For surface analyses of semiconductor devices and various functional materials, it has become indispensable to analyze valence states at nanometer scale due to the rapid developments of nanotechnology. Since a method for microscopic mapping dependent on the chemical bond states has not been established so far, we have developed a photoelectron emission microscopy (PEEM) system combined with synchrotron soft X-ray excitation. The samples investigated were Si/SiOx micro-patterns prepared by O2+ ion implantation in Si(001) wafer using a mask. PEEM images excited by various photon energies around the Si K-edge were observed. The lateral spatial resolution of the system was about 41 nm. The brightness of each spot in PEEM images changed depending on the photon energy, due to the X-ray absorption intensity of the respective chemical state. Since the surface of this sample was topographically flat, it has been demonstrated that the present method can be applied to observations of the microscopic pattern, depending not on the morphology, but only on the valence states of silicon. We have also in-situ measured the changes of the PEEM images upon annealing, and elucidated the mechanism of the lateral diffusion of oxygen and valence states of silicon at the nanometer scale.
Gas chromatography/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (GC/REMPI-TOFMS) using an ultraviolet nanosecond laser was employed in the trace analysis of polycyclic aromatic hydrocarbons (PAHs). A standard sample that contained 16 PAHs on the priority list of the Environmental Protection Agency of the United States of America (U.S. EPA) was measured. A sample of river water that had been pretreated by means of solid-phase extraction was analyzed by GC/MS based on electron impact ionization (EI) and REMPI to evaluate the performance of the analytical instrument. The results suggested that REMPI is superior to EI for soft ionization, and suppresses the background signal due to aliphatic hydrocarbons. Thus, GC/REMPI-TOFMS is a more reliable method for the determination of PAHs present in the environment.
A quantitative method for the determination of urea in serum was studied. An ion chromatograph (IC) with a conductivity detector was used in this method, where the chromatograph was modified by placing an immobilized urease column between the injection loop and a guard column of the cation analysis column. Immobilized urease was prepared by the adsorption of urease on cedar sawdust with triethylenetetramine. The adsorption capacity of urease was 190 mg g−1, and its activity was 3500 U g−1. The conversion efficiency of urea to ammonium ion was 100%, and the half life of immobilized urease was 60 days. It was possible to use the immobilized urease in a pH range of 3.0 to 9.0, and at temperatures up to 60°C. The determination of urea was attempted by IC attaching an immobilized urease column. The limit of detection of urea was 0.2 mg L−1, and the calibration curves of urea were very linear over 0.8 − 25 mg L−1. The urea concentration in the human serum could be determined with a standard deviation of 0.06 − 0.13 within 5 min after injecting the serum sample.
A fast, accurate, precise and sensitive capillary electrophoresis method for the simultaneous determination of dextromethorphan hydrobromide, phenylephrine hydrochloride, paracetamol and chlorpheniramine maleate has been developed. Response surface methodology with a central composite design was used for optimization of the concentration of the buffer, pH of the buffer and applied voltage. Therefore, working with Na2HPO4 buffer (pH 8.00, 0.01 M) at 20 kV as an applied voltage in the capillary electrophoresis method were found to be suitable; under these optimal conditions, these four active ingredients were separated in about 7 min. This developed method was validated and successfully applied to a pharmaceutical preparation, sugar-coated tablet, and the results were compared with a high-performance liquid chromatographic method developed by us.
A method was developed for fast and simultaneous determination of tetrafluoroborate (BF4−), thiocyanate (SCN−) and hexafluorophosphate (PF6−) by high-performance liquid chromatography using a silica-based monolithic column and direct (non-suppressed) conductivity detection. Chromatographic separation was performed on a Chromolith Speed ROD RP-18e column with tetrabutylammonium hydroxide (TBA) + citric acid + acetonitrile as eluent. The effects of the types of eluent, TBA concentration, acetonitrile volume fraction, eluent pH, column temperature and flow rate on the retention of anions were investigated. The optimized chromatographic conditions were selected. Under the optimal conditions, the baseline separation of BF4−, SCN− and PF6− was achieved without any interference by other anions (F−, Cl−, Br−, I−, NO3−, ClO3− and SO42−). The detection limit (S/N = 3) was 0.42, 0.46 and 1.42 mg L−1 for BF4−, SCN− and PF6−, respectively. The present method was successfully applied to the determination of BF4−, SCN− and PF6− in ionic liquids.
