In a weak acid medium, protein reacts with a monoazo dye of chromotropic acid, such as Chromazol KS (CALKS), Acid Chrome Dark Blue (ACDB), Chrome Blue SE (CBSE), Acid Chrome Blue K (ACBK), Chlorophosphonazo I (CPAI), Arsennazo I (AAI) and Chromotrope 2R (CT2R), to form a combination product. This results in a significant enhancement of the resonance Rayleigh-scattering (RRS) intensity, and the corresponding RRS spectrum appears. The characteristics of the RRS spectra of the combination products and the optimum conditions for the reactions were investigated. The intensity of RRS is directly proportional to the concentration of protein in a certain range. The RRS methods have high sensitivity for the determination of protein, the detection limits for bovine serum albumin (BSA) are 10.0 - 30.2 ng/ml, and the sensitivity order is CALKS > AAI ≈ CPAI > ACBK ≈ CT2R > ACDB > CBSE. The selectivity for CALKS has been examined, and the method was applied to the determination of a µg amount of protein in a synthetic sample with satisfactory results.
In pH 0.6 - 2.0 HCl-sodium acetate buffer solution, proteins react with an acidic monoazo dye such as Orange G, Methyl Orange, Methyl Red and Orange IV to form a combination product. This results in a significant enhancement of resonance Rayleigh scattering (RRS) and a new RRS spectrum appears. Owing to the fact that Orange G-protein system is the most sensitive, it was taken as an example to study. The RRS spectral characteristics of its combination product and the optimum condition for the reaction were investigated. The intensity of RRS is directly proportional to the concentration of protein in the range of 0 - 5.0 µg/mL. The method has high sensitivity; its detection limits are 2.6 ng/mL for BSA, 3.4 ng/mL for HAS and 7.1 ng/mL for α-chymotrypsin, respectively. A new method for the determination of trace amounts of proteins on the basis of RRS spectra has been developed.
The use of derivative UV-spectrophotometry is proposed for the simultaneous quantification of promazine hydrochloride in the presence of sulfoxide, and vice versa. For this purpose, mathematical parameters were established for generating derivative spectra of analytes. The determination of promazine was made using the first-order derivative (Δλ = 10 nm, second polynomial degree) at 268 nm. The quantification of sulfoxide was achieved by applying third-derivative spectra (Δλ = 14 nm, sixth polynomial degree) based on measurements of the amplitude at 342 - 344 nm. An elaborated method was successfully used to determine analytes in commercial promazine pharmaceuticals. The obtained results agreed well with those obtained by the HPLC method.
A kinetic flow-injection (FI) method is described for the determination of hydrogen peroxide. This method is based on an iron(III)-catalyzed oxidative coupling of 4-aminoantipyrine with N,N-dimethylaniline by hydrogen peroxide. By measuring the change in the absorbance of the dye formed at 560 nm, 1 × 10-6 - 6 × 10-4 M hydrogen peroxide could be determined with a sampling rate of 15 h-1. The relative standard deviation (n = 30) was 0.8% for 5 × 10-5 M hydrogen peroxide. There was little interference of the co-existing ions and compounds. After introducing some immobilized enzyme reactors to the FI system, the proposed method allowed the determination of glucose and uric acid ranging from 1 × 10-6 to 6 × 10-4 M with relative standard deviations of below 2%. The applicability of the method was demonstrated by determining these substances in serum samples.
Nickel hexacyanoferrate (NiHCF) film was prepared and characterized on gold and thiol self-assembled monolayers (SAMs)-modified gold electrodes. It was found that the film exhibited some different electrochemical characteristics compared with that found on a carbon electrode. In the presence of K+, the film exhibited a redox peak at about 0.5 V. The peak potential shifted linearly with the K+ concentration over the range of about 0.1 mM - 0.1 M with slopes of 54 - 60 mV per log[K+]. However, in solutions containing Na+, Li+ or NH4+ ion the film did not generate well-defined peaks, or even a visible redox peak. Therefore, the film showed a selective potential response to K+. The voltammetric behavior of NiHCF film varied with thiols, the preparation procedure and the solution pH. Under certain conditions, the characteristics of the film could be improved to some extent.
