In Situ Measurement of Polymer Layer Thickness in Porous Layer Open Tubular (PLOT) Columns Using Optical Absorbance in the Near-IR Range

Highly reproducible fabrication of porous layer open tubular (PLOT) structures in fused silica capillaries is often challenging; thus, methods to measure layer thickness growth in real time represent a powerful tool for the production of such columns. The work presented herein demonstrates the application of optical absorbance in the near-infrared (near IR) range for the in-process measurement of polymer layer growth inside fused silica capillaries during the fabrication of PLOT columns. The proposed technique can be used for both onand off-line measurements of layer thickness for thermaland photoinitiated polymerisation methods, performed in either polytetrafluoroethylene (PTFE)or polyimide-coated capillaries. Measurements of layer thickness were carried out at λ 700 nm, using 100 μm and 8 μm optical fibres, yielding relative standard deviation (%RSD) values of 27% and 22%, respectively.