A preconcentration system attached to a GC/C/MS (gas chromatography/combustion/mass spectrometer) was developed to determine the carbon-isotope composition of methane in volcanic gases with extremely low concentration. With this system, we can analyze the carbon isotope ratio (13C/12C) of 0.7 - 6 nmol methane with a precision of ±1.6‰, unlike other conventional methods without preconcentration (150 - 1000 nmol CH4 with a precision of ±0.2‰). This system was test-ed with volcanic gas samples from Satsuma-Iwojima volcano, suggesting a mixture of magmatic and thermogenic origins for methane.
A 13.56-MHz Grimm-style glow discharge plasma in which pulsated bias currents are introduced was investigated con-cerning the analytical applications. The d.c. bias currents driven by a self-bias potential are conducted through the r.f. plasma body by using a low-pass filter circuit and a variable resistor. Excitation by a modified r.f. plasma can yield larger emission intensities. By modulating the bias current associated with phase-sensitive detection, the emission inten-sities can be measured at very low noise levels, enabling the detection limit to be improved more. A detection limit of 3×10-4 mass % was obtained for Mn determination in Fe-based binary alloy samples, whereas 1.4×10-2 mass % Mn was obtained in the conventional excitation of an 80-W r.f. discharge plasma.
A thermal-lens microscope which we developed was applied to an ultramicro quantity determination of a dye in an aque-ous solution filling a microchannel (150 µm wide and 100 µm deep) fabricated in a quartz glass substrate. The detection volume, which corresponded to the confocal volume, was estimated to be 1.3 fl. The detection limit of the dye molecules was 160 ymol, and the calibration line showed good linearity in the sub-zmol-to-zmol region. This detection sensitivity is equivalent to that of laser-induced fluorometry. The thermal-lens signal measured in the microchannel was more stable than that measured in a liquid micro space between a slide glass and a cover glass, which was much wider than the microchannel. This may have been due to a suppression of convection in the microchannel. The thermal lens method can be applied to non-fluorescent chemical species, and is thus very suitable detection method for integrated chemistry sys-tems.
The effects of supporting electrolytes used for anodizing a glassy carbon (GC) electrode in triethylene glycol on the extent of the 2-(2-carboxymethoxyethoxy)ethoxy group introduced on the anodized electrode surface were investigated. To evaluate these influences, cyclic voltammetry of phosphate buffer (pH 7.0) solutions of epinephrine as a cationic marker, and 3,4-dihydroxyphenylacetic acid and ascorbic acid as anionic markers was carried out at GC electrodes anodized in the glycol containing LiClO4, LiBF4, Mg(ClO4)2, H2SO4, CH3SO3H, CH3CH2SO3Na, or HOCH2CH2SO3Na. By comparing the extent to which the electrode reaction of the cation was conserved, while those of the anions were regressed, HOCH2CH2SO3Na was shown to be the supporting electrolyte of choice for anodization to introduce a mole-cule with a terminal carboxyl group on the electrode surface most effectively. The modified electrode obtained with the supporting electrolyte allows compounds existing as cationic and neutral species at pH 7.0 (norepinephrine, dopamine, 3-methoxytyramine, and catechol) to show voltammetric responses, and prevents those existing as anionic species (vanillo-mandelic acid and uric acid) from entering electrochemical reactions.
A flow-injection amperometric method for glycerol determination in samples relevant to the industrial production of soaps, detergents and such is presented. A nickel-chromium alloy micro-cylindric electrode was used as the electrochemical detector, which after a pretreatment exhibited good repeatability and stability. The method involved glycerol oxidation by an inactive Ni(OH)2 surface film to a Ni(III) layer, usually described as NiOOH (formed in the range from 0.40 to 0.50 V vs. Ag/AgCl), and reduction back to the starting hydroxide. The influence of sodium hydroxide (0.1 - 1.0 mol l-1) and potassium chloride (0.5 - 3.0 mol l-1) concentrations and sample-injected volume (10 - 100 ml) on the linear dynamic range, stability and response time of the electrode were evaluated. The proposed system handles about 60 samples per hour and is very stable and suitable for industrial control. Results within 20 and 80%(w/v) glycerol are precise (rsd <2%) and in agreement with the conventional procedures.