An electrochemical quartz crystal impedance system (EQCIS) was used to study the resonance behavior of an AT-cut 9-MHz piezoelectric quartz crystal (PQC) with its Au electrode partially immersed in KCl, Na2SO4 and NaClO4 aqueous solutions, respectively. An in situ determination of the immersed area and the height of the electrode was achieved by simultaneous measurements of the PQC electroacoustic admittance and the electrochemical impedance. The rising of the solution meniscus for a gold electrode partially immersed in aqueous solutions was found at oxygen reduction potentials and evaluated versus the electrolyte, electrolyte concentration, solution pH and oxygen concentration. The solution meniscus rising was explained based on a lowering of the contact-angle hysteresis and a continued collection of the water product at the solid-gas-solution interface during oxygen reduction.
Horseradish peroxidase was incorporated in a kieselguhr membrane. The electron-transfer process of the enzyme was examined by cyclic voltammetry. It was observed that the electron-transfer reactivity of horseradish peroxidase was greatly enhanced, and that direct electrochemistry was accordingly feasible. Using the merits of the direct electron-transfer reactivity of horseradish peroxidase and its specific enzymatic catalysis towards hydrogen peroxide, an unmediated hydrogen peroxide biosensor was constructed. The calibration plot of this hydrogen peroxide sensor was linear in the range of 2.0 × 10-6 mol/L - 6.5 × 10-4 mol/L. The relative standard deviation was 4.1% for 6 successive determinations at a concentration of 1.0 × 10-4 mol/L. The detection limit was 1.0 × 10-6 mol/L.
A definitive method is described for the indirect assay of milligram quantities of D(+)-glucose by coulometric titration. D(+)-Glucose was aerobically oxidized by glucose oxidase in an acetate buffer solution (pH 5.1). Subsequently, the enzymatically formed hydrogen peroxide was titrated coulometrically with electrogenerated hypobromite in sodium bromide-sodium tetraborate medium of pH 8.6, with biamperometric end-point detection. Parameters affecting the enzymatically catalyzed oxidation and coulometric titration were evaluated. The optimized conditions for the oxidation of up to 20 mg of D(+)-glucose include the addition of 4500 U of glucose oxidase and stirring over a 10-min interval at 25°C. Under proposed conditions, the assay values of several commercial D(+)-glucose reagents were somewhat lower than the guaranteed minimum values, with RSDs (n = 5) of 0.071 - 0.106%.
The change in composition of the surface layer of β-Si3N4 whiskers was examined after heat treatment in atmosphere. At 873 K, the β-Si3N4 whisker was barely oxidized. At 1273 K, the oxidation of the surface layers of the whisker occurred easily. With the β-Si3N4 oxidation, the Si-N bond gradually changed into the Si-N-O bond, and finally became the oxidized layer (amorphous layer) of the whisker surface. It was assumed that the whisker surface has a gradient interface structure which gradually changes from the oxide layer of the whisker’s outer surface to the nitride crystal of the inside layer. It was confirmed that impurity elements such as Y and Ca existed mainly in the amorphous region near the interface between the amorphous layer and the crystal layer.
Tributylphosphine oxide (TBPO) is proposed as an extractant for the extraction of lead(II) and copper(II) from salicylate media. The optimum conditions were evaluated by varying the experimental parameters, such as the pH, sodium salicylate concentration, tributylphosphine oxide (TBPO) concentration, shaking period and various diluents. The probable extracted species, deduced from log-log plots were Pb(HSal)2·2TBPO and Cu(HSal)2·2TBPO. The extraction took place through a solvation mechanism. The method permits the binary separation of lead(II) and copper(II) from commonly associated elements as well as the mutual separation of lead(II) and copper(II). The method is applicable to the determination of lead(II) and copper(II) in various alloys as well as environmental and pharmaceutical samples.
Extraction of 2-(2-pyridylazo)-1-naphthol-4-sulfonate anion with solvated hydroxonium ion was carried out using 14 kinds of alcohols and 1-octanol/octane mixed solvents as a solvent at 25°C. Alcohols are 1-pentanol, 1-hexanol, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1-octanol, 2-octanol, 3-octanol, 1-nonanol, 2-nonanol, 3-nonanol, 5-nonanol and 1-decanol. Among them, 1-octanol was found to be extremely high in extractability for 2-(2-pyridylazo)-1-naphthol-4-sulfonate anion with hydroxonium cation. The extraction equilibrium for the systems using 1-octanol/octane mixed solvents was analyzed in detail in order to examine the extraction mechanism for these extraction systems. 2-(2-Pyridylazo)-1-naphthol-4-sulfonate anion was found to be extracted with the hydroxonium ion solvated by three 1-octanol molecules as an ion-pair. The extraction and partition constants of the ion-pair of 2-(2-pyridylazo)-1-naphthol-4-sulfonate anion with solvated hydroxonium ion were estimated in the 1-octanol/octane mixed solvent systems.
