LimsPulse
Chromatography

Gas Chromatograph (GC)

Separates volatile compounds in a heated capillary column using a flowing inert gas and measures each one as it leaves, usually with a flame ionisation detector. Used in pharma QC for residual solvents, volatile impurities and some assays.

  • Pharmaceutical
  • Petrochemical
  • Food & flavour
  • Environmental
  • Forensic
  • Chemicals
Photo of a Gas Chromatograph (GC)
Photo: Sarka Na kopci, CC BY-SA 4.0 (cropped), via Wikimedia Commons
Follow your site SOP
This is a typical operating sequence for learning. Your instrument model and approved SOP take precedence.
STAGE 1

Before you start

  1. 1Check the instrument is within its calibration due date and has no 'out of order' label.
  2. 2Check cylinder pressures for carrier, hydrogen and air; replace a cylinder before it falls below about 10–15 bar so contaminants are not drawn into the system.
  3. 3Check the gas traps' indicators and the septum and liner usage counts against your replacement schedule.
  4. 4Install the column specified in the method with new ferrules, cut squarely, at the correct insertion depth for the inlet and detector. Record it in the column log.
  5. 5Leak-check the new fittings with an electronic leak detector.
  • Gas cylinders must be chained or strapped upright and moved only with a cylinder trolley and the valve cap fitted.
  • Never use liquid leak-detection soap on capillary fittings; it can be drawn into the column.
STAGE 2

Start-up

  1. 1Turn on carrier gas first and let it purge the column for 10–15 minutes before heating the oven, so oxygen does not damage the hot stationary phase.
  2. 2Set the inlet temperature, split ratio, column flow or pressure and oven programme from the method.
  3. 3Heat the detector; for an FID, set hydrogen, air and make-up flows and ignite the flame. Confirm ignition from the signal jump or by holding a cold mirror or spanner over the exhaust to see condensation.
  4. 4Condition a new column as the supplier directs, then run one or two blank programmes until the baseline is stable.
  • Hydrogen is extremely flammable. Turn hydrogen on only when the column is fitted to the detector, and keep the oven door closed so a leak cannot build up in the oven.
  • Do not exceed the column's maximum temperature limit printed on its tag.
STAGE 3

Running samples

  1. 1Create the sequence: blank, system suitability injections, standards and samples, with bracketing standards as the method requires.
  2. 2Run the blank and confirm no interfering peaks at the analyte retention times (septum bleed and carry-over show up here).
  3. 3Check system suitability (resolution, %RSD, tailing, S/N) meets the method limits before processing any sample result.
  4. 4Process chromatograms with the approved integration method; document any manual integration with a reason.
  • If system suitability fails, stop and investigate. Results from a failed run cannot be reported.
STAGE 4

Shutdown

  1. 1Cool the oven, inlet and detector to standby temperatures.
  2. 2Turn off hydrogen and air to the FID (the flame goes out).
