Masami Shibukawa

An alternating trilinear decomposition algorithm with application to calibration of HPLC–DAD for simultaneous determination of overlapped chlorinated aromatic hydrocarbons

In this paper an alternating trilinear decomposition (ATLD) algorithm that is an improvement of the traditional PARAFAC algorithm without any constraints is described as an alternative algorithm for decomposition of three‐way data arrays. It is based on an alternating least squares principle and an improved iterative procedure that, in a real trilinear sense, uses the Moore–Penrose generalized inverse with singular value decomposition. Its performance is compared with that of the traditional PARAFAC algorithm by a series of Monte Carlo simulations with different noise levels. It was found that the ATLD algorithm has a capability to converge faster than the traditional PARAFAC algorithm. The ATLD‐based second‐order calibration retains the second‐order advantage that calibration in the presence of unknown interferents can be performed to provide satisfactory concentration estimates. Both algorithms have been used for simultaneous determination of overlapped chlorinated aromatic hydrocarbons measured by means of a high‐performance liquid chromatograph with a diode array detector.

Extraction behaviour of metal ions in aqueous polyethylene glycol–sodium sulphate two-phase systems in the presence of iodide and thiocyanate ions

Abstract The distribution behaviour of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Li(I) was studied in an aqueous two-phase system formed from a polyethylene glycol and sodium sulphate in the presence of thiocyanate or iodide ion. From the distribution ratios determined as a function of the iodide or thiocyanate concentration, the extracted species were assumed. In the SCN − system Cu(II), Zn(II) and Co(II) distribute into the PEG-rich phase predominantly as Cu(SCN) 4 2− , Zn(SCN) 4 2− and Co(SCN) 4 2− and Fe(III) as Fe(SCN) 4 − , respectively. On the other hand, Cd(II) is extracted as Cd(SCN) 2 in the SCN − system, while as CdI 4 2− in the I − system. The extractabilities of the metal ions depend not only on the stabilities of the metal thiocyanate or iodide complexes but also on those of their sulphate complexes. A selective separation of Cd(II) from the other metal ions studied was accomplished in the aqueous two-phase system by using iodide ion as an extracting reagent for Cd(II) and an ammonium buffer as a masking reagent for Cu(II).

Determination of ethanol in alcoholic beverages by high-performance liquid chromatography-flame ionization detection using pure water as mobile phase.

A method for the determination of ethanol in alcoholic beverages by high-performance liquid chromatography-flame ionization detection (HPLC-FID) was developed. An FID system could be directly connected to an HPLC system using pure water as a mobile phase. In a durability test using triacontylsilyl (C30)-silica gel stationary phase for 96 h, no significant change in the retention time of four alcohol compounds was observed. So the HPLC separation of alcoholic beverages was carried out on the C30-silica gel stationary phase. On application to the analysis of six kinds of alcoholic beverages, ethanol could be determined accurately by the proposed method.

Separation and determination of quaternary ammonium compounds by high-performance liquid chromatography with a hydrophilic polymer column and conductometric detection

Abstract An HPLC method has been developed for separation and determination of long alkyl chain quaternary ammonium compounds. A column packed with a hydrophilic polymer packing, Shodex Asahipak GF-310 HQ, and a water–acetonitrile mixture containing 4,4′-bipyridyl and hydrochloric acid were used to depress hydrophobic adsorption of the quaternary ammonium compounds and increase the sensitivity of the conductometric detection with a micromembrane suppressor. Dodecyltrimethylammonium, cetyltrimethylammonium, tetradecyldimethylbenzylammonium and stearyltrimethylammonium ions can be completely separated from one another and quantified at 0.1 nmol level.

Interfacial water on hydrophobic surfaces recognized by ions and molecules.

Recent spectrophotometric and molecular dynamics simulation studies have shown that the physicochemical properties and structures of water in the vicinity of hydrophobic surfaces differ from those of the bulk water. However, the interfacial water acting as a separation medium on hydrophobic surfaces has never been detected and quantified experimentally. In this study, we show that small inorganic ions and organic molecules differentiate the interfacial water formed on the surfaces of octadecyl-bonded (C(18)) silica particles from the bulk water and the chemical separation of these solutes in aqueous media with hydrophobic materials can be interpreted with a consistent mechanism, partition between the bulk water phase and the interfacial water formed on the hydrophobic surface. Thermal transition behaviour of the interfacial water incorporated in the nanopores of the C(18) silica materials and the solubility parameter of the water calculated from the distribution coefficients of organic compounds have indicated that the interfacial water may have a structure of disrupted hydrogen bonding. The thickness of the interfacial water or the limit of distance from the hydrophobic surface at which molecules and ions can sense the surface was estimated to be 1.25 ± 0.13 nm from the volume of the interfacial water obtained by a liquid chromatographic method and the surface area, suggesting that the hydrophobic effect may extend beyond the first solvation shell of water molecules directly surrounding the surfaces.

