Showing papers in "Analytical Sciences in 2001"

Fluorescence-quenching phenomenon by photoinduced electron transfer between a fluorescent dye and a nucleotide base.

Abstract: Fluorescently labeled oligonucleotide probes have been widely used in biotechnology, and fluorescence quenching by the interaction between the dyes and a nucleobase has been pointed out. This quenching causes big problem in analytical methods, but is useful in some other cases. Therefore, it is necessary to estimate the fluorescence quenching intensity under various conditions. We focused on the redox properties of some commercially available fluorescent dyes, and investigated dye-nucleotide interactions between a free dye and a nucleotide in aqueous solution by electrochemical and spectroscopic techniques. Our results suggested that the quenching was accompanied by photoinduced electron transfer between a thermodynamically quenchable excited dye and a specific base. Several kinds of fluorescent dyes labeled to the 5'-end of oligonucleotide C10T6 were prepared, and their quenching ratios compared upon hybridization with the complementary oligonucleotide A6G10. The quenching was completely reversible and their efficiencies depended on the attached fluorophore types. The fluorescence of 5-FAM, BODIPY FL or TAMRA-modified probe was strongly quenched by hybridization.

Estimation of the antioxidant activities of flavonoids from their oxidation potentials.

Abstract: A simple electrochemical method for estimating the antioxidant activity (AA) of flavonoids has been developed The proposed method is based on a measurement of the half-wave potential (E 1/2 ) of the first oxidation wave of flavonoids by using flow-through column electrolysis At the same time, the lipid peroxidation (LPO) inhibiting effects of these flavonoids were determined A quantitative structure-activity relationship was obtained to describe the AA of flavonoids: IC 50 (μM) = 3036 + 15150E 1/2 (V) - 1263log P (r = 0852), where IC 50 represents the concentration for 50% inhibition of LPO, and P represents the octanol/water partition coefficient This method is expected to be useful for the quick screening of flavonoid antioxidants, and evaluating the AA of flavonoid-containing foods and medicinal plants

Integrated multilayer flow system on a microchip.

Abstract: We utilized microchip technology and found that the multilayer flow of liquids can be formed in microchannels. Liquid/liquid interfaces were formed parallel to the side wall of the microchannels, because the surface tension and friction force are stronger than the force of gravity. A water/ethylacetate/water interface was formed in a 70-µm-wide and 30-µm-deep channel. The interface was observed to be quite stable and to be maintained for a distance of more than 18 cm. As an example of a multilayer flow application, we demonstrated the liquid/liquid extraction of Co-dimethylaminophenol complex in a microchannel. The solvent-extraction process of the complex into m-xylene in the multilayer flow was found to reach equilibrium in 4 s, while it took 60 s in a simple two-phase extraction.

Multielement Determination and Speciation of Major-to-Trace Elements in Black Tea Leaves by ICP-AES and ICP-MS with the Aid of Size Exclusion Chromatography

Abstract: A multielement determination of major-to-trace elements in black tea leaves and their tea infusions was carried out by ICP-AES (inductively coupled plasma atomic emission spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry). Tea infusions were prepared as usual tea beverage by brewing black tea leaves in boiling water for 5 min. About 40 elements in tea leaves and tea infusions could be determined over the wide concentration range in 8 orders of magnitude. The extraction efficiency of each element was estimated as the ratio of its concentration in tea infusions to that in tea leaves. From the experimental results for the extraction efficiencies, the elements in black tea leaves were classified into three characteristic groups: (i) highly-extractable elements (>55%): Na, K, Co, Ni, Rb, Cs and Tl, (ii) moderately-extractable elements (20 - 55%): Mg, Al, P, Mn and Zn, and (iii) poorly-extractable elements (<20%): Ca, Fe, Cu, Sr, Y, Zr, Mo, Sn, Ba and lanthanoid elements. Furthermore, speciation of major-to-trace elements in tea infusions was performed by using a combined system of size exclusion chromatography (SEC) and ICP-MS (or ICP-AES). As a result, many diverse elements were found to be present as complexes associated with large organic molecules in tea infusions.

