The redox potential of a system involving metal ions can be modified by the complexation of metal ions with a suitable ligand. By using this phenomenon, novel redox systems which are applicable to quantitative analyses of metal ions have been developed. Some potentiometric titrations of metal ions and new types of spectrophotometric determinations of metal ions and complexing agents based on the ligand effect are presented in full detail. Estimation of complexing capacity in natural water and a new kinetic-catalytic method for copper(II) are also discussed. In addition, novel potentiometric flow titration has been proposed based on the relationship of the flow rates between titrant and sample solutions.
The laser two-photon ionization of pyrene and several aromatic compounds was investigated in three hydrocarbon solvents by exciting them at 240, 266 and 299 nm using the fourth-harmonic of a Nd:YAG laser and a Raman shifter. The photoionization process consisted of one-photon and two-photon processes at 240 and 266 nm without deaeration, but was a two-photon process even at 240 nm when oxygen was removed. The two-photon ionization efficiency of pyrene was larger upon excitation at shorter wavelengths and in solvents with a larger electron mobility. However, because of large blank signals of the solvents, the detection limits of these molecules were poorer than those previously reported.
A precise method for the determination of monosaccharides is described. Monosaccharides were separated as their aminopyrazine derivatives using reversed-phase HPLC and were detected at 410 nm by a fluorescence detector with excitation at 245 nm. The 8 monosaccharides tested were completely separated in about 20 min, and the detection limits were 45 - 800 fmol. Particularly, strong fluorescence was observed for N-acetylated monosaccharide and sensitive determination could be carried out. The monosaccharide composition of several glycoproteins was also determined by reversed-phase HPLC and anion-exchange HPLC, and the results were consistent with the reported values.
The extraction of aluminium(III) with 2-methyl-8-quinolinol derivatives (HA), such as 2-methyl-8-quinolinol (HMQ), 2-methyl-5-methoxymethyl-8-quinolinol (HMO1Q), and 2-methyl-5-octyloxymethyl-8-quinolinol (HMO8Q), from a weakly acidic solution into heptane was studied in both the absence and presence of 3,5-dichlorophenol (Hdcp) as the synergist. In the absence of Hdcp, aluminium(III) was not extracted with HMQ and HMO1Q due to a steric hindrance of the methyl group at the 2-position at all, but was slightly extracted with HMO8Q. The unusual extraction behavior of aluminium(III) with HMO8Q should be ascribed to the formation of a hydrophobic aluminium(III)-HMO8Q complex. Aluminium(III) was quantitatively extracted with HA into heptane upon the addition of Hdcp. The large synergism of Hdcp was ascribed to the formation of an inner-sphere complex, Al(dcp)(A)2, in an aqueous phase and an outer-sphere complex, Al(dcp)(A)2·Hdcp, in the organic phase. The compositions of extracted aluminium(III)-HA-Hdcp were assigned to be Al(dcp)(A)2·Hdcp. The synergistic extraction constants (Kex,s = [Al(dcp)(A)2·Hdcp]org[H+]3[Al3+]-1[HA]org-2[Hdcp]org-2) for Al(dcp)(A)2·Hdcp are 10-5.75±0.12 (HMQ), 10-4.74±0.05 (HMO1Q), and 10-3.98±0.19 (HMO8Q), respectively, at I = 0.1 M (H, Na) ClO4 (1 M = 1 mol dm-3) and 25°C.
The Gibbs free energy (ΔG°tr), enthalpy (ΔH°tr), and entropy changes (ΔS°tr) for transfer of 18-crown-6 (18C6) from water to various polar nonaqueous solvents were precisely determined by solvent extraction. By using these data, and the known values of thermodynamic quantities for transfer of alkali metal ions (M+) and those for complexation in water and the nonaqueous solvents, we calculated the thermodynamic parameters of transfer of the M(18C6)+ complexes from water to the solvents from the Ph4As+/Ph4B- assumption via a thermodynamic cycle. The ΔH°tr and ΔS°tr values of the M(18C6)+ complexes vary considerably with the solvent and with the alkali metal ion, and also those of 18C6 do with the solvent. The values of ΔH°tr and ΔS°tr are all positive and large, reflecting strong hydrogen bonding between 18C6 and water. 18C6 complexes with Rb+ and Cs+ are enthalpically more stable in a given solvent than those with Na+ and K+. This shows that Na+ and K+ in the complexes are more effectively shielded by 18C6 from surrounding solvents than Rb+ and Cs+. Among all the M(18C6)+ complexes, positive ΔH°tr value from water to DMF is found only for Na(18C6)+. It is concluded from this and the other results that the Na(18C6)+ complex undergoes hydrophobic hydration more strongly than the other complexes do.
The compound 3-acryloylaminobenzanthrone (AABA) has been proposed as a fluorescent carrier for preparing an ethanol-sensitive fiber optode. For immobilizing the fluorescent carrier on a glass surface, copolymerization under UV irradiation was employed after the glass surface was silanized by introducing vinyl groups. A new monomer, 1,2-cyclohexanediol diacrylate (CDDA), was proposed as a cross-linking agent. An optode sensing membrane containing cross-linked AABA, formed after superficial solidification under UV irradiation, was mounted in a flowing system using a plastic-clad fused silica bifurcated fiber-optic bundle. The optode system is well guaranteed to prevent the fluorescent carrier from leaching, and can be utilized for an ethanol assay in a flowing mode. The analytical performance characteristics were evaluated. In an ethanol concentration range of 5 - 90% the fluorescence response obeys the Stern-Volmer equation. A preliminary application of the optode device for determining ethanol in liqueur samples shows the feasibility of using the proposed system in analytical practice.
