A selective and highly sensitive liquid chromatographic method for the determination of ganciclovir (anti-virus drug) in human serum was described. After ganciclovir and acyclovir (internal standard; IS) were extracted with solid-phase extraction cartridge from serum, they were converted into fluorescent derivatives by reaction with phenylglyoxal in a phosphate buffer (pH 5.8) at 20°C for 30 min. The derivatives were separated by reversed-phase column with a mixture of acetonitrile-1 mM phosphate buffer (pH 6.2) (18:82, v/v), and were then detected spectrofluorometrically at 512 nm with excitation at 365 nm. Extraction recoveries were 87.0 - 91.6% for ganciclovir and 86.8 - 92.3% for IS. The detection limit for ganciclovir spiked to serum was 5 ng ml^-1 serum (306 fmol on column) at a signal-to-noise ratio of three. The accuracy and precision of this method were 7.6% and 5.0% even at low concentration (20 ng ml^-1). The within- and between-day variations are lower than 7.6% and 8.1%, respectively.

View full abstract

The construction and performance characteristics of an ion-selective electrode for fentanyl-drug cation, based on an ion-pair complex with tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate anion in a PVC matrix were studied. A linear response for 1 × 10^-5 mol dm^-3 to 1 × 10^-2 mol dm^-3 drug with a slope of 57.9 ± 0.5 mV/decade was established. The optimum pH range was 2 to 6. The lower detection limit was 6.29 × 10^-6 mol dm^-3 fentanyl citrate (2.1165 µg cm^-3 fentanyl). There were negligible interferences from a number of inorganic cations, structural analogues, and some common drug additives in injections. The electrode proposed has been successfully applied to determine fentanyl citrate in injections. The results correlated well with those obtained by the United States Pharmacopoeia standard procedure.

View full abstract

Solvent extraction mechanisms of some metallic ions, Mn(II), Zn(II), Ni(II), and Co(II), from aqueous phase to 1,2- dichloroethane (DCE) were examined by electrochemical impedance spectroscopy (EIS) and other electrochemical methods. Diffusion-limiting currents were observed in the i-E curves. Such a diffusion-limiting current corresponds to the transfer rate of the metallic ion from the aqueous phase to the DCE phase, and it was found that the extraction rates followed the order of Mn(II)<Zn(II)<Ni(II)<Co(II). The capacitive semicircle due to the time constant of the charge transfer resistance and the interfacial capacitance was described in the electrochemical impedance on the Nyquist plane. A simulation was performed for the experimental result of EIS. The solvent extraction of metallic ions across aqueous phase/DCE phase was discussed by using reaction parameters such as the rate constant and the interfacial capacitance. In the solvent extraction accelerated by an electrochemical driving force, a rate constant increased with the increase of the potential. The value of interfacial capacitance depended on the kind of metallic ions, and it was found out that the interfacial capacitance was related to the amount of the intermediate at the interface.

View full abstract

Colorful luminescence images were obtained from some feldspar slices after X-ray irradiation. According to a ternary diagram of feldspars, afterglow color images (AGCI) were generously distinguished into two groups, giving intensely bluish or green coloration along the alkali feldspar (Or-Ab) line and weak reddish coloration along the plagioclase (An-Ab) line. In the former feldspar group, blue AGCI samples can be attributed to ordered crystals formed at a relatively slow cooling rate, whereas reddish AGCIs could be assigned to disordered crystals, presumably reflecting a rapid cooling process at formation or thermal alteration. In a microcline, alternative patterns of AGCI are closely related to a perthite structures, consisting of matrix microcline parts and stripe albite phases. Thermoluminescence color image (TLCI) patterns showed blue coloration similar to AGCIs in alkaline feldspars. Among the present feldspars, no homogeneously distributed luminescence existed. On the basis of the present results, the necessity for a single aliquot technique is emphasized for luminescence dating using feldspars.

View full abstract

An equation that can describe the concentrations of ionic sites required for a Nernstian potentiometric response slope of neutral ionophore-incorporated ion-selective liquid membranes is presented. This equation is derived from a model based on electrical diffuse layers on both the membrane and the aqueous sides of the interface, in which the phase boundary potential is correlated to the surface charge density as well as the salt concentrations in the bulk membrane and aqueous solution. To experimentally and accurately confirm the validity of this equation, response characteristics of field effect transistors covered by neutral ionophore-based liquid membranes with varying concentrations of a derivative of tetraphenylborate as an anionic site but free of ionic impurities were examined. The observed membrane potentials and the response slopes for membranes with various concentrations of anionic sites were in good agreement with the values calculated from the theory presented in this paper with the measured complexation stability constants for the relevant systems. This result indicates that the theoretical prediction based on the proposed equation for the anionic site concentration is accessible for the preparation of neutral ionophore-incorporated ion-selective liquid membranes, which show Nernstian response slopes for the primary ions.

View full abstract

A micro glucose sensor consisting of an interdigitated array gold microelectrode was developed. The interdigitated array structure, which has 10 µm band width and 10 µm band gap, was fabricated in a small region (2.5 × 5 mm²) on a quartz substrate. Glucose oxidase was chemically fixed onto the electrode surface through self-assembled monolayer of 11-mercaptoundecanoic acid; ferroceneacetic acid was used as electron mediator. Electrochemical properties of the glucose oxidase-immobilized microelectrode were investigated by cyclic voltammogram measurements. Results confirmed that the reductive ferroceneacetic acid generated at counter electrode diffuses through a narrow band gap (10 µm) and can reach the working electrode surface.