Liquid chromatographic determination of ornithine and lysine based on intramolecular excimer-forming fluorescence derivatization.

Abstract: A highly sensitive and selective fluorometric determination method for ornithine and lysine has been developed. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent, 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester (PSE), followed by reversed-phase liquid chromatography (LC). The analytes, containing two amino moieties in a molecule, were converted to the corresponding dipyrene-labeled derivatives by reaction with PSE. The derivatives afforded intramolecular excimer fluorescence (450-550 nm) which can clearly be discriminated from the normal fluorescence (370-420 nm) emitted from PSE and monopyrene-labeled derivatives of monoamines. The structures of the derivatives and the emission of excimer fluorescence were confirmed by LC with mass spectrometry and with three-dimensional fluorescence detection system, respectively. The PSE derivatives of ornithine and lysine could be separated by reversed-phase LC on ODS column with isocratic elution. The detection limits (signal-to-noise ratio = 3) for ornithine and lysine were 3.5 and 3.7 fmol, respectively, for a 20-microl injection. Furthermore, this method had enough selectivity and sensitivity for the determination of ornithine and lysine in normal human urine.

Dynamic study of metal-ion incorporation into porphyrins based on the dynamic characterization of metal ions and on sitting-atop complex formation.

Abstract: We succeeded in the detection of the sitting-atop (SAT) copper(II) complex of TPP (5,10,15,20-tetraphenylporphyrin) in acetonitrile (AN) as a solvent with a very low Bronsted basicity, where two pyrrolenine nitrogens in the Cu(II)-SAT complex coordinate to the metal ion and two protons still remain on the pyrrole nitrogens. The structure parameters around the copper(II) ion in the Cu(II)-SAT complex, as determined by a fluorescent EXAFS method, suggest an axially elongated and equatorially distorted six-coordinate geometry. We measured the rates of the formation reaction of the SAT complexes for a series of transition metal(II) ions in AN using the stopped-flow technique. We propose the mechanism where there is a rapid deformation equilibrium of the porphyrin ring prior to the rate-determining step of the bond rupture of a coordinated solvent molecule on the metal(II) ion. Furthermore, we measured the rates of the deprotonation reaction of the Cu(II)-SAT complex by some Bronsted bases and indicated that the rate-determining step is the attack of the base on the proton of the pyrrole nitrogen in the SAT complex. Finally, a unified mechanism relevant to the porphyrin metalation mechanism has been proposed.

Studies on the matched potential method for determining the selectivity coefficients of ion-selective electrodes based on neutral ionophores: experimental and theoretical verification.

Abstract: A theory is presented that describes the matched potential method (MPM) for the determination of the potentiometric selectivity coefficients (KA,Bpot) of ion-selective electrodes for two ions with any charge. This MPM theory is based on electrical diffuse layers on both the membrane and the aqueous side of the interface, and is therefore independent of the Nicolsky-Eisenman equation. Instead, the Poisson equation is used and a Boltzmann distribution is assumed with respect to all charged species, including primary, interfering and background electrolyte ions located at the diffuse double layers. In this model, the MPM-selectivity coefficients of ions with equal charge (ZA = ZB) are expressed as the ratio of the concentrations of the primary and interfering ions in aqueous solutions at which the same amounts of the primary and interfering ions permselectively extracted into the membrane surface. For ions with unequal charge (ZA not equal to ZB), the selectivity coefficients are expressed as a function not only of the amounts of the primary and interfering ions permeated into the membrane surface, but also of the primary ion concentration in the initial reference solution and the delta EMF value. Using the measured complexation stability constants and single ion distribution coefficients for the relevant systems, the corresponding MPM selectivity coefficients can be calculated from the developed MPM theory. It was found that this MPM theory is capable of accurately and precisely predicting the MPM selectivity coefficients for a series of ion-selective electrodes (ISEs) with representative ionophore systems, which are generally in complete agreement with independently determined MPM selectivity values from the potentiometric measurements. These results also conclude that the assumption for the Boltzmann distribution was in fact valid in the theory. The recent critical papers on MPM have pointed out that because the MPM selectivity coefficients are highly concentration dependent, the determined selectivity should be used not as "coefficient", but as "factor". Contrary to such a criticism, it was shown theoretically and experimentally that the values of the MPM selectivity coefficient for ions with equal charge (ZA = ZB) never vary with the primary and interfering ion concentrations in the sample solutions even when non-Nernstian responses are observed. This paper is the first comprehensive demonstration of an electrostatics-based theory for the MPM and should be of great value theoretically and experimentally for the audience of the fundamental and applied ISE researchers.

