Description

TAPPI T 604 – Sulfur Dioxide in Sulfite Cooking Liquor

1. Scope

1.1 This method is for the volumetric analysis of sulfite liquors used in the manufacture of sulfite pulp. Themethod is basically that developed by G. V. Palmrose (1) and is based on titration with potassium iodate for the total SO2and titration with sodium hydroxide for the free SO2. Liquor containing lignin derivatives requires corrective procedureswhich are given.

1.2 Sulfur dioxide in cooking liquor can be present as one or two of the following three forms: (1) dissolvedsulfur dioxide and sulfurous acid; (2) ammonium, calcium, magnesium, or sodium bisulfite; or (3) ammonium or sodiumsulfite (monosulfite). Four bases, ammonium, calcium, magnesium, and sodium have been commercially utilized; limitedsolubility problems with calcium and magnesium monosulfites restrict these liquors to combinations of (1) and (2),whereas sodium and ammonium monosulfites are soluble in the upper ranges of pH and allow combinations of (2) and(3) to be utilized.