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www.thinkSRS.com/products/MPA.htm Melting Point Determination Application Note #1 Introduction A few basic guidelines must be carefully followed to avoid errors during melting point determinations with OptiMelt. The way in which the sample is prepared and the instrument is programmed have the greatest influence on the accuracy and reproducibility of a melting point measurement. Subjective interpretation of the changes observed in the sample (visually and/or automatically) during the analysis can also lead to unreliable results. Background The melting point of a substance is the temperature at which the material changes from a solid to a liquid state. Pure crystalline substances have a clear, sharply defined melting point. During the melting process, all of the energy added to a substance is consumed as heat of fusion, and the temperature remains constant. A pure substance melts at a precisely defined temperature, characteristic of every crystalline substance and dependent only on pressure (though the pressure dependency is generally considered insignificant). Determining the MP is a simple and fast method used in many diverse areas of chemistry to obtain a first impression of the purity of a substance. This is because even small quantities of impurities change the melting point, or at least clearly enlarge its melting range. Melting point determinations are more than just a classroom exercise in the organic chemistry lab. The test is still an important technique for gauging purity of organic and pharmaceutical compounds. The determination of melting points is one of the oldest identification and test methods for organic substances. The melting point is easy to measure, tabulate and classify. Extensive collections of tables give the exact values of many pure, inorganic and organic compounds. The MP determination is a fast and cost- effective technique which remains a strong link to the vast pre-instrumental chemistry literature. Capillary Method The procedural rules for melting point determinations are defined in the pharmacopeias. The medical handbooks include minimum requirements for the Stanford Research Systems Phone: (408) 744-9040 Melting Point Determination www.thinkSRS.com/products/MPA.htm design of the melting point apparatus and for performing the measurements. Automated melting point determination procedures are generally included. Very often, the pharmacopeias also list special methods for difficult or unusual cases of melting point determination. 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 sampl