The application of deuterium-palladium electrodes in the coulometric-potentiometric determination of bases in ketone media

The application of deuterium-palladium electrodes as generator, indicator and reference electrodes for the determination of organic bases in acetone and methyl ethyl ketone has been investigated. Deuterium dissolved in palladium is oxidized at a potential that is close to the oxidation potential of hydrogen in palladium and more negative than the oxidation potentials of the bases titrated, indicator, and the solvents used. The anodic oxidation of deuterium dissolved in palladium proceeds with 100% current efficiency in the solvents investigated. The relative errors for the determination of 5 x 10(-4)M solutions of bases are less than 1%.     

Coulometric generation of H(+) and D(+) ions in aqueous media by anodic oxidation of hydrogen and deuterium dissolved in palladium

Coulometric generation of H(+) and D(+) ions in aqueous media by the oxidation of hydrogen and deuterium dissolved in palladium, is described. Hydrogen and deuterium dissolved in palladium were found to be oxidized at more negative potentials than the oxidation potentials of water and other components present. The H(+) and D(+) ions generated were used for the titration of tris(hydroxymethyl) aminomethane, piperidine, triethylamine and sodium tetraborate, the end-point being determined potentiometrically with a glass electrode and an SCE. In titrations of 0.001-0.1M solutions of the bases, the current efficiency was 100%.     

Potentiometric determination of pK(A) of organic bases in acetone by the application of coulometry

A coulometric-potentiometric method for the determination of pK(A) values of organic bases in anhydrous acetone is described. The bases were titrated with protons obtained by anodic oxidation of hydrogen dissolved in palladium, in the presence of sodium perchlorate as the supporting electrolyte. A pair of glass electrodes was used for measuring directly the difference between the half-neutralization potentials of the standard and the base being studied. The pK(A) values obtained were close to those reported in the literature. The effect of the supporting electrolyte concentration on the pK(A) values of some of the bases was also studied.     

Coulometric generation of protons by oxidation of hydrogen dissolved in palladium, in non-aqueous media

Coulometric generation of H(+) ions by the oxidation of hydrogen dissolved in palladium, in media such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetic anhydride and acetic acid-acetic anhydride mixture, for use in titration of bases, has been investigated. The hydrogen is oxidized at potentials which are much more negative than those of the bases and other components present in the solution. Titrations of numerous bases have established that the oxidation is quantitative and proceeds with 100% current efficiency.     

Determination of autoprotolysis constants of some non-aqueous solvents using coulometric titration

Autoprotolysis constants of acetonitrile, propionitrile, nitromethane, ethylene carbonate and dimethyl sulphoxide were determined using a coulometric — potentiometric method with a hydrogen/palladium electrode as generator. The method is based on the titration of a strong base, tetrabutylammonium hydroxide, with H⁺ ions generated by anodic oxidation of hydrogen dissolved in palladium. The titration was carried out in a galvanic cell with glass and calomel electrodes at 25°C. The pK_s values for the investigated solvents are: acetonitrile, 28.8; propionitrile, 24.6; nitromethane, 23.7; ethylene carbonate. 21.5; and dimethyl sulphoxide 29.1. These data are in accordance with those reported in the literature.     

Coulometric generation of H+ ions by oxidation of thiols at a platinum anode and by oxidation of mercury in acetic acid—acetic anhydride

The coulometric generation of hydrogen ions by anodic oxidation of propane-1-thiol, butane-1-thiol, 2-mercaptopropionic acid, heptane-1-thiol, 2-mercaptoethanol, methyl and ethyl thioglycollate and p-thiocresol in acetic acid—acetic anhydride (1 + 6 v/v) is described, together with the possibility of coulometric generation of protons by mercury oxidation in the presence of p-thiocresol in the same solvent system.Current-potential curves for the solvent, indicator, titrated bases, mercury and the investigated thiols showed that in acetic acid—acetic anhydride (5 + 95, v/v), mercury and the investigated thiols are oxidized at potentials which are much more negative than those of the titrated bases and other components present in the solution.Titration of potassium hydrogenphthalate and sodium acetate with protons generated by the oxidation of thiols, and of sodium acetate, lithium acetate and pyridine with protons generated by the oxidation of mercury, demonstrated that the oxidation of both thiols and mercury proceeds quantitatively with 100% current efficiency.     

