To calibrate the pH meter to adjust the pH of the Warthin-Starry stain, what type of solution should be used?

• A. An acidic solution
• B. A neutral solution
• C. A basic solution
• D. An alkaline solution

Answer: (A)

The pH meter must be calibrated with buffers that match the pH range you plan to measure. For the Warthin-Starry stain, the solution needs to be in an acidic environment to properly develop the stain. Therefore, calibration should be done with an acidic buffer so the meter reads accurately in the acidic range. If you calibrate with a neutral or basic buffer, the meter’s response in the acidic region will be misrepresented, leading to incorrect pH adjustment of the staining solution and potentially poor staining results. Using an acidic calibration buffer ensures the device is accurate where you actually need it.