The Cobalt-3,5-Dimethylpyrazole Reaction

The reaction of 3,5-dimethylpyrazole with cobalt (II) ion in aqueous solution was first observed by Fischer in 1925 (1). He investigated a series of organic compounds as precipitants for the common metal ions and noted that aluminum, cobalt, iron, and zinc (among others) formed precipitates with 3,5-dimethylpyrazole. Surprisingly enough, preciphation was not observed with copper and nickel. A reagent capable of differentiating between cobalt and nickel was thus potentially available. In 1930, Heim (2) used 3,5-dimethylpyrazole for the determination of cobalt ion in solutions of cobalt salts after separation of interfering ions. The blue-violet precipitate formed in basic solution was filtered, washed, dried, and weighed as Co(C5H7N2)2 . More recently, the use of the reagent as a precipitant for cobalt has been advanced (7). Procedures are outlined for the determination of cobalt in organic compounds after destruction of the organic matter by sulfuric acid and peroxide oxidation. Present interest in the cobalt-3,5-dimethylpyrazole system was concerned with the possible colorimetric determination of the metal ion with the reagent. Solubility of the colored material in a nonaqueous medium with retention of coloration would form the basis of such a method. Solubility to yield a colored solution (the precipitated species would remain as an undissociated species) might be expected from the similarity to the cobalt (1) acetylacetonate complex which is soluble in most organic solvents

The Solubility and Thermal Decomposition Characteristics of Some Tetraphenylarsonium Compounds

The tetraphenylarsonium perchlorate, perrhenate, pennanganate, tetraphenylborate, dichromate, trichoro-cobaltate (II) and tetrachlorozincate (II) salts were isolated and characterized. The solubilities of the pure salts in water at 25° were determined using spectrophotometric methods. Thermal data were obtained for the pure salts using the technique of thermal gravimetric analysis. Results of the above studies show that tetraphenylarsonium chloride is valuable as a precipitant for perchlorate and perrhenate ions. The reagent also shows promise as a precipitant for the dichromate and tetraphenylboron ions

The Direct Spectrophotometric Determination of Fluoride Ion

A direct method for the determination of fluoride ion in the parts per million range is described. The color reaction of fluoride ion and lanthanum chelate of 3-aminomethylalizarin- N,N-diacetic acid forms the basis for the spectrophotometric method. The intense blue fluoride complex in a mixed solvent system of 16% dimethylformamide- 84% water is stable and independent of pH in the range of 4.6-5.6. Other halogens and common anions do not interfere in the measurements. Interfering ions are removed through ion exchange separations. Results on the determination of fluorine in selected samples are presented

Determination of Perchlorate Ion With Tetraphenylarsonium Chloride

A detailed study of precipitation reaction of perchlorate ion with tetraphenylarsonium chloride is reported. Optimum conditions for quantitative precipitation of perchlorate ion were determined. A gravimetric and a spectrophotometric method for perchlorate ion are proposed. The spectrophotometric method is based upon dissolution of (C6H5)4AsClO4 in acetonitrile and subsequent measurement of absorbance at 264 mμ. Results on selected samples prove both methods to be accurate and reproducible

The Spectrophotometric Determination of Copper with Bis-3,3\u27-(5,6-Dimethyl-1,2,4-Triazine)

A new reagent, bis-3,3\u27-(5,6-dimethyl-1,2,4-triazine), BDMT, is proposed for the colorimetric determination of copper. The reagent is water soluble and is easily prepared in the laboratory. An intensively colored orange complex, Cu(BDMT)2+1, is formed upon reaction of copper(I) ion and the reagent in aqueous solution at pH 5.0. The complex exhibits a wavelength of maximum absorption at 444 mμ with a molar absorptivity of 9,700. The perchlorate salt of the complex is readily extracted into nitrobenzene from aqueous solution. A proposed spectrophotometric method for the determination of copper is both accurate and precise

Gas Chromatography for the Undergraduate Student

Gas chromatography has attained a position of prominence as a separation technique and as a tool for qualitative identification and quantitative determination. As such, it should rightly be discussed and applied in the undergraduate curriculum. A gas chromatograph suitable for teaching purposes has been designed and constructed in this laboratory. Experimentation applicable to the undergraduate laboratory is presented

On piecewise trivial Hopf—Galois extensions

We discuss a noncommutative generalization of compact principal bundles that can be trivialized relative to the finite covering by closed sets. In this setting we present bundle reconstruction and reduction

Pyridine Thioamides as Analytical Reagents for lron

Thiopicolinamide and pyridine-2, 6-dithioamide were investigated as spectrophotometric reagents for iron. Both reagents form soluble blue colored species with iron (II) ion in basic solutions. The tris-thiopicolfuarnide-iron (II) complex exhibits a wavelength of maximum absorption at 615 mμ with a molar absorptivity of 13,600. The bispyridine-2, 6-dithioarnide-iron (II) complex exhibits a wavelength of maximum absorption at 600 mμ with a molar absorptivity of 21,000. A sensitive method for the determination of iron based upon the latter complex is proposed

Space Charge Limited Transport and Time of Flight Measurements in Tetracene Single Crystals: a Comparative Study

We report on a systematic study of electronic transport in tetracene single crystals by means of space charge limited current spectroscopy and time of flight measurements. Both $I$-$V$ and time of flight measurements show that the room-temperature effective hole-mobility reaches values close to $\mu \simeq 1$ cm$^2$/Vs and show that, within a range of temperatures, the mobility increases with decreasing temperature. The experimental results further allow the characterization of different aspects of the tetracene crystals. In particular, the effects of both deep and shallow traps are clearly visible and can be used to estimate their densities and characteristic energies. The results presented in this paper show that the combination of $I$-$V$ measurements and time of flight spectroscopy is very effective in characterizing several different aspects of electronic transport through organic crystals.Comment: Accepted by J. Appl. Phys.; tentatively scheduled for publication in the January 15, 2004 issue; minor revisions compared to previous cond-mat versio

A New Sensitive Reagent for the Spectrophotometric Determination of Copper

N,N\u27-bis(β-1-piperazylethyl) dithiooxamide forms soluble, colored chelates with a number of the transition metal ions. This reagent might have several advantages over other substituted dithiooxamides, since both it and the chelates are water soluble. In solution the reagent acts as a dihydroxy base, deriving its basicity from the presence of the substituent piperazine rings. Potentiometric titration with hydrochloric acid yielded K1= 1.70 x 10-5 and K2 = 1.14 x 10-5 for the two basic dissociation constants. In the presence of copper (II) ion this reagent forms two chelate species which were determined absorptimetrically to have the compositions Cu2R and CuR. The latter complex, containing the metal ion and the ligand in equimolar quantities, is suitable for use in the spectrophotometric determination of copper at concentrations as low as 0.05 mg per liter. Formed under conditions of an excess of reagent in ammoniacal solution, this complex exhibits a molar absorptivity of about 18,000 at its wave length of maximum absorption. Although the reagent is not specific for copper, the simplicity of the method and its high sensitivity recommend its use in the determination of copper