Storage for Schiff reagent.

• A. Room temperature, up to 6 months
• B. 4 C, up to 3 months
• C. -20 C, up to 1 year
• D. 2-8 C, up to 2 weeks

Answer: (B)

Schiff reagent is an aqueous, light-sensitive solution used in the periodic acid–Schiff (PAS) reaction. After periodic acid oxidizes carbohydrates to aldehydes, Schiff reagent reacts to give the magenta color. Because the reagent is prone to gradual oxidation and microbial growth, keeping it cold slows degradation and preserves its aldehyde-detecting power. Storing it at 4°C in a tightly closed, light-protected bottle maintains potency for about three months, which is a practical balance between stability and practicality in a lab setting.

If kept at room temperature, the reagent degrades faster, leading to weak staining or nonspecific background. Freezing is not appropriate for this water-based solution because it can cause precipitation or separation and may not re-dissolve uniformly upon thawing, reducing its effectiveness. A shelf life of only two weeks at 2–8°C would require frequent prep of fresh reagent and is not typical for routinely used staining work.