The extraction behaviors of bismuth(III) with carboxylic acid (HL), which have not yet been clearly elucidated, because of the precipitation of hydroxide, were studied using the 2-bromoalkanoic acid in benzene and in hexane systems under aqueous conditions of high acidity at I = 1.0 M ((H,Li)NO3). The extraction equilibria were analyzed based on the initial concentration of nitric acid and the concentration of bismuth(III) extracted in the organic phase. The extracted species and the logarithmic values of the extraction constant (log Kex) were found to be a single species of BiL3(HL)3 for the systems of 2-bromooctanoic acid/benzene (log Kex = -1.66) and 2-bromohexadecanoic acid/benzene (-1.58), and to be two species of BiL3(HL)4 (-1.01) and Bi3L9HL (-1.62) for the system of 2-bromooctanoic acid/hexane, where the monomer was dominant at a higher reagent concentration.
As an attempt to elucidate the factor(s) responsible for the poor performance of a copper(II)-phthalocyanine aminopropyl-silica gels (Cu-PCSD) column for HPLC, the silanol and/or amino groups remaining on Cu-PCSD were endcapped with trimethylchlorosilane (TMCS) or N-trimethylsilylimidazole (TMSI). The trimethylsilylated Cu-PCSDs (Cu-PCSD-TMCS and -TMSI) were investigated concerning their performance as an HPLC-stationary phase in the separation of π-electron-rich polyaromatic hydrocarbons (PAHs), such as mutagenic anthracene and pyrene. As a result, trimethylsilylation with TMSI, which reacts only with silanol-groups, was not effective to improve the column efficiency. In contrast, trimethylsilylation by TMCS, which reacts with both the silanol- and amino-groups, improved the theoretical plate numbers (N) for PAHs separation with the Cu-PCSD column, indicating that the low N values on the Cu-PCSD column were caused by electrostatic interactions between PAHs and the remaining amino-groups on Cu-PCSD. Furthermore, the retention data of mutagenic heterocyclic amines (HCAs) indicated that the remaining amino groups interact with the polar groups of HCAs.
A spectral mapping technique (SPM) was employed for separating the strength and selectivity of the retention of 41 barbituric acid derivatives and 5 organic modifiers on a porous graphitized carbon column (PGC). The potency values calculated by SPM were considered to be indicators of the capacity of drugs to bind to the surface of PGC and the capacity of organic modifiers to remove the drugs from the surface. The dimensionality of the multidimensional selectivity maps was reduced to two by a nonlinear mapping technique. Calculations indicated that molecular lipophilicity plays a negligible role in the strength and selectivity of retention, proving that the retention mechanism of PGC deviates from those of traditional reversed-phase stationary phases. Sterical and electronic parameters exerted the highest influence on the retention, emphasizing the importance of the polar interaction and the sterical correspondence between the surface of PGC and the solute molecules.
In a radio-frequency-powered glow discharge lamp, a d.c. bias current which is driven by a self-bias voltage can lead to an enhancement of the emission intensities excited by the plasma. The driving frequency of the r.f. plasma is an important parameter to determine the self-bias voltage; lower r.f. frequencies induce greater self-bias voltages. The effects of the bias current introduction on the emission characteristics were compared between a 13.56-MHz plasma and a 6.78-MHz plasma. As a result, the 6.78-MHz plasma offered a better analytical performance, probably due to higher self-bias voltages, if the introduced Ar pressure was optimized. This method was applied to a Mo determination in Fe-matrix alloy samples. At bias currents of 40 - 50 mA, the emission intensities of the Mo I 379.82-nm line were about 10-times larger than those obtained with the conventional plasma when the 6.78-MHz plasma was produced at an r.f. power of 60 W. The detection limit obtained for this calibration was 2.0 × 10-4 mass % Mo at an 80-W r.f. power and at a d.c. bias current of 68 mA.
