Which pH value range is the ideal buffer for peripheral blood smears?

• A. 7.0 to 7.4
• B. 5.5 to 6.0
• C. 6.0 to 6.2
• D. 6.4 to 6.8

Answer: (D)

A slightly acidic buffer around pH 6.4–6.8 is ideal because it optimizes the interaction of the Wright-type dyes with cellular components. The nucleus is stained by basic dyes, while the cytoplasm takes up eosin; at this pH range the dyes ionize and bind in a way that gives crisp nuclear detail and correct cytoplasmic coloration across blood cells. If the pH is too low, nuclear staining can become too dark or granular and cytoplasmic tones may shift unfavorably; if too high, nuclear detail fades and differentiation between cell types is reduced. Thus, 6.4 to 6.8 provides the best balance for clear, interpretable peripheral blood smears.