Evaluation of the surface charge properties of porous graphitic carbon stationary phases treated with redox agents

The effect of treatment of porous graphitic carbon (PGC) stationary phases with hydrogen peroxide and with sodium sulfite on the retention behavior of analyte compounds has been investigated using benzene, aromatic sulfonate ions, and benzyltrialkylammonium ions as model compounds. It is shown that the retention times of the cationic analytes are increased by treating the PGC column with the reducing agent, while decreased by treating it with the oxidizing agent. On the other hand, the retention times of the anionic analytes are decreased by treating the column with the reducing agent, while increased by treating it with the oxidizing agent. The effect of the redox treatment on the retention of benzene is negligibly small. The investigation of the ion-exchange property of the PGC packings have shown that PGC has anion-exchange property and the anion-exchange capacity is decreased by treating PGC with the reducing agent, whereas it is increased by treatment with the oxidizing agent. This means that the modification of the retention selectivity of the PGC stationary phases with redox treatment can be interpreted in terms of the change of the surface charge. The mechanism of chemical modification of the PGC stationary phase with redox treatment is discussed on the basis of the experimental results obtained on the ion-exchange capacity and the redox activity.

New Molecular Motif for Recognizing Sialic Acid Using Emissive Lanthanide–Macrocyclic Polyazacarboxylate Complexes: Deprotonation of a Coordinated Water Molecule Controls Specific Binding

A new molecular motif--lanthanide-macrocyclic polyazacarboxylate hexadentate complexes, Ln(3+)-ABNOTA--was found to specifically bind to sialic acid with strong emission enhancement and high affinity. The selectivity toward sialic acid over other monosaccharides was one of the highest among artificial receptors. Also, the novel binding mechanism was investigated in detail; binding selectivity is controlled by interactions between sialic acid and both the central metal and a hydroxyl group produced by deprotonation of a coordinated water molecule in the Ln(3+) complex.

Multistep pH-Peak-Focusing Countercurrent Chromatography with a Polyethylene Glycol-Na2SO4 Aqueous Two Phase System for Separation and Enrichment of Rare Earth Elements

Multistep pH-peak-focusing countercurrent chromatography was developed for separation and enrichment of rare earth metal ions using a polyethylene glycol-Na(2)SO(4) aqueous two phase system (ATPS) and pH stepwise gradient elution. Metal ions in a sample solution are chromatographically extracted in a basic stationary phase (polymer-rich phase of the ATPS) containing a complexation ligand such as acetylacetone at the top of the countercurrent chromatography (CCC) column. After the sample solution is introduced, the mobile phases of which the pH values have been adjusted with buffer reagents are delivered into the column by stepwise gradient elution in order of decreasing pH. Each metal ion is concentrated at a pH border formed between the zones of different pH in the CCC column through extraction with a complexing agent into the stationary phase at the front side of the border (basic region) and back extraction into the mobile phase at the back side of the border (acidic region), moving toward the outlet of the column with the pH border. Mutual separations of La(III), Ce(III), Nd(III), Yb(III), and Sc(III) were achieved by the present method using five step pH gradient elution, and each rare earth metal ion was effectively enriched at each of the five pH borders. The mechanism for formation of pH profile of the column effluent and the potential of this technique for preparative scale separation are also discussed.

Redox Reaction Catalyzed by a Porous Graphite Carbon Packing and its Application to Selectivity Enhancement of High-performance Liquid Chromatography Separation of Metal Complexes

A new HPLC method was developed for the selective separation of metal complexes by using a redox reaction as a secondary chemical equilibrium. In a study of the reversed-phase ion-pair liquid chromatography of trans-1,2-diaminocyclohexanetetraacetate (DCTA) complexes of transition metal ions, it was noted that the redox reaction between the divalent and trivalent cobalt complexes were extremely accelerated by using a porous graphite carbon (PGC) column. This finding was ascribed to the catalytic effect of the PGC. The retention of Co–DCTA complex can be modified by treating the PGC column with the eluent containing sodium sulfite. The cobalt complex was completely separated from 1000-fold molar excess of the BiIII, FeIII, CuII, and NiII complexes.

Development apparatus for thin-layer gel chromatography in organic solvent systems

An apparatus is devised for development of thin-layer gel chromatograms, which is easy to handle and gives reproducible results even with volatile organic solvent systems. The print technique with a silicone-treated paper can facilitate detection of the samples chromatographed.