The principle of flow ratiometry for high-throughput titration, which we recently proposed for potentiometric titration, was extended to photometric titration. The flow rate (FB) of a base solution containing an acid-base indicator was linearly varied in response to a control voltage (Vc) generated from a computer. With the total (acid + base) flow rate (FT) being kept constant, the base solution was merged with an acid solution, which was aspirated to the confluence point at a flow rate of FT - FB. Downstream, the relative transmittance of the mixed solution was measured at the maximum absorption wavelength of the base form of the indicator. Initially, a feedback-based control was applied, where the scan direction of Vc was reversed from upward to downward, and vice versa, whenever the transition of the indicator at the equivalence point (EP) was sensed. Next, the scan range of Vc was further limited to the range just around EP by using fixed triangular waves. These processes avoided scanning in a range of no interest. Thus, an unprecedentedly high throughput rate (maximally 34 titrations per minute, corresponding to 1.76 s per titration) was realized with reasonable precision (RSD < 0.5%).
Three staining methods using SYBR® Gold Nucleic Acid Gel Stain (SYBR Gold) as a fluorescent dye were evaluated for the agarose gel electrophoretic detection of DNA. The methods involve prestain, in-gel stain, and poststain methods. DNA markers and polymerase chain reaction (PCR) products obtained by minisatellite variant repeat-PCR (MVR-PCR) amplification in a D1S8 locus were used as model DNA and practical samples, respectively. Among the three methods tested under the usual electrophoretic conditions, a prestain method using a 10000-fold diluted SYBR Gold solution showed most excellent features regarding cost and rapidity to use with good stainability and resolution over loaded DNA amounts of about 98 ng to 300 ng. The prestain method was found to be applicable to the analysis of DNA in MVR-PCR products from a human hair root.
We investigated whether methane, ethylene and ethane gas can be detected in gas emanating from human skin, which is called skin gas. Skin gas was collected with a homemade stainless-steel trap system, which was cooled with liquid nitrogen, and analyzed with a gas chromatograph fitted with a flame ionization detector (FID). Skin-gas samples were obtained by covering a hand for 30 min with a polyfluorovinyl bag in which pure helium gas was introduced. The bag, the trap system and GC were set up online to avoid any contamination by air. Methane, ethylene and ethane in skin gas were successfully collected at an average amount emanated for 30 min (from ten subjects) of 150 ± 63, 20 ± 11 and 17 ± 8 [mean ± SD] pg/cm2, respectively.
A reliable and convenient system to generate accurate and stable standard gas mixtures of various atmospheric compounds at parts-per-billion levels has been developed. The system is of simple design; the generator is a coil consisting of an inner tube of microporous polytetrafuluoroethylene (PTFE) membrane tubing and an outer tube of silicone tubing. An aqueous solution of the given compound continuously flows through the inner microporous tube and the purge gas flows through the annulus between the inner and outer tubes. In addition to the generation of gas mixtures based on Henry's law, the proposed flow-type system offers generation based on chemical reactions, leading to a distinct advantage of the availability of continuous sources of various compounds. The generation system was tested for preparing standard gas mixtures of HCHO and H2O2 on the basis of Henry's law, and those of HNO2, NO, and SO2 on the basis of chemical reactions. A stable generation of the desired low concentrations of various kinds of gas mixtures can be readily achieved by adjusting the concentration of the solution without the use of high-dilution flow.
This study investigated the protonation of nitrogen atoms in porphyrins with meso-phenyl p-substituted by an electron-withdrawing group using N 1s X-ray photoelectron spectroscopy (XPS), the N K X-ray absorption near-edge structure (XANES), and the discrete variational (DV)-Xα molecular orbital (MO) method. Both tetraphenylporphyrin (TPP) and tetrakis(p-sulfonatophenyl)porphyrin (TSPP) have a single structure: the former has two protonated and two non-protonated N atoms in the porphine ring; the latter has four protonated N atoms in the porphine ring. In contrast, a combination of XPS, XANES, and DV-Xα MO calculations shows that tetrakis(p-carboxyphenyl)porphyrin (TCPP) has a dual structure: one structure has two protonated and two non-protonated N atoms; the other has four protonated N atoms. Furthermore, this result was also considered based on the protonation constants of N atoms in the porphyrins. The correlation between the strength of electron-withdrawing groups and protonation to N atoms in porphyrins can be described using the spectral patterns of the N 1s XPS and N K XANES spectra.
