Structural analysis of packed beds in capillary-LC columns

Continued study in ultra-high pressure liquid chromatography in our lab revealed the need for a method of determining the packing structure of our capillary columns. SEM images obtained of our column packing were not quantitative or diagnostic and did not provide spatial information.; A contactless conductivity detector was adapted to scan capillary columns in order to determine the local packing density along the capillary's length. The contactless conductivity detector was a reliable method to determine the general packing density of a column, but a much finer spatial resolution than ∼3-mm was desired.; Laser-induced fluorescence was then explored to measure packing density since a focused laser can provide a finer spatial resolution. A fluorescence detector was designed for the red visible spectral region, but the background of the polyimide capillary coating proved to be too large. The near infrared spectral region was then utilized and yielded a ∼160-fold improvement in the signal to background ratio. A problem with the imaging of the detector was identified from the large (∼8-%) variability in the measurement of open tubular capillary scans. Fluorescence microscopy with an imaging array reduced this variation to ∼4-%, by allowing the selection of pixels within an image when interpreting data.; A study was performed in order to correlate column inner diameter, with efficiency and packing density. As in previous studies, the columns were more efficient as the column's inner diameter decreased. The retention factor was calculated for comparison to the previous trend of increasing packing density with increasing column inner diameter. The fraction of mobile phase was calculated using a flow rate/deadtime and the fluorescence method. Although the methods conformed to the established trends, the flow rate/deadtime method yielded consistently low values while the fluorescence method gave values close to the anticipated value of 0.4.; The ratio of the volume of stationary phase to the volume of mobile phase and the partition coefficient (which should remain constant) was calculated from each method. From the data collected, the flow rate/deadtime measurement method may have the potential to be more reproducible than the fluorescence method but does not provide any spatial information.