High-performance frontal analysis (HPFA) wasapplied to investigate the binding properties of semotiadil(R-isomer, Ca-channel blocker) and levosemotiadil (S-isomer,Ca- and Na-channel blocker), an enantiomeric pair of drugs under devel-opment, to human serum albumin (HSA). An on-line HPLC systemconsisting of a HPFA column, an extraction column and an analytical HPLC column was used to determine the unbound concentrations of theseenantiomers. The experimental data were subjected to Scatchard analyses to estimate the binding parameters. The binding affinity of levosemo-tiadil(K=6.59×105 M-1, n=0.97) is aboutthree-times stronger than that of semotiadil (K=2.15×105M-1, n=0.99). These results did not change in thepresence of warfarin, but were significantly decreased by the addition ofdiazepam, indicating that both enantiomers are bound at the diazepam siteon HSA molecule.
We demonstrated fast separation of DNA fragments in a short slab gel through the minimization of band-broadening. A discontinuous buffer system was used to reduce band-broadening from sample introduction, and a high spatial resolution thermal lens microscope (TLM) was used to reduce such an effect from the detector. Bands of DNA fragments were sharpened into 100 µm, which was about 1/10 of the bandwidths inconventional continuous slab gel electrophoresis. The 100 base pair ladder DNA sample, which ranges from 100 bp to 2000 bp, was completely separated within 15 min with a migration distance of 18 mm and was detected by TLM after silver staining. These results suggested the possibility of fast separation of DNA fragments in a miniaturized discontinuous slab gel. As well as the inherent properties of parallel separation of slab gel, high throughput separation can be obtained, which is significant for DNA analyses such as DNA sequencing, genetic diagnosis and forensic identification analyses.
A postcolumn phosphate-selective fluorescence detection system was developed for the determination of phospholipids by high-performance liquid chromatography. Phospholipids were separated on a silica gel column and then on-line hydrolyzed by photolysis in the presence of titanium dioxide under UV-irradiation (253.7 nm). The resultant orthophosphate was reacted with a molybdenum reagent to form phosphomolybdic acid, which was then reacted with the alkaline thiamine reagent. Finally, the fluorescence intensity of the resultant thiochrome converted from thiamine by phospho-molybdic acid was measured by setting the excitation wavelength at 380 nm and the emission wavelength at 442 nm. The calibration curves for phospholipids under the gradient elution programwere linear (correlation coefficient, 0.984 - 0.991) in the range 0.02 - 0.5 mg ml-1 (injection volume, 10 µl). When every 2 µg each of five phospholipids was repeatedly injected into this system, the relative standard deviations were between 4.14 and 4.76% (n=5).
We investigated a column with varying physical properties. A change in velocity was induced by a continuously varying the diameter inside the column. Analytical dimensions of the column were used.The diameter was continuously reduced from the analytical one (4.0 mm) to a diameter typical for narrow-bore columns (2.5 mm). Our interest was focused on the efficiency of a conical column and on the mobile phase velocity in it. The results obtained with the conical column were compared to those obtained with the conventional analytical column and the narrow column. The diameter of the narrow column (3.3 mm) was the same as the average diameter of the conical column. The advantage of the conical column over the narrow column was the greater loadability of the conical column and better dynamic efficiency. Compared to the conventional analytical column, a higher linear velocity at the same flow rate was achieved. Therefore, the retention times were shorter and consumption of the mobile phase was smaller.
We developed a difference interferometric slab optical waveguide (SOWG) refractive index (RI) sensor for flow analysis which used a prism coupling method. The highest sensitivity of 7.2×10-7 (ΔRI unit) was obtained with a glass SOWG fabricated with a radio frequency sputtering method for solution samples such as sucrose solutions and mixtures of ethanol and water; here sensitivity was defined as the ΔRI which gives the signal intensity of 10-4 in absorbance unit. The sensitivity is almost the same level as that of a surface plasmon resonance sensor.
This paper describes the construction of an electrode of the second kind, Pt|Hg|Hg2(Salic)2|Graphite, sensitive to salicylate. This electrode responds to the salicylate ion with a sensivity of 58.66 mV/decade over the range 6.0×10-4 - 1.0×10-1 mol/l at pH 6.0 and an ionic strength of 0.500 - 3.00 mol/l, adjusted with NaClO4. The electrode is easily constructed, shows a fast response time, is low in cost, has excellent response stability, and has a lifetime greater than 18 months, which is much longer than those reported earlier for other systems. The influence of 10 different carboxylate and inorganic anions on the electrode response showed that there was negligible interference by most of these ions. It was used to determine aspirin in tablets (after hydrolysis of acetylsalicylic acid to salicylate) by means of the standard additions method. The results obtained using this electrode for aspirin determination, in three different samples of antithermic drugs, compared favorably with the results given by the British Pharmacopoeia method.
