To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.
Ca K edge X-ray absorption fine structure (XAFS) spectroscopy was utilized for the characterization and quantification of calcium carbonate polymorphs and their mixtures. The advantage of the XAFS is the small sample quantity required for measurements, and a flexible sample environment. The near-edge XAFS spectra of calcite, aragonite and vaterite were measured with the conversion electron yield (CEY) method, and the obtained spectra showed characteristic features that can be utilized as fingerprints. The quantification of mixed polymorphs was examined by using a linear combination fitting of reference XAFS spectra. Though the quality of the fits was satisfactory, discrepancies in the evaluated values were observed between those with X-ray diffraction (XRD) and XAFS. The nonuniformity of samples may be enhanced by the surface sensitivity of the CEY method.
Knowledge about the spatial distribution and the local concentration of trace elements in tissues is of great importance, since trace elements are involved in many biological functions of living organisms. However, there are few methods available to measure the spatial (two (three)-dimensional) elemental distribution in animal brain. X-ray microfluorescence with synchrotron radiation is a multielemental mapping technique, which was used in this work to determine the topographic of iron, zinc and copper in coronal sections of female Wistar rats of different ages. Young (14 days old) and middle-aged (20 months old) rats (n = 8) were analyzed. The measurements were carried out at the XRF beam line at the Synchrotron Light National Laboratory (Campinas, Brazil). Two-dimensional scanning was performed in order to study the tendency of elemental concentration variation. The acquisition time for each pixel was 10 s/step and the step size was 300 µm/step in both directions. It was observed that the iron distribution was more conspicuous in the cortical area, thalamus and bellow the thalamus. On the other hand, the zinc distribution was more pronounced in the hippocampus. The iron, copper and zinc levels increased with advancing age. Therefore, this study reinforces the idea that these elements are involved in the chemical mechanisms of the brain that induce some neurological diseases, since they are also present in high levels in specific areas of the brain, such as the hippocampus and the substantia nigra of patients with these disorders.
We investigated x-ray energy distribution in an x-ray microbeam produced by a polycapillary x-ray lens in combination with a sealed-type x-ray tube. This polycapillary x-ray lens has an output focal distance (OFD) of approximately 15 mm. The size of the x-ray microbeam and its OFD were estimated by using a wire scanning method. In our case, the sizes of the x-ray microbeams at the output focal distance were 49 µm for Mo Lα, 36 µm for W Lα, and 28 µm for Mo Kα. The spot sizes depend on the energy of the x-ray fluorescence. The reason for the energy dependence is that x-ray capillary optics is based on the principle of propagation through glass capillaries by means of x-ray total external reflection. The evaluated OFD values of Mo Lα and Mo Kα were slightly changed in 17 µm. However, a deviation of 100 µm from the OFD caused only a 3% increase of the focal spot size. Therefore, we concluded that the OFD showed no significant dependence on x-ray energy.
A portable instrument for two-dimensional X-ray fluorescence imaging was assembled with an X-ray source using a pyroelectric crystal, which was driven by a 9-V dry battery, a Si-PIN detector, a slit, and pulse motors. Line scanning for a mug and a knife-edge-scan of an iron sheet were carried out using this spectrometer. The sensitivity of the spectrometer was sufficient for elemental analysis of a mug using a 1 mm2 slit, and several elements, such as Co, Ni, Zn, Pb and Zr, were detected. The estimated spatial resolution using a 0.8-mm pinhole was 3.5 mm.
This paper describes how the Kα/Kβ count rate ratio of the characteristic X-rays of a given element can be applied to determine the depth at which a layer or a grain of that element is located. The theoretical background and a basic description of the Kα/Kβ technique are given in the introduction. The experimental part of the paper deals with measurements of thick standard pure iron, intermediately thick iron foils, and layers prepared with a powder of Prussian blue. All these specimens were analyzed alone, and they were also analyzed overlaid with a low Z matrix. The light matrix consisted of sheets of paper of known thickness. Paper was chosen, because we take into account the subsequent application of this technique to surveys of historical monuments. The relation between the Kα count rate, the Kα/Kβ count rate ratio, and the distribution of iron in the paper matrix are presented here.
This review includes our researches and other methodologies related to flow-based techniques, such as flow injection analysis (FIA) and sequential injection analysis (SIA). The methods will demonstrate semi-and full automated FIA and SIA, including liquid-liquid and liquid-solid extraction. FIA using alternative chemical reactions in the aqueous solution was applied to the trace analysis of metals in biological and environmental samples. For durable liquid-liquid extraction, several phase separators were designed. Moreover, multi-channel FIA with newly designed flow cells and SIA with lab-on-valve devices have been used for the simultaneous and successive determination of metals and organic compounds. On-line solid phase extraction (SPE) has also been proposed for highly sensitive analysis of organic and inorganic compounds.
