RESUMEN
A continued investigation of the primary steps in diphenylamine (DPA) decomposition in nitrocellulose (NC) propellants is presented. The study is based on analytical data obtained by reversed-phase liquid chromatographic separation of the initial degradation products of DPA. Spectrophotometric detection, rather than the amperometric detection used in part I of this work (A. Bergens and R. Danielsson, Talanta, 1995, 42, 171), was employed in order to detect N-nitroso-DPA as well as DPA, 2-nitro-DPA and 4-nitro-DPA. The results have been studied with the rate parameter optimization program described in part I and simulations suggest that the decomposition of DPA includes unknown reaction steps. More satisfying curve fits were, for example, obtained when the initial reaction for conversion of DPA into N-nitroso-DPA was considered to consist of a two step process with an intermediate. This intermediate could act as a stabilizer as well as DPA and N-nitroso-DPA, particularly at lower temperatures.
RESUMEN
The consumption of diphenylamine (DPA) in two nitrocellulose (NC) based propellants subjected to a heat storage test at 85 degrees has been studied. A previously developed method based on reversed-phase liquid chromatography with dual-amperometric detection was used to monitor the concentrations of DPA, 2-nitro-DPA and 4-nitro-DPA during the test. A numerical model based on first order rate equations was fitted to the obtained analytical data with the use of a specially written curve fitting program. The model implemented in the program describes the initial nitrosation and nitration steps of DPA in aging NC propellants. The use of matrices in the calculation of concentration-time (CT) curves enables the introduction of a general algorithm which can be readily changed in order to simulate any system of first order reactions. The program can therefore be used in other applications such as mechanistic studies in organic synthesis. The general simulation algorithm allows inclusion of unknown (not analysed) components in the reaction mechanism. In this application, it was possible to simulate the course of N-nitroso-DPA which is not detectable by the amperometric principle.
RESUMEN
A method for the determination of the stabilizing additives Acardite II, Centralite I and diphenylamine in single- and double-base propellants has been developed, based on oxidative differential pulse voltammetry with a glassy-carbon electrode in a 1:1 v v acetonitrile-methanol medium. The voltammetric behaviour of Acardite II and Centralite I was briefly studied to find the proper experimental conditions. For analysis, aliquots of a crude sample extract in dichloromethane are added directly, with no prior treatment, to the measurement cell. The analysis is performed by the standard-addition method. The relative standard deviation is typically 1.0-1.5%. The concentration range accessible with the differential pulse technique, 0.5-100 muM, is quite sufficient for the levels of stabilizers used in powders and propellants. The utility of the method is exemplified by the monitoring of stabilizer consumption in three different propellants subjected to accelerated degradation at 90 degrees .
RESUMEN
DU90%--the number of drugs that account for 90% of DDDs--and adherence to guidelines in this segment were proposed by the Swedish Medical Quality Council (MKR) as indicators for assessing the quality of drug prescribing. We tested these indicators at a primary health care (PHC) center in Stockholm. Bar-coded prescriptions purchased at pharmacies were compared with the guidelines issued by the regional drug committee. The data were presented and discussed at the PHC center. Although the DU90% method neither examines the appropriateness of use nor provides outcome data, it was shown to be an inexpensive, flexible and simple method for assessing the general quality of drug prescribing.