Influence of the average content of sulfur in polysulfide polymers on the depolymerization of polysulfide polymers by dithionite ions

The results of our studies show that it is possible to depolymerize polysulfide polymers with a nominal sulfur content in excess of 2 per segment of polymer, without previous desulfurization, in order to obtain disulfide polymers. For this purpose it is necessary to take larger amounts of sodium dithionite per segment of polymer, than with a disulfide polymer, to obtain approximately the same of the average molecular weight of the depolymerized product. It is also possible to complete depolymerization with an amount below 2 moles of sodium hydroxide per mole of sodium dithionite, though the upper limit of the ratio of Na₂S₂O₄ to NaOH, at which depolymerization occurs, remains unchanged, i.e., 1:4. During the depolymerization reaction the occurrence of larger or smaller amounts of hydrosulfide, depending on the labile sulfur content, as well as the change of the color of the reaction dispersion, first white, then bright yellow or gray, thereafter white again and, finally, dingy pink, was observed. The reaction, representing in the best way the optimum conditions of depolymerization and the actual relations in the reaction system, is proposed.     

Spectrophotometric determination of microamounts of mercury(II) and sulfide ions in aqueous solution

Ammonium (2′,3′-dihydroxy pyridyl-4′-azo)benzene-4-arsonate (DHP-4A) provides a simple, rapid, and sensitive spectrophotometric microdetermination of mercury(II) in aqueous solution. The magenta colored 1:2 metal to ligand complex formed has a molecular extinction coefficient 6.25 × 10⁴ liters mol^?1 cm^?1 at the maximum absorption of 535 nm in highly alkaline medium. Beer's law is obeyed up to 3.8 ppm and Sandell's sensitivity (for an absorbance of 0.001) is 0.0032 μg of mercury(II)/cm². The mercury(II) complexed with DHP-4A has also been used in microdetermination of sulfide ions using ligand exchange reaction. The optimum concentration range of sulfide ions which can reproducibly be determined is 0.16-5.05 μg/10 ml and sensitivity of sulfide ions determination (for an absorbance 0.001) is 7.3 × 10^?4 μg/cm².     

Electrochemical determination of sulfide and sulfite ions by pneumatoamperometry

Sulfide and sulfite ions in aqueous solution are converted through acidification to hydrogen sulfide and sulfur dioxide, which are purged from solution with nitrogen carrier gas. The volatile species are detected through oxidation in 1 M sulfuric acid at an anodically polarized platinum electrode separated from the gas stream by a gas-permeable polymer membrane. Mixtures of sulfide and sulfite are separated and determined independently through pH control during acidification. Interferences from metal ions, which form sulfide precipitates, and other anions, which form volatile species on acidification, are discussed.     

XAFS analysis of coprecipitation of zinc by sulfide ions in an acidic solution

The fluorescence XAFS (X–ray absorption fine structure) technique using synchrotron radiation was applied to characterize zinc in the Hg–Zn, Cd–Zn, and Bi–Zn coprecipitates, and to elucidate the reaction mechanism of the coprecipitation of zinc from a strong acidic solution. Hg L_II–, Cd K–, and Bi L_III–edge XAFS spectra suggested that the respective host materials of the coprecipitates listed above are metacinnabar (HgS), greenockite (CdS), and bismuthinite (Bi₂S₃) and that existence of zinc has not affected the local structure of the host metal sulfides in each system. On the other hand, the Zn K–edge XAFS spectra of each coprecipitate indicated that the chemical forms of zinc compounds are controlled by the crystal structure of the host sulfides.The shapes of the Zn K–XAFS spectra of the Hg–Zn and Cd–Zn coprecipitates showed a strong resemblance to those of crystalline standards ZnS, wurtzite and spharelite. It was suggested that the two coprecipitated phases (HgS, ZnS) and (CdS, ZnS) may form a solid solution in the Hg–Zn and Cd–Zn coprecipitates. The local structure around the zinc(II) ion in the Bi–Zn coprecipitate is the same as that around hexaaqua–zinc(II) ions, and adsorption of soluble ions or mechanical occlusion from the mother liquor is regarded as a driving force of coprecipitation in the Bi–Zn system.     

