ELSEVIER Chemometrics and Intelligent Laboratory Systems 29 (1995) 243-254 Chemometrics and intelligent laboratory systems Quantitative determination of stabiliser in a single base propellant by chemometric analysis of Fourier transform infrared spectra Torbjijrn Lindblom a, Alfred A. Christy bY * , Fred 0. Libnau b a zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Celsius Materialteknik, S-691 51 Karlskoga, Sw eden b Department zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Chemistry, CJniuersi@ of Bergen, N-5007 Bergen, Norway Received 12 December 1994; accepted 22 February 1995 Abstract The main constituent in a propellant is nitrocellulose, which by nature is unstable, and consequently it has to be stabilised with, e.g., diphenylamine. In order to determine the remaining shelflife of the propellant, the amount of stabiliser is deter- mined. The method mostly used for this purpose, high-performance liquid chromatography (HPLC), is however complex and time consuming. Partial least squares calibration of the infrared spectroscopic profiles of the stabiliser and its derivatives in the propellant against their respective quantities (determined by HPLC) was tested to find out whether the quantitative deter- mination of the above was possible. The initial results show that the cross-validated calibration model yields quantitative determination of the stabiliser and its derivatives within an error limit of 10% in predicted values. The correlation between the measured and predicted values was better than 0.94 for the stabiliser and its three first derivatives. Keywords: High-performance liquid chromatography; Data processing; Calibration; Stabilisers; Multivariate analysis; Propellants; Partial least squares; Fourier transform 1. Introduction Nitrocellulose, a nitrate ester, is used as the main constituent in propellants. Since nitrocellulose, is an unstable compound, it has to be stabilised with, e.g., diphenylamine (DPA) or Centralit I (CI, dimeth- yldiphenylurea). During ageing of the propellant NO, is liberated and reacts with water forming nitric acid, which will catalyse further decomposition of the pro- pellant causing an auto-catalytic decomposition * Corresponding auhor eventually. The general view is that the stabiliser will react with the NO, formed during the ageing of the propellant at a faster rate than the propellant itself, thus stopping the acid catalysed ester hydrolysis. Controlling the amount of stabiliser in the propellant is therefore of immense importance. The stabiliser used in our case was DPA. It reacts with NO, and forms three products: N-nitroso- diphenylamine (NNODPA), 2-nitrodiphenylamine (2-NDPA), 4-nitrodiphenylamine (4-NDPA) (see Fig. 1). Whilst the depletion of DPA has been widely studied as a part of stability surveillance programs, the reaction mechanisms have received less attention [1,2]. In Fig. 1 the N-nitrosation of DPA can occur 0169.7439/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SsDrO169-7439(95)00025-9