FLOW DEPENDENCE AND SENSITIVITY OF THE REFRACTIVE-INDEX GRADIENT MEASUREMENT WITH THE Z-CONFIGURATION FLOW CELL AT LOW REYNOLDS-NUMBER

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-configuration flow cell. The RIG measurement is shown to depend upon carefully probing the radial-concentration gradient (orthogonal to the direction of flow) of an analyte. A fiber optic graded refractive Index (GRIN) lens combination provided a narrow collimated beam that facilitated accurate probing of the RIG and far-field 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 experimentally 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 translatlonal 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. © 1990, American Chemical Society. All rights reserved.