The appearance regularity of the Ga+ primary ion ToF-SIMS fragment pattern of metals and inorganic compounds is discussed. For inorganic compounds formulated like M-A, where the valence of the cation M is +n, that of the anion A is -p; also, the chemical composition of the ToF-SIMS fragment is MxAy, the rule nx ≥ (py + 1) is satisfied for positive ion fragments and nx ≤ (py + 1) for negative ones. For example, for an oxide fragment of chemical composition MxOy (valence of M is +n), the chemical composition of the fragment appears obeying the rule nx ≥ (2y + 1) for positive ions and nx ≤ (2y + 1) for negative ones, respectively. The regularity of ToF-SIMS fragment patterns of sulfides, nitrates, sulfates etc. is discussed. Further, when the Ga+ primary ion ToF-SIMS fragment patterns of metals are observed, it can be inferred that the overlapped particle emission occurs from metal surfaces through alloying and/or clustering of Ga with metal on surfaces.
Fluorescent dyes have been widely employed as optical indicators of the membrane potential difference in cells, isolated organelles and lipid vesicles that are too small to make microelectrode measurements feasible. We describe here the application of a carbocyanine dye, 3,3′-dipropylthiodicarbocyanine iodide [DiS-C3-(5)], to monitor the transmembrane potential changes induced by a variation of the K+ concentration for the cells of Escherichia (E.) coli and photosynthetic bacterium Rhodospirillum (R.) rubrum. The cells were first incubated in buffers containing DiS-C3-(5) and K+ ions of various concentrations until the fluorescence intensity reached a constant value. Valinomycin was then added to the solution, which caused changes in the fluorescence intensity, depending on the K+ concentrations. The membrane potential is shown to have a linear relationship with the fluorescence intensity of DiS-C3-(5). The results demonstrate that the K+ concentrations inside intact cells are 4.6 mM and 5.3 mM for E. coli and R. rubrum, respectively. The diffusion potentials of K+ ions were determined using the Nernst equation over the range of -1.3 mV to 44 mV, corresponding to K+ concentrations of 5 mM - 25 mM outside of the cells.
Highly sensitive chiral labeling reagents, (1R,2R)- and (1S,2S)-2-(2,3-anthracenedicarboximido)cyclohexanecarboxylic acids [(1R,2R)- and (1S,2S)-A] and (1R,2R)- and (1S,2S)-2-(2,3-naphthalenedicarboximido)cyclohexanecarboxylic acids [(1R,2R)- and (1S,2S)-A′], were prepared. Reagent A has enabled us to discriminate the enantiomers of anteiso fatty alcohols up to C9 methyl branching by 1H NMR, and both reagents A and A′ have allowed up to C16 methyl branching at the 10-15 molar level by fluorescence detected reversed-phase HPLC.
A carbon-paste electrode spiked with 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone was constructed by the incorporation of 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone in a graphite powder silicon oil matrix. It shown by cyclic voltammetry and double potential-step chronoamperometry, which this ferrocene derivative modified a carbon-paste electrode, can catalyze the ascorbic acid oxidation in an aqueous buffered solution. It has been found that under the optimum conditions (pH 7.00), the oxidation of ascorbic acid at the surface of this carbon paste modified electrode occurs at a potential of about 260 mV less positive than that of an unmodified carbon-paste electrode. The catalytic oxidation peak current was linearly dependent on the ascorbic acid concentration, and a linear calibration curve was obtained in the range of 6 × 10-5 M - 7 × 10-3 M of ascorbic acid with a correlation coefficient of 0.9997. The detection limit (2σ) was determined to be 6.3 × 10-5 M. This method was also used for the determination of ascorbic acid in some pharmaceutical samples, such as effervescent tablets, ampoules and multivitamin syrup, by using a standard addition method. The reliability of the method was established by a parallel determination against the official method.termined to be 6.3 × 10-5 M. This method was also used for the determination of ascorbic acid in some pharmaceutical samples, such as effervescent tablets, ampoules and multivitamin syrup, by using a standard addition method. The reliability of the method was established by a parallel determination against the official method.
In this paper, we described a glucose biosensor based on the co-electrodeposition of a poly(vinylimidazole) complex of [Os(bpy)2Cl]+/2+ (PVI-Os) and glucose oxidase (GOX) on a gold electrode surface. The one-step co-electrodeposition method provided a better control on the sensor construction, especially when it was applied to microsensor construction. The modified electrode exhibited the classical features of a kinetically fast redox couple bound to an electrode surface and the redox potential of the redox polymer/enzyme film was 0.14 V (vs. SCE). For a scan rate of up to 200 mV s-1, the peak-to-peak potential separation was less than 25 mV. In the presence of glucose, a typical catalytic oxidation current was observed, which reached a plateau at 0.25 V (vs. SCE). Under the optimal experimental conditions, the steady-state electrooxidation current measured at 0.30 V (vs. SCE) was linear to the glucose concentration in the range of 0 - 30 mM. Successful attempts were made in blood sample analysis.