Kinetic determination of selenium using the reduction of nile blue with sulfide ions

The catalytic effect of Se(IV) was first observed in the reaction of the reduction of Nile Blue with sulfide ions. Optimal conditions for the determination of selenium by this reaction were found. The dependence of the reaction rate on the concentration of Se(IV) was linear in the concentration range 0.008-0.16 μg/mL. Solvent extraction with dithiophosphoric acids was proposed for the separation of selenium from the interferents. A procedure for the extraction-kinetic determination of selenium with the detection limit 0.006 μg/mL was developed.     

A microcalorimetric study of the association of hexacyanoferrate(II) ions with calcium and magnesium ions in aqueous solution

Using flow microcalorimetry, the ion association reaction M²⁺(aq)+Fe(CN) ₆ ^4– (aq)=MFe(CN) ₆ ^2– (aq) (M=Ca, Mg) has been studied at 25°C over the ionic strength range 0.02 to 0.08 mol-dm^–3. Analyses of the data to obtain H^o, the enthalpy change at infinite dilution, are described. The value obtained for H^o is sensitive to the kind of functions used to correct for non-ideal behavior.     

Spectrophotometric determination of cyanide ions through ligand exchange reaction in solution

Summary A simple spectrophotometric method for the determination of trace amounts of cyanide ions in aqueous medium, using a heterocyclic azo dye complexed with mercury(II) for the first time, is described. The visual comparative method has been used in which a stronger complexing anion displaces a coloured reagent from the metal-ligand complex. Ammonium (2-amino-3-hydroxy-pyridyl-4 azo)benzene-4-arsonate (AHP-4A) complexed with mercury(II) has been used for the determination of 0.13–1.46g/ml of cyanide ions with fair accuracy. The anion has also been determined, when cyanide ion reacts with mercury(II)-(AHP-4A) complex, probably forming a bridged complex. The increase in absorbance is proportional to the cyanide ion concentration in the range of 0.04–0.37g/ml, but this method is not very precise. The effect of foreign ions has also been studied. The sensitivities of other mercury(II) complexes in the determination of cyanide ions have been compared.

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Zusammenfassung Eine spektrophotometrische Methode zur Bestimmung von Spuren Cyanid in wäßrigem Milieu mit Hilfe eines mit Hg(II) komplexierten heterocyklischen Azofarbstoffes wurde beschrieben. Hierbei verdrängt ein stärker komplexierendes Anion das Farbreagens aus dem Metallkomplex. Ammonium(2-amino-3-hydroxypyridyl-4-azo)benzol-4-arsenat (AHP-4A) in komplexer Verbindung mit Hg(II) wurde für die genaue Bestimmung von 0,13–1,46g CN^–/ml verwendet. Das Anion wurde auch nach der Reaktion von Cyanid mit Hg(II)-(AHP-4A)-Komplex (wahrscheinlich zu einer Brückenverbindung) bestimmt. Der Anstieg der Extinktion ist der Cyanidkonzentration im Gebiet 0,04–0,37g/ml proportional, aber dieses Verfahren ist nicht sehr genau. Der Einfluß von Fremdionen wurde untersucht. Die Empfindlichkeit anderer Hg(II)-Komplexe wurde zum Vergleich herangezogen.

     

Development of new analytical methods for the determination of caffeine content in aqueous solution of green coffee beans

Background

This study was conducted to develop fast and cost effective methods for the determination of caffeine in green coffee beans. In the present work direct determination of caffeine in aqueous solution of green coffee bean was performed using FT-IR-ATR and fluorescence spectrophotometry. Caffeine was also directly determined in dimethylformamide solution using NIR spectroscopy with univariate calibration technique.

Results

The percentage of caffeine for the same sample of green coffee beans was determined using the three newly developed methods. The caffeine content of the green coffee beans was found to be 1.52 ± 0.09 (% w/w) using FT-IR-ATR, 1.50 ± 0.14 (% w/w) using NIR and 1.50 ± 0.05 (% w/w) using fluorescence spectroscopy. The means of the three methods were compared by applying one way analysis of variance and at p = 0.05 significance level the means were not significantly different. The percentage of caffeine in the same sample of green coffee bean was also determined by using the literature reported UV/Vis spectrophotometric method for comparison and found to be 1.40 ± 0.02 (% w/w).

