Examination of the hexamethylenetetramine procedure for separation of thorium from rare earths and for determination of thorium.
An examination has been made of the efficiency of the gravimetric reagent hexamethylenetetramine in the separation of thorium from rare earths and in the determination of thorium. Losses to the filtrate, beaker and filter paper are evaluated as well as the extent of rare earth and other contamination of the thorium hydroxide precipitate. When hydroxylamine is used as the reducing agent to keep cerium in the tervalent state, excellent separations are obtained. The efficacy of the reagent is offset by the loss of small amounts of thorium to the precipitation vessel, the scavenging properties of the precipitate for silica and the difficulty in evaluating a true reagent blank.
Direct determination of small quantities of rare earth and yttrium oxides in thoria by emission spectroscopy.
Methods are proposed for the determination of submicrogram quantities of rare earth and yttrium oxides in thorium oxide by emission spectroscopy, without previous separation or concentration of these oxides in the sample. It is possible to volatilise these refractory materials from the thoria using silver chloride as the carrier. The carrier distillation technique in conjunction with relatively high dispersion spectroscopy (0.8-1.1 A/mm) makes possible analyses at levels which were previously only feasible by preconcentration methods (e.g., La(2)O(3) and Y(2)O(3), 5 ppm; Nd(2)O(3) and Sm(2)O(3) 10 ppm; CeO(2) and Pr(6)O(11), 20 ppm in a 10-mg sample of ThO(2)).
New method for analysis of enzymatic reactions: Thermolysin-catalyzed synthesis of aspartame precursor
Aspartame is an artificial sweetener which is 200 times sweeter than sucrose. A precursor of aspartame, N-(benzyloxycarbonyl)-l-aspartyl-l-phenylalanine methyl ester (Z-APM) was synthesized and hydrolyzed with thermolysin in an aqueous monophasic system. Graphical plotting methods and/or nonlinear regression have been used to analyze enzymatic reactions because of the nonlinearity of enzymatic rate equations. There are, however, problems: the former require accurate measurement of the initial reaction rate and the latter gives no analytical information. The authors proposed a method to solve the nonlinear enzymatic rate equations with respect to the concentration of a product with the Taylor expansion, especially for the reversible Theorell-Chance mechanism (Murakami, Y., Hirata, M., and Hirata, A., J. Ferment. Bioeng., 82, 246–252, 1996). This solution, however, is complex for practical use. In this paper, a simpler solution to explain the thermolysin-catalyzed synthesis of Z-APM is obtained. New methods to determine the kinetic parameters, especially for the reversible Theorell-Chance mechanism, based on the approximated solution are proposed. The results calculated using the obtained kinetic parameters can satisfactorily explain the experimental results, which demonstrates the effectiveness of the proposed analysis. We must know the relation between the concentrations of substrates and a product, and accurately evaluate of the result obtained using Taylor expansion when we determine the kinetic parameters using our newly developed methods. The methods to determine the kinetic parameters of the reversible Theorell-Chance mechanism described in this paper is, however, expected to be applied to general enzymatic reactions.