View full abstract

Organic solvent-free mobile-phase systems in ion-pair reversed-phase partition high-performance liquid chromatography (IPRP-HPLC) are demonstrated; using urea at 3.0 - 7.0 molal (mol kg^-1) as a modifier in a mobile phase on an octadecylsilanized silica column, four nitrophenolates and metal 4-(2-pyridilazo)resorcinol (PAR) chelates (in PAR chelates system an aqueous mobile phase with 15 wt% methanol was used) were separated rapidly within 6 min at no sacrifice to the separation efficiency. On the addition of urea in the mobile phase, reduced retention times of nitrophenolates and naphthalenesulfonates and also diminution of the height equivalent to a theoretical plate were observed. The addition of urea and guanidium chloride (GuCl) in the mobile phase gave rise to a decrease in the mobile phase volume; in turn, this meant an increased volume of the stationary phase. As the concentration of urea and GuCl in the mobile phase increased, the volume of the mobile phase in the column decreased within about 70% and 40% at 7.0 molal of urea and GuCl, respectively. A decrease in the mobile phase volume suggests an increase in the extent of solvation of the bonded hydrocarbon chain of the stationary phase. The possible explanations for the LC behavior with the urea and GuCl are turned into reduction of hydrophobic interaction in LC processes, solute partitioning and entangling of alkyl chain brushes, with the addition of urea. The water structure breakers, urea and GuCl, most likely affect the solvation states of both solute molecules and the hydrocarboneous stationary phase by changing the nature of the water solvent, which provides a new technique for fine tuning of the LC resolution of the analytes.

View full abstract

A simple and highly sensitive spectrophotometric method for the determination of ascorbic acid (AA) was established by using iron(III) and p-carboxyphenylfluorone (PCPF) in a cationic surfactant micellar medium. The apparent molar absorptivity of the proposed method, which does not require an extraction procedure, was 2.05 × 10⁶ dm³ mol^-1 cm^-1 at 655 nm. Beer’s law was obeyed in the concentration range of 0.02 - 0.12 µg/cm³ for AA. The procedure was successfully applied to assays of AA in pharmaceutical preparations. It is suggested that the method is based on a coupled redox-complexation reaction in which the first step is the oxidation of AA by iron(III), and the second step includes the formations of the iron(II)-PCPF (1:2) complex and the dehydroascorbic acid-iron(III)-PCPF (1:1:2) complex.

View full abstract

Highly sensitive successive determinations for Pt^II and Se^IV ions have been developed based upon reactions with 1,4-dibromo-2,3-diaminonaphthalene (Br₂DAN), which forms a near-infrared (NIR) absorbing complex (ε = 1.2 × 10⁵ l mol^-1 cm^-1 at 800 nm) and an emissive complex (ex. 386 nm, em. 604 nm) for Pt^II and Se^IV ions, respectively, in acidic aqueous micellar solutions. In the presence of a cationic surfactant, cetyltrimethylammonium chloride, the detection limits for Pt^II and Se^IV ions are 1.2 ng ml^-1 (3σ) and 0.98 ng ml^-1 (S/N = 3), respectively. Hydrobromic acid plays a key role to enhance the color development of the NIR-absorbing Pt^II complex. The influences of Cu^II and Zn^II ions at the normal human serum levels are readily tolerated, and interference from Fe^III ion at 35 µmol l^-1 is circumvented by the addition of 50 µmol l^-1 of polyaminocarboxylates, such as EDTA.

View full abstract

An analytical method based on solid surface room temperature phosphorescence (SSRTP) for the determination of rescinamine was developed. Signal enhancements were obtained by heavy atom effect, use of surfactant agent and use of basic medium. Alternatively, an ultraviolet treatment of the analyte was tried in order to induce a phosphor with higher phosphorescence quantum efficiency. A limit of detection of 2.70 ng and linear dynamic range of 2 orders of magnitude were achieved in paper substrate treated for background reduction. A study was performed to verify potential interferences of several pharmacological active ingredients that could be associated with rescinamine in a pharmaceutical preparation. The method was tested by analyzing rescinamine in three different laboratory-made tablets.

View full abstract

In this paper, a new optimization strategy is put forward which locates as many potential unimodal regions as possible in the search space. The potential optima can be further explored by a global optimization method for searching in the identified unimodal regions. The proposed strategy was evaluated by the optimization of test functions. The results obtained by this approach are comparable with those achieved by variable step size generalized simulated annealing (VSGSA) and a genetic algorithm (GA). Finally, we used this strategy in a clustering analysis of a tobacco data set.

View full abstract

The thermal decomposition of cerium(III) acetate hydrate, Ce(CH₃CO₂)₃·1.5H₂O, in helium was successfully studied by the simultaneous measurement of TG-DTA and EGA by mass spectrometry (TG-DTA-MS) as well as that of X-ray diffractometry: DSC (XRD-DSC). TG-DTA-MS was useful to elucidate the complicated successive reactions accompanying the formation of intermediate products. Crystalline cerium(III) anhydrous acetate appeared at 212°C and transformed to another phase at 286°C. Cerium(III) anhydrous acetate decomposed in the temperature range of 300 - 700°C to cerium(IV) oxide via four decomposition steps; the chemical compositions of the three decomposition intermediate products were presumed to be Ce₂O(CH₃CO₂)₄, Ce₂O₂(CH₃CO₂)₂ and Ce₂O₂CO₃. The endothermic dehydration and the exothermic crystallization were characterized by simultaneous XRD-DSC. It has been demonstrated that cerium(III) changed to cerium(IV) in the final step. A detailed decomposition mechanism of Ce(CH₃CO₂)₃·1.5H₂O is discussed.

View full abstract