The transfer of Cd2+, Pb2+, Hg2+, Pd2+, and Cu2+ ions across polarized nitrobenzene/water (NB/W) interface assisted by 1,4,7,10,13,16-hexathiacyclooctadecane (HTCO) present in NB-phase has been studied by means of cyclic voltammetry. Voltammograms of Cd2+ and Pb2+ ions can be interpreted as being due to the reversible transfer of the ions assisted by the formation of 1:1 metal(M)-HTCO complex in NB-phase. The formal formation constants of [PbHTCO]2+ and [CdHTCO]2+ complexes in NB-phase have been determined to be 1011.7±0.3 and 107.9±0.3 M-1, respectively, using the formal potentials of non-assisted ion(M)-transfer at NB/W interface (ΔWNBφ0′M). The ΔWNBφ0′M’s of Cd2+ and Pb2+ ions and Zn2+ and Tl+ ions as well have been determined on the basis of the tetraphenylarsonium-tetraphenylborate assumption and of the polarographic reversible half-wave potentials of the ions in NB- and W-media reported by previous authors. Voltammograms of Hg2+ and Pd2+ ions have been explained by that 1:1 M-HTCO complex is formed and soluble in both NB- and W-phases. The formal potentials of the transfer of [HgHTCO]2+ and [PdHTCO]2+ complex ions at NB/W interface have been determined. Voltammograms of Cu2+ ion are of irreversible nature.
In combination with an ion pair extraction of potassium salts by dicyclohexyl-18-crown-6 (DC18C6), extraction behavior of anions with a diphenylthiourea (DPTU) from aqueous phase into nitrobenzene has been examined. The extraction selectivity of potassium salts follows a Hofmeister series: NO3->Br->Cl->OAc-. The extractability of KCl by DC18C6 is significantly enhanced upon the addition of DPTU in organic solution. The slope analysis of the extraction equilibrium reveals a 1:1 complex formation between DPTU and Cl-. The hydrogen-bonding interaction of DPTU with Cl- is confirmed by the 1H NMR analysis in d5-nitrobenzene. For qualitative evaluation, solid-liquid extraction of KCl into d5- nitrobenzene containing DPTU and DC18C6 has been examined by 1H NMR analysis. Similar to the liquid-liquid extraction, an efficient synergistic effect of DPTU for the extraction of KCl is clarified.
The separation of glycyl-leucyl-phenylalanine and its homologous was studied by reversed phase high-performance liquid chromatography. A solvatochromic interpretation (the linear solvation energy relationship and Reichardt’s ENT scale) and a non solvatochromic interpretation (Πrs factor) showed that the optimum eluent for convenient separation on a C18 stationary phase was acetonitrile/0.1 M (mol l-1) sodium citrate buffer pH 3.0, 12/88 (v/v). The retention mechanism involved appeared to be governed mainly by dipole-dipole interaction and to be influenced by the hydrogen acceptor nature of acetonitrile. In the experimental conditions, separation was only slightly influenced by the ionized status (cationic form) of the studied peptides. Finally, separation was improved by using a phenyl-bonded silica stationary phase.
Flexible hosts, 6A,6B-, 6A,6C-, and 6A,6D-bis-dansylglycine-modified β-cyclodextrins (β-1, β-2, and β-3, respectively) have been synthesized as a fluorescent chemo-sensor for organic guests including terpenoids and bile acids. Molecular sensing abilities obtained as fluorescence spectral changes of these hosts on accommodation of guests were almost twice those of γ-analogues. The sequence of binding ability of β-analogues is β-2> β-1> β-3. The molecular recognition behaviors of dansyl moieties of the title compounds are studied by induced circular dichroism (ICD), fluorescence, and absorption spectra without and with the guest. These spectral variations suggest that the appended moieties move out far from the cavity of β-cyclodextrin when host-guest complexation occurs.
The complex-formation reaction of hydroxycalix[n]arene-p-sulfonates, Hj1nn- (n=4,8; j=n/2, n=6; j=2), with various metal ions were studied while focusing on the uranyl ion, UO22+, by the pH-titration method at 25°C and μ=0.1. From the pHtitration data for Hj1nn-, the acid-dissociation constants were determined to be as follows: pKa1=3.25, pKa2=12.8 for H2144-, pKa1=3.28, pKa2=4.86 for H2166-, and pKa1=3.73, pKa2=4.39, pKa3=8.07, pKa4=10.1 for H4188-. These results indicate that the present ligands are relatively strong multi-protonic acids which release j mol of proton from one mol of ligand, Hj1nn-, having n mol of hydroxyl group in a weakly acidic-to-alkaline aqueous solution. The tetramer ligand, H2144- formed two unstable 1:2 (UO22+:ligand) complexes, [(UO22+)(146-)2(H+)]9- and [(UO22+)(146-)2]10-, and a hexamer ligand, H2166- formed four 1:1 complex species, such as [(UO22+)(168-)]6-, [(UO22+)(168-)(H+)-1]7-, [(UO22+)(168-)(H+)-2]8-, and [(UO22+)(168-)(H+)-3]9- with UO22+. Their selective reactivity to UO22+ over other various metal ions was evaluated based on their pKa values, stability constants and the compositions of the complexes including that for the octamer ligand, H4188-, for which the complex-formation reactions with various metal ions were already studied and found to form an extremely stable 2:1 complex, [(UO22+)2(1812-)(H+)-3]11-.