A pressure-controlled on-column injection method was developed for microcolumn liquid chromatography. The system was assembled from a syringe pump, a Model M-445 Six-Way Micro Selection Valve, a separation column and a UV detector. The injection volume could be regulated by changing the applied pressure and/or the sample loading time. The system was evaluated in the ion-exchange mode. The system was applied to the determination of anions in river-water samples.
A new sensitive chromogenic reagent, 9,10-phenanthaquinone monoethylthiosemicarbazone (PET), has been synthesized and used in the spectrophotometric determination of Tl(III). In HNO3, H2SO4 or H3PO4 acids, PET can react immediately at room temperature with Tl(III) to form a red 2:1 complex with a maximum absorption at 516 nm. The different analytical parameters affecting the extraction and determination processes have been examined. The calibration curve was found to be linear over the range 0.2 - 10 μg cm-3 with a molar absorptivity of 2.2 × 104 dm3 mol-1 cm-1 . Sandell’s sensitivity was found to be 0.0093 μg cm-2. No interference from macroamounts of foreign ions was detected, except for Pd(II). However, Pd(II) does not affect the determination process, because its complex with PET has its λmax at 625 nm. The proposed method has been applied to the determination of Tl(I and III) in synthetic and natural samples after separation by flotation (in oleic acid/kerosene) and solid-phase extraction (on polyurethane foam) techniques. The two methods were found to be accurate and not subject to random error, but solid-phase extraction was preferred because it is cheap, simpler and there is no contamination risk coming from flotation reagents.
A commercial humic acid dissolved in water was fractionated to nine samples by means of ultrafiltration (UF); the nominal molecular weight used for UF membranes was 1 k - 200 kDa. Concerning the nine samples, copper(II) complexing capacities (CuCC) and conditional stability constants (β) of the formed copper(II) complexes were measured by a solvent extraction method. A total organic carbon (TOC) and the UV-VIS absorption ratio (E350 nm/E450 nm) were also measured. From a comparison of these data, it was found that a) humic acids in each fraction formed two kinds of copper(II) complexes with different stability; b) the β values obtained from each fraction were almost the same; c) large CuCC values were observed in the molecular weight range from 10 kDa to 20 kDa and below 1 kDa; d) molecules with molecular weight higher than 50 kDa scarcely had any copper(II) complexing ability; e) the values of CuCC/TOC of each fraction were in the range from 1.7 to 3.4 × 10-7 mol mg-1.
It has previously been pointed out that two different mechanisms exist in the reversed-phase (RP) HPLC of polypeptides, including proteins. We systematically investigated the separation of various peptides and proteins over a wide range of molecular weight using a nonporous octadecylsilyl (ODS) silica-gel column to provide a precise explanation for the separation mechanism of polypeptides, including proteins in RP-HPLC. As a result, we clarified that a critical point between a typical reversed-phase partition mode applicable to small peptides (molecular weight <3000) and a characteristic elution mode applicable to proteins is in the vicinity of the molecular weight of 3500 - 4500. We also proposed a new concept, the “Transitional Desorption Mode”, as a separation mechanism that can precisely explain the RP-LC separation of a wide range of polypeptides including proteins.
A GC/FID methodology for determination of twenty-one free amino acids in quince fruit (pulp and peel) and jam is described. The sample preparation was simple, involving a SCX Solid-Phase Extraction (SPE) purification step and a fast derivatization with ethyl chloroformate for gas chromatographic analysis. The chromatographic separation was achieved using a CP-Sil 19 CB wcot fused-silica capillary column. Under the chosen conditions, with temperature and pressure programming, this capillary column was able to separate all the amino acids not only in a short time but also with good separation. The GC/FID procedure is rapid, sensitive, reproducible and accurate. The detection limit values for amino acids were low, between 0.004 and 0.115 μg/mL, and the method was precise. As a general rule, the recovery values were high. Due to its rapidity and low cost, this technique can be useful in the quality control of quince products.
An indirect method for the determination of silicon in blood samples has been developed. The proposed method overcame interference from a large amount of salts and phosphate in blood samples, and enabled us to determine the silicon contents in serum and whole blood by the same operation. After blood samples were digested by microwave heating, silicon, present as silicate in the sample solution, was reacted with molybdate to form a silicomolybdate complex. The complex was then separated from unreacted molybdate by a cation-exchange resin column. The molybdate liberated from the complex was spectrophotometrically determined in place of silicon. Since the method is not affected the composition of matrices between serum and whole blood, it could achieve good precision and accuracy, and could also estimate the silicon contents in erythrocytes from those in serum and whole blood. The sensitivity of the method was almost equal to that of the conventional silicomolybdenum blue method, and the calibration curve was linear up to 50 μmol l-1 of silicon with a detection limit of 1.1 μmol l-1 in whole blood. The mean concentrations of silicon in five healthy subjects were 11 μmol l-1 for serum, 28 μmol l-1 for whole blood and 50 μmol l-1 for erythrocytes. Thus, the obtained distribution ratio between serum and erythrocytes was in the range of 0.15 - 0.39, and was found to be included in a narrow range.
