The diffusion of protons in porous media was observed and evaluated using a pH-imaging microscope with a flat semiconductor. Small particles were packed on the sensing surface of the flat sensor, followed by the addition of a lactic acid droplet on the top of the packed particle layer. The pH distribution accompanied by the diffusion of lactic acid was visualized at the bottom of the layer using the flat sensor. The difference in the diffusion property was confirmed depending on the particle type. The effective diffusion coefficients of the lactic acid in some porous media were estimated by combining the experimental results and mathematical calculation.
The electrooxidation of dopamine (DA) and ascorbic acid (AA) was studied using gold electrodes modified by a cationic self-assembled monolayer of [Os(bpy)2(bpy-(CH2)13SH)]2+ by cyclic voltammetry. At an [Os(bpy)2(bpy-(CH2)13SH)]2+/Au electrode, the oxidation peak of DA shifted to a much more positive potential as compared with that of a bare gold electrode, while the oxidation peak potential of AA showed a slightly negative shift due to their different electrostatic interactions with the cationic monolayer. Thus, a sufficient potential difference was achieved for distinguishing the electrochemical responses of DA and AA. However, when CH3(CH2)11SH was mixed into the cationic monolayer, the enhanced packing of the mixed monolayer blocked the access of DA or AA to the electrode, resulting in further positive shifts for both oxidation-peak potentials.
A voltammetric determination of adriamycin (ADM) at a carbon paste electrode (CPE) in the presence of cetyltrimethylammonium bromide (CTAB) is described. ADM strongly adsorbs on the surface of the electrode by the adsorption of CTAB, thereby affecting the reduction current. This method provides a detection limit below 10-10 mol/L for ADM. The experimental parameters, which influence the voltammetric responses of ADM, e.g. the pH value, variety and concentration of surfactants and the scan rate, were optimized. The reduction peak current changes linearly with the ADM concentration over the range from 2.5 × 10-8 mol/L to 5 × 10-6 mol/L. The detection limit is 4 × 10-10 mol/L for an accumulation time of 3 min. The coefficient of variation, determined at 4 × 10-6 mol/L ADM, is 3.0% (n = 8). Using this method, ADM in the patient’s urine samples, which undergoes active ADM chemotherapy, was determined.
A simple and rapid in situ preconcentration method for the determination of dissolved manganese in environmental waters has been developed based on solid-phase extraction using a Sep-Pak C18 cartridge. Manganese in water samples, which was taken into a graduated syringe to easily perform the operation for collecting manganese at sampling sites, was converted into a stable complex with 4-(2-pyridylazo)resorcinol (PAR) at pH 10 immediately after sample collection. The formed Mn-PAR complex was collected by a Sep-Pak C18 cartridge, which was packed with C18-bonded silica. The complex was stable in the Sep-Pak C18 cartridge for at least one month. The retained complex was quantitatively eluted with 0.5 M hydrochloric acid. The manganese was determined by graphite-furnace AAS. The proposed method was successfully applicable to brackish lake water samples to investigate the behavior of dissolved manganese in brackish lakes.
This paper describes the development of the depth profiling method of ultra trace metal impurities in polytetrafluoroethylene (PTFE) wares based on contamination-free sampling followed by acid-vapor extraction and its application to evaluate the washing method for PTFE wares. A contamination-free sampling process was achieved by scraping the surface of PTFE wares with the cleft face of a silicon wafer followed by exposing the PTFE scraped to highly pure acid-vapor. The concentration of metal impurities in extractants was determined by ICP-MS equipped with an electrothermal vaporizer (ETV-ICP-MS). The blank values of Al, Cr, Fe, Ni and Cu by the depth profiling method were 0.006, 0.004, 0.005, 0.002 and 0.003 ng, respectively. By analyzing the depth profile of beakers, the distributions of ultra trace (ng g-1 level) metal impurities were clarified. An examination of the washing methods by the depth profiling method also clarified that exposing to acid-vapor was more effective than the acid-dipping method for the elimination of metal impurities.
