At pH1 Alcian blue positivity is limited to highly acidic glycosaminoglycans (heparin/ chondroitin/dermatan/keratan  sulphates, that I understand).

At pH3 Hyaluronic acid-containing molecules are also positive. At pH0.5 only dermatan/keratin  sulphate are positive.

One may alternatively use the CEC method to demonstrate the various “mucins”, to a high degree of selectivity.

Both methods rely on charge densities, that I understand.