The use of micellar media in constant-energy synchronous fluorescence spectrometry has been proposed. The influence of some aqueous micellar systems on the determination of pyrene, perylene and benzo[a]pyrene has been investigated. The presence of these micellar systems allows their determination in aqueous media, thus avoiding the use of an organic solvent, and greatly enhances the fluorescence signals. The combination of a constant-energy synchronous scanning technique and a micellar system provided a single spectrum for the simultaneous identification and quantitative determination of the three polycyclic aromatic hydrocarbons (PAHs). Further there was no energy transfer among them, making the measurement simple and fast. A constant-energy difference of 2800 cm-1 was selected. The analytical characteristics of the proposed method in the presence of anionic micelles of sodium dodecylsulfate (SDS) were studied. The detection limits were at a level of ng ml-1. Analysis of water samples from two different origins spiked with known amount of pyrene, perylene and benzo[a]pyrene also gave satisfactory results, and total average recoveries were greater than 97.1%.
A coprecipitation method with ytterbium hydroxide was studied for the determination of cadmium in water samples by graphite-furnace atomic absorption spectrometry. Up to 40 ng of cadmium in water samples was quantitatively coprecipitated with ytterbium hydroxide at pH 8.0 - 11.2. The concentration factor was 100 fold. The coprecipitated cadmium was sensitively determined without any influence of ytterbium and the calibration curve was linear from 0.1 to 4 ng/mL of cadmium. The detection limit (signal/noise = 2) was 2.9 pg/mL in 100 mL of the initial sample solution. Twenty-nine diverse ions tested did not interfere with the determination in at least a 10000-fold mass ratio to cadmium. The proposed method was successfully applied to the determination of cadmium in spring water.
A rapid separation and preconcentration method was developed for the determination of trace metals Cu, Zn, Cd, and Pb in seawater using a minicolumn packed with thiol cotton fiber (TCF) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Preconcentration parameters, such as seawater sample volume and flow rate and eluent hydrochloric acid concentration, volume and flow rate, were optimized. Under the optimized conditions, trace metals Cu, Zn, Cd, and Pb in seawater can be determined with no interference from saline matrices. When a sample volume of 1500 ml and a sample flow rate of 15 ml min-1 were used, the preconcentration factor of 1500 and RSD value of < 7% at ng ml-1 were achieved. The accuracy of the recommended method was verified by the analysis of certified reference materials.
A new and simple flow injection method followed by atomic absorption spectrometry has been developed for the indirect determination of ascorbic acid. The proposed method is based on oxidation of ascorbic acid to dehydroascorbic acid using a solid-phase manganese dioxide (30% m/m suspended on silica gel beads) reactor. The flow of the sample through the column reduces the MnO2 to Mn(II) in an acidic carrier stream of 6.3 mM HNO3 (pH 2.2) with flow rate of 4.0 ml/min at room temperature; Mn(II) is measured by atomic absorption spectrometry. The absorbance of Mn(II) is proportional to the concentration of ascorbic acid in the sample. The calibration curve was linear up to 30 mg/L, with a detection limit of 0.2 mg/L for a 220 µL injected sample volume. The developed procedure was found to be suitable for the determination of AsA in pharmaceuticals and foods with a relative standard deviation better than 1.09% and a sampling rate of about 95 h-1. The results exhibit no interference from the presence of large amounts of organic compounds. The reliability of the method was established by parallel determination against the 2,6-dichlorophenol-indophenol methods.
A simple flow injection spectrophotometric method for the determination of nitrite is described. Nitrite injected into the flow system reacts with thiourea in acidic medium and the generated thiocyanate ion reacts with Fe(III) in the reagent solution to produce a highly colored product. The influences of chemical and physical parameters including reagent concentrations, sample volume injected, flow rates of the carrier and reagent solutions, reaction coil length and reaction temperature, were studied and optimum values of these parameters were established. Under the optimum conditions, the calibration curve for nitrite was linear over the concentration range 0.36 - 90 µg ml-1 without preconcentration and over the range 3.8 - 500 ng ml-1 with a simple online preconcentration step using an anion exchange column. The corresponding detection limits were 0.36 µg ml-1 and 3.8 ng ml-1, respectively. Up to 25 samples can be analyzed per hour, with an average relative standard deviation of ≤ 1.2%. Interferences by various foreign ions were studied and the method was applied to the determination of nitrite in water and spiked water samples.
A new method is proposed for the simple preparation of random silver micro and nano-electrode arrays. This employs acoustic streaming directed at a glassy carbon surface to “mechanically” attach particles from a suspension of metal colloidal or other small particles. The particles tend to adhere to the substrate at points of imperfection such as scratches, crevices etc. These arrays are compared with arrays formed by the electro-deposition of silver at a glassy carbon substrate, with the silver being partially stripped off, leaving a stable micro and nanoparticle array on the surface. Both surfaces are characterised using optical and atomic force microscopy. The two types of electrodes are evaluated to their analytical utility via the electrochemical reduction of halothane and their performance compared with that of a silver macroelectrode. A notable increase in sensitivity and peak current is observed.
