OptiMelt Automated Melting Point System - Stanford Research ...

68 Maintenance and Calibration Chapter 4Step 7Once the melt is completed, or clear points have been detected, a Report is generated.Compare the visual results (manual entries for clear point) for the three capillaries againsteach other. The clear points for the three capillaries must fall within ±0.3 °C of each otherto be considered acceptable.A spread in melting point values among the three samples larger than ±0.3 °C could besymptomatic of a heating asymmetry in the oven block caused by unbalanced heaters.However, it is most often caused by subtle differences in sample packing, sample heightsand sample placement in the slots. Repeat the measurement if a large spread is observed,taking special care to prepare all three capillaries in the exact same way. Consult thefactory for additional recommendations if no improvement is detected.If this CRS has a single Rated MP, then calculate the average of the three clear points forthis CRS. This is the Measured MP (MP Measured ) for this CRS.If this CRS has a specified melting point range, instead of a single Rated MP, thencalculate the mean melting point (average of onset and clear points) for each capillary.Use the average of the three mean melting points for this CRS as the Measured MP(MP Measured ).TipsWhenever possible, use the MeltView software to visualize the melts and to store acomplete record of the analysis. The ability to replay a melt on a computer screen is notonly important to confirm and fine tune your visual determinations, but also to providecomplete documentation in accordance to GLP guidelines.Step 8Calculate the melting point ranges (MP Range = clear point - onset point) for the threecapillaries. The MP Range must be less than 2 °C (at 1 °C/min ramping rate) to beacceptable.If the measured MP Range exceeds 2 °C (at 1°C/min ramping rate), check the rampingrate and the sample preparation procedure to eliminate any potential experimental errorsand repeat the determination if necessary. If no improvement is observed consult thefactory for additional information.TipsThe melting point range for a pure substance melted at 1 °C/min ramping rate is typically1.25 ± 0.25 °C. Larger ranges are observed at higher ramping rates (As a general rule, theMP Range scales with the square root of the ramping rate).If a melting point range larger than 2 °C (at 1°C/min ramping rate) is observed, and nosample contamination is suspected, a malfunction of the instrument should be suspectedand the instrument should be serviced. Contact the factory or your local representative foradditional information.OptiMelt Automated Melting Point System