Abstract: Method for detecting a basic target species in a fuel composition, involving (i) contacting the composition with a solid (for example paper) substrate carrying a spectroscopically active indicator which is capable of reacting with the target species, and (ii) detecting the spectroscopic response of the indicator on or following its contact with the fuel composition. The target species may be a detergent or dispersant additive or a constituent thereof, for example in an automotive fuel. The spectroscopic response may be a colour change, and the indicator may for example be a phenolphthalein indicator such as tetrabromophenolphthalein ethyl ester (HTBPE). Also provided is a test kit for use in the invented method, which may comprise a reference, such as a colour chart, with which to compare the spectroscopic response of the indicator. The indicator-carrying substrate is suitably packaged in a protective atmosphere.

Abstract: Method for detecting a basic target species in a fuel composition, by (i) adding a spectroscopically active indicator which is capable of reacting with the target species, and (ii) detecting the spectroscopic response (suitably a colour change) of the fuel composition to the presence of the indicator. The method may be used to detect an additive such as a detergent or dispersant additive, in particular in an automotive gasoline or diesel fuel or a lubricating oil. Also provided is a kit for carrying out the method, in particular in the field. The indicator may be a phenolphthalein indicator such as tetrabromophenolphthalein ethyl ester (HTBPE).

Abstract: A Fischer-Tropsch derived fuel component is provided in a fuel composition to alter the spectroscopic response of the composition to the presence of a spectroscopically active indicator. The Fischer-Tropsch derived component may be used to increase the detectability of the indicator, and/or to increase the resolution of an analytical test subsequently carried out on the composition. Also provided is a method for investigating a property of a fuel composition, by adding a spectroscopically active indicator and detecting a subsequent spectroscopic response in the composition, wherein the composition contains a Fischer-Tropsch derived fuel component. Further provided is a fuel composition containing a spectroscopically active indicator and a Fischer-Tropsch derived fuel component. The spectroscopic response may be a visible response such as a colour change.

Abstract: The invention provides a diesel fuel additive for reducing fouling of injectors in diesel engines consisting of at least an effective concentration of a nitrogen-containing compound of general formulaCH.sub.3 (CH.sub.2).sub.n --A--NH.sub.2 (I)wherein n is 4 to 18 and A is --CH.sub.2 -- or --CO--, or a mixture thereof as an additive in a diesel fuel comprising a major proportion of a diesel oil and a method for using said additive.