The construction and performance characteristics of a novel chromate ion-selective membrane sensor are described and used for determining chromium(III) and chromium(VI) ions. The sensor is based on the use of a rhodamine-B chromate ion-associate complex as an electroactive material in a poly(vinyl chloride) membrane plasticized with o-nitrophenyloctyl ether as a solvent mediator. In a phosphate buffer solution of pH 6 - 7, the sensor displays a stable, reproducible and linear potential response over the concentration range of 1 × 10-1 - 5 × 10-6 mol l-1 with an anionic Nernstian slope of 30.8 ± 0.5 mV decade-1 and a detection limit of 1 × 10-6 mol l-1 Cr(VI). High selectivity for Cr(VI) is offered over many common anions (e.g., I-, Br-, Cl-, IO4-, CN-, acetate, oxalate, citrate, sulfate, phosphate, thiosulfate, selenite, nitrate) and cations (e.g., Ag+, Ca2+, Sr2+, Co2+, Ni2+, Cu2+, Mn2+, Fe2+, Zn2+, Cd2+, Al3+, Cr3+). The sensor is used for determining Cr(VI) and/or Cr(III) ions in separate or mixed solutions after the oxidation of Cr(III) into Cr(VI) with H2O2. As low as 0.2 µg ml-1 of chromium is determined with a precision of ±1.2%. The chromium contents of some wastewater samples were accurately assessed, and the results agreed fairly well with data obtained by atomic absorption spectrometry.
Electrochemical impendence spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed to investigate the barrier properties and electron transfer of derivatized thiol self-assembled monolayers (SAMs) on gold in the presence of surfactants. The thiol derivatives used included 2-mercaptoethanesulfonic acid (MES), 2-mercaptoacetic acid (MAA), and N-acetyl-L-cysteine (NAC). A simple equivalent circuit was derived to fit the impedance spectra very well. The negative redox probe [Fe(CN)6]3-/4- was selected to indicate the electron-transfer efficiency on the interface of the studied electrodes. It was found that by changing the surface structure of SAMs, different surfactants could regulate the barrier properties and electron-transfer efficiency in different ways. A positively charged surfactant lowered the electrostatic repulsion between the negative redox probe and negatively charged surface groups of a monolayer, while enhancing the reversibility of electron transfer by virtue of increasing the redox probe concentration within the electric double-layer region. A neutral surfactant showed no significant effect, while a negative surfactant hindered the access and reaction of redox probe by electrostatic repulsion of same-sign charges.
Cyclic voltammetric (CV) and chronoamperometric (CA) behaviors of 1,3,5-triphenylformazan (TPF), 3-(p-nitrophenyl)-1,5-diphenylformazan (PNF) and 3-(m-nitrophenyl)-1,5-diphenylformazan (MNF) were studied in dimethyl sulfoxide medium. TPF was found to give a single sharp cathodic CV peak corresponding to a gain of one-electron per molecule. The diffusion coefficient and the number of electrons transferred were calculated using the Baranski equation with the CV-data obtained by an ultramicroelectrode. Standard rate constants for the reduction were calculated by the Klingler-Kochi technique. The electrochemical data obtained support the mechanism proposed by Umemoto.
An electrochemically prepared thin film of cobalt pentacyanonitrosylferrate (GC/CoPCNF) was used as a surface modifier for glassy carbon electrodes. The oxidation of ascorbic acid on a glassy carbon electrode modified with GC/CoPCNF as a working electrode was studied using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry in a 0.25 M KNO3 + 0.25 M phosphate buffer (pH 7) solution. The glassy carbon modified with CoPCNF showed good electrocatalytic activity toward ascorbic acid oxidation. The kinetics of the catalytic reaction was investigated, and the average value of the rate constant (k) for the catalytic reaction and the diffusion coefficient (D) were evaluated by different approaches for ascorbic acid, and were found to be 3.3 ± 0.3 × 102 M-1 s-1 and 3.2 ± 0.3 × 10-6 cm2 s-1, respectively.
The development of a distributed-feedback dye laser, with a pulse width and a line width of 25 ps and 8.78 pm, respectively, is described. Using this nearly Fourier-transform-limited pulse, we measured the first singlet-excited-state lifetime of 1,2,4-trichlorobenzene. The tunable picosecond dye laser developed herein has a potential for the lifetime measurement and the efficient multiphoton ionization of aromatic hydrocarbons with a larger number of chlorine atoms and shorter excited-state lifetimes.
