The number of surface functional groups of Ulva lactuca, their absolute concentrations, and acid dissociation constants (pKas) were determined through potentiometric titrations in sodium chloride solutions at various ionic strengths (0.01 M – 5.0 M). Dehydrated BCR-279 Ulva was compared to fresh Ulva specimens. Finally, a titration in seawater was compared to titrations in sodium chloride. It was determined based on the FITEQL 4.0 Fortran code that there are three (possibly four) surface functional groups. It was also determined that their zero ionic strength pKas were around 4.1, 6.3, and 9.5 and their absolute concentrations are approximately 4.6 x 10-4 mol/gram of Ulva, 5.1 x 10-4 mol/gram of Ulva, and 5.7 x 10-4 mol/gram of Ulva, respectively. Fresh Ulva was shown to have similar pKas, but lower concentrations. Finally, the seawater titration indicates that the non-carbonate alkalinity of seawater far exceeds the concentration of functional groups on the Ulva sample.

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