Determination of additives in fuels using automated flow injection analysis with chemiluminescence detection
The overall objective of this thesis was to develop field deployable instrumentation for the selective, sensitive determination of additives in diesel fuels using flow injection with chemiluminescence detection. The target analytes were the detergent dodecylamine and the lubricity additive P655. Chapter One describes the types of additives that are used in fully formulated diesel fuels in order to improve performance and outlines the need for robust analytical methods to be able to detect their presence / absences in fuels at the point of distribution, i.e. at the petrol pump. Flow injection (FI), and chemiluminescence (CL) are described as suitable techniques for sample preparation and detection respectively. The application of FI-CL for the quantitative determination of various analytes is reviewed, with the focus on real sample matrices. Finally the technique of solid phase extraction is discussed as a means of selective analyte preconcentration / matrix removal prior to FI-CL detection Chapter Two describes the development and optimisation (both univariate and simplex) of an FI-CL method for the determination of dodecylamine in acetonitrile / water mixtures using the catalytic effect of amines on the peroxyoxalate / sulphorhodamine 101 CL reaction. The linear range for dodecylamine was 0 - 50 mg Lˉ¹ with a detection limit of 190 µg Lˉ¹ and RSDs typically < 4 %. The effect of indigenous diesel compounds on the CL response is also investigated. Chapter Three investigates the applicability of the method developed in Chapter Two to determine dodecylamine in diesel fuels. Solid phase extraction was needed prior to analysis by FI-CL. The development of a solid phase extraction that is compatible with the FI-CL system is detailed. GC-NPD and GC-MS analysis are used in order to validate the solid phase extraction procedure. A range of diesel fuels have been spiked with an additive package containing dodecylamine and have been analysed off-line using FI-CL. Recoveries for all diesel fuels analysed were < 72 % and all fuels could by identified from the corresponding base fuel. Chapter Four describes the design and construction of a fully automated on-line solid phase extraction flow injection chemiluminescence analyser for the determination of dodecylamine in diesel fuel. Details of the automation and programming using LabVIEW are described. Results obtained using the automated on-line system are compared with results obtained using off-line SPE with FI-CL detection from Chapter Three. Recoveries for all fuels except SNV were < 71 %, and all fuels except SNV could be positively identified from the corresponding base fuels. No significant differences were found between the on-line and off-line results (within 95 % confidence limits). Chapter Five investigates the feasibility of determining the lubricity additive P655 in diesel fuel using FI-CL. The optimisation and development of a method using the competing reactions of periodate with alcohols and periodate with the CL oxidation reaction with pyrogallol is discussed, and the development of a solid phase extraction procedure for the extraction of P655 from an organic matrix is described. The limit of detection for P655 using SPE without preconcentration was 860 mg Lˉ¹ and was linear in the range 0 - 10000 mg Lˉ¹ (R² = 0.9965).