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Melting point tests provide a fast and simple method to verify the purity of solid samples in the lab after synthesis or in manufacturing as a quality control check.
Preparing the samples correctly will ensure results are accurate and comparable. We've taken a look at the proper way to prepare samples for melting point analysis below.
[caption id="attachment_10413" align="aligncenter" width="534"] Testing melting point with the Stuart SMP 10 melting point apparatus[/caption]
Equipment needed;
- Desiccator plus desiccant
- Spatulas
- Watch glass
- Glass rod
- Melting point apparatus
- Melting point capillary tubes
- Your samples
- Appropriate PPE (powder free gloves to avoid sample contamination, plus lab coat and goggles)
Method of sample preparation;
- Place a small amount of your sample (2-5 g is sufficient)on a watch glass and roughly spread out with the spatula. Place the watch glass into the desiccator to dry overnight.
- Remove the watch glass from the desiccator and use the end of the glass rod to grind thew sample to a fine powder. Coarse samples with large crystals mean the heat does not transfer evenly through the sample, and can give erroneous results.
- Check if your melting point tube is closed at one end - if it is open at both ends, seal one end by melting over a bunsen burner.
- Gather the ground sample into the centre of the watch glass, and press the open end of a melting point tube into the powder
- Invert the melting point tube so that the closed end is facing down, and the sample is at the top. Gently tap on the work bench until the powdered sample falls down to the closed end of the tube.
- Repeat steps 4Â and 5Â until you have 2-4mm of sample in the end of the melting point tube.
- Turn on the melting point apparatus and set the required test temperature, then begin the test as per the user manual instructions.