Despite environmental and geochemical interests, Cr and Fe have been left beyond the reach of determinations by ICP-MS due to severe interferences originating from Ar. The applicability of a dynamic reaction cell (DRC)-ICP-MS has been examined for determinations in environmental and geochemical samples. The reaction with NH3 in the DRC system provides an eligible technique to determine Cr, because of a greater improvement in the signal/noise (S/N) ratio due to an effective elimination of interferences arising from Ar (ArC, ArN and ArO), and makes it possible to analyze Cr even at sub-μg L−1 levels. As compared to non-DRC mode analyses, the DRC technique using m/z 56 appeared to be preferable for Fe determination in most terrestrial waters because of effective suppression of 40Ar16O+. In addition, the effects of cluster ions, such as 39K14N1H3+ and 40Ca14N1H2+, on Fe determination were also negligibly small. Measurements using 54Fe by the DRC mode are also advantageous for Ca-rich samples, such as limestone and dolomite.
Stable isotopic compositions and elemental contents of the H, C, N, and O in 163 rice samples were analyzed. The samples were taken from three different farming countries; Japan (n = 103), United States of America (n = 30), and Australia (n = 21), in addition of Asian rice samples from Thailand (n = 2), Vietnam (n = 1), and China (n = 6) as comparison. They were mostly short grain samples known as “Koshihikari,” with several samples of middle and long grains included. All samples were grown in the presence of either natural manure or artificial fertilizer. The climate of the rice farming environment was diverse, from arid to humid. Excluding δD data showing large uncertainty, according to the statistical analysis of the principal components based on the stable isotopic compositions such as δ13C, δ15N, and δ18O of rice samples, the Japanese rice samples were clearly distinctive from the Australian and the American rice samples. This fact may be explained by the regional differences in isotopic signatures of the climate, utilized nutrition, and/or quality of irrigation water among the farming countries. This statistical distinction could be one of the useful tools to extract the rice samples grown in Japan from those grown in the other countries.
This paper described the investigation of surface-modified quantum dots (QDs) as a fluorescence probe for the detection of cardiolipin. A single-step method for preparation of non-toxic and photo-stable cadmium telluride (CdTe) QDs capped by L-cysteine in aqueous solution was developed. The prepared QDs were characterized by high-resolution transmission electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectrometry and spectrofluorometry. These functional QDs were used as a fluorescence probe for cardiolipin determination based on the fluorescence quenching. The optimum fluorescence intensity was found to be at pH 7.4 with QDs concentration of 4 × 10−5 mol L−1. The effect of other phospholipids on the intensity of CdTe QDs showed a low interference response. Under optimized conditions, the quenched fluorescence intensity was linear with the concentration of cardiolipin in the range of 1.33 × 10−7 − 10.4 × 10−7 mol L−1 (r = 0.9976) and a detection limit (S/N = 3) of 18.5 nmol L−1. The proposed method was applied to the determination of cardiolipin content of HepG2 cell samples before and after oxidative stress with satisfactory results.
High-resolution CeLγ4 emission spectra of CeF3, Ce2S3, CeF4, and CeO2 have been measured using a multicrystal, multidetector spectrometer. The spectra exhibited substantial differences depending on the chemical environment of the Ce ions. By comparing the observed CeO2 spectrum with the band calculations, we determined that the observed chemical effects of the main emission line were primarily attributable to the transitions of the Ce5p band; the high-energy tail at around 6.539 keV was assigned to the ligand p→Ce2s cross transition. Further, a key difference between CeLγ4 and EuLγ4 is discussed with reference to CeL1- and EuL1-X-ray absorption fine-structures (XAFS). Possible applications of CeLγ4 emissions to material characterization are also suggested.
The simultaneous determination of albendazole (ABZ) and praziquantel (PZQ) was performed by different mathematical approaches: second derivative spectrophotometry (SDS), classical least squares, regression of partial least squares and principal components regression based on spectral data of drugs dissolved in methanol-hydrochloric acid solution. The detection limits for multivariate calibrations were determined by creating a surrogate variable signal. SDS presented the best analytical features. The recoveries of ABZ and PZQ from the synthetic samples were near to 100 ± 5%. The methods were applied in veterinary pharmaceutical formulation whose mass ratio ABZ:PZQ is 10:1; the results obtained were according to nominal content.
