Question

In determination of melting point why is a new capillary tube used in each new determination

Answer 1

Answer:

The pharmacopeias regard the capillary method as the standard technique for  melting point determination. In this methodology, a thin glass capillary tube  containing a compact column of the substance to be determined is introduced  into a heated stand (liquid bath or metal block) in close proximity to a high  accuracy thermometer.

The temperature in the heating stand is ramped at a  user-programmable fixed rate until the sample in the tube transitions into the  liquid state.

While determining a melting point, several observations and the  temperatures are recorded.

Tips

• The metal heating stand of OptiMelt can accommodate three capillary

tubes so that up to three independent samples can be analyzed at the

same time. A platinum resistance thermometer, in close proximity to the

sample slots, is used to read the temperatures during the melt.

• Your OptiMelt includes a vial of precision melting point capillaries

specifically designed to fit the sample slots and provide the most uniform

and repeatable results.

The capillary method described by most pharmacopeias relies on a visual

detection of the melt. However, some modern instruments, such as OptiMelt,  enable automated detection of the melting point and melting range, while at the  same time providing a view of the sample during the process.