Parameters important in fabricating enzyme electrodes using self-assembled monolayers of alkanethiols.

Abstract: The fabrication of enzyme electrodes using self-assembled monolayers (SAMs) has attracted considerable interest because of the spatial control over the enzyme immobilization. A model system of glucose oxidase covalently bound to a gold electrode modified with a SAM of 3-mercaptopropionic acid was investigated with regard to the effect of fabrication variables such as the surface topography of the underlying gold electrode, the conditions during covalent attachment of the enzyme and the buffer used. The resultant monolayer enzyme electrodes have excellent sensitivity and dynamic range which can easily be adjusted by controlling the amount of enzyme immobilized. The major drawback of such electrodes is the response which is limited by the kinetics of the enzyme rather than mass transport of substrates. Approaches to bringing such enzyme electrodes into the mass transport limiting regime by exploiting direct electron transfer between the enzyme and the electrode are outlined.

Effect of the excitation source on the quantum-yield measurements of rhodamine B laser dye studied using thermal-lens technique.

Abstract: A dual-beam transient thermal-lens technique was employed for the determination of absolute fluorescence quantum-yield measurements of Rhodamine B laser dye in different solvents. We investigated the effect of excitation on the absolute fluorescence quantum yield of Rhodamine B. 514 nm radiation from an argon ion laser was used as a cw excitation source and 532 nm pulses from a Q-switched Nd:YAG laser were used as a pulsed excitation source. The fluorescence quantum-yield values were found to be strongly influenced by environmental effects as well as the transient nature of the excitation beam. Our results also indicate that parameters, like the concentration of the dye solution, aggregate formation and excited state absorption, affect the absolute values of the fluorescence yield significantly.

Comparison of Different Digestion Methods for Total Decomposition of Siliceous and Organic Environmental Samples

Abstract: A comparison was made of different digestion methods for the total decomposition of siliceous and organically environmental samples prior to their analysis by inductively coupled plasma optical emission spectrometry (ICP-OES). In the present study, three different digestion methods, including microwave-assisted, hot plate heating and pressurized digestion (pressure bomb), were employed for the determination of nine heavy metals, i.e. Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in sediment, soil, sludge and oil. The investigation of different combinations of acids through their analytical performance demonstrated that HCl plays a vital role in the determination of silver. The combination of HNO3 and HCl possesses more reactive ability in oxidizing organic matter. The recoveries of all elements of interest in sediment (NIST 2704) obtained by different digestion methods were found to be 86% to 113%, while microwave assisted digestion with various combinations of HNO3-HCl-HF and HNO3-HClO4-HF was considered to be a viable alternative to the conventional digestion systems because of its more intensive reaction conditions. The analytical results of four certified reference materials with different matrices, including sediment (GBW 07305), soil (GBW 07411), sludge (BCR R-143) and oil (NIST 1085a), by the microwave-assisted acid digestion method indicated that the recoveries of all elements of interest were more than 85% and the throughput of applied analytical method could be elevated significantly.

Ultrasensitive optical DNA biosensor based on surface immobilization of molecular beacon by a bridge structure.

