How are pure crystalline substances characterized?

Automatic purity check through melting point analysis

Melting point determination can be used as a simple, accurate and reliable analytical method for characterizing crystalline pharmaceutical ingredients. Pure substances melt exactly at a defined temperature, but the same substances have a lower and less precise melting point in a wide temperature range when they are contaminated with impurities. This behavior can therefore be used to check the purity and identity of a substance - important QC parameters for pharmaceutical substances.

Qualitative determination of the purity of the substance
Let's assume we have two batches A and B of acetylsalicylic acid, a well-known pain reliever. For the melting point analysis, the operator prepares individual melting point capillaries with the corresponding samples from pure batch A, pure batch B and a mixture in a weight ratio of 50/50% from batches A and B. If the melting temperatures of all three samples are the same, it means that batches A and B are identical and have the same purity. If the melting point of the batch mix is ​​between the higher melting point of batch A and the lower melting point of batch B, it can be concluded that both batches are salicylic acid and batch B contains more impurities than batch A. Thus, a simple melting point experiment provides excellent results Information on an important parameter for pharmaceutical quality control: purity.

Automatic workflows with MP90 and LabX
The MP90 Excellence melting point system enables the simultaneous measurement of six melting point capillaries. This unique function serves as the perfect support for the required workflow, as two capillaries of batches A and B can be measured in one run. The LabX PC software increases the efficiency and safety of the workflow by displaying work instructions on the touchscreen and guiding the operator through the entire process. After completion of the measurement, the mean value is automatically calculated for each pair of capillaries. Based on this value, an automatic evaluation of the sample purity can take place. The results and the video of the melting point analysis are securely stored in the LabX database and are available at any time for the subsequent visual inspection. LabX helps avoid test errors by supporting the entire workflow directly on the instrument on which the test is being performed.

Automatic evaluation of results
In LabX you can define up to three tolerance limits for results for the automatic evaluation of the measured melting points. The first value indicates that the melting point is within the expected tolerances. The second value indicates that the impurities have lowered the melting point to such an extent that countermeasures should be taken or production must be stopped if the third limit value is also exceeded. The corresponding results are clearly highlighted in the results overview using color-coded tags and comments. The setting of tolerance values ​​supported by LabX and the evaluation of results contribute to reliable and neutral quality control.