthetic cathinones are classified as Ågdesignated substancesÅh, and comprise a new class of illegal drugs. In order to offer rapid and expert testimony on these drugs, a screening method that uses direct analysis in real time (DART ^TM) time-of-flight (TOF) mass spectrometry (MS) was developed. DART enabled the direct introduction of a sample without any pretreatment, such as extraction and cleanup. The positive-ion mode was suitable for ionization in TOF-MS. It was also possible to accurately measure the mass of each drug. The mass spectra clearly showed all peaks representing the protonated molecules of synthetic cannabinoids (14 types) and synthetic cathinones (three types). The analysis of samples of herbal products, plant leaves, and tablets was possible without any pre-processing of the samples. As a result, stimulants, cannabis components, and several synthetic cannabinoids (such as JWH-210, AM2201, JWH-203, JWH-081, 4-methylehcathinone, and naphyrone) were identified in each sample. With DART-TOF-MS, the mass spectrum was obtained in a few seconds. The analysis with DART-TOF-MS was proven to be useful for screening controlled substances.

Ultra high-speed liquid chromatography (ultra high-speed LC) has become an increasingly popular method in analytical research fields. This novel analytical system provides fast and efficient chromatographic separation over a wide range of flow rate and pressure. In this study, we applied an ultra high-speed LC system to the analysis of active ingredients, such as loxoprofen sodium hydrate and some additives in the drug formulation. As part of the ultra high-speed LC system utilized in this study was a LaChrom Ultra system (Hitachi, Tokyo, Japan) equipped with a L-2455U diode array detector and a LaChrom Ultra C18 (particle size, 2 μm) column ; as a result, short time stability tests of drugs were accomplished efficiently. Loxoprofen sodium hydrate is one of the most popular non-steroidal anti-inflammatory drugs (NSAIDs) used in Japan. The use of generic products has been strongly encouraged in order to reduce healthcare costs. The active ingredients, strengths, dosage forms and regimen of generic products are the same as those of the innovator's products. However, there are many generic products of loxoprofen sodium hydrate. The most important factor in selection is information concerning the quality of the product. For oral drug products, dissolution tests should be performed, since they provide important information concerning the bioequivalence of generic products. After dissolution tests of brand-name drugs and generic products, their elution behaviors were evaluated by high-speed analysis. We achieved a fast analysis of loxoprofen within 1.0 min, and compared the elution behavior between, the brand-name drug and generic products.

Admicellar chromatography was studied for the mutual separation of pharmaceuticals. Admicellar columns were prepared by passing acetonitrile solutions containing dodecyltrimethylammonium chloride (DTAC) through a silica gel column (Mightysil Si 60). Successful separations of pharmaceuticals were achieved by optimizing the experimental conditions such as the pHs, DTAC concentrations, and acetonitrile fractions. For example, benzalkonium chloride was separated from benzethonium chloride with the use of 1.0% DTAC in 20% acetonitrile at pH 6. A DTAC aqueous solution (0.5%, pH 7) was successfully used for the mutual separation of sulfa drugs (e.g., sulfadiazine, sulfathiazole, sulfapyridine, and sulfamerazine). Methoxyphenols (o-, m-, and p-isomers) were separated from each other by using 0.5% DTAC in 5% acetonitrile at pH 5.

The hydrolysis of p-nitrophenyl phosphate (NPP) was catalyzed at pH 9.5 and 40°C by a dinuclear Ce(IV)-thiacalix[4]arenetetrasulfonate (TCAS) complex in a Michaelis-Menten manner. The Michaelis constant (K_m) and turnover number (k_cat) were 1.3 × 10⁻³ M and 5.5 × 10⁻³ s⁻¹, respectively. The coexistence of micelles of cetyltrimethylammonium chloride (cationic surfactant, CTAC) further accelerated the NPP hydrolysis with improved K_m and k_cat values of 2.0 × 10⁻⁴ M and 1.1 × 10⁻² s⁻¹, respectively, whereas Triton X-100^® (nonionic surfactant) and sodium dodecyl sulfate (anionic surfactant) were not effective even above the critical micelle concentrations. The possible enrichment of NPP and Ce(IV)-TCAS in CTAC micelles may result in more favorable formation of the substrate-catalyst complex, providing a decreased K_m value. The micellar environment may also enhance activation of the substrate, providing an increased k_cat value.

A novel method for the sensitive determination of an antimicrobial agent, cetylpyridinium chloride (CPC), in water was developed. Traces of CPC in water were highly concentrated to sodium dodecyl sulfate–alumina admicelles. The fluorescence of perylene co-extracted into the admicelles was significantly quenched by CPC. Fluorescence quenching was represented by the Stern-Volmer equation in the CPC concentration range of 0–6 μM (0–2 mg L⁻¹). The Stern-Volmer constant (K_SV = 8.6 × 10⁵ M⁻¹) was significantly increased from the value (K_SV = 1.9 × 10³ M⁻¹) in the SDS micellar system. On the other hand, fluorescence quenching was negligibly small in the presence of 10 μM each of benzalkonium chloride, cetyltrimethylammonium chloride, dodecylbenzene sulfonate, Brij-35, or Triton X-100. The proposed method was successfully applied to the determination of CPC in synthetic water samples.

A compact column oven for pressurized hot water liquid chromatography (PHW-LC) has been prepared that utilizes photoirradiation from a halogen lamp as a heat source. The controllability of the column temperature was examined by monitoring the retention properties of several model compounds. When thymidine was used as a model compound, a reasonably linear vanÅft Hoff plot up to 150°C was obtained. The relative standard deviations of the retention factors obtained at 90, 100 and 110°C were within 0.54, 0.74 and 0.20%, respectively, indicating good enough reproducibility (n = 3). In addition, the correlations among the molecular parameters [logP value, water solubility (S_w) and polarizability (α)], geometrical parameters [polar surface area (PSA) and molecular surface area (S)], electrical parameter [dipole moment (μ)] and thermodynamic parameter [hydration energy (E_h)] were examined for adenosine, thymine and thymidine in relation to their retention behaviors. Strongly positive correlations recognized between the retention factors and α, PSA or S indicated that the retention in the present PHW-LC is ruled by the equilibration of the adsorption. The observed change in the correlation coefficient below and above 100°C suggested a discontinuous change in the property of water.