In refractometry, how much sample is required?

• A. One drop
• B. One milliliter
• C. A few microliters
• D. A teaspoon

Answer: (A)

The amount of sample needed in refractometry is determined by the need to create a thin, uniform film that completely covers the prism surface so the light can pass through a consistent sample path. A single drop provides just enough liquid to form that smooth, continuous film without pooling or creating air gaps. Too much sample, like a milliliter or a teaspoon, would overflow or form thick layers that disrupt the optical contact and introduce measurement errors. A few microliters might be sufficient in some setups, but the standard practice and most common teaching is that one drop yields reliable, repeatable readings.