Applicability of 0.05 mol kg potassium hydrogen phthalate as reference value pH standard in water–organic solvent mixtures

The applicability of 0.05 mol kg⁻¹ potassium hydrogen phthalate (KHPh(S), S=the solvent under study) as reference value pH standard (RVS) was studied in water–organic solvent mixtures. Phthalic acid in various aqueous organic solvent mixtures was titrated potentiometrically with Bu₄NOH (MeOH), using a pH-ISFET and a glass electrode as pH-sensors, and the buffer capacity of the HPh⁻ solution was roughly estimated from the difference between the first and second half-neutralization potentials. The influence of potassium ion to the buffer capacity was also studied, titrating KHPh and Et₄NHPh with CF₃SO₃H and Bu₄NOH (MeOH) and comparing the titration curves. The KHPh solution loses its buffer capacity if the solvent mixture has an aprotic property. For aqueous mixtures of protophilic aprotic solvents (e.g. DMSO and DMF), it is unsuitable as RVS if the water content is less than ca. 40 (v/v)%. The necessity of selecting subsidiary pH standard(s) is suggested for the solvent systems in which KHPh is inapplicable.     

Complexometric determination of palladium(II) using thioacetamide as a selective masking agent

A simple, rapid and accurate complexometric method for the determination of palladium(II) is proposed, based on the selective masking property of thioacetamide towards palladium(II). In the presence of diverse metal ions, palladium(II) is complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5-5.5 (acetic acid-sodium acetate buffer) with standard lead nitrate solution using xylenol orange as indicator. An excess of a 0.5% aqueous solution of thioacetamide is then added to displace EDTA from Pd(II)-EDTA complex. The released EDTA is titrated with the same standard lead nitrate solution as before. Reproducible and accurate results are obtained in the concentration range 0.5 mg - 17.80 mg of palladium with relative error of +/- 0.16% and coefficient of variation not exceeding 0.26%. The effect of diverse ions is studied. The method is used for the determination of palladium in its complexes, catalysts and synthetic alloy mixtures.     

基于电化学方法测定饮用水源水中的痕量铜离子

本文建立了一种饮用水源水中痕量溶解态铜离子（Cu²⁺）的定性和定量电化学检测方法. 该方法首先通过电化学循环伏安法于玻碳电极表面制备粒径约为70 nm的金纳米粒子（Au NPs）,然后采用方波阳极溶出伏安法进行待测水样中Cu²⁺的定性定量分析. 研究结果表明,对于标准溶液,方法的检出限为1.3μg·L^-1,线性范围在2 ~ 50μg·L^-1之间,常见重金属离子对其定性定量分析几无影响. 在此基础上,将该方法应用于福建省重要的饮用水源水--闽江中游水样中Cu²⁺的含量分析,所得测试结果与国家标准方法（石墨炉原子吸收光谱法）无显著性差异,标准偏差在20%以内. 本方法具有电极制备简单、测定成本低以及分析快速等优点,进一步优化电极制备方法以提高方法的重现性和定量准确度,将可望用于现场测定各种饮用水源水中的痕量溶解态Cu²⁺.     

示波极谱滴定的研究(ⅩⅠⅩ)——利用氨羧络合剂自身的切口示波极谱络合滴定法

本文提出利用氨羧络合剂自身的切口来指示滴定终点,对那些示波图上无切口或者切口迟顿难以直接滴定的金属进行直接滴定,为CO、Ni、Mn、Ca、Mg、Sr及稀土离子的简便滴定方法.     

Kinetic–catalytic–spectrophotometric determination of low concentrations of molybdenum in white wines

The paper describes the determination of the molybdenum content in white wines based on its catalytical action on the kalium iodide oxidation by hydrogen peroxide in acid medium.

The optimum reaction conditions (the catalyst, KI and H₂O₂ concentrations, the pH value, the order of the reagent additions, the temperature) have been found by studying the effect of the reaction variables.

