We employed CHNS-O elemental analysis (EA) to measure the bulk chemical composition of the networks (Table ). The EA results showed a similar trend to XPS, with sulfonation densities increasing upon an increase in catalyst-to-monomer ratio, confirming a good dispersion of acidsites both at the surface and throughout the bulk of the networks. At higher catalyst-to-monomer ratios (≥2), the EA results deviate quite significantly from XPS, with SHCP-10 measured as containing 3.8 mmol•g -1 of SO3H compared to 4.6 mmol•g -1 in XPS. This is due to water adsorption owing to the increased hydrophilicity of the networks with higher sulfonation densities. This can be observed in the S:O atomic ratios calculated from EA, which ideally should be 1:3 but is as high as 1:5.4 in SHCP-10. Furthermore, XPS cannot consider H when determining at.% of elements present, leading to a slight overestimation. Therefore, the real concentration of SO3H likely lies somewhere between the values determined by XPS and EA.