A combination of three different simple pretreatments is useful and convenient for speciation of As by atomic absorption spectrometry in combination with hydride generation. One of the three pretreatments involves no pre-reduction of As(V) to (III) (PT1). The next one involves pre-reduction by KI (PT2), and the last one involves mineralization of organic As by K2S2O8 and NaOH (PT3) followed by PT2. Micro-wave radiation is effective in PT2 and PT3. The proposed method takes advantage of incomplete but reproducible recovery of As(V) with PT1. The recovery coefficient of As(V) in PT1, κ, is introduced. The value of κ is kept constant during each experimental run under a condition of constant NaBH4 concentration. The actual amount of each form of As is obtained by solving simultaneous equations which are derived from As amounts detectable after each of the three pretreatments. Analytical results of speciation of As for model sample solutions, containing up to 40 ppb total As, are satisfactory.
For the speciation of trace iron in rain water, the concentration (CL) of labile iron was determined by a catalytic spectrophotometric method based on the oxidation of o-phenylenediamine with hydrogen peroxide. The total concentration (CT) of iron was determined by the same method after acid decomposition to obtain the concentration (CT-CL) of non-labile iron. For the particle fraction (particle size ≥0.45 µm), 0.1 M HCl-soluble iron was determined by atomic absorption spectrometry. Coexisting humic substances were spectrofluorometrically determined as humic acid. Labile iron was found in the fraction of molecular weight (MW) <103 and estimated as FeOH2+ and Fe(OH)2+ from the chemical equilibria of hydroxo iron(III) ions. Non-labile iron was found in the particle fraction and characterized as acid-soluble iron hydroxide and humic iron aggregates as well as acid-insoluble compounds, like oxides and silicates. Labile iron was also found in the particle fraction of initial rainfall samples and characterized as iron complexed on humic iron aggregates. The above speciation results were confirmed by the analysis of synthetic samples.
Direct current polarography (DCP), differential pulse polarography (DPP) and differential pulse anodic stripping voltammetry (DPASV) have been successfully used for the simultaneous determination of trace metals in meta rhyolite rock samples. The polarograms/voltammograms of sample solutions were recorded in 0.1 M KCl, 0.1 M ammonium tartrate and 0.1 M KSCN supporting electrolyte separately. The results indicated the presence of Zn2+, Fe3+, Mn2+, Cu2+ and UO22+ metal ions. Uranium gave a well-defined polarographic wave/peak with E1/2/EP -0.26/-0.26 V vs. SCE in 0.1 M KSCN. The method of standard addition was for the quantitative analysis of trace metals, which revealed the following results: Zn2+ (22.22), Fe3+ (147.10), Mn2+ (5.50), Cu2+ (28.58) and UO22+ (0.059) mg g-1 of the sample. The observed voltammetric results were compared with those obtained using AAS. Statistical treatment of the observed voltammetric data revealed high accuracy and good precision of the determination.
A new method for determination of trace rare earth impurities in high-purity La2O3 by HPLC combined with electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) is proposed. The chromatographic retention behaviors of matrix (La) and rare earth impurities were studied using 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (P507) resin as the stationary phase and dilute nitric acid as the mobile phase. It was found that the use of EDTA as an eluent enables effective elution of rare earth impurities from a HPLC column. The influence of EDTA in ETV-ICP-AES was also discussed. The experimental results showed that a favorable separation between matrix (La) and rare earth impurities could be obtained within 30 min. The method proposed has been applied to the analysis of high-purity La2O3; the results obtained were in good agreement with those obtained by ICP-MS. Under the optimum conditions, the detection limits (DLs) for 14 rare earth elements (REEs) were in the range of 0.8 ng/ml (Yb) to 48 ng/ml (Ce). The recoveries of 14 REEs were in the range of 90% to 110%.
The peroxidase-like catalytic activity of ion-exchangers modified with some metal complexes of thiacalixarenetetrasulfonate (Me-TCAS, Me=Fe3+, Fe2+, Co2+, Mn2+, Cu2+, Zn2+ and Ni2+) was investigated based on a color reaction catalyzed by peroxidase. The ion-exchanger modified with Fe3+-TCAS showed the highest activity among the metal complexes tested, and was applied to the determination of hydrogen peroxide. The calibration curve for the ion-exchanger modified with Fe3+-TCAS was linear over the range from 10 to 100 μg of hydrogen peroxide in a 1 ml sample solution. Moreover, the method using glucose oxidase and the ion-exchanger modified with Fe3+-TCAS was applied for the determination of glucose. The ion-exchanger modified with Fe3+-TCAS may be applicable for the determination of hydrogen peroxide in place of peroxidase.
The chemical oscillating reaction of the MnSO4-KBrO3-diacetoneH2SO4 system has been studied in a continuous-flow stirred-tank reactor (CSTR), and the new characteristics of nonlinear kinetics of this oscillating system are reported. The effects of the temperature, flow rate, concentration of reactants and acidity were investigated. Two different oscillating states (bistability) were observed in this system; the transient color, waveform, potential, oscillating amplitude and period of the two states were different. A change in the solution acidity or flow rate can translate one state to the other, and the two states can exist under the same experimental conditions. Potential and spectrophotometric methods were used to track the change in the reaction intermediates, and possible mechanism of this oscillating system is proposed.