The influence of some metallic ions (Ca²⁺, Mg²⁺, Zn²⁺, Cd²⁺, Fe²⁺ and Fe³⁺) and complexing anions (F⁻, C₂O²⁻₄, EDTA⁴⁻) on the catalyzed reaction rate was elucidated.

The molybdenum concentration was estimated by the tangent, fixed-time and fixed-absorbance method. The obtained average values for molybdenum content in white wines are within the 1.77×10⁻⁷–1.83×10⁻⁷ mol l⁻¹ range.     

Gas phase hydrogen deuterium exchange reactions of a model peptide: FT-ICR and computational analyses of metal induced conformational mutations

We utilized gas phase hydrogen/deuterium (H/D) exchange reactions and ab initio calculations to investigate the complexation between a model peptide (Arg-Gly-AspRGD) with various alkali metal ions. The peptide conformation is drastically altered upon alkali metal ion complexation. The associated conformational changes depend on both the number and type of complexing alkali metal ions. Sodium has a smaller ionic diameter and prefers a multidentate interaction that involves all three amino acids of the peptide. Conversely, potassium and cesium form different types of complexes with the RGD. The [RGD + 2Cs − H]⁺ species exhibit the slowest H/D exchange reactivity (reaction rate constant of 6 × 10⁻¹³ cm³molecule⁻¹s⁻¹ for the fastest exchanging labile hydrogen with ND₃). The reaction rate constant of the protonated RGD is two orders of magnitude faster than that of the [RGD + 2Cs − H]⁺. Addition of the first cesium to the RGD reduces the H/D exchange reaction rate constant (i.e., D₀) by a factor of seven whereas sodium reduces this value by a factor of thirty. Conversely, addition of the second alkali metal ions has the opposite effect; the rate of D₀ disappearance for all [RGD + 2Met − H]⁺ species (MetNa, K, and Cs) decreases with the alkali metal ion size.     

Coulometric generation of acetylions by oxidation of mercury in acetic anhydride and in acetic acid/acetic anhydride mixture

Coulometric generation of acetyl (CH₃CO⁺) ions by oxidation of mercury in acetic anhydride and in acetic acid/acetic anhydride (5:95, v/v) is described. Current/potential curves for solvents, titrated bases, indicator and mercury showed that in both these solvents mercury is oxidized at potentials which are much more negative than those for the titrated bases and other components present in the solution. Quinoline, triethanolamine, triethylamine, pyridine and quinolin-8-ol in acetic anhydride, as well as triethylamine, 2,2′-bipyridine, 2,4,6-collidine, pyridine and sodium acetate in acetic acid/acetic anhydride were titrated with acetyl ions generated by the oxidation of mercury. In this way, it was established that the oxidation of mercury to mercury (I) ions proceeds quantitatively with 100% current efficiency.     

Coulometric generation of H+ ions by anodic oxidation of esters of gallic acid,phenols and ascorbic acid in propylene carbonate

The application of esters of gallic acid (methyl, ethyl, propyl, butyl, octyl and dodecyl gallate), phenols (pyrocatechol and pyrogallol) and ascorbic acid for the coulometric generation of H⁺ ions in propylene carbonate, is described. The current-potential curves recorded for these depolarizers, titrated bases, indicator and the solvent used showed that the investigated depolarizers are oxidized at lower potentials than the oxidation potentials of other components in the solution H⁺ ions formed by the oxidation of these depolarizers were used for the titration of organic bases (pyridine, piperidine and quinoline) with visual and potentiometric end-point detection. The current efficiency was 100%.     

Determination of palladium(II) using thiosemicarbazide as a replacing reagent

A simple, rapid, accurate, and selective complexometric method is proposed for the determination of palladium(II). Palladium(II), with associated diverse metal ions, is first complexed by adding a known excess of EDTA, and the uncomplexed EDTA is back titrated with lead nitrate solution in acetic acid-sodium acetate buffer (pH 5.0–6.0) until the end-point. Thiosemicarbazide (1%) solution in water is added to displace EDTA from the Pd-EDTA complex. The released EDTA is then titrated with the lead nitrate solution. Reproducible and accurate results are obtained in the concentration range of 1–10 mg of palladium with a relative error of less than 0.4% and a standard deviation of less than 0.02. The interference of many commonly associated metal ions was also studied. Advantages of this method over other complexometric methods of palladium determination are high-lighted.     