A simulation study of the separation of binary mixtures by the continuous dual-flow countercurrent extraction was executed. This simulation method was demonstrated to be efficient for the estimation of the separation results and also for the optimization of the separation conditions while recycling one of the two phases.
The standard deviation and relative standard deviation of measurements in the refractive index detection of liquid chromatography are predicted based on the 1/f fluctuation model which is made up of white noise and the Markov process. First, repeated measurements and Monte Carlo simulation corroborate the reliability of this prediction in the absence of flow pulsation. Pulsation, if any, can be distinguished in the frequency space from the 1/f noise which is common to most analytical instruments. In this case, the uncertainty prediction is also available without modifying the prediction theory, if a zero window is set at the time period of a fundamental tone of the pulsation (virtual invalidation of pulsation). The zero window is used for determining the zero level relative to which the signal intensities are summed for a signal area (measurement). A maltose determination is taken as an example.
The apparent comlexation of crown ethers with polyammonium ions chemically bonded on polystyrene-divinylbenzene copolymer resin has been chromatographically studied in methanol and acetonitrile. The retention of crown ethers with chemically bonded ammonium ion resins is affected by the nature of the counteranions; the retention is enhanced with large and poorly solvated counteranions, but is reduced with small and well solvated counteranions. In the present study, the retention mechanisms are discussed based on the retention data obtained by changing various factors, such as the crown cavity sizes, the structures of the polyammonium ions, counteranions, and the molar ratios of mixed counteranions in the stationary phase. The complexation and ion-pair formation equilibria play important roles in determining the over-all retention of crown ethers.
A rapid and simple method for the determination of anionic surfactants in tap water has been developed. The official analytical method in Japan for the determination of anionic surfactants in tap water requires tedious procedures and requires large amounts of chloroform as the extract solvent; it was greatly improved by the present spectrophotometric method using Methylene Blue. Our present method requires only one half of sample (50 ml), one tenth of the extraction solvent (chloroform=5 ml), and one sixth of the analytical time compared with the official analytical method.
A combination of palladium and sodium azide is proposed as a mixed modifier for cadmium determination in urine by graphite-furnace atomic absorption spectrometry using calibration against matrix-free standard solutions. It permits the use of a pretreatment temperature of 900 - 1000°C and markedly reduces the background absorption caused by inorganic salt matrices. The urine was simply diluted 1+1 with the addition of 1% HCl, Pd and NaN3. The recovery of cadmium obtained from urine was higher than 95%. The relative standard deviation at a cadmium level of 2.10 - 4.56 µg l-1 was smaller than 4%. The detection limit (3 s, n=20) is 0.16 µg l-1 of cadmium.
Rhodium and iridium were preconcentrated from a fairly large volume of their aqueous solutions using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) and tetraphenylborate onto microcrystalline naphthalene in the pH ranges 5.0 - 6.5 and 3.5 - 5.5, respectively. The solid mass obtained after filtration was dissolved in 5 ml of dimethyl formamide (DMF). A derivative spectrophotometric method using a zero-crossing technique measurement is described for their simultaneous determination in mixtures. The determination of rhodium and iridium in the concentration ranges 0.15 - 12.5 and 0.25 - 10.0 µg in 5 ml of the final DMF solutions, respectively, shows good linearity in the calibration plots. The detection limits are 72 ng and 133 ng for rhodium and iridium, respectively. Favorable selectivity in the pres-ence of common ions was achieved by adding EDTA after complex formation. Various parameters were studied in order to optimize the conditions for the simultaneous determination of rhodium and iridium in various synthetic samples corre-sponding to their standard alloys.