Melting Point Apparatus: How It Works and How to Choose One
A melting point test is one of the quickest ways to check the identity and purity of a solid. A pure crystalline substance melts sharply at a characteristic temperature; impurities usually lower the melting point and make it melt over a wider range. That is why melting point apparatus is found in almost every pharmaceutical QC lab, pharmacy college and chemistry teaching lab.
How the capillary method works
- A small amount of dry, finely powdered sample is packed into a thin glass capillary tube, closed at one end, to a height of a few millimetres.
- The capillary is placed in a heated block or oil bath next to a thermometer or temperature sensor.
- The temperature is raised quickly to a few degrees below the expected melting point, then slowly, typically about 1°C per minute.
- You watch the sample through a magnifier and record the temperature when it starts to melt and when it is completely liquid. That is the melting range.
Tips for accurate results
- Dry and powder the sample well; moisture and coarse crystals widen the melting range.
- Pack evenly and keep the sample height consistent between tests.
- Heat slowly near the melting point. Heating too fast is the most common cause of high readings.
- Check calibration regularly with reference standards of known melting point.
- Follow your pharmacopoeia or in-house method for ramp rate and reporting.
Basic or digital apparatus?
Our PT-122 melting point apparatus is a simple, economical instrument for melting points up to 300°C using capillary tubes. It suits teaching labs and routine checks. Capillaries are available in 75 mm (PT-122/10) and 100 mm (PT-122/15) lengths, in packs of 100.
Our PT-125 digital melting point apparatus is the better choice for QC labs. It has:
- a range from 2°C above room temperature to 300°C, readable to 1°C;
- a digital temperature indicator with PT-100 sensor;
- a built-in magnetic stirrer that keeps the oil bath at an even temperature;
- an electronic heating-rate controller with HIGH/LOW range;
- a magnifier and glare-free illuminated background for clear viewing;
- an SS 304 body, supplied with 175 ml of silicone oil and a box of capillaries.
Quick comparison
| PT-122 | PT-125 digital | |
|---|---|---|
| Range | Up to 300°C | Room temperature +2°C to 300°C |
| Temperature reading | Thermometer | Digital, PT-100 sensor, 1°C |
| Heating-rate control | Basic | Electronic, HIGH/LOW |
| Bath stirring | No | Built-in magnetic stirrer |
| Best for | Teaching labs, routine checks | Pharmaceutical QC, R&D, contract testing |
Frequently asked questions
Why does an impure sample melt at a lower temperature?
Impurities disrupt the crystal structure, so the solid starts melting earlier and melts over a wider range. A sharp melting range close to the reference value is a good sign of purity.
What heating rate should I use?
Heat quickly to a few degrees below the expected melting point, then at about 1°C per minute, or as your pharmacopoeia or method specifies.
What is the maximum temperature of your melting point apparatus?
Both the PT-122 and the PT-125 measure melting points up to 300°C.
Which capillaries do I need?
Glass capillaries closed at one end. We supply 75 mm and 100 mm capillaries in packs of 100.
How do I get a quotation?
Use “Make an enquiry” on the product page, WhatsApp 8199900060 or email popular1942@gmail.com.