Abstract: A novel biotinylated molecular beacon (MB) probe was developed to prepare a DNA biosensor using a bridge structure MB was biotinylated at the quencher side of the stem and linked on a biotinylated glass cover slip through streptavidin, which acted as a bridge between MB and glass matrix An efficient fluorescence microscope system was constructed to detect the fluorescence change caused by the conformation change of MB in the presence of complementary DNA target The proposed biosensor was used to directly detect, in real-time, the target DNA molecules The bridge immobilization method caused the proposed DNA biosensor to have a faster and more stable response Under the optimal conditions, the newly developed DNA biosensor showed a linear response toward ssDNA in the range of 5 - 100 nM with a detection limit of 2 nM It was interesting to note that the described biosensor was reproducible after being regenerated by urea

Highly sensitive determination of plasma cytokines by time-resolved fluoroimmunoassay; effect of bicycle exercise on plasma level of interleukin-1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF alpha), and interferon gamma (IFN gamma).

Abstract: A highly sensitive time-resolved fluoroimmunoassay of human plasma cytokines is described. The cytokines such as interleukin-1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF alpha) are known to be acute inflammatory cytokines and it has been reported that these cytokines are secreted into blood by physical exercise. In this study, a sandwich-type immunoassay of cytokines was established using a europium chelate BHHCT-Eu3+ as a powerful labeling material. The minimum detection limits of cytokines, i.e. IL-1 alpha, TNF alpha, and interferon gamma (IFN gamma) were about 1/10 smaller than those of enzyme-linked immunosorbent assay currently used. By this immunoassay we investigated cytokine increase/decrease in plasma which was thought to derive from the myocytes damaged by bicycle exercise. Healthy young men performed two kinds of bicycle ergometer exercises, under conditions of an incremental and a constant loading. Blood samples were taken before, during, and after exercises, and the concentration levels of plasma IL-1 alpha, TNF alpha, and IFN gamma were determined. In the case of incremental exercise, IL-1 alpha increased significantly at the first stage but decreased to the basal level from the second stage, in spite of heavier exercise. In the case of 30 min constant exercise, the level of plasma IFN gamma increased in recovery period, 2 h after the light-exercise. TNF alpha level was significantly higher in a heavy-exercise. The concentration of IL-1 alpha peaked at the early stage of the incremental exercise; this fact has not been reported in previous studies. This cytokine is unique in showing a sudden increase during the early stage, while others increase after the exercise. Our highly sensitive assay made it possible to detect a slight change in plasma cytokines.

Fluorescence spectral study of interaction of water-soluble metal complexes of Schiff-base and DNA.

Abstract: The fluorescence spectral characteristics and the interaction of several water-soluble metal complexes of Schiff-base with DNA are described. Among the complexes tested, Mn-Schiff-base bound to DNA showed a marked decrease in the fluorescence intensity with a blue shift of the excitation and emission peaks. Some hypochromism in the UV absorption spectra was also observed. KI quenching and competitive binding to DNA between Mn-Schiff-base and ethidium bromide (EB) were studied in connection with other experimental observations to show that the interactive model between Mn-Schiff-base and DNA is an intercalative one. The pH and salt effect on the fluorescence properties was also investigated. The linear relationship between F/F0 and the concentration of calf thymus DNA covers 3.0 x 10(-6)-2 x 10(-4) mol L-1, which can be utilized for determining traces of calf thymus DNA with a detection limit of 8.0 x 10(-7) mol L-1 in base pairs.

Lead-selective membrane potentiometric sensor based on an 18-membered thiacrown derivative.

Abstract: A PVC-based membrane electrode for lead ions based on hexathia-18-crown-6-tetraone as membrane carrier was prepared. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a lead concentration range from 1.0 x 10(-6) to 8.0 x 10(-3) M at 25 degrees C, and was found to be very selective, precise and usable within the pH range 3.0-6.0. The electrode was successfully used as an indicator electrode in potentiometric titration of lead ions and in direct determination of lead in water samples.

