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A simple model based upon Polseullle flow Is reported that allows the prediction of the sensitivity In the refractive Index gradient (RIG) measurement with the Z-conflguratlon flow cell. The RIG measurement Is shown to depend upon carefully probing the radial-concentration gradient (orthogonal to the direction of flow) of an ahalyte. A fiber optic graded refractive Index (GRIN) lens combination provided a narrow collimated beam that facilitated accurate probing of the RIG and far-fleld observation of the beam deflection, for subsequent comparison to the position-sensitive detector output. The flow rate range Investigated was at a low Reynolds number, Re < 10 In the cylindrical flow cell bore. Both the predicted and experimental measured RIG data are directly proportional to linear flow velocity and Inversely proportional to both the axial length variance of the analyte concentration and the analyte translational diffusion coefficient. The linear flow velocity and axial length variance dependence on RIG sensitivity were examined, and the model was found to closely predict the experimentally observed RIG sensitivity. Band-broadening contributions In the RIG detector are critically accounted for In the calculations. Measuring the radial concentration gradient was found to be over 2 orders of magnitude more sensitive than measuring the axial concentration gradient of a typical analyte peak for microbore liquid chromatography conditions.

Spectrophotometry analysis of engine oil for wear metal to detect engine malfunctions and failing engine components is the basis of the United States Air Force Spectrophotometric Oil Analysis Program (SOAP). This program was abandoned for C-130 transport aircraft because of difficulties in correlating the atomic emission spectroscopy data with engine problems. Principal component analysis (PCA), a factor analysis method, reveals information and structure not previously apparent in the C-130 oil analysis data. These results suggest that the C-130 SOAP program could be made viable with the significant advantages obtained through incorporation of PCA.