Operation and calibration procedures of melting point apparatus

Purpose : Operation and calibration procedures of melting point apparatus

SCOPE : Is applicable to the operation and calibration procedures of melting point apparatus

RESPONSIBILITY : Quality Control Analyst shall be responsible to follow the procedure mentioned in this SOP

ACCOUNTABILITY:  QC Head and QA Head shall be accountable for compliance of this SOP

ATTACHMENTS : Calibration format for melting point apparatus


Pre-analysis preparation

Instrument is clean and free from dust.

Plug in the instrument

Ensure that all the regulators are in on-position

Fill the beaker with silicone oil up to the mark. Place the magnetic rotor in the beaker


Silicone oil expands rapidly when heating starts and is likely to overflow if more quantity of oil is introduced into the beaker. Similarly, the rotor must not be dropped in the beaker after it is placed on the apparatus, as it may break the beaker due to the magnetic pull.

Place the beaker filled with oil and rotor on the instrument. A circular felt ring is fitted to the beaker housing. Cover the beaker with the Teflon lid which is fitted to the heater and temperature sensor. The lower part of the heater and sensor are immersed into the oil. Connect the sensor to the sensor socket provided on the apparatus.

CAUTION: The position of the probe must not be disturbed.

Turn on the instrument pressing the MAINS key

Measurement procedure

Use the capillary sealed at one end. Introduce the sufficient quantity of the substance to be examined into the capillary and lightly tap it to give a compact column on the height about 4 mm.

Wipe out the capillary from outside to make sure that no dust or powder particles stuck to the surface which may contaminate the oil in the bath.

Adjust the stirrer (STIRRER on the front panel) to ensure uniformity of temperature within the bath.

Turn the heater control knob (HEATER) clockwise to the high temperature range

The LOW position is selected for melting points up to 150°C; and the switch is set to HIGH position for higher melting points.

To control the intensity (brightness) of the illuminator it is provided with the INTENSITY regulator at the rear right hand side of the instrument.

Press the START key. The green pilot lamp and red indicating lamp will glow indicating that the heater is «ON». The temperature starts increasing.

When the temperature is about 10º С below the presumed melting point reduce the rate of heating by turning the knob anticlockwise. Adjust the heating rate preferably to about 1º С per minute.

When the temperature is 5º С below the presumed melting point, place the capillary tube into the heating block.

Watch through the magnifying lens the tips of the capillaries containing the samples under test. At the exact stage, when the sample passes into the liquid phase, press the STOP key to arrest the digital reading from changing. Record the melting point temperature

Repeat the procedure 2-3 times and calculate the average melting point temperature.

Calibration procedure

Determine the melting point of the reference standards( or other substances, which are used for theses purposes):

  1. Vanillin.
  2. Acetanilide.
  3. Sulphanilamide.
  4. Caffeine

The observed melting point temperatures must be within the range of the standard temperatures

Calibration frequency: once a month.

Completion of the analysis

Press the CLEAR key to observe the temperature of the silicone oil in the beaker. Turn the heater control knob anticlockwise to its minimum. Turn off the stirrer with the STIRRER regulator

Turn off the instrument pressing the MAINS key

Unplug the instrument

Maintenance and safety instructions.

Do not turn the heater control knob to start heating unless the heater is immersed into the oil.

Do not keep the heater control knob in its maximum for a long time.

Avoid contamination of oil bath. Avoid water getting into the oil bath