Purge Gases and Flow RatesPurge Gases and Flow RatesThe DSC Q Series™ instruments utilize purge gases during experiments.
Select from the following topics for more information:
DSC experiments should always be conducted with a purge gas. With a Mass Flow Controller (MFC), you can switch between two gases for your experiments. Each gas is plumbed separately to the gas ports on the back of the instrument.
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.
Recommended DSC Purge Gases: Helium, nitrogen, oxygen, air, argon.
Recommended Pressure DSC Cell Purge Gases: Nitrogen, air, oxygen, carbon monoxide, carbon dioxide, hydrogen, helium, argon
If you are planning to run subambient experiments with the LNCS, 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.
If you are using an RCS 90 or RCS 40 for cooling, nitrogen may be used as 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.
Purge gas can be obtained from a pressurized cylinder or an in-house supply source. Gas supplied from an in-house source should be passed through a sieve dryer to remove any trace of moisture before it enters the DSC.
The gases are passed through a mass flow controller (MFC), which is inside the DSC cabinet. The flow rate for the MFC is set through the instrument control software. See Specifying the connected purge gases for information.
Switching occurs via a solenoid activated from your experimental method.
If you are using a purge gas that is not one of the available options, you can select "outside purge," which fully opens the MFC valve requiring that the flow rate be controlled using an external flow meter. Or you can select a purge gas type from the drop-down list that has similar characteristics to the one you want to use (e.g., conductivity) and use that calibration table for controlling the flow rate via the MFC.
CAUTION: The mass flow controller is not designed to work with corrosive gases.
WARNING: Do not use hydrogen or any other explosive gas in the DSC. If you are using samples that may emit harmful gases, vent the gases by placing the DSC near an exhaust.
WARNING: Do not use any liquid in the purge lines.
The gas entries on the Notes Page of the Experiment View are used to specify the gas (#1 or #2) and the associated flow rate for each run. These settings will automatically set the gas and flow rate on a run by run basis. The scheduled run's purge settings will take effect immediately once the Apply button is clicked. To change the gas type, access Instrument Preferences.
Recommended Flow Rate: 50 mL/min
The gas flow requirements are different for each method, however, you can use the following guidelines as a starting point to set up the gas purge and air cool flow rates:
DSC cell with Quench Cooler:
purge gas = 50 mL/min with nitrogen or 25 mL/min with helium
air cool = none
DSC cell with LNCS:
purge gas = 50 mL/min with nitrogen (starting temperature above ambient) or 25 mL/min with helium (starting temperature is less than ambient).
air cool = optional*
base purge required
DSC cell with RCS:
purge gas = 50 mL/min with nitrogen or 25 mL/min with helium
air cool = optional*
base purge required
DSC cell with Finned Air Cooling System:
purge gas = 50 mL/min with nitrogen or 25 mL/min with helium
air cool gas = 20 to 120 psi**
* Use to augment the base purge during conditioning and/or when opening the cell lids.
** The pressure is internally regulated to 15 psi by a valve in the instrument.
You can set up your method so that the purge gas is switched during the procedure. This is done using the Gas Segment, which controls the switching of the gas between Gas 1 and 2. In addition, you can also change the flow rate within a method using the flow rate method segment.
During an active experiment you can switch gases using the Control/Gas menu or the GAS button on the instrument's Control touch screen.