A new derivative spectrophotometric method for rapid and selective trace analysis of Ga3+ and In3+ and for their simultaneous determination using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in a cationic micellar medium is reported. Molar absorptivity and Sandell’s sensitivity of 1:1 Ga3+ and In3+ complexes at their λmax 553 nm and 558 nm are: 7.22 × 104 l mol-1 cm-1 and 5.85 × 104 l mol-1 cm-1, and 0.96 ng cm-2 and 1.96 ng cm-2, respectively. Linearity is observed in the concentration range 0.023 - 0.700 μg ml-1 for gallium and 0.076 - 1.52 μg ml-1 for indium; IUPAC detection limit is 0.012 and 0.035 ng ml-1, respectively. These metal ions interfere with the determination of each other. However, 0.07 - 0.70 μg ml-1 Ga3+ and 0.115 - 1.150 μg ml-1 In3+ could be determined simultaneously when present together by the derivative method without any prior separation. The proposed procedures have been successfully applied for the individual and simultaneous determination of gallium and indium in synthetic binary mixtures, standard reference materials and environmental samples.
A simple and sensitive method has been developed for the determination of phosphate in the ng ml-1 concentration range. The method utilizes the quantitative extraction of the Molybdenum Blue species of phosphate by polyurethane foam (PUF) discs prior to a diffuse reflectance spectrometric (DRS) measurement of the colored foam. A preconcentration factor of 150 has been achieved for a 100 ml sample volume. The effect of the pH of the solution on the rate of color development of the phosphomolybdenum blue has been carefully examined. A calibration graph has been established based on the Kubelka-Munk function (F(R)695), which was found to favorably correlate with the phosphate concentration. The lower detection limit (3σ) was found to be 5 ng ml-1, with a working analytical range of 5 - 70 ng ml-1. At the same time, the chromaticity coordinates y (CIE 1931) and v′ of the CIELUV (1976) were found to show good correlation with the concentration of phosphate in water. On the other hand, the calculated color temperature has been found to excellently correlate with the phosphate concentration. The different experimental parameters were thoroughly investigated.
An enzymeless sensor based on a multi-walled carbon nanotubes-dicetyl phosphate (MWCNT-DCP) film modified vitreous carbon electrode was developed for the determination of hypoxanthine. The MWCNT-DCP film modified electrode showed a remarkable enhancement effect on the oxidation peak current of hypoxanthine. Under the optimized conditions, the oxidation peak current is proportional to the concentration of hypoxanthine over the range from 5.0 × 10-7 to 2.0 × 10-4 mol L-1 with a detection limit (S/N = 3) of 2.0 × 10-7 mol L-1. The MWCNT-DCP film modified electrode has been successfully used to detect hypoxanthine in fish samples.
A method has been developed for the qualitative analysis of paeonol, paeoniflorin and their derivatives in Paeoniae Radix by high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS). Gradient elution with acetonitrile-water solvent system was employed in an HPLC-ESI-MS study. The negative-ion ESI mode was suitable for these compounds. The peaks were identified by their mass spectra, UV spectra and fragments of their MS2 spectra. The structures of three unknown compounds are inferred in this paper.
An improved method for a suitable derivatization of polyhydroxylated steroids having one or two tert-hydroxyl groups at the 5β-, 14α-, 17α-, 24-, and/or 25-positions by capillary gas chromatography (CGC) is described. By using trimethylsilyl triflate as a silylating reagent and 2,6-lutidine as a catalyst, each of 5β-cholane and 5α-cholestane series of steroids was successfully transformed into trimethylsilyl (TMS) ether derivatives to give a single CGC peak under mild conditions. More bulky triethylsilyl (TES) etherification of 14α- and 17α-hydroxy compounds provided multiple CGC peaks arising from completely- and/or incompletely-derivatized TES ethers accompanied by their thermal elimination products.
A simultaneous determination of cationic and nonionic surfactants has been developed using ion-association titration. Tetrabromophenolphthalein ethyl ester (TBPE) was used as an indicator. Benzalkonium reacted with TBPE to form a blue ion-associate in the organic phase. When tetrakis(4-fluorophenyl)borate was added dropwise to the solution, the color of the organic phase turned to yellow at the equivalence point. In addition, when a large amount of potassium ion was added to a solution including Triton X-100, Triton X-100 could be determined by the same technique as described above because of formation of the K+-Triton X-100 cation. The proposed method is available for the stepwise determination of cationic and nonionic surfactants in mixtures.
