The theory of dispersion of chemically active solutes in a rectilinear flow field: The vector problem

In this paper and its sequel we seek an understanding of diffusion and reaction processes in multicomponent systems under convective conditions. To do this, we construct dispersion approximations to c, the solution of the vector convective diffusion equation, and to its transverse average, . Dispersion coefficients are not the direct route to dispersion approximations in the vector problem. Yet constant long time dispersion coefficients exist and imply a rearrangement of the Hermite expansion of . We deduce the rearrangement and introduce useful approximations thereto.     

Simultaneous determination of fluorine and chlorine in silicate rocks by a rapid spectrophotometric method

A rapid accuiate method is described for simultaneous determination of fluorine and chlorine in silicate rocks by taking, separate aliquots of the single sample dissolution. Fluorine, without separation, was determined by means of the zirconium-criochrome cyanine R complex, whereas chlorine was determined by means of the stable iron (III) thiocyanate complex. The mctliod was tested with standard rocks. Results with geochemical standards were comparable with analyses reported by others. Application to several acidic, mafic, and ultramafic rock samples, gave results with a relative standard deviation of less than 5 %.     

Tautomerism in the 5-pyrazolone series 1(H)-5-pyrazolones and indazolones

Structure (I) is shown to be the correct formulation for the compound hitherto considered to be the “azine” of ethyl acetoacetate; I rearranges to IV. Both IV, 1(H)-3-methyl, and 1(H)-3-phenyl, 5-pyrazolones and related compounds are shown to exist in the enolic form (VII) in the solid state and predominantly so in the solvents in which they are soluble. Similarly the indazolones are found to be represented exclusively by the enolized structure XII. The acetates of both series are reformulated where necessary on the basis of spectroscopic data, and the high frequencies found for the carbonyl groups in the IR are shown to reflect a lack of conjugation with the π-electrons of the heterocyclic ring.     

Direct determination of free methionine in soy-based infant formula

A method was developed for the direct determination of free methionine in soy-based infant formula, with analyte separation and quantitation by reversed-phase liquid chromatography (LC), and UV absorbance at 214 nm, respectively. Sample preparation required only dilution with mobile phase and syringe filtration. Using a 0.02M KH2PO4 mobile phase (pH adjusted to 2.9 with 85% o-phosphoric acid) and 0.7 mL/min flow rate, methionine eluted at approximately 8 min, and total run time was 14 min after column regeneration with acetonitrile-water. System linearity was demonstrated as peak area versus analyte concentration, ranging from 80 to 120% of the formula specification for free methionine (r > 0.999, and all residuals < 0.45%). Intermediate precision relative standard deviation values were < 1.5% for ready-to-feed and reconstituted powder samples, and recoveries ranged from 98.0 to 103.5% for inter-method comparison with an amino acid analyzer method. The limit of quantitation was 3 mg methionine/L in the "as fed" infant formula. Despite the relatively weak UV absorptivity of methionine, the 214 nm signal was sufficiently intense in the 30-65 mg/L (201-436 microM) range to afford quantitation by peak area proportionation versus a 2-point external standard calibration. This direct UV detection after reversed-phase LC separation provides a simple and accurate method for determining free methionine without derivatization.     

PROPERTIES OF AN UNUSUAL PHOTOPRODUCT OF U.V. IRRADIATED THYMIDYLYL-THYMIDINE

Abstract— One of the four major photoproducts formed by UV irradiation of TpT in aqueous solution has a number of unusual properties. This compound, which we arbitrarily call TpT⁴, is produced irreversibly from TpT with single-hit kinetics and seems to represent a novel pathway for TpT photolysis different from the conventional cyclobutane ring dimer formation. This communication describes the preparative isolation of TpT⁴ by ion-exchange chromatography on DEAE-cellulose and its UV, fluorescence and IR spectra. TpT⁴ has an absorption maximum at 325 mμ, fluoresces at 405 mμ when excited at 325 mμ, and has an IR spectrum consistent with the assumption that one of the thymine rings has been converted to a pyrimidin-2-one structure. In addition, TpT⁴ appears to have both pyrimidine rings linked together and does not contain a peroxide group as previously supposed. Spectrophotometric titration shows that TpT⁴ has a pKâ of 10.75 and is unstable to prolonged treatment at extreme pH. A model structure consistent with the present data is given. This model contains the glycosidic and phosphodiester bonds intact with a 5-methylpyrimidine-2-one ring and a thymine ring joined in ether linkage at the C₄ positions, with an OH at the C₄ position in the thymine ring.     

Hemostatic efficacy and tissue reaction of oxidized regenerated cellulose hemostats

Oxidized regenerated cellulose (ORC) has been used as an absorbable hemostat since World War II. In the present study, hemostasis time was determined in a spleen incision model in swine. The effect of mass on absorbable hemostat efficacy and hemostasis time was evaluated by standardizing the ORC materials on a mass basis. The median hemostasis time for a single layer of the new nonwoven ORC was as much as 51 % shorter than woven ORC (P < 0.001). The mean hemostasis time for nonwoven ORC was not affected by the mass of hemostat applied to the wound. The hemostatic efficacy of woven ORC increased with the mass (layers) of hemostat applied to the wound. Nonwoven ORC is significantly faster in achieving hemostasis than woven ORC, and its hemostatic efficacy is not influenced by the mass of material applied. Tissue reaction was minimal and the material was fully absorbed by 14 days.