Make-up gas (MUG) flow
The make-up gas (MUG) flow mixes with the carrier gas in the flow cell to reduce peak broadening. Increasing the MUG can produce sharper peaks but will reduce sensitivity. Decreasing the MUG increases sensitivity but can reduce peak resolution.
The MUG connects to the rear port on LUMA and is usually nitrogen gas. The normal flow rate is 1.0 - 5.0 mL/min, with a default setting of 2.5 mL/min. It is recommended to always keep the MUG flow > 1.0 mL/min to prevent build-up of contamination in the flow cell. Details on how to optimise the flow rate for improved sensitivity can be found here.
To measure the flow using a volumetric flow meter, first set the carrier gas (CG) column flow rate for the method (usually about 0.8 - 1.2 mL/min). Connect the flow meter to the exhaust gas (EXH) position on LUMA (middle port) and record the reported flow rate, in mL/min. Use the following calculation to determine the MUG flow rate:
MUG flow rate = EXH flow rate - CG column flow rate
To measure the flow using a mass flow meter, set the gas type to nitrogen and repeat the steps above. To calculate the MUG flow rate, use one of the following calculations, depending on whether you're using He or H2 carrier has:
For He carrier gas: MUG = EXH - CG
For H2 carrier gas: MUG = EXH - (CG x 0.25)
System purge gas (SYS) flow
The system purge gas (SYS) flow keeps moisture and oxygen from the atmosphere out of the optical path within LUMA. The SYS connects to the front port on LUMA and is usually nitrogen gas. The normal flow rate is 100 mL/min.
To measure the flow, use a mass flow meter (set to nitrogen) or a volumetric flow meter. Use the LUMA disk tool (or flat-head screwdriver) to remove the two screws on the sides of the LUMA front panel. Lower the front panel and connect the flow meter to the 1/16" stainless steel purge line.
Carrier gas (CG) flow
In some troubleshooting situations, it may be necessary to measure the carrier gas (CG) flow rate at the EXH port. Turn off the AuxEPC connected to the MUG port, disconnect the fitting from the port and attach a 1/16" blanking nut. Connect a mass flow meter (set to your carrier gas type) or a volumetric flow meter to the EXH port.