ISO 9020:1994

The method specified is based on reacting free formaldehyde and alcohol formaldehyde semiacetals in a test portion with excess sodium sulfite solution at a temperature of 0 °C to form hydroxymethane sulfonate, titrating the excess sodium sulfite with iodine solution, decomposing hydroxymethane sulfonate with sodium carbonate solution and titrating the sodium sulfite liberated with iodine solution. The method is applicable to resins resulting from the polycondensation of urea and melamine with formaldehyde and to furan resins resulting from the polycondensation of furfuryl alcohol with formaldehyde without further modification.