The probing depth of conversion electron/He ion yield XAFS methods has been studied in order to apply these methods to estimate the local distortion of strontium titanate thin films on thick substrates. Several strontium titanate thin film samples with different thicknesses were prepared and the edge-jump amplitudes at both the Sr and Ti K-edges were obtained. The probing depths were estimated to be 300 nm for the Sr K-edge and 30 nm for the Ti K-edge by the conventional exponential fit. The XAFS spectra and the probing depths measured by conversion electron and He ion yield methods is much the same, though the background curves are different.
The electrochemical polymerization of aniline on a platinum electrode in aqueous HClO4 and H2SO4 solutions has been studied by means of in situ Fourier-transform infrared (FTIR) reflection spectroscopy. The spectra, taken at early stage of the polymerization in both solutions, exhibited the absorption characteristic of polyaniline (PAn) in an emeraldine state, even at a highly positive potential (≥+0.7 V vs. Ag/AgCl (saturated KCl)). Polymer growth in H2SO4 was accompanied by an increase in the molar ratio of [HSO4-]/[SO42-], indicating that the protons generated during the oxidation of aniline react with SO42- to afford HSO4-, and that polymer growth is facilitated. In contrast, such proton-scavenging behavior was not observed in a HClO4 solution, and the growth of PAn was suppressed owing to the accumulation of protons. Under the condition that aniline was extremely consumed, the produced PAn was subjected to oxidative degradation, which was competitive with the growth process of PAn. The major degradation species was identified to be p-benzoquinone.
A novel nebulizer called a sonic spray nebulizer (SSN) was developed to introduce microliter sample solution for ICP-AES with a high nebulization efficiency. At a sample uptake rate of 50 µl min-1, the detection limit of ICP-AES with the SSN is comparable to that with a conventional concentric nebulizer (CCN) at a typical sample uptake rate of 850 µl min-1. The absolute sensitivity of the SSN was improved by an average factor of 13, compared to that of the CCN. The SSN system is capable of introducing a sample solution at a rate as low as 1 µl min-1 with a relative standard deviation (RSD) of about 2%; therefore, the SSN nebulizer should be very useful for introducing biological or other samples in very limit-ed volumes.
The properties of chitosan to adsorb metal ions and to dissolve in some organic acids were applied to the preconcentration and determination of copper(II) in water samples by tungsten metal furnace atomic absorption spectrometry. Copper(II) was quantitatively adsorbed onto chitosan over the pH range of 5.0 - 9.0. The chitosan adsorbed copper(II) was separated from the sample solution by a membrane filter, then dissolved in 2.0 cm3 of 0.1 mol dm-3 acetic acid. An aliquot of this resulting solution was introduced directly into a tungsten metal furnace, and the absorbance of copper was measured by atomic absorption spectrometry. An ashing temperature of 900°C and an atomizing temperature of 2500°C were selected, respectively. The detection limit for copper(II) was 0.002 µg dm-3 (S/N≥3). A quantitative recovery was obtained over the 50 - 500 dm-3 range of the sample solution. The relative standard deviations (n=5) were 3.8% for 0.10 µg Cu(II)/100 cm3, 4.7% for 0.05 µg Cu(II)/100 cm3. The proposed method was applied to the determination of trace amounts of copper(II) in water samples.
A flow injection analysis method is proposed for the spectrophotometric determination of trace amounts of bromide based on its catalytic effect on the oxidation of 4,4′-bis(dimethylamino)diphenylmethane (tetrabase) by Chloramine T in a weakly acidic solution. The effects of the reagent concentrations are studied at two pH values: 3.2 adjusted with sulfuric acid and 3.8 with acetate buffer. Although the sensitivity is slightly lower and the background noise is larger at pH 3.8, several ions show less interference at pH 3.8 than at pH 3.2. The detection limit is 1 µg l-1 and the calibration graph for bromide is linear up to 40 µg l-1, showing a slightly negative deviation in the higher concentration range. The relative standard deviations for 1.0, 10.0 and 40.0 µg l-1 of bromide are 6.4, 0.79 and 0.45%, respectively, at pH 3.2 and 8.7, 1.2 and 0.38%, respectively, at pH 3.8. Bromide in water samples can be determined at a sampling rate of 100 h-1 with 300 µl sample injections. The procedure is applied successfully to the determination of bromide in natural waters.
A multi-residue technique is presented for the extraction and quantitative determination of some widely used organochlorine pesticides such as lindane, heptachlor, aldrin, dieldrin, endrin and p,p′-DDT in soil. The chlorinated pesticides were extracted from soil with different solvents, followed by clean-up of the sample extract using C18 solid phase extraction cartridge; the analytes were eluted with hexane and determined by gas chromatography with electron-capture detection. Average recoveries exceeding 89% were obtained for the pesticides. The solid phase extraction method was applied to extract the lindane from contaminated soil and soil-leachates. Column leaching tests were performed; we found some movement of the lindane between operationally defined soil phases or layers.