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Determination of Total Organic Carbon (TOC) in Soda Ash and Other High Carbonate Samples

“Determination of Total Organic Carbon (TOC) in Soda Ash and Other High Carbonate Samples” Wheat Ridge, CO: Coulometrics, Inc.

A.E. King – Coulometrics, Inc.

There is a need for determination of total organic carbon (TOC) in high carbonate matrices for several industries. Within the Rocky Mountain region the determination is required by the soda ash industry and in energy development projects. For soda ash (Na2CO3) the determination is required because organic contamination results in discoloration of glass manufactured using the soda ash. TOC determination is required for oil shales to determine their potential value as oil sources and to evaluate potential environmental contamination by the highly contaminated retort waters formed in processing oil shales. Sufficient amounts of carbonates are present to prevent determination of TOC accurately, or at all, by the difference between the total carbon and carbonate carbon levels. Procedures for removing the carbonate interference are difficult and time consuming. The amounts of organic carbon varies from a few ppm for some soda ash to over 40,000 ppm from some waters. Preliminary information suggests that a portion of the organics in the samples are humic acid solution which are required in conventional analysis procedures.

The conventional method of analysis of high carbonate samples has been to dissolve the samples in sufficient acid to give a resulting solution of pH of 2 to 3, purge out dissolved CO2 then oxidize organic materials using silver catalyzed persulfate oxidation. Evolved CO2 is trapped in an ascarite absorption tube and weighed. This method has a number of disadvantages including its required 90 to 120 minute analysis time.