Quantification of Inorganic Carbon at High pH in BG11 Algal Growth Media

Highlights Modified titration method is required for accurate inorganic carbon measurement. Modified titration and carbon analyzer of similar accuracy. Accuracy of both methods decreased with increasing pH (10.3–11.5). Carbon analyzer accuracy decreased after one week of sample refrigeration. Empirical equations provided to support adaptation of modified titration method. ABSTRACT. Algal carbon capture holds promise for mitigating CO 2 emissions, especially at high pH when CO 2 diffusion is chemically enhanced. Key to the design of high-pH algal systems is accurate inorganic carbon measurement, which can be difficult due to CO 2 diffusion during measurement and storage, as well as complexity of growth media. The objective is to compare accuracy of three measurement methods: unmodified titrations, titrations modified to account for the presence of non-carbonate buffers, and spectroscopy via a carbon analyzer. Accuracy was assessed using standards prepared in BG11 medium at pH 9.6–11.5. Unmodified titrations were consistently inaccurate. Modified titrations and the carbon analyzer were statistically of similar accuracy, although the carbon analyzer provided more precise measurements. Accuracy statistically declined with increasing pH across methods and with one week of storage prior to carbon analyzer measurement; thus, prompt measurement of high pH samples is recommended. Practical recommendations based on access to equipment, labor intensity, and sustainability are provided for researchers. Keywords: Algae, Carbon capture, Growth medium, High pH, Inorganic carbon measurement, Titration.