Guidelines When Using the LNCSGuidelines When Using the LNCS
Once the LNCS is properly installed, the system conditioned and calibrated, the following guidelines should be maintained during standard experimental operation.
A dry, moisture-free gas source is required for the cooling gas (LNCS) purge and the base purge when using the LNCS, in addition to the standard cell purge gas. Dry nitrogen is recommended for this purge. These gases must remain on continuously. If they do not, the atmospheric moisture will enter and contaminate the system.
The LNCS Purge is automatically on whenever the cell is opened by the AutoLid to prevent moisture from entering the system. (NOTE: This does not function when the cell lid is manually opened.) It is strongly recommended that the cell lids be in place anytime that a sample is not being actively loaded or unloaded. Turn the LNCS purge on using Control/Air Cool/On prior to removing the lids. Turn the LNCS purge off after the lids are in place.
Important: If you are planning to run subambient experiments, use helium as the purge gas. If you are using the LNCS for rapid cooling above ambient (i.e., isothermal crystallization), then nitrogen may be used as a purge gas.
NOTE: Please make sure that you run your experiments with the same gas that you used to calibrate the system. For example, if you calibrate using nitrogen, make your runs with nitrogen.
Access the Tools/Instrument Preferences/Cooler Page of the DSC instrument control software. Verify that the correct cooler type (LNCS) is selected and check Leave LNCS on. Check the LNCS Autofill if below option, then enter a percentage to automatically fill the LNCS, if desired. This indicates that you want the LNCS to automatically fill at the end of an experiment when the level of liquid nitrogen falls below the specified percent. The fill process, when activated, will fill to completion before advancing to the next scheduled run. If left unchecked, you will need to manually fill the LNCS when needed. (Default = checked, 40%)
When setting up experiments, be sure to verify the post-test conditions. The temperature window should be enabled and a temperature range above ambient should be used to prevent the cell from cooling down between experiments.
When setting up an Autosampler sequence, access the Instrument Preferences/Autosampler Page and select the desired sequence-end option for the LNCS.
Important: DO NOT open the DSC cell at below ambient temperatures to prevent frost and moisture buildup in the cell. If this occurs, the conditioning and calibration steps may have to be repeated.
Important: Once the DSC-LNCS system has been conditioned, it is recommended that you do NOT turn off the LNCS between runs, if the best possible baseline performance is desired.
Important: Operating without an effective base purge, allowing the cell to remain at the lower temperature limit without heater power (e.g., without post-test conditions) for extended periods of time, and/or removing the LNCS from the cell when the flange temperature is below ambient can result in excessive moisture in the cell and requires extended time for drying such as performing Step 1 of Conditioning the LNCS.
WARNING: Do not exceed 100°C with the LNCS cooling head installed and the LNCS power off. Serious damage to the cooling head could occur.
CAUTION: We recommend that you do not use the LNCS when running isothermal experiments above 400°C. The life of the DSC cell heating element can be shortened if the LNCS is used at high temperatures for extended periods.
NOTE: Once the cooling flange reaches operating temperature, it condenses any moisture present. If the initial moisture level is too high, or if the atmosphere moisture subsequently entering the heat exchanger enclosure is not minimized, then artifacts can be observed in the heat flow signals. Typically, but not exclusively, the artifacts are observed between 0 and 100°C, which increase in intensity over time.