Conclusion

New simple, rapid and inexpensive methods were developed for direct determination of caffeine content in aqueous solution of green coffee beans using FT-IR-ATR and fluorescence spectrophotometries. NIR spectrophotometry can also be used as alternative choice of caffeine determination using reduced amount of organic solvent (dimethylformamide) and univariate calibration technique. These analytical methods may therefore, be recommended for the rapid, simple, safe and cost effective determination of caffeine in green coffee beans.

     

油菜蜂花粉浸取液中黄酮含量的电导滴定测定

采用电导滴定法对芦丁标样及对花粉浸取液中黄酮进行了测定并与分光光度法进行比较,相对标准偏差小于5％,加标回收率94％～105％。     

Infrared determination of calcium or lithium nitrate in acetone solution determination of calcium or lithium in the presence of strontium or barium

A method is proposed for the infrared determination of calcium or lithium in the presence of strontium or barium. A mixture of the nitrates is treated with acetone which dissolves only the calcium or lithium nitrate. The strontium or barium nitrate is filtered off. The nitrate is evaporated to about 2 ml with a stream of dry air and then diluted to 5 ml with acetone. The infrared spectrum is scanned from 860 to 800 cm(-1) and the nitrate peak at 824 cm(-1) for calcium and 827 cm(-1) for lithium is measured. The recommended range is 1-80 mg of calcium or lithium nitrate in the presence of up to about 200 mg of strontium or barium nitrate.     

The thermodynamic characteristics of complex formation between calcium ions and L-leucine in aqueous solution

Complex formation of L-leucine with calcium ions in aqueous solution was studied by potentiometric titration at 298.15 K and ionic strength values I = 0.5, 1.0, and 1.5 (KNO₃). The formation of the CaL⁺ and CaHL²⁺ complex particles was established and their stability constants were determined. The enthalpies of protolytic equilibria of leucine and formation of calcium ion complexes with leucine were determined calorimetrically at 298.15 K and I = 0.5 (KNO₃). The thermodynamic characteristics of complex formation between calcium ions and L-leucine were calculated.     

Biogenic synthesis of calcium oxalate crystal by reaction of calcium ions with spinach lixivium

In this paper, we report a biogenic synthesis protocol for preparation of calcium oxalate (CaC₂O₄, CaOx) crystal at room temperature by a simple protein-mediated reaction of aqueous Ca²⁺ ions with the C₂O₄²⁻ ions spontaneously released from spinach. The aggregation of calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) with a rod-like morphology was mainly formed in the spinach root lixivium, and the proportion of COM crystal in the aggregation increased with the concentration of Ca²⁺ ions increasing, however, spindle-shaped crystal was mainly obtained in the spinach leaf lixivium and the content of COM in the product was higher than that obtained in the root lixivium with the similar concentration of Ca²⁺ ions. COM phase disappeared and only COD crystal with morphology of tetragonal bipyramidal prisms presented in the product when the leaf lixivium was replaced by the leaf broth. The biomolecules such as proteins with molecular weight of 31 kDa liberated from the spinach root are negative-charged, which played important roles for the control of CaOx crystal growth in the root lixivium corresponding to the changes of protein secondary structures after reaction with Ca²⁺ ions. This research was potentially important for unraveling the biomineralization mechanism of CaOx crystal.     

Raman spectroscopic determination of oxoanions in aqueous polysulfide electrolyte solutions

The equilibrium distribution of aqueous sodium polysulfide solutions is investigated over a wide concentration range using Raman spectroscopy technique. A total of eighteen bands were determined in the spectra recorded for aqueous electrolyte solutions of different S:Na ratios. Beyond the presence of four polysulfide (S_n²⁻) species, where “n” varied between 2 and 5 as reported in previous literature, the originality of this study is to show the presence of oxidised sulfur species in these aqueous polysulfide solutions. A detailed comparison of all the bands for polysulfide and oxoanion species determined in this study with those cited in literature is summarised.     

Flow injection spectrophotometric determination of calcium, phosphate and chloride ions in milk.

