LimsPulse
Refractometer · Calibration procedure

Refractive index with reference liquid

Measures purified water and a certified refractive index reference liquid and compares each reading with its known value at 20 °C.

Photo of a Refractometer
Photo: Roco190, CC BY-SA 4.0 (cropped), via Wikimedia Commons
PURPOSE

Why this is checked

Confirms the refractometer reads true across its working range, so identity results for oils and solvents are correct.

Frequency

Typically every 6 or 12 months and after repair; a water check is often done daily or before use. As defined in your SOP.

Learn how the Refractometer works
YOU WILL NEED

Standards & tools

  • Freshly prepared purified water (nD at 20 °C about 1.3330)
  • Certified refractive index reference liquid close to the range you test, e.g. a nominal 1.48 standard, with certificate
BEFORE YOU START

Prerequisites

  • Prism at 20.0 °C and stable
  • Prism clean and dry
  • Reference liquid within expiry and at room temperature
PROCEDURE

Step by step

  1. 1Place purified water on the prism, close the cover and wait for temperature stability.
  2. 2Take the reading and record it. Clean and dry the prism.
  3. 3Repeat with the certified reference liquid.
  4. 4Take three readings of each on fresh portions if your SOP requires, and use the mean.
  5. 5Calculate the difference between the reading and the known value.
RECORD

Example observation table

StandardKnown value (nD at 20 °C)ObservedDifferenceResult
Purified water1.332991.33301+0.00002Pass
Certified RI liquid1.479921.47998+0.00006Pass
CALCULATION

How to calculate the result

Difference = Observed − Known value
  1. Water: 1.33301 − 1.33299 = +0.00002
  2. Reference liquid: 1.47998 − 1.47992 = +0.00006
ACCEPTANCE CRITERIA

Pass if

  • Each difference within the limit in your SOP, which combines the instrument specification and the certificate uncertainty (commonly within ±0.0002 for pharmacopoeial work; tighter for high-resolution instruments).
IF IT FAILS

What to do

  • Clean the prism, check the temperature and repeat.
  • If it still fails, adjust the instrument with water as the manufacturer describes and repeat the reference check.
  • If it fails again, label it 'Out of calibration', call service and assess recent results.
In LimsPulse · Calibration Management

LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.

See how