The development and validation of new technology for the accurate and traceable metering of high value fluids is presented here. The focus of this doctoral submission is on the determination of fluid density by the measurement of relative permittivity. A prototype cell, comprising a re-entrant cavity resonator, for the precise determination of the relative permittivity of gases and hydrocarbon liquids over a wide range of both pressures and temperatures has been developed for this work. Accuracies of measurement of relative permittivity with the re-entrant cavity resonator technique of better than 1 ppm may be achieved. Reference quality relative permittivity measurements were performed and expressions developed for ethylene which are specific to industrial metering applications ( 0 ≤ t ≤ 30°C and 5 ≤ p ≤ 10 MPa). The uncertainty in values of density calculated from the mapping relationship is approximately 0.03 % in density at a 95 % confidence level. The laboratory facility used to perform the fluid mapping or characterisation was based around a high-performance RF network analyser as the principle measuring instrument. However, an on-line instrument must be simple to operate, relatively compact, robust and considerably less expensive; particularly if it is to be widely deployed. The aimed accuracy in the measurement of relative permittivity of the on-line instrument was 5 ppm; a factor of five lower than the laboratory instrument. For the on-line instrument, the re-entrant cavity resonator was incorporated into a feedback oscillator circuit as the frequency determining element. The accuracy of measurement of relative permittivity of the on-line instrument was 2.5 ppm; a factor of two greater than the aimed accuracy. This accuracy of frequency measurement is only achievable over a relatively narrow range of operating conditions, which is ultimately a limiting factor in the applicability of the on-line instrument for high precision relative permittivity measurements in the field.

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Raman spectroscopy, laser-induced fluorescence, and sum-frequency generation (SFG) spectroscopy are used to investigate the behavior of compressible mobile phases and stationary phases under a variety of chromatographic conditions. Efforts to understand and optimize separations employing compressible mobile phases have been limited by a lack of understanding of the mobile phase density gradient. Mobile phase compressibility leads to gradients in linear velocity and solute retention and affects separation speed and efficiency, especially in packed columns. This work describes on-column density measurement of CO2, a common carrier fluid for SFC and SGC, in packed capillary columns using Raman microspectroscopy. On-column detection by laser-induced fluorescence is used to observe the effect of the mobile phase density gradient on separation speed and efficiency, and experimental efficiency is compared to a theoretical model. Additionally, SFG spectroscopy allows for probing the structure of model monomeric and polymeric C18 stationary phases under pressure; this provides a basis for correlating selectivity with pressure-induced structural changes in stationary phase materials. Together, this work provides a more complete understanding of the role of column pressure and fluid compressibility on the speed, efficiency, and selectivity of chemical separations.