Determination of Sodium Metabisulfite in Process ECP-2 Accelerator Tank

“S INTRODUCTION The concentration of sodium metabisulfite (Na2S2O5) in an ECP-2 bleach accelerator sample is determined by a manual or potentiometric titration using an iodine (I3) titrant. In the method an excess of iodine is added to the sample. Sodium metabisulfite and Kodak persulfate bleach accelerator, PBA-1, present in the sample react with a portion of the iodine. The iodine that did not react with sodium metabisulfite and PBA-1 is then titrated with standardized sodium thiosulfate, using manual (starch indicator) or potentiometric endpoint detection. In order to determine the sodium metabisulfite concentration, the contribution of PBA-1 in the titration must be accounted for. This is done by subtracting a factor in the calculation of sodium metabisulfite concentration. The factor is calculated based on the PBA-1 concentration as determined by method ECP-0027-01 and it's iodimetric equivalent weight. The measured level of sodium metabisulfite in the sample may be lower than the amount added during mixing. This is due to either a reaction of PBA-1 and sodium metabisulfite that can result in a lower equilibrium concentration of sodium metabisulfite, or aerial oxidation of sodium metabisulfite. Use of this method requires handling potentially hazardous chemicals. Material Safety Data Sheets (MSDS) should be consulted for each chemical before use. These can be obtained from each chemical supplier.