For TCO2 measurement, which method alkalinizes all CO2 to bicarbonate for measurement?

• A. Enzymatic (alkalinize all CO2 to HCO3)
• B. Electrode-based (acidify all to CO2 gas)
• C. Colorimetric
• D. Photometry/Pulse oximeter

Answer: (A)

Total CO2 measurement requires converting every inorganic carbon species in the sample (CO2, bicarbonate, and carbonate) into a single form so one measurement represents the whole pool. The enzymatic method does this by alkalinizing the sample and using carbonic anhydrase to rapidly convert CO2 to bicarbonate, ensuring all inorganic carbon ends up as HCO3−. Once all carbon is in the bicarbonate form, it can be quantified enzymatically, giving an accurate TCO2 value.

The other approaches don’t accomplish this. acidifying to CO2 gas targets pCO2 rather than total inorganic carbon, so it doesn’t reflect the full TCO2. Colorimetric or photometric readouts describe detection methods rather than guaranteeing complete conversion to a single carbonate form, so they’re not the standard way to measure total CO2.