The source of signal variations that governs the analytical performance of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was investigated in this study. In order to specify the source of signal variations of LA-ICPMS, laser-induced plasma (LIP) Fe emission, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals were used as internal standards for the determination of trace elements in low-alloy steel certified reference materials (BS 50D and JSS 1005- 1008). Fe I 373.5 nm emission signals from LIP were measured, while trace element LA-ICP-MS signals were collected. After that, the LIP emission signals, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals were used as internal standards, and the analytical performance was evaluated by the RSDs and the correlation coefficients (r) of the calibration curves. The improvement factors were dependent on the internal standardization methods. Analytical precisions (RSDs) of trace element LA-ICP-MS signals were improved by factors of 1.5 - 3.3 using LIP Fe emission signals as an internal standard. The improvement factors of 2.5 - 5.9 and 4.1 - 17 were obtained by using LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals as internal standards, respectively. Better correlation coefficients (r) were also obtained using the LA-ICP-MS signal compensation (0.9985 by LA-ICP-MS Fe+ and 0.9996 by LA-ICP-MS Ni+) rather than the LIP Fe emission compensation (0.9932). In this paper we compare and discuss the analytical performance achieved by LA-ICP-MS using LIP Fe emission, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals as internal standards.
A new optode membrane for the sensitive determination of berberine based on fluorescence quenching of a conjugated polymer, poly(2,5-dimethoxy-phenyldiacetylene) (PDPA), is proposed. Incorporated in a membrane composed of plasticized poly(vinyl chloride) (PVC), the conjugated polymer exhibits better stability than those small sensing molecules regarding its excellent optical properties and lipophilic characteristics. Moreover, upon the introduction of a negatively charged lipophilic additive (tetraphenylborate salt) into a PVC membrane, the optode displayed enhanced sensitivity. In addition, satisfactory analytical sensing characteristics for determining beberine were obtained in terms of the selectivity, reversibility and reproducibility with a detecting range of between 7.5 × 10-7 mol l-1 and 7.5 × 10-4 mol l-1. The optode membrane has been applied to determine berberine in commercial tablets. The results showed a good agreement with those obtained by the pharmacopoeial method.
Capillary zone electrophoresis was employed for the determination of histamine using end-column amperometric detection with a carbon fiber microelectrode, at a constant potential. The optimum conditions of separation and detection were 10 mmol/L phosphate buffer, pH 5.6 for the buffer solution, 15 kV for the separation voltage, and 1.35 V (versus SCE) for the detection potential. The linear range was from 6.3 × 10-7 to 1.5 × 10-5 mol/L with the regression coefficient of 0.9997, and the detection limit was 4.0 × 10-7 mol/L (S/N = 3). The proposed method was successfully applied to the direct determination of histamine in the beer samples without any sample clean-up procedures.
Cross-linked chitosan was synthesized with chitosan and ethylene glycol diglycidyl ether. The adsorption behavior of trace amounts of metal ions on the cross-linked chitosan was systematically examined by packing it in a mini-column, passing a metal solution through it and measuring metal ions in the effluent by ICP-MS. The cross-linked chitosan adsorbed mercury and precious metals (Pd, Pt, and Au) at pH values from acidic to neutral. Especially, mercury in concentrated hydrochloric acids could be adsorbed on cross-linked chitosan quantitatively by an anion-exchange mechanism in the form of a stable chloride complex. This method was applied to the removal of mercury from commercially available hydrochloric acid; more than 97% of mercury was removed, and the residual mercury in the hydrochloric acid (Grade: for trace analysis) was found to be 0.15 ppb. Mercury adsorbed on the cross-linked chitosan could be easily desorbed with an eluent containing 1 M hydrochloric acid and 0.05 M thiourea. The thus-refreshed crosslinked chitosan could be repeatedly used for the removal of mercury in hydrochloric acid.
A first-derivative spectrophotometric method for the simultaneous determination of Zr and Mo with Alizarin Red S is described. Measurements were made at the zero-crossing wavelengths at 490.5 nm for Zr and 446.0 nm for Mo. The calibration graphs were linear at 0.5 - 20 and 0.5 - 13.0 μg ml-1 for Zr and Mo, respectively. The possible interfering effects of various ions were studied. Only iron was interfered in this system. The validity of the method was examined by using some mixtures of Mo and Zr. The method was applied in different matrix in both presence and absence of some foreign metal ions.
