OptiMelt Automated Melting Point System - Stanford Research ...

Chapter 1 Getting Started 95. Enter the Start temperature (°C)The Start temperature is programmed by touching the Start button on the touchscreenLCD and entering a number using the displayed numeric keypad.The Start temperature is the temperature at which the sample capillaries are introducedinto the heating stand, and serves as the starting point for the heating ramp.TipThe Start temperature should be at least 5 °C below the known melting point of thesample(s).6. Enter the Stop temperature (°C)The Stop temperature is programmed by touching the Stop button on the touchscreenLCD and entering a number using the displayed numeric keypad.The Stop temperature is the temperature at which the heating ramp is terminated.TipA Stop temperature at least 10 °C higher than the Start temperature is recommended forthis procedure.7. Enter the ramp Rate (°C/min)The ramp Rate is programmed by touching the Rate/min button on the touchscreen LCDand entering a number using the displayed numeric keypad.The ramp Rate is the fixed rate of temperature rise between the Start and Stoptemperatures for the heating ramp (see Fig. 5). A ramp Rate of 1 °C/min is recommendedfor routine determinations. For ramping rates of 1 °C/min, a melting range of about 1–2 °C is typically recorded for pure substances.Tip• The ramp Rate is the most important instrument parameter affecting the accuracy andreproducibility of measurement of melting points. Rates up to 2 °C/min arereasonable for routine determinations. Higher rates are only recommended for quickdeterminations on substances with unknown melting points. Purity determination andprecision measurements are performed at a maximum heating rate of 0.5 °C/min,though the recommendation is to stay at 0.1–0.2 °C/min whenever feasible. Samplesthat start to decompose at temperatures below their melting point, are usuallymeasured at ramp rates above 5 °C/min to avoid contamination from byproducts.Mixed melting point determinations (described later) can be performed with ramprates as large as 10 °C/min.• OptiMelt systems are calibrated at the factory using a 1 °C/min ramp rate. Atemperature offset calibration procedure should be carried out for routine operation ata different ramp rate (see Chapter 4).OptiMelt Automated Melting Point System