Flow dependence and sensitivity of the refractive index gradient measurement with the Z-configuration flow cell at low Reynolds number

Abstract

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.

A Microscale-Molecular Weight Sensor: Probing Molecular Diffusion between Adjacent Laminar Flows by Refractive Index Gradient Detection

“…A RI-based detector originally developed by Pawliszyn provided very sensitive measurements of the RIG created by the axial concentration gradient of an analyte as it passes through a capillary. − This system probed the RIG by measuring the deflection angle of a laser beam. RIG detection has also been developed where the radial concentration gradient was probed. − The data were found to be dependent on the diffusion coefficient of the analyte, and thus the molecular weight, when the appropriate FIA sample introduction conditions were met. , The scale of this previous molecular weight sensor system was significantly larger compared to the μ-MWS dimensions we report here. Furthermore, the time scale for the molecular weight determination was longer, ∼90 s 31,32 versus 3 s with the μ-MWS described here.…”

“…RIG detection has also been developed where the radial concentration gradient was probed. [23][24][25] The data were found to be dependent on the diffusion coefficient of the analyte, and thus the molecular weight, when the appropriate FIA sample introduction conditions were met. 31,32 The scale of this previous molecular weight sensor system was significantly larger compared to the µ-MWS dimensions we report here.…”

“…Refractive index (RI) detection has been widely used in traditional-scale HPLC and CE for many years, − and more recently, RI detection has been developed for microscale analysis. − This universal technique has been widely used to analyze polymers, sugar, proteins, and other analytes that do not appreciably absorb or fluoresce. A RI-based detector originally developed by Pawliszyn provided very sensitive measurements of the RIG created by the axial concentration gradient of an analyte as it passes through a capillary. − This system probed the RIG by measuring the deflection angle of a laser beam.…”

“…Refractive index (RI) detection has been widely used in traditional-scale HPLC and CE for many years, [15][16][17][18][19][20][21][22][23][24][25] and more recently, RI detection has been developed for microscale analysis. [26][27][28][29][30] This universal technique has been widely used to analyze polymers, sugar, proteins, and other analytes that do not appreciably absorb or fluoresce.…”

Computer simulation and theory of the diffusion- and flow-induced concentration dispersion in microfluidic devices and HPLC systems based on rectangular microchannels

“…Such influences in open-tubular chromatography have been treated theoretically first by Taylor [15] and Golay [16,17]. The corresponding results have been generally adopted for flow-through systems based on different channel types [18][19][20][21][22][23][24]. Microfabricated devices usually incorporate channels that roughly have a rectangular cross-section.…”