A polymeric ODS column was applied to the resolution of triacylglycerol positional isomers (TAG-PI), i.e. 1,3-dioleoyl-2-palmitoyl-glycerol (OPO) and 1,2-dioleoyl-3-palmitoyl-rac-glycerol (OOP), with a recycle HPLC system. To investigate the ODS column species and the column temperatures for the resolution of a TAG-PI pair, a mixture of OPO and OOP was subjected to an HPLC system equipped with a non-endcapped polymeric, endcapped monomeric, endcapped intermediate, or non-endcapped monomeric ODS column at three different column temperatures (40, 25, or 10°C). Only the non-endcapped polymeric ODS column achieved the separation of OPO and OOP, and the lowest column temperature (10°C) showed the best resolution for them. The other pair of TAG-PI, a mixture of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (PPO) was also subjected to the system equipped with a non-endcapped polymeric or monomeric ODS column at five different column temperatures (40, 32, 25, 17, and 10°C). Thus, POP and PPO were also separated on only the non-endcapped polymeric ODS column at 25°C. However, no clear peak appeared at 10°C. These results would indicate that the polymeric ODS stationary phase has an ability to recognize the structural differences between TAG-PI pairs. Also, the column temperature is a very important factor for separating the TAG-PI pair, and the optimal temperature would relate to the solubility of TAG-PI in the mobile phase. Furthermore, the recycle HPLC system provided measurements for the separation and analysis of TAG-PI pairs.
A flow-injection (FI) spectrophotometric procedure exploiting merging zones is proposed for the determination of azithromycin in pharmaceutical formulations. The method is based on the reaction of azithromycin with tetrachloro-p-benzoquinone (p-chloranil) accelerated by hydrogen peroxide and conducted in a methanol medium, producing a purple-red color compound (λmax = 540 nm). The FI system and the experimental conditions were optimized using a multivariate method. Beer's law is obeyed in a concentration range of 50 - 1600 µg mL-1 with an excellent correlation coefficient (r = 0.9998). The detection limit and the quantification limit were 6.6 and 22.1 µg mL-1, respectively. No interference was observed from the common excipients, and the recoveries were within 98.6 to 100.4%. The procedure was applied to the determination of azithromycin in pharmaceuticals with a high sampling rate (65 samples h-1). The results obtained by the proposed method were in good agreement with those obtained by the comparative method at 95% confidence level.
A selective and sensitive analytical procedure for rapid arsenic determination by gas-diffusion flow injection analysis with amperometric detection was developed. The method is based on the arsenite reduction by NaBH4. Derived arsine diffuses through a PTF membrane into the acceptor flow stream and is amperometrically determined on a platinum working electrode. The limit of detection (3σ) at room temperature was 5 µg/dm3 of As(III). The relative standard deviation for a 1 mg/dm3 As(III) standard was 1.96% for six repetitive injections. Arsenic(V) was determined after its prereduction with potassium iodide. Arsenic determination was not interferred with by 1 mg/dm3 Sb(III), 5 mg/dm3 Sn(II), 10 mg/dm3 Se(IV), 1 mg/dm3 As(V), 1 mg/dm3 hydrasine, 1 mg/dm3 Fe(II) or 0.5 mg/dm3 Fe(III) solution. The throughput of this method was 60 analyses per hour. This method was successfully applied to arsenic determination in some power plant waste water samples.
A new heterogeneous precipitate of an organic-inorganic composite cation-exchanger poly-o-toluidine Zr(IV) phosphate was utilized for the preparation of a Hg(II) ion-sensitive membrane electrode for the determination of Hg(II) ions in real aqueous as well as in real samples. The electrode showed good potentiometric response characteristics, and displayed a linear log[Hg2+] versus EMF response over a wide concentration range of 1 × 10-1 - 1 × 10-6 M with a Nernstian slope of 30 mV per decade change in concentration with a detection limit of 1 × 10-6. The membrane electrode showed a very fast response time of 5 s and could be operated well in the pH range 2 - 8. The selectivity coefficients were determined by the mixed-solution method, and revealed that the electrode was selective in the presence of interfering cations; however most of these did not show significant interference in the concentration range of 1 × 10-1 - 1 × 10-4 M. The lifetime of the membrane electrode was observed to be 120 days. The analytical utility of this electrode was established by employing it as an indicator electrode in the potentiometric titrations of Hg2+ ions from a synthetic mixture as well as drain water.