Flow injection procedures for the determination of calcium, phosphate and chloride ions in milk samples are described. The reactions are based on the formation of coloured complexes and their spectrophotometric monitoring. A sample pre-treatment with acetate buffer was carried out owing to the complexity of the sample matrix. For chloride, a rapid and reliable automated procedure for direct measurement of its content in milk (using a dialyser to eliminate interferences) is also described. After optimizing the sample pre-treatment and flow injection variables, the procedures were applied to commercial milk; the results obtained agreed satisfactorily with those of the reference methods. With 50 mm3 samples, a working range of 0-15 ppm for calcium, 50-150 ppm for phosphate and 5-100 ppm for chloride is covered with a precision of better than 1.1%. The sample throughput was higher than 50 samples h-1. These preliminary experiments are the basis for the automation of the determination of calcium, phosphate and chloride ions using a computer-controlled, self-designed and laboratory-built autoanalyser.     

Amperometric determination of trivalent arsenic in sulphuric acid solution in the presence of fluoride ions

The polarographic reduction of 1 mM KMnO₄ at a dropping mercury electrode was studied in H₂SO₄ solutions containing varying amounts of sodium fluoride. The amperometric titration of sodium arsenite with potassium permanganate was carried out at – 0.9 volt (SCE) in acid medium containing fluoride ions that are capable of forming stable fluoride complexes. It was revealed that the titration was successful at 0.028% NaF and 0.54 N H₂SO₄. The effect of [AsO ₂ ^– ] revealed suitability of the method for the quantitative determination of very small amounts of trivalent arsenic ranging from 1.5 mg/ml to 1.5 µg/ml.

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Amperometrische Bestimmung von trivalentem Arsen in schwefelsaurer Lösung in Gegenwart von Fluorid-Ionen

Zusammenfassung Die polarographische Reduktion von 1 mM KMnO₄ wurde an der tropfenden Quecksilberelektrode in H₂SO₄-Lösungen mit verschiedenem Gehalt an Natriumfluorid untersucht. Die amperometrische Titration von Natriumarsenit mit Kaliumpermanganat wurde bei – 0.9 V (SCE) in saurem Medium in Gegenwart von Fluorid-Ionen, die zur Ausbildung stabiler Fluoridkomplexe befähigt sind, ausgeführt. Die Titration bei 0.028% NaF und 0.54N H₂SO₄ erwies sich als vorteilhaft. Eine quantitative Bestimmung von geringen Mengen von dreiwertigem Arsen als [AsO ₂ ^– ] im 1.5-mg- bis 1.5-µ/ml-Bereich ist möglich.

     

高分子基质作用下多孔碳酸钙的仿生合成

依据生物矿化的基本原理,通过仿生合成的方法,以聚丙烯酰胺作为基质合成了一种有机、无机复合的多孔碳酸钙材料.用X射线粉末衍射(XRD)分析、扫描电子显微镜(SEM)、傅里叶变换红外吸收光谱(FT-IR)和电导率测定等手段对所得复合碳酸钙进行了表征,结果发现该多孔CaCO3晶体为方解石型,并且在结晶过程中,聚丙烯酰胺与CaCO3之间存在着相互作用,本文讨论了这种作用的可能机理.     

Titrimetric determination of thiocyanate and thiosulphate ions by oxidation with iodine in alkaline solution

Thiocyanate (2.7-90 mug) and thiosulphate (4.5-90 mug) ions are oxidized by iodine in alkaline media to sulphate ions. After acidification, the excess of iodine is extracted into chloroform, and the iodide ions formed in the redox reaction subjected to an amplification reaction. Either a titrimetric or a spectrophotometric finish may be used. Each thiocyanate and thiosulphate ion results in the ultimate production of 19 and 24 iodine molecules, respectively.     

A highly regular hexapod structure of lead sulfide: solution synthesis and Raman spectroscopy

A highly regular hexapod-like structure of PbS with six symmetric arms has been synthesized by a simple and mild chemical solution route. The hexapod-like PbS structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The results show that each arm is perpendicular to the other four, and opposite to the last one. The arms are about 0.3-0.6 microm long, which have about 40-60 nm tips and 150-200 nm base. And the arm shows an icicle-like structure and some clear steps, and grows along 100 directions. The most possible growth mechanism discussed herein is based on the characterization results. The Raman spectra of the hexapod-like PbS structure were investigated. The results show that our products are sensitive to the laser and can be photodegraded easily.