Broadband Vibrational Sum Frequency Generation Spectroscopy of a Liquid Surface

Abstract: An important advance in surface science has been the evolution of sum frequency generation to the application of studying surface structure and chemistry of liquid surfaces at the molecular-level by probing the vibrational signatures of surface molecules. Recently, broad-bandwidth sum frequency generation (BBSFG) spectroscopy has become an important tool for investigating gas-solid interfaces. BBSFG spectroscopy allows, theoretically, a surface sum frequency spectrum to be acquired within one pulse of the laser. In this paper, the viability of BBSFG to study inherently small nonlinear response interfaces and the time-resolving capability of this surface-selective technology are demonstrated. Presented here are the first published accounts of spectra from a liquid surface utilizing the broad-bandwidth sum frequency technology with acquisition times as low as 500 milliseconds.

Novel Biosensor for the Rapid Measurement of Estrogen Based on a Ligand-Receptor Interaction

Abstract: A bioaffinity sensor was developed aiming at the detection of estrogen. This biosensor system is based on the specific binding of estrogen to its receptor immobilized on a gold disk electrode. The recombinant DNA encoding human estrogen receptor ligand-binding domain was expressed in bacteria using the histidine-tag fusion system. The expression of the fusion protein was under control of a bacteriophage T7 promoter, and the protein was purified under native conditions by affinity chromatography, which is based on a specific interaction between a histidine-tag, located in the N-terminus of the protein, and the Ni(II) chelate adsorbent. The protein was immobilized on an Au-electrode with Ni(II)-mediated chemisorption using a histidine tag and thiol-modified iminodiacetic acid. Cyclic voltammetric measurements showed that the reversible electrochemical reaction of a ferrocyanide/ferricyanide redox couple was suppressed by the presence of estrogen in a concentration-dependent manner. It seems reasonable to suppose that the electrostatic property of the protein layer on the electrode surface was altered by complexation with estrogen. These data suggest that this biosensor is applicable to the evaluation binding activities of the chemicals toward the human estrogen receptor.

Tungsten coil devices in atomic spectrometry: absorption, fluorescence, and emission.

Abstract: In this work, tungsten coil (W-Coil) devices are used as atomizers for electrothermal atomization atomic absorption spectrometry (ETAAS), electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS), and electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES). For most cases in ETAAS and ETA-LEAFS, limits of detection (LODs) using the W-Coil are within a factor of ten of those observed with commercial graphite furnace systems. LOD for Cd by W-Coil AAS is 10 pg, while LODs for As, Se, Cr, Sb and Pb by W-Coil LEAFS are 950, 320, 1400, 330, and 160 fg, respectively. The compact W-Coil device makes it an ideal atomizer for portable atomic spectrometry instrumentation, especially when coupled with a miniature charge coupled device spectrometer. Alternatively, the atomizer can be used as an inexpensive, modular add-on to an existing commercial ICP-AES system; and the thermal separation of Pb with interference elements Al, Mn, and Fe is demonstrated.

Spectrophotometric determination of periodate, iodate and bromate mixtures based on their reaction with iodide.

Abstract: A rapid, simple, precise and accurate method is proposed for the determination of ternary mixtures of periodate-iodate-bromate based on their reaction with iodide ion at different pH values. The absorbance was measured at 352 nm. Three sets of reaction conditions were developed. In the first set of conditions, only periodate reacted with iodide, but in the second set the periodate and iodate reacted with iodide and in the third set the three ions reacted with iodide during the first 3 min after initiation of the reaction. The method could be used for individual determinations of periodate, iodate and bromate in the concentration range of 0.05-8.0 microg/ml, 0.05-5.0 microg/ml and 0.2-12 microg/ml, respectively. The data were evaluated by simultaneous equations.

Evaluation and comparison of two selective extraction procedures for heavy metal speciation in sediments.

