The color of cola beverages interferes in the colorimetric determination of phosphoric acid. This interference is not significant if the sample is diluted sufficiently (1). However, a previous step where phosphoric acid is separated from the rest of the sample would be desirable. Therefore, we carried out the chromatographic separation of phosphoric acid by using an anionic exchange resin (Dowex 1-XH 100-200 mesh, Bio-Rad). The resin was suspended in deionized water and loaded into a 50-mL syringe. The column was washed twice with 150 mL of a 1 M HCl solution and then 5 mL of degassed cola was loaded into the chromatographic column. Afterwards, 200 mL of a 3 M HCl solution was passed in 10-mL aliquots through the column. At this pH, phosphoric acid (pKa1 = 2.1) is eluted from the column because its predominant form is H3PO4 and the cationic particles of the resin cannot retain it. The eluted solution was collected and transferred into a 250-mL volumetric flask. This solution can be used for phosphoric quantification (1, 2). However, the sample dyes were still attached to the resin. The column was washed with 50 mL of an 8 M HCl solution to elute sample dyes. The acid wash was followed by a final wash with 250 mL of deionized water. This chromatographic separation took approximately 30 minutes.
Literature Cited
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