A simple, sensitive and rapid spectrophotometric method was developed for the determination of thallium(III) using trifluoperazine hydrochloride (TFPH). The method is based on the oxidation of TFPH by thallium(III) in a phosphoric acid medium to form a red-colored radical cation with an absorption maximum at 505 nm. Beer’ law is valid over the concentration range of 0.5 - 6.5 μg ml-1 of thallium(III). The molar absorptivity and Sandell’s sensitivity of the color system are 2.14 × 104 l mol-1 cm-1 and 0.0095 μg cm-2, respectively. The optimum reaction conditions and other analytical parameters were evaluated. The tolerance limit of the method towards various ions usually associated with thallium has been studied. The proposed method has been successfully applied to the analysis of thallium in alloys, minerals, standard reference material, water, and urine samples.
The spectrophotometric determination of Ca2+ with chlorophosphonazo III (CPN) has been carried out by a circulatory flow injection (FI) method. A cation-exchange mini-column for the on-line regeneration of the main reagent was incorporated in this FI system, allowing a repetitive determination of Ca2+. A solution of 4.0 × 10-5 M CPN in a 0.05 M acetate buffer (pH 5.0) in a single reservoir (50 ml) was continuously circulated at a constant flow rate of 1.5 ml min-1. Into the stream, an aliquot (20 μl) of a sample containing Ca2+ was quickly injected by means of a 6-way valve. The complex formed was monitored spectrophotometrically at 670 nm in the flow system. Then, the stream passed through a cation-exchange column, which was introduced after the flow-through cell. A successful ligand-exchange reaction of Ca2+ between the CPN reagent and a cation exchanger, as well as a simultaneous regeneration of the free reagent took place. The stream then returned to the reservoir. The regeneration and recycling of the CPN reagent allowed as many as 300 repetitive determinations of 2.5 mg l-1 Ca2+ solutions with the same 50 ml circulating solution.
The sensitivity improvement of a flow-injection spectrophotometric method for the determination of ammonia was examined based on an indophenol blue coloration reaction with salicylate and hypochlorite in the presence of manganese(II) as a reaction promotion catalyst. The optimal conditions for achieving higher sensitivity of ammonia determination were examined using a three-line flow system. The limit of detection corresponding to a signal-to-noise ratio (S/N) of 3 was 0.005 mg l-1 (≡ 5 ppb) of NH4+. A calibration graph was linear in the range from 5 ppb to 1000 ppb of ammonium ion. The relative standard deviations (n = 9) for 50 ppb and 100 ppb of ammonium ion were 6.4% and 2.2%, respectively. The proposed method was applied to the determination of ammonia in the exhaust gas of a thermal power plant. Prior to the FIA determination, ammonia in the exhaust gas was absorbed into a boric acid solution; the absorption solution was then analyzed by the proposed FIA.
Using a portable near infrared (NIR) spectrometer, we discriminated flours for making Japanese noodles (Soba), not only relying on a statistical and mathematical approach, but also on a chemical interpretation of the NIR spectra. In original NIR spectra, the particle-size difference, which results in an undesired systematic variation, was extracted and interpreted as the first-principal component factor by a principal-component analysis. The discrimination of flour materials cannot be satisfied by this factor. However, after a standardized treatment for the original spectra, the particle-size effects were eliminated; alternatively, differences in the chemical contents were extracted as principal-component factors. Using these factors, flour material discrimination was achieved much better. This study suggests a novel idea of utilizing the wavelength contribution ratio spectra for interpreting the factors extracted from the principal-component analysis for the NIR spectra. This report also describes the relationship between the NIR spectra and the chemical-analysis data.
A novel highly water-soluble tetrazolium salt, WST-1 (4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3- benzene disulfonate sodium salt), can be reduced to water-soluble formazan with a superoxide anion. Here, the WST-1 assay was applied to detect the superoxide anion generated during the Maillard reaction. A sample solution containing carbonyl compounds such as glyceraldehyde and glycolaldehyde (5 mM) and Nα-acetyl-L-lysine (10 mM) was incubated for 2 days at 37°C. The detection of a superoxide anion generated in the sample was performed by the WST-1 assay, and the result was compared with the cytochrome c assay. The reduction of WST-1 was almost perfectly (86 - 96%) inhibited by the addition of the superoxide dismutase (SOD). On the contrary, the reduction of cytochrome c was slightly (20 - 25%) inhibited by the addition of SOD. A similar result was observed for the addition of 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron). These results mean that the specificity of WST-1 to the superoxide anion was superior to that of cytochrome c. It was also possible to continuously monitor superoxide anion generation during the Maillard reaction by the coexistence of WST-1 in the reaction solution.