A quantitative structure activity relationship (QSAR) study of 8-azaadenine, as antagonists for the A1 receptor, is described. A genetic algorithm (GA) method was used as the feature selection tool, and an adaptive neuro-fuzzy inference system (ANFIS) was employed for feature mapping. The best descriptors (GATS4v and BELv7) were applied to train the ANFIS model. The optimum number and shape of related functions were obtained through a subtractive clustering algorithm. The ability and robustness of the GA-ANFIS model in predicting the affinity of 8-azaadenine derivatives (pKi) are illustrated by validation techniques of Leave One Out, heuristic and randomized methods. The results have indicated that the proposed model of ANFIS in this work is superior over two other methods, radial basis function (RBF) and multiple linear regression (MLR).
The ability to scavenge superoxide anion radicals (•O2−) was determined using an oxygen electrode. The method is based on the determination of •O2− generated by the reaction of nitrilotriacetatoiron(III) with hydrogen peroxide and a decrease in the concentration of •O2− by a scavenging reaction, converting into a change in the generation of oxygen molecules through an electron-transfer reaction from •O2− to nitrilotriacetatoiron(III). Oxygen generation, which enhanced proportionally with an increase in the concentration of hydrogen peroxide, was inhibited depending on the concentration of superoxide dismutase. Hence, we applied the present reaction system to evaluate the •O2−-scavenging abilities of an antioxidant, measuring the degree of inhibition of oxygen generation using an oxygen electrode. A good correlation was obtained between the present method and conventional colorimetry, monitoring the formation of blueformazan by the reaction of nitro blue tetrazolium with •O2−, to estimate the •O2−-scavenging activities of antioxidants.
A simple and rapid method for the determination of ferulic acid in pharmaceutical formulations by didodecyldimethylammonium bromide (DDAB)/Nafion composite film-modified carbon paste electrode is presented. The electrochemical behavior of ferulic acid at the proposed electrode was investigated by cyclic voltammetry and a well-defined oxidation peak was observed at +0.44 V versus saturated calomel electrode in 0.1 M acetate buffer (pH 5.5) solutions. Some experimental parameters affecting the electrochemical response of the modified electrode were optimized. Under optimal conditions, the oxidation peak currents of ferulic acid increase linearly with the concentration of ferulic acid in the range from 2.0 × 10−6 to 1.2 × 10−4 M with a detection limit of 3.9 × 10−7 M (S/N = 3). The proposed method was successfully applied to the determination of ferulic acid in pharmaceutical tablets.
This study examined the potential utility of DNA sequence analysis to discriminate and identify plant material in forensic investigations. DNA was extracted from plant leaf fragments of 11 species stored for 5 to 22 years after collection. The trnH-psbA intergenic spacer and 316 bp of the rbcL gene were successfully amplified and sequenced for all fragments except for the trnH-psbA spacer of one sample. All of the plant samples were discriminated in pairwise comparisons of the sequences. Using a combination of local and global genetic databases is likely to provide greater reliability in search results to identify forensic samples from sequence data.
Fatty acids (FAs) are biological molecules that are used as major metabolic fuels, and are concerned in important metabolic processes. We have performed a non-invasive and technically rapid and simple method for collecting sweat from humans, followed by GC/MS determination. The sweat was collected from each volunteer (the middle finger) by spraying 70% ethanol aqueous solution (no harmful solvent) into a 1.5-cm3 plastic vial. Analysis of FAs in sweat showed that the sweat solution contains lauric acid (C12:0), myristic acid (C14:0), palmitic acid (C16:0), oleic acid (C18:1), and stearic acid (C18:0). Here, it is demonstrated that FA concentrations for 4 young subjects correlated positively with percent of body fat (r = 0.78) and that the total FA levels for them increased progressively with increasing fasting time when a subject fasted throughout the experiment.
A simple way was proposed to make a monolithic column for a high pressure electroosmotic pump (EOP). It is in-situ synthesized inside the silica capillary from potassium silicate solution and no frit is required. Compared with common approaches to make columns for EOP, the present method is robust and fast (<4 h). For pure water, a stand-alone EOP operated at 15 kV applied voltage is capable of generating a flow rate of 3.1 μL/min and a maximum static pressure of ∼5.4 MPa.