GC · Calibration procedure
Injector precision
Checks that the autosampler and inlet deliver the same amount of sample each time, by calculating the %RSD of peak areas from replicate injections.
PURPOSE
Why this is checked
Every quantitative GC result assumes the injection is reproducible. Poor injector precision shows up as variable peak areas and failed system suitability.
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
- Certified test mixture or a solution of a stable compound such as n-dodecane or n-tetradecane in hexane (concentration as per your SOP)
BEFORE YOU START
Prerequisites
- New septum and clean liner fitted
- Suitable column (e.g. 5% phenyl polysiloxane) and FID conditions set as in the calibration SOP
- Baseline stable after a blank injection
PROCEDURE
Step by step
- 1Inject the test solution six times in split mode at a fixed volume (e.g. 1 µL).
- 2Integrate the main peak in each chromatogram with the same integration parameters.
- 3Calculate the mean, standard deviation and %RSD of the peak areas.
- 4Optionally calculate the %RSD of retention time as well.
RECORD
Example observation table
| Injection | Retention time (min) | Peak area (pA·s) |
|---|---|---|
| 1 | 8.412 | 245,310 |
| 2 | 8.413 | 243,880 |
| 3 | 8.411 | 246,920 |
| 4 | 8.412 | 244,150 |
| 5 | 8.414 | 247,360 |
| 6 | 8.412 | 245,020 |
CALCULATION
How to calculate the result
%RSD = (Standard deviation ÷ Mean) × 100
- Mean area = 245,440 pA·s
- Standard deviation (n − 1) = 1,426
- %RSD = 1,426 ÷ 245,440 × 100 = 0.58%
ACCEPTANCE CRITERIA
Pass if
- Typically %RSD of peak area not more than 2.0% for FID with split injection (n = 6), or the limit in your SOP.
IF IT FAILS
What to do
- Replace the septum and liner and check the syringe for sticking or air bubbles.
- Check the split vent flow and inlet for leaks.
- Service the autosampler and repeat the test.
- Do not use the instrument until it passes.
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.