Analysis for sulfate ion in the biodegradation of anionic detergents

A turbidimetric method is described for determining sulfate ion in parts per million formed during the biodegradation of surface-active organic sulfates or sulfonates. The procedure involves the precipitation of barium sulfate under controlled conditions, using a reagent consisting of 0.5% gelatin and 1% barium chloride in 50% ethanol. Gelatin stabilizes the barium sulfate suspension and helps prevent the formation of turbidity from barium chloride and detergent. Ethanol destroys any protective colloid action that may inhibit the precipitation of barium sulfate. Corrections were necessary for turbidity caused by the microorganisms and in a few instances for turbidity caused by the reaction of detergent and barium chloride. Absorbance was read against a blank at 420 mμ using 5 cm cells. Parts per million sulfate were read from a standard curve. Phosphates do not interfere in the determination. Presented at the AOCS Meeting, Chicago, October 1967. E. Utiliz. Ees. Dev. Div., ARS, USDA.