Abstract: Two sequential extraction procedures (the former proposed by the Standard, Measurements and Testing-SM&T-program of European Union and the latter derived from those of Tessier and Forstner with various modifications) have been compared, by analyzing a reference material (CRM 601) certified for the content of heavy metals in the three solutions resulting from the SM&T procedure. Scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) was used to evaluate the composition of the residues after various extractions. Reliable results, both in terms of precision and accuracy, were obtained for the first two steps of the SM&T scheme. As regards the third step, because it was modified during this work, a direct comparison of our results with those certified is not possible. SEM analysis confirmed that the scheme previously used in the laboratory was more aggressive compared to the SM&T procedure, which has also the advantage that the only CRM available for metal partitioning in sediments is certified using this method.

Electrode reaction of Pu3+/Pu couple in LiCl-KCl eutectic melts: comparison of the electrode reaction at the surface of liquid Bi with that at a solid Mo electrode.

Abstract: The electrode reaction of Pu3+/Pu couple at the interface between LiCl-KCl eutectic melt containing PuCl3 and liquid Bi phase was investigated by cyclic voltammetry at 723, 773 and 823 K. For comparison, the system was also studied using a solid Mo electrode in place of the liquid Bi electrode. It was found that the electrode reaction of Pu3+/Pu couple at the Bi electrode was almost reversible. The redox potentials of Pu3+/Pu couple at the liquid Bi electrode in the LiCl-KCl eutectic melt containing 0.87 wt% PuCl3 (0.0014 mole fraction) at 723, 773 and 823 K were observed to be more positive by 0.575, 0.572 and 0.566 V, respectively, than those at the Mo electrode. These differences in potential were thermodynamically analyzed by assuming a lowering of the activity of Pu in Bi phase according to the alloy formation of PuBi2.

Elimination of the Uninformative Calibration Sample Subset in the Modified UVE(Uninformative Variable Elimination)-PLS(Partial Least Squares) Method

Abstract: In order to increase the predictive ability of the PLS (Partial Least Squares) model, we have developed a new algorithm, by which uninformative samples which cannot contribute to the model very much are eliminated from a calibration data set. In the proposed algorithm, uninformative wavelength (or independent) variables are eliminated at the first stage by using the modified UVE (Uninformative Variable Elimination)-PLS method that we reported previously. Then, if the prediction error of the ith (1 < or =i< or = n) sample is larger than 3sigma, the corresponding sample is eliminated as uninformative, where n is the total number of calibration samples and sigma is the standard deviation calculated from the other n(-1) samples. Calculation of sigma by the leave-one-out manner enhances the ability to identify the uninformative samples. The final PLS model is constructed precisely because both uninformative wavelength variables and uninformative samples are eliminated. In order to demonstrate the usefulness of the algorithm, we have applied it to two kinds of mid-infrared spectral data sets.

Voltammetric Determination of Lead at Chemically Modified Electrodes Based on Crown Ethers

Abstract: The feasibility of fabricating lead-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The thus-formed electrodes were able to bind Pb(II) ions chemically, and gave better voltammetric responses than unmodified ones. The crown ethers studied and compared were 18-crown-6 and dibenzo-18-crown-6. With a 5% 18-crown-6 CME, Pb(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.02 ppm. It was possible to selectively pick up Pb(II) from a solution of several other ions at an open circuit through complexation. A simultaneous analysis of Cu(II) and Pb(II) was also attempted. By differential pulse anodic stripping voltammetry Pb(II) could be quantified over the range of 1 to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Ag(I), Fe(III), Ca(II) and Mg(II) was also studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.

Methylcellulose-immobilized Reversed-phase Precolumn for Direct Analysis of Drugs in Plasma by HPLC.

Abstract: We evaluated a new restricted access media (RAM) precolumn for direct analysis of drugs in plasma using a column switching HPLC system. The new RAM material was prepared by the modification of the external surface of porous silica with hydrophilic methylcellulose (MC), followed by modification of the internal surface with octadecylsilane (ODS). The external surface of the MC-immobilized ODS silica material (MC-ODS) suppressed the adsorption of proteins, while the internal surface of MC-ODS retained various types of drugs, such as ketoprofen, propranolol, caffeine and atenolol in plasma samples. In addition, MC-ODS allowed direct analysis of drugs in a 1000-microL plasma sample to monitor trace amounts of analytes contained. Reduced efficiency and clogging of the MC-ODS precolumn and/or the analytical column were not observed even after the repetitive injection of plasma sample up to 40 mL. Our results indicated that the MC-ODS precolumn could be used in pharmacodynamic and clinical studies.

