For proper calibration, which solution should be used to calibrate a refractometer?

For proper calibration, which solution should be used to calibrate a refractometer?

• A. Tap water
• B. Distilled water
• C. Plasma
• D. Urine

Answer: (B)

Calibrating a refractometer requires a reference with a known, stable refractive index. Pure distilled water provides that reliable baseline because it contains essentially no dissolved solids. Its refractive index at the calibration temperature is well established, so you can adjust the instrument to that known value and set the zero (or reference point) accurately for subsequent measurements. Temperature matters because refractive index changes with temperature, so calibration should be done at the specified temperature (often around 20°C). Tap water contains minerals and impurities that alter the refractive index and vary from sample to sample, making it unsuitable for an accurate calibration reference. Plasma and urine are biological fluids with variable compositions, which would give inconsistent reference values and lead to inaccurate readings. Thus, distilled water is the correct calibration solution.

Calibrating a refractometer requires a reference with a known, stable refractive index. Pure distilled water provides that reliable baseline because it contains essentially no dissolved solids. Its refractive index at the calibration temperature is well established, so you can adjust the instrument to that known value and set the zero (or reference point) accurately for subsequent measurements.

Temperature matters because refractive index changes with temperature, so calibration should be done at the specified temperature (often around 20°C). Tap water contains minerals and impurities that alter the refractive index and vary from sample to sample, making it unsuitable for an accurate calibration reference. Plasma and urine are biological fluids with variable compositions, which would give inconsistent reference values and lead to inaccurate readings. Thus, distilled water is the correct calibration solution.