In order to increase the predictive ability of the PLS (Partial Least Squares) model, we have developed a new algorithm, by which uninformative samples which cannot contribute to the model very much are eliminated from a calibration data set. In the proposed algorithm, uninformative wavelength (or independent) variables are eliminated at the first stage by using the modified UVE (Uninformative Variable Elimination)-PLS method that we reported previously. Then, if the prediction error of the ith (1 ≤ i ≤ n) sample is larger than 3σ, the corresponding sample is eliminated as uninformative, where n is the total number of calibration samples and σ is the standard deviation calculated from the other n-1 samples. Calculation of σ by the leave-one-out manner enhances the ability to identify the uninformative samples. The final PLS model is constructed precisely because both uninformative wavelength variables and uninformative samples are eliminated. In order to demonstrate the usefulness of the algorithm, we have applied it to two kinds of mid-infrared spectral data sets.
Individual solvation numbers around the nickel(II) ion have been determined by titration Raman spectroscopy in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) mixtures at 298 K. The in-plane bending vibration (δ(O=C-N)) of DMF and the stretching vibration (ν(N-CH3)) of DMA were used in the present analysis. These Raman bands of solvent molecules shift to higher frequencies upon coordination of the solvent molecules to the metal ion. By analyzing the band intensities of free and bound solvent molecules with increasing concentration of the metal ion, the solvation number around the metal ion can be evaluated. Because the individual solvation numbers of DMF and DMA around the nickel(II) ion in the mixture are determined independently, the total solvation number is obtained as their sum. It was found that the total solvation number remains 6 in all mixtures of the DMA mole fraction x = 0 - 1. Although DMF and DMA have practically the same electron-pair donor capacities, the nickel(II) ion prefers DMF to DMA, and an equal solvation number is attained at x = 0.75. This is ascribed to the solvation steric effect of DMA.
α-Benzilmonoxime has been used for the extraction and determination of cobalt at microgram amount. The reagent reacts with cobalt(II) in the pH range of 8.8 - 9.3 to form a yellow-color chelate, which is extracted in chloroform, toluene, and some other non-polar solvents. The chelate is stable in chloroform for about one day. Under the optimum conditions of the α-benzilmonoxime concentration and pH of 9.0, Beer’s law was obeyed in the concentration range of 0.08 - 2.2 µg/ml cobalt. The molar absorptivity of the extracted species was 2.55 × 104 dm3/mol cm at 380 nm, with a detection limit of 0.01 µg/ml cobalt. Relative standard deviations of 0.4, 0.8 and 2.3% were found for the determination of cobalt concentrations of 2.2, 1.1 and 0.08 µg/ml, respectively. The effect of diverse ions on the determination of 1.00 µg/ml of cobalt has been studied. The method was applied to the determination of cobalt in vitamin B12 and B-complex ampoules, a Co2O3-Co3O4 laboratory chemical mixture and some synthetic alloy samples. The method is sensitive, simple, rapid and accurate.
Iodometry is one of the easiest, most rapid and accurate methods for the determination of a relatively small amount of oxidizing agent, such as residual chlorine. Starch has long been used as a useful color indicator in iodometry. However, we found that PVA (polyvinyl alcohol with partially saponificated; e.g., saponification degree of 88%) is a more useful color indicator than starch. For example, at 20°C, the PVA indicator gave similar profiles of iodine concentration vs. titration efficiencies (percent recoveries) to those of starch at 0°C. At 0°C, the PVA indicator detected 1.1 mg I2/L (11 µg I2: with 10 mL sample volume) with a high percentage of recovery ( = 95%). Furthermore, at 20°C an iodine concentration of 0.36 mg/L (which corresponds to a residual chlorine concentration of 0.1 mg Cl2/L) could be detected using PVA color indicator assuming an appropriate correction.
It has been confirmed from circular dichroism (CD) spectral changes of aqueous solutions of ΔLLL-fac(S)-[Co-(L-cys-N,S)3]3- that the absolute configurational inversion to the ΛLLL isomer is remarkably accelerated by zinc(II), while it is retarded by cadmium(II). In the diluted solutions of these metal ions containing excess ΔLLL-fac(S)-[Co(L-cys-N,S)3]3-, the observed inversion rate constant linearly depends on the zinc(II) concentration with an intercept, while it is not affected by the cadmium(II) concentration. The kinetic behavior has been explained by difference between zinc(II)- and cadmium(II)-interactions with lone pairs on sulfur donor atoms of fac(S)-[Co(L-cys-N,S)3]3-. It has also been proposed that concentrations of zinc(II) and cadmium(II) can be simultaneously determined by the kinetic measurements.