Measuring the melting point of a substance is a critical quality control (QC) test in pharmaceuticals, as it helps to identify the substance and determine its purity. Here’s how melting point is typically measured in QC:
Methods for Measuring Melting Point
- Capillary Tube Method: A small sample of the substance is placed in a capillary tube, which is then heated in a melting point apparatus. The temperature at which the substance melts is observed and recorded.
- Open Capillary Method: Similar to the capillary tube method, but the capillary tube is not sealed.
- Kofler Hot Stage Method: A small sample of the substance is placed on a hot stage, which is heated slowly. The temperature at which the substance melts is observed and recorded.
- Differential Scanning Calorimetry (DSC): A thermal analysis technique that measures the heat flow into or out of a sample as it is heated or cooled. The melting point is determined by the peak temperature of the endothermic melting peak.
Equipment Used
- Melting Point Apparatus: A device specifically designed to measure the melting point of a substance.
- Thermometer: A device used to measure temperature.
- Hot Stage: A device used to heat a sample slowly and uniformly.
- DSC Instrument: A thermal analysis instrument used to measure the heat flow into or out of a sample.
Procedure
- Prepare the Sample: Obtain a small sample of the substance to be tested.
- Load the Sample: Load the sample into the melting point apparatus or onto the hot stage.
- Heat the Sample: Heat the sample slowly and uniformly.
- Observe the Melting Point: Observe the temperature at which the substance melts and record the result.
Calculations
- Melting Point: The temperature at which the substance melts is recorded as the melting point.
- Melting Range: The range of temperatures over which the substance melts is recorded as the melting range.
Reporting Results
- Melting Point Value: Report the melting point value in degrees Celsius (°C).
- Melting Range Value: Report the melting range value in degrees Celsius (°C).
- Uncertainty: Report the uncertainty of the measurement, if applicable.
Regulatory Requirements
- USP: The United States Pharmacopeia (USP) provides guidelines for measuring the melting point of substances.
- EP: The European Pharmacopoeia (EP) provides guidelines for measuring the melting point of substances.
- ICH: The International Council for Harmonization (ICH) provides guidelines for validating analytical methods, including those used to measure melting point.
Read also:
- Melting Point Database
- Identification Tests in Pharmaceutical Analysis
- Pharmaceutical Quality Control Interview Questions and Answers
Resource Person: Dhruv Jayswal