Calibration of Melting Point Apparatus

1. Introduction

The melting point of a substance is a critical physical property used in pharmaceuticals to confirm identity, assess purity, and detect impurities. A melting point apparatus must be calibrated to ensure accurate and reliable temperature measurements.

2. Objective

To verify that the melting point apparatus measures temperatures accurately within defined tolerance limits, using certified reference materials.

3. Principle

Calibration is performed by determining the melting points of primary reference standards (or certified melting point standards) with known, traceable melting temperatures.
The measured value is compared to the certified value, and deviations are checked against permissible limits.

4. Materials & Equipment

• Melting point apparatus (digital or manual)

• Certified reference substances (e.g., USP, BP standards such as caffeine, vanillin, benzoic acid)

• Thermometer or temperature sensor (if required)

• Calibration record sheets

5. Procedure

1. Clean the Capillary Tubes: Use clean, dry, thin-walled tubes.

2. Fill the Sample: Pack a small amount of reference standard powder into the bottom.

3. Set the Apparatus: Adjust the heating rate (commonly 1–2 °C/min for calibration).

4. Record the Melting Point Range: Note the temperature where melting starts (first drop formation) and where it ends (completely molten).

5. Compare with Certified Values:

   $$\text{Deviation}=\text{Observed MP}-\text{Certified MP}$$

6. Acceptance Criteria: Deviation must be within ±0.5 °C (per pharmacopeial limits, unless otherwise specified).

7. Document Results: Record observed temperatures, certified values, and pass/fail status.

6. Calibration Frequency

• Before first use

• At regular intervals (e.g., every 6 months)

• After repairs or suspected malfunction

7. Regulatory References

• USP <741> Melting Range or Temperature

• Ph. Eur. 2.2.14

• ICH Q2(R1) (Analytical Method Validation)

• GMP & GLP guidelines

Example Acceptance Statement

“Melting point apparatus ID: MPA-01 measured USP benzoic acid melting point at 122.4 °C (certified 122.5 °C), deviation = –0.1 °C. Result within ±0.5 °C tolerance — suitable for use.”