Concentration polarisation arising during the filtration of bovine serum albumin (BSA) and Dextran Blue is studied by two non-intrusive techniques. The first technique, which measures overall layer build up, is a further development of a radio isotope technique previously introduced. The second technique uses a micro-array of semiconductor photosites to measure infrared absorption of species in the polarised layer. The development of the polarised region is observed as a function of distance perpendicular to the membrane surface. The experiments with the radio isotope labelled proteins using different pore size membranes demonstrated that there is a large similarity between filtration with different pore size membranes - from microfiltration to ultrafiltration. The amount of solute retained dynamically above the membrane is within half an order of magnitude, over pore sizes differing by 2 orders of magnitude. The directly observed concentration polarisation profiles followed generally expected trends, and demonstrated the large solute concentrations that exist near the membrane surface.