With a Ni ion-implanted glassy carbon electrode (GCE) as the working electrode in 0.1 mol/l HAc-NaAc (pH=4.62) solution, a sensitive reductive wave of adriamycin was obtained by linear-sweep voltammetry. The peak potential was -0.55 V (vs. SCE). The peak current was proportional to the concentration of adriamycin over the range of 5.2×10-7 - 1.0×10-5 mol/l and the detection limit was 2.7×10-7 mol/l. The behavior of the reduction wave was studied and the wave was applied to the determination of adriamycin in urine. The reduction process was quasi-reversible. AES and XPS experiments showed that Ni was surely implanted into the surface of the GCE, and the implanted Ni at the GCE improved the electrocatalytic activity.
An electrochemical impedance spectroscopy (EIS) was used for the investigation of the solvent extraction of Mn(II) across water/1,2-dichloroethane interface. The electrochemical measurement allows one to obtain direct information concerning the charge transfer rate across the interface. The electrochemical impedance showed a capacitive semicircle and Warburg impedance on the Nyquist plane. The capacitive semicircle originates from the charge transfer resistance and the interfacial capacitance. The appearance of the Warburg impedance indicates the contribution of the diffusion process to the total charge transfer rate. A theoretical expression which presents the electrochemical impedance for Mn(II) solvent extraction was derived. The solvent extraction mechanism was discussed including some results in a simulation.
A chemiluminescence (CL) sensor for vitamin K3 (menadione sodium bisulfite, MSB) combined with a flow-injection system is presented in this paper. It is based on the auto-oxidation of bisulfite liberated from MSB in alkaline media in the presence of Tween 80 sensitized by Rhodamine 6G immobilized on a cation-exchange column. The sensor responds linearly to the MSB concentration in the range of 0.5 - 10 μg/ml with a detection limit (3σ) of 2.6 μg/l. The analysis can be performed within 1 min with a relative standard deviation of <5%. The sensor is stable for over 250 determinations and has been successfully applied to the determination of MSB in injections and tablets.
A carbon paste electrode modified with copper porphyrin occluded into zeolite cavity was developed for sensing hydrazine in flow system. The sensor presented a high sensitivity and selectivity for hydrazine concentration in the flow system. The flow system was optimized by factorial design considering a two level, three factor factorial design (the factors were applied potential, sampling volume and flow rate). The sensitivity and analytical frequency were considered as the most important parameters for the system. The best condition for the system was sampling volume of 50 μl, applied potential of 270 mV vs. SCE and a flow rate of 1 ml min-1. In this optimized condition, the electrode can improve its stability, sensitivity and selectivity. The operational range was between 5 up to 60 μmol l-1, adjusted by the equation Y=1.9(±0.1)+0.20(±0.01)[hydrazine]-0.0014(±0.0001)[hydrazine]2, with a correlation coefficient of 0.9995 for n=8. The analytical frequency was about 70 determinations per hour and the system was stable for at least two months in continuous use.
A novel strategy for implementing a generalized standard addition method (GSAM) in a simple two-channel flow injection (FI) system and for correcting matrix effects and spectral interferences in multicomponent analysis is described. The FI-GSAM system exploits the concentration gradients of the sample and the standard solution, requires only one standard solution per analyte and provides several addition levels using a single simultaneous injection of the sample and of each standard solution. Because the matrix effects change at every addition level, a novel mathematical model for this FIGSAM has been derived. The method was critically evaluated for simultaneous K, Ca and Na determinations by flame photometry in synthetic samples with different ethanol or glycerol contents, added to the samples to promote matrix effects. The results show good agreement with the expected values, with the relative error and the overall relative standard deviation usually being <5% (n=5) for 2.5 - 5.0 Na, 20.0 K and 1000 mg l-1 Ca. The elapsed time for the simultaneous determination of three analytes was about 2 min, consuming 400 μl of the sample and 100 μl of each standard solution.
