OptiMelt Automated Melting Point System - Stanford Research ...

Chapter 3 Melting Point Determination 49• Some chemists choose to make their own capillary tubes. This is not recommendedfor accurate and reproducible results. The use of commercial capillaries, with tightmanufacturing tolerances, is strongly recommended instead.• For precision measurements, the optimum filling height of 2-3 mm must be strictlyobserved.• The use of a packing wire to compact a sample can lead to excessive bubbleformation and trapping during the phase transition. Do not use a packing wire ifexcessive bubble formation interferes with the detection of the meniscus and clearpoints of your sample.Tube CleaningFailure to clean the glass tubing before making capillary tubes is one of the chief causesof low melting points and wide melting ranges. The presence of alkali on the surface ofthe sample tubes is one of the main problems. This is generally not an issue with premade,commercially available melting point capillaries.ImportantIf you must make your own tubes, make sure the glass stock is cleaned by rubbing theinside with dilute solution of a neutral detergent, rinsing with dilute (10%) HCl, andfinally rinsing thoroughly with distilled water.OptiMelt Automated Melting Point System