示波极谱滴定研究(Ⅸ)——四苯硼钠滴定钾

提出了一个用四苯硼钠在交流示波极谱图上的切口来指示终点的测定常量钾的容量方法。方法快速、准确,干扰很少。     

Extraction and spectrophotometric determination of trace amount of Pd(II) with 2,2'-dithiodianiline

A method for the extraction-spectrophotometric determination of palladium with 2,2′-dithiodianilline (DTDA) is described. DTDA–Pd(II) complex is extracted from an aqueous solution with pH 3 into isobutyl methyl ketone (IBMK) layer. The absorbance is measured at 397 nm and the molar absorptivity found to be 1.47×10⁶ l mol⁻¹ cm⁻¹. The complex system conforms to Beer's law over the range 0.3–220 ng ml⁻¹ palladium (II). The effect of pH (1–6), NaClO₄ concentration, DTDA concentration and shaking time were studied. The ratio of the metal ion to ligand molecules in the complex and its stability constant were found to be 1:1 and 1.45×10⁶, respectively. The tolerance limit for many cations and anions have been determined. Finally the method has been applied successfully to the determination of palladium in synthetic mixtures, alloy and catalyst samples.     

Formation of doubly charged atomic ions in the inductively coupled plasma

Experimental and theoretical studies dealing with the formation efficiency of M²⁺ ions, which reduce the analytical signal of M⁺ ions and cause spectral interferences in the inductively coupled plasma mass spectrometry (ICP-MS), have been discussed. Inconsistencies in the results have been pointed out and goals have been formulated for further investigations necessary to correct those spectral interferences. The range of elements that form most readily M²⁺ ions has been determined. Partition functions and reduced thermodynamic potentials of atoms, M⁺ and M²⁺ ions of elements with the lowest second ionization potentials have been calculated. The Saha equation and the thermodynamic simulation were used to calculate the formation efficiency of M⁺ and M²⁺ ions for a selected group of elements in ICP. The results have been compared with experimental and theoretical data available in the literature. The accuracy of the calculations and their applicability to the prediction of the formation efficiency of M⁺ and M²⁺ ions in ICP and other spectral sources has been demonstrated. The main factors responsible for the disagreement between experimental and theoretical values of the formation efficiency of M⁺ and M²⁺ ions have been determined.     

Lead ion selective PVC membrane electrode based on 5,5'-dithiobis-(2-nitrobenzoic acid)

A PVC membrane electrode for lead ions based on 5,5′-dithiobis-(2-nitrobenzoic acid) as membrane carrier was prepared. The electrode exhibits a Nernstian response for Pb²⁺ over a wide concentration range (1.0×10⁻²–4.0×10⁻⁶ M). It has a relatively fast response time and can be used for at least 3 months without any divergence in potentials. The proposed electrode revealed good selectivities for Pb²⁺ over a wide variety of other metal ions and could be used in a pH range of 2.0–7.0. It was used as an indicator electrode in potentiometric titration of lead ions and in direct determination of lead in water samples.     

PHOTOCHEMISTRY OF REDUCED LUMIFLAVIN IN ITS ACIDIC FORM

Abstract— The photooxidation of reduced lumiflavin in its acidic form, LfH 3 ⁺, takes place in two consecutive steps. Upon illumination of LfH 3 ⁺ in its absorption band at 313 nm the semiquinone, LfH 3 ⁺, is formed. Two LfH 2 ⁺ ions are consumed for every LfH 2 ⁺ formed. Illumination of the semiquinone in its absorption band at 495 nm causes further oxidation so that the oxidized LfH⁺ ion is formed. In this reaction one LfH 3 ⁺ ion is photolyzed for every LfH⁺ formed. In addition, a hydrogen atom is released in the photooxidation of LfH 2 ⁺. Mechanisms for the two photoreactions are proposed.