HPLC/UV analysis of proteins in dairy products using a hydrophobic interaction chromatographic column.

Abstract: High-performance liquid chromatography using a Chrompack P-300-RP column containing a polystyrene-divinylbenzene copolymer-based packing was examined to analyze bovine milk protein components. The separation of major raw-milk proteins could be performed rapidly and reliably with this HPLC/UV method. The determinations were performed in the linear ranges of 0.01-2.0 mg/ml for alpha-lactalbumin, 0.04-2.5 mg/ml for caseins and 0.02-2.0 mg/ml for beta-lactoglobulin. The validity of the method was verified. Since the chromatographic column enabled the quantification of only "native" milk proteins, the extent of denaturation and loss of milk proteins could be examined. Thus, evaluation of heat-induced proteins denaturation was carried out in raw milk heated for 5 min at pre-determined temperatures.

Application of an HPLC-FTIR modified thermospray interface for analysis of dye samples.

Abstract: Previously, we developed a reversed-phase HPLC method compatible to high performance liquid chromatography diffuse reflectance Fourier-transform infrared (HPLC-FTIR) thermospray interface for the analysis of dyes. Dye separation achieved with a mixed-mode (SCX-ODS) column using a small gradient (90 to 80% water with acetic acid) and pH 3.25; 10 to 20% acetonitrile was considered to be suitable for HPLC-FTIR. A constant-voltage setting for the thermospray temperature (227°C) was successfully used for this gradient condition. The HPLC-separated components deposited as a series of concentrated spots on a moving tape were scanned by specially developed HPLC-FTIR software. Excellent repeatability of the thermospray deposition FTIR chromatograms and IR spectra was obtained. The interface-derived spectra of the separated components of formulated and purified reactive dyes were compared and differences in spectral features were observed.

Thermal Decomposition of Cerium(III) Acetate Hydrate by a Three-dimensional Thermal Analysis

Abstract: The thermal decomposition of cerium(III) acetate hydrate, Ce(CH3CO2)3·1.5H2O, in helium was successfully studied by the simultaneous measurement of TG-DTA and EGA by mass spectrometry (TG-DTA-MS) as well as that of X-ray diffractometry: DSC (XRD-DSC). TG-DTA-MS was useful to elucidate the complicated successive reactions accompanying the formation of intermediate products. Crystalline cerium(III) anhydrous acetate appeared at 212°C and transformed to another phase at 286°C. Cerium(III) anhydrous acetate decomposed in the temperature range of 300 - 700°C to cerium(IV) oxide via four decomposition steps; the chemical compositions of the three decomposition intermediate products were presumed to be Ce2O(CH3CO2)4, Ce2O2(CH3CO2)2 and Ce2O2CO3. The endothermic dehydration and the exothermic crystallization were characterized by simultaneous XRD-DSC. It has been demonstrated that cerium(III) changed to cerium(IV) in the final step. A detailed decomposition mechanism of Ce(CH3CO2)3·1.5H2O is discussed.

Acceleration of an enzymatic reaction in a microchip.

Abstract: micro total analysis systems (μ-TAS),1 or labs-on-a-chip,2 have become of major interest, especially to analytical chemists due to its desirable characteristics, such as reduction in reagent consumption, required space, and analysis time. Taking these advantages, we have demonstrated many applications, including flow-injection analysis,3,4 solvent extraction,5–7 immunoassay,8,9 organic synthesis10 and laser reaction control.11 There have been, however, no intensive studies focused on chemical or biochemical reactions themselves in a liquid microspace so far. In this letter, we report on the acceleration of an enzymatic reaction in a microchip and preliminary kinetic studies of the reaction.