TFPB was introduced as a charged ionophore for atropine selective electrodes. Typical Nernstian responses were found (57.78, 58.95 and 58.41 mV/decade) for PVC-membrane electrodes incorporating NPOE, DOS, and DDP as plasticizers. They exhibited practical linear ranges of 9.1 × 10-3 - 10-6, 9.1 × 10-3 - 10-6 and 9.1 × 10-3 - 10-7 M, respectively. It works in the sub-micro scale of atropine concentrations. The optimum pH-range was 3.18 - 8.97. The selectivity coefficient values were estimated for different organic and inorganic cations. They were interpreted by using the “Relative Selectivity Concept”, which was introduced for the first time. The new concept was applied for comparing the selectivity properties of previously reported electrodes. The effect of the presence of ephedrine, caffeine, glucose, Na+, Ca2+, and Mg2+ on the calibration graphs of the electrodes was studied.
An amperometric horseradish peroxidase (HRP) inhibition biosensor has been substantially constructed by the help of N,N-dicyclohexylcarbodiimide (DCC), N-hydroxysuccinimide (NHS). The preparation steps and the biosensor response to phenylhydrazine were monitored by electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and chronoamperometry. The proposed biosensor could be applied to determine phenylhydrazine in a 0.10 M phosphate buffer solution containing 1.2 mM hydroquinone and 0.50 mM H2O2 by phenylhydrazine, inhibiting the catalytic activity of the HRP enzyme in the reduction of H2O2. The system was optimized to realize a reliable determination of phenylhydrazine in the range of 2.5 × 10-7 to 1.1 × 10-6 M with a detection limit of 8.2 × 10-8 M and a correlation coefficient of 0.999. The modified electrode displayed good reproducibility, sensitivity and stability for the determination of phenylhydrazine.
The mechanism of the solvent extraction of cytochrome c (Cyt c) via reverse micelle formation was studied from an electrochemical point of view. Potentiometric measurements showed that the Galvani potential difference of the oil/water (O/W) interface played a crucial role in the spontaneous extraction of Cyt c with bis(2-ethylhexyl)sulfosuccinate (AOT). However, the dependence of the extraction efficiency on the concentration of an aqueous electrolyte (KCl) could be explained not by the effect of the interfacial potential, but by the change in the interfacial tension (γ). Electrocapillary measurements showed that the adsorption of AOT anions to the O/W interface resulted in a significant decrease of γ in a higher potential range, where reverse micelles were formed. The bottom level of γ in the higher potential range was increased with [KCl]. The lower extraction efficiency for higher [KCl]'s was elucidated by a “size exclusion effect”. This was also supported by water-content measurements by the Karl Fisher method.
In the present work, a sensitive spectroscopic assay based on surface-enhanced Raman spectroscopy (SERS) using gold nanoparticles as substrates was developed for the rapid detection protein-protein interactions. Detection is achieved by specific binding biotin-modification antibodies with protein-stabilized 30 nm gold nanoparticles, followed by the attachment of avidin-modification Raman-active dyes. As a proof-of-principle experiment, a well-known biomolecular recognition system, IgG with protein A, was chosen to establish this new spectroscopic assay. Highly selective recognition of IgG down to 1 ng/ml in solution has been demonstrated.
Fluoxymesterone, an anabolic steroid with the 17α-methyl,17β-hydroxy group, has been developed as an oral formulation for therapeutic purposes. However, it is also used illegally in racehorses to enhance racing performance. In this study, we detected 9α-fluoro-17,17-dimethyl-18-norandrostane-4,13-dien-11β-ol-3-one by gas chromatography/mass spectrometry (GC/MS), which has not been reported as a fluoxymesterone metabolite so far in horse. It was synthesized for use as a reference standard, and characterized on the basis of 1H NMR and 13C NMR spectra, as well as GC/MS EI mass spectra of TMS derivatives. It was excreted as the main metabolite in horse urine, and its reference standard could be synthesized easily. Therefore, this metabolite could be a useful target for a doping test of fluoxymesterone in racehorses.
To analyze a curing process of epoxy resin in terms of molecular motion, we adapted a pulsed NMR method. Three kinds of 1H spin-spin relaxation times (T2L (long), T2S (short) and T2M (intermediate)) were estimated from observed solid echo train signals as the curing process proceeded. A short T2S value below 20 µs suggests the existence of a motion-restricted chain, that is, cured elements of resin, and its fraction, PS, sigmoidally increased with the curing time. On the other hand, the fraction of T2L, PL, decreased with the reaction time reciprocally against PS, suggesting the disappearance of highly mobile molecules raised from pre-cured resin. The spin-lattice relaxation time, T1, was also measured to check another aspect of molecular motion in the process. T1 of the mixed epoxy resin and curing agent gradually increased just after mixing both of them. This corresponds to an increment of a less-mobile fraction, of which the correction time is more than 10-6 s, and also means that the occurrence of a network structure whose mobility is strongly restricted by chemically bonded bridges between the epoxy resin and curing agent. The time courses of these parameters coincided with those of IR peaks pertinent to the curing reaction. Therefore, pulsed NMR is a useful tool to monitor the hardening process of epoxy resin in real time non-distractively in terms of the molecular motion of protons.
