INSTRUMENT MAINTENANCE
PRACTICAL TASK P16. GC GAS FLOW RATE Outline The two instrumental variables that control the passage of compounds through a particular GC column are temperature and carrier gas flow rate. The latter is easily checked by measuring the time taken for a soap bubble to travel a certain volume carried by the gas as it exits the column. Procedure 1. Confirm that the gas is switched and adjusted to the appropriate pressure. 2.
Connect the flow gauge to the exit point as shown. 3.
Squeeze the bulb a few times until a stable soap bubble forms and begins to travel. 4.
Measure the time it takes to travel from the 0 to the 5 mL marker. 5.
Repeat this twice more. 6.
Calculate the average time taken. 7.
Calculate the flow rate in mL/min using the formula below. Flow Rate = 60 x volume ÷ average time If you have followed the procedure, the volume is 5. Reporting Requirements Use the standard Performance Check reporting sheet. There is no standard value or pass/fail. Simply record the gas pressure and flow rate (mL/min).