GC · Calibration procedure
Carrier gas flow accuracy
Compares the carrier gas flow set by the electronic pressure control with the flow measured by a calibrated flow meter.
PURPOSE
Why this is checked
Column flow controls retention times and efficiency, and split vent flow controls how much sample reaches the column. Inaccurate flows change retention, sensitivity and peak areas.
Frequency
Typically every 6 or 12 months, and after major repair or relocation, as defined in your calibration SOP.
Learn how the GC worksYOU WILL NEED
Standards & tools
- Calibrated electronic (digital) gas flow meter suitable for the carrier gas used, traceable to national standards
BEFORE YOU START
Prerequisites
- Instrument leak-checked and gas supply at normal pressure
- For column flow, connect the flow meter to the column outlet (detector end disconnected) or use the manufacturer's test column/restrictor
- Set the flow meter to the correct gas type (helium, nitrogen or hydrogen)
- Oven at a fixed temperature (e.g. 40 or 50 °C) so viscosity is constant
PROCEDURE
Step by step
- 1Set the column flow to the first value (e.g. 1.0 mL/min) in constant-flow mode and wait 2–3 minutes to stabilise.
- 2Record the mean of three flow meter readings.
- 3Repeat at other flows used by your methods (e.g. 2.0 and 5.0 mL/min).
- 4Measure the split vent flow at a typical setting (e.g. 50 mL/min) by connecting the flow meter to the split vent outlet.
- 5Calculate the % error for each setting.
RECORD
Example observation table
| Measured at | Set flow (mL/min) | Observed flow (mL/min) | % error |
|---|---|---|---|
| Column outlet | 1.0 | 0.98 | −2.0 |
| Column outlet | 2.0 | 2.03 | +1.5 |
| Column outlet | 5.0 | 4.94 | −1.2 |
| Split vent | 50.0 | 49.1 | −1.8 |
CALCULATION
How to calculate the result
% error = (Observed − Set) ÷ Set × 100
- Set 2.0 mL/min, observed 2.03 mL/min
- % error = (2.03 − 2.0) ÷ 2.0 × 100 = +1.5%
- Within a typical ±5% limit, so it passes
ACCEPTANCE CRITERIA
Pass if
- Typically within ±5% of the set value for column and split flows (some SOPs use ±10% at very low flows). Use the limit in your SOP.
IF IT FAILS
What to do
- Label the instrument 'Out of calibration' and stop using it.
- Leak-check the inlet, septum and column fittings, and confirm the correct column dimensions are entered in the software.
- Check the flow meter gas setting and repeat.
- Get the EPC module serviced or recalibrated by an engineer, then repeat the full test.
MORE
Other GC calibrations
In LimsPulse · Calibration Management
LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.