The uptakes of molecular iodine and bromine by both strong acid cation (Dowex 50W-X4 and X8) and strong base anion (Dowex 1-X4 and X8) exchange resins have been studied in aqueous solutions at 25°C. An empirical formula for the amount of solute taken up by the resin in mmol per gram of dry resin, Q, as a function of the solute concentration in M (mol dm-3), C, was derived. Direct proportional relationships between Q and C have been found, except for the bromine-anion exchanger system. In contrast to the cation-exchange resin, the anion exchanger exhibits extremely high affinity for I2 and Br2.
The formation of a liquid organic ion associate in an aqueous sample was applied to the concentration and determination of cadmium in environmental water samples. Cadmium was converted into a complex with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS) in a 40-mL sample solution, and was extracted into a liquid ion associate of phenolsulfonate and benzethonium during phase formation. More than 400-fold enrichment was easily attained by this technique, because the volume of the liquid organic phase formed was very small, ca. 2 µL. After dilution of the organic phase with a small volume of 2-methoxyethanol, the cadmium in the solution was determined by GF-AAS. The detection limit was 0.09 ng/L (3σb). This method was applied to the determination of cadmium in river water and seawater.
Electrochemically enhanced DNA detection was demonstrated by utilizing the couple of a synthesized ferrocene-terminated peptide nucleic acid (PNA) with a cysteine anchor and a sacrificial electron donor [Fe(CN)6]4-. DNA detection sensors were prepared by modifying a gold electrode surface with a mixed monolayer of the probe PNA and 11-hydroxy-1-undecanethiol (11-HUT), protecting [Fe(CN)6]4- from any unexpected redox reaction. Before hybridization, the terminal ferrocene moiety of the probe was subject to a redox reaction due to the flexible probe structure and, in the presence of [Fe(CN)6]4-, the observed current was amplified based on regeneration of the ferrocene moiety. Hybridization decreased the redox current of the ferrocene. This occurred because hybridization rigidified the probe structure: the ferrocene moiety was then removed from the electrode surface, and the redox reaction of [Fe(CN)6]4- was again prevented. The change in the anodic current before and after hybridization was enhanced 1.75-fold by using the electron donor [Fe(CN)6]4-. Sequence-specific detection of the complementary target DNA was also demonstrated.
The electrochemical oxidation of (±)-α-tocopherol on a porous graphite electrode was performed in the presence of methanol, and successive separation and detection of the products were performed by an on-line liquid chromatography/mass spectrometry system. Three products were identified, one of which was determined to be α-tocopheryl quinone, because its m/z was 469 [M+Na]+. The other two products showed identical mass and UV spectra, and were suspected to be diastereomers of 9-methoxy-α-tocopheron, because their molecular weights were m/z 483 [M+Na]+, and also because it is known that the chemical oxidation of α-tocopherol by benzoyl peroxide or N-bromosuccinimide in the presence of methanol should provide 9-methoxy-α-tocopheron. To confirm that these two compounds were diastereomers, a circular dichroism detector was used. The signs of both peaks detected by the circular dichroism detector at 230 nm were opposite. In addition to observations of identical mass and ultraviolet spectra, these results indicated that the two products were diastereomers of 9-methoxy-α-tocopheron, whose stereochemistry is different at the newly generated chiral center of the 9-position. The on-line use of a circular dichroism detector with an electrochemical cell/liquid chromatography system may expand the utility of the system to study the metabolism of a chiral drug.
A method using an incidence-angle dependence of the spectral intensity was proposed to determine a particle size in a particle-size measurement by applying an infrared attenuated-total-reflection (ATR) technique. A formula, which is proportional to the infrared ATR-spectral intensity, was constructed as a function of the particle size, amount of particles, and incidence angle, φ. Its φ dependences were calculated for SiO2 particles of less than a mono layer on a Ge prism, and differed at every particle size. Some simulations of determining both particle size and particle amount were carried out for the samples of particles with sizes of 1 to 3 kinds by using algebraic-simultaneous equations with the software of Mathematica 5.2, and resulted in showing its usefulness.
Total nitrogen has been determined by using a model developed between the conventional chemical measurements and diffuse reflectance spectra in the near-infrared region. Samples (244) from different types of soils with total nitrogen contents ranging from 0.20 to 13.60% (m/m) were modeled by partial least-squares regression (PLS), multi-layer perceptron feed-forward networks (MLP) and radial basis function networks (RBFN). The RBFN model produced a better square error of prediction (SEP) of 0.048 and R2 = 0.93 in a procedure that is simpler, faster and less dependent on the initial conditions.