The chemometric calibration performance was systematically investigated by two parameters (changing the chemical matrix as well as the signal-to-noise ratio) of the NIR (near-infrared) spectrum. Three different analytes (hexane, cyclohexane, toluene) were selected and heptane was used as a solvent. The degree of spectral difference significantly affected the calibration performance. The largest structural difference between the analyte and the solvent provided the best calibration result for a given signal-to-noise ratio. Additionally, the signal-to-noise ratio of the spectra also directly influenced the calibration performance. Overall, the spectral difference and signal-to-noise ratio were the major factors for governing the chemometric calibration performance, especially in the low-concentration range.
The parameters affecting the absolute radiochemical yield of the isotopic exchange reaction between radioiodine (125I-) and iodohippuric acid isomers on molten ammonium acetate as a medium exchange at 120°C without any carrier added (radioiodine, 125I-) was determined. The isotopic exchange reactions of radioiodine as 125I-for iodine-127 of o- and p-iodohippuric acid isomers occur more rapidly than m-iodohippuric acid isomer. These reactions proceed by nucleophilic second order substitution reaction. The kinetics and thermodynamic parameters of these isotopic exchange reactions were determined. The absolute radiochemical yield and radio pharmaceutical purity were determined by HPLC and TLC techniques.
A flow-injection system has been developed for the determination of 2-propanol in the surface cleaning solutions used in the copper continuous cast rod making system. Adsorption chromatography in nitric acid medium was used for the on-line separation of oily substances in the sample solution. Cerium(IV) diammonium nitrate was utilized as the chromogenic reagent for the spectrophotometric detection of 2-propanol. The system permits a throughput of one sample per hour for the oily sample, and of 12 samples per hour for the none-oily sample. The reproducibility has been proven to be satisfactory with a relative standard deviation of less than 6.0% (2.2%(V/V) 2-propanol level, n = 23). The detection limit is 0.01%(V/V).
Plural samples were simultaneously analyzed in a capillary electrophoresis (CE)-chemiluminescence (CL) detector system, taking advantage of a micro-space area for reaction/detection at the tip of the capillary. The CL reaction of 1,10- phenanthroline and hydrogen peroxide was adopted and a Cu(II) sample was used as a model. Three different length capillaries were inserted into a flow-type CL detection cell made of a Teflon tube. Three samples migrated in the corresponding capillaries at the same time and mixed with the CL reagent at the tip of capillary to produce CL. The simultaneous analysis of plural samples in the present system supported the possibility that a real sample could be determined more easily, rapidly, and precisely with the calibration curve.
Crystal structure of trans-dibromobis(triphenylphosphine)platinum(II) was determined by X-ray-crystallography. The complex crystallizes on an inversion center in distorted square planar coordination around platinum with triphenylphosphine ligands in trans positions to each other and with two molecules of dichloromethane as solvate.
C17H19O2N5 is monoclinic, P21/n. Unit-cell dimensions at 293 K are a = 10.802(1), b = 24.085(2), c = 12.933(1)Å, β = 106.119(6)°, V = 3232.4(6)Å3, Dx = 1.271 g/cm3, and Z = 8. The R value is 0.068 for 3017 observed reflections. There are two independent molecules in the asymmetric unit, denoted by A and B. In A, the dihedral angle between the adenine moiety and the phenyl ring is 73.2(3)° [in B, the angle is 83.9(2)°]. For A, the tetrahydropyranyl ring adopts a half-chair conformation [for B, chair conformation]. The packing in the crystal is entirely due to van der Waals forces.
The reaction between CoCl2·6H2O and 2-1-(2-thiazolylazo)-p-cresol (TAC) in acetone resulted in six coordinated cobalt(III) complex, [Co(TAC)2]Cl3. Two TAC ligands coordinate with cobalt ion forming four five membered chelate rings. The cobalt ion is octahedrally coordinated by a phenolic oxygen, azo nitrogen and nitrogen in thiazole rings. Three chloride ions are disordered.
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)Å, V = 2768(1)Å3, Z = 8, Dcalc = 1.254 g/cm3, μ = (Mo Kα) = 0.87 cm-1. The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration.
C14H12O2Se is monoclinic, P21/c. Unit-cell dimensions at 293 K are a = 8.1055(7), b = 5.8403(11), c = 26.0302(17)Å, β = 94.560(5)°, V = 1228.3(3)Å3, Dx = 1.575 g/cm3, and Z = 4. The R value is 0.048 for 2144 observed reflections. The dihedral angle between the phenyl rings is 74.9(2)°. There is an intermolecular hydrogen bond between two symmetry related carboxyl groups with an O1···O2 distance of 2.668(6)Å. The molecules in the crystal are packed at normal van der Waals distances.