A highly sensitive method for the determination of bisphenol-A in water with semi-micro column high-performance liquid chromatography using 2-methoxy-4-(2-phthalimidinyl)phenylsulfonyl chloride as a fluorescent labeling reagent has been developed. The labeling reaction was carried out at 70°C for 20 min in borate buffer (pH 9.5). The derivative eluted at 11.6 min on a reversed-phase column with methanol-water (78:22, v/v) at a flow-rate of 0.2 ml/min. The fluorescence was monitored at 308 nm for excitation and 410 nm for emission. The detection limit (S/N = 3) was 10 fmol per injection. The labeling yield was about 95%.
Homogentisic acid γ-lactone (HAL) chemiluminescence (CL) was applied to the determination of horseradish peroxidase (HRP) encapsulated in liposomes. HRP was detected after the lysis of HRP-trapped liposomes with Triton X-100. CL response rate, detection limit and linear range of calibration curve for HRP in HAL CL were compared with those in p-iodophenol (p-IP)-enhanced luminol CL. Maximal light emission in HAL CL appeared more rapidly compared to that in p-IP enhanced luminol CL, thus resulting in remarkable reduction of CL measurement time. The detection limit for HRP in HAL CL was the same as that in p-IP-enhanced luminol CL. The linear range of calibration curve for HRP in HAL CL was improved by a factor of 50 compared with that in p-IP-enhanced luminol CL. From these results, it was found that HAL CL were superior to p-IP-enhanced luminol CL for the determination of HRP encapsulated in liposomes.
A method for determination of ultratrace amounts (ppq levels) of ruthenium(III) was developed using a copper(II)-phthalocyanine-3,4′,4″,4′′′-tetrasulfonic sodium salt (Cu-PTS) as an indicator in a potassium bromate autocatalytic reaction system. A satisfactory calibration curve of ruthenium(III) ion was obtained by the time measurement in the concentration range of 1 × 10-13 M to 5 × 10-12 M with the relative standard deviation (RSD) of 2.8% (n = 5). The determination limits (3 σ) were 3.30 × 10-14 M (3.34 ppq).
When terbium ion (Tb3+)-norfloxacin (NFLX) complex is issued a fluorescent probe, in a buffer solution of pH = 7.6, NADP can remarkably enhance the fluorescence intensity of the Tb3+-NFLX complex at λ = 545 nm. The enhanced fluorescence intensity of Tb3+ is in proportion to the concentration of NADP. The dynamic range for the determination of NADP is 1.11 × 10-7 - 6.16 × 10-5 mol l-1, with a detection limit of 4.31 × 10-8 mol l-1. This method is simple, practical and relatively free of interference from coexisting substances, so it can be successfully applied to determination of NADP in synthetic water samples.
On the basis of Eu(III)-4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-di-carboxylic acid chelate (BCPDA) that was synthesized and characterized for time-resolved fluoroimmunoassay (TRFIA), Donkey anti-hepatitis B surface (anti-HBs) was labeled with BCPDA-Eu3+. Coomassie Brilliant Blue was used to determine the protein concentration and radio immunoassay (RIA) for detecting the biological activity in the labeled protein. Optimal conditions for the protein labeling were obtained by monitoring the reaction. Results suggested that the protein could be labeled with BCPDA under relatively moderate conditions. As a practical application, a protein-BCPDA-Eu3+ chelate was obtained by using BCPDA-protein that reacted with EuCl3 under certain conditions. Some properties of BCPDA and protein-BCPDA-Eu3+, such as absorption spectrum, emission spectrum and fluorescence lifetime, were discussed. The detection limit and the linear working range of the established method were also investigated.
The preparation and characterization of p-tert-butylcalixarene-1,3-bis(allyloxyethoxy)ether (CA-BAE) chemically coated capillaries via a free-radical reaction with vinyltriethoxysilane (VTES) that was attached onto the inner wall previously were carried out. IR spectra and decreased electroosmotic flow (EOF) suggested that the capillary was successfully coated with CA-BAE. A slight slope of EOF versus pH at 5 < pH < 9 would help to make the separation reproducible. The CA-BAE-coated capillary showed improved separations of toluidine isomers, naphthol isomers and polycyclic aromatic hydrocarbons (PAHs) compared with an uncoated capillary. The special selectivity indicates that there is a certain extent of host-guest interactions between the solutes and the CA-BAE coating.
A method was developed to analyze the distribution of sulfur compounds in model sulfur compounds by potentiometric titration, and applied to analyze hydrotreated transformer base oil. Model thioethers were oxidized to corresponding sulfoxides by tetrabutylammonium periodate and sodium metaperiodate, respectively, and the sulfoxides were titrated by perchloric acid titrant in acetic anhydride. The contents of aliphatic thioethers and total thioethers were then determined from that of sulfoxides in solution. The method was applied to determine the organic sulfur compounds in hydrotreated transformer base oil.