The chemical species produced by dissolving silica in sodium hydroxide (NaOH) and potassium hydroxide (KOH) solutions were measured by FAB-MS (fast atom bombardment mass spectrometry). As a system for a comparison, silica gel was dissolved in a sodium chloride (NaCl) solution. The pH of the NaCl solution was controlled and a NaCl solution containing silica was measured by FAB-MS. NaOH and KOH solutions contain the monomer (Si(OH)3O-; m/z=95), monomer-Na+ and K+ complexes (Si(OH)2O2Na-; m/z=117, Si(OH)2O2K-; m/z=133), dimer (Si2(OH)5O2-; m/z=173), dimer-Na+ and K+ complexes (Si2(OH)4O3Na-; m/z=195, Si2(OH)4O2K-; m/z=211), cyclic tetramer (Si4(OH)7O5-; m/z=311), linear tetramer (Si4(OH)9O4-; m/z=329) and cyclic tetramer-Na+ and K+ complexes (Si4(OH)6O6Na-; m/z=333, Si4(OH)6O6K-; m/z=349). The results for the monomer, dimer and cyclic tetramer silica observed in our study are consistent with the results of a 29-Si NMR measurement. The relative-intensity ratios of these species vary with the pH. It is notable that the production rate of the dimer is superior to those of other chemical species, such as the monomer, monomer-Na+, cyclic tetramer and linear tetramer in NaOH solution. In a KOH solution, the dimer concentration increases initially and becomes constant when the cyclic tetramer concentration starts to increase with increasing pH. In a NaCl solution, monomer-Na+ complexes (Si(OH)2O2Na-; m/z=117, Si(OH)O3Na2-; m/z=139), dimer (Si2(OH)5O2-; m/z=173), dimer-Na+ complexes (Si2(OH)4O3Na-; m/z=195, Si2(OH)3O4Na2-; m/z=217, Si2(OH)2O5Na3-; m/z=239), trimer (Si3(OH)7O3-; m/z=251), trimer-Na+ complexes (Si3(OH)6O4Na-; m/z=273, (Si3(OH)5O5Na2-; m/z=295), cyclic tetramer (Si4(OH)7O5-; m/z=311), and cyclic tetramer-Na+ complexes (Si4(OH)6O6Na-; m/z=333, Si4(OH)5O7Na2-; m/z=355) of silica are observed. NaCl solution contains monomer-Na+ (m/z=117), dimer (m/z=173), dimer-Na+ (m/z=195), cyclic tetramer (m/z=311) and cyclic tetramer-Na+ (m/z=333) complexes, which are in chemical equilibrium, and their relative intensity ratios are almost constant regardless of the pH of the solution.
A method for the determination of Cu, Zn, Fe, Ni and Cd in geological samples by flame atomic absorption spectrophotometry (FAAS) after preconcentrating by Aspergillus niger immobilized on sepiolite has been developed. The column adsorption method was used for the preconcentration studies. Effects of pH, amount of adsorbent, elution solution, flow rate and interfering ions on the recovery of the analytes have been investigated. Recoveries of Cu, Zn, Fe, Ni and Cd on Aspergillus niger immobilized sepiolite were 98.01±0.06%, 98.8±0.5%, 98.0±0.4%, 96.4±0.8% and 94.8±0.6% at 95% confidence level, respectively. The breakthrough capacity of the adsorbent was found as 0.093, 0.078, 0.067, 0.085 and 0.102 mmol/g for Cu, Zn, Fe, Ni and Cd, respectively. The proposed method was applied to the determination of trace metals in geological samples, such as AGV-1, JG-1a and Wismuterz II. Trace metals have been determined with about 5% relative error.
A batch-type chemiluminescence detection cell using a peroxyoxalate system was easily combined with capillary electrophoresis equipment; the device was operated without any tedious procedures. Peroxyoxalate reagents and hydrogen peroxide were examined in detail concerning their usage and concentration with the cell. Fluorescence-labeled α-amino acids showed the detection limits of 10 - 100 nM order (S/N=3), which were approximately 2 or 3 orders of magnitude lower than those obtained with the absorbance. A mixture sample of the labeled α-amino acids was successfully separated and detected.
A simple, rapid, highly sensitive and selective method for the extractive spectrophotometric determination of micro amounts of vanadium(V) has been worked out using 6-chloro-3-hydroxy-7-methyl-2-(2-thienyl)-4H-chromen-4-one (CHMTC) as a complexing agent in a weakly acidified (HCl, pH 0.84 - 1.09) medium. The greenish-yellow complex is quantitatively extractable into carbon tetrachloride, and shows maximum absorbance at 417 - 425 nm. The method obeys Beer’s law up to 0.9 μg V ml-1, having molar absorptivity and Sandell’s sensitivity of 8.26×104 dm3 mol-1 cm-1 and 0.0006 μg V cm-2, respectively. As many as 39 cations and 14 anions and/or complexing agents do not interfere. The method has good reproducibility and can be satisfactorily applied to the determination of vanadium in steels, reverberatory flue dust and water samples.