Which pair correctly describes the two common methods for measuring bicarbonate in clinical chemistry?

• A. ISE after acidification and enzymatic (UV) after alkalinization
• B. ISE after alkalinization and enzymatic after acidification
• C. Colorimetric after acidification and ISE after alkalinization
• D. UV spectrophotometry after acidification and amperometric after alkalinization

Answer: (A)

Bicarbonate is measured by converting the inorganic carbon balance into a form that a detector can read, using pH to shift between CO2 and bicarbonate. Two common approaches use different pretreatments to make bicarbonate detectable by the chosen method.

If you acidify, bicarbonate is driven to CO2. In this setup, an ion-selective electrode configured to sense CO2 (or a detector that responds to that CO2 amount) can quantify how much bicarbonate was present before acidification. That’s a practical way labs get a bicarbonate readout using an ISE after acidification.

If you alkalinize, all inorganic carbon is converted to bicarbonate (and carbonate mixtures lean toward bicarbonate at high pH). In this condition, an enzymatic method read by UV detects bicarbonate via a coupled reaction that ultimately reflects the bicarbonate concentration.

So the pairing described—using ISE after acidification and enzymatic (UV) detection after alkalinization—fits these two common pretreatment-detection combinations. The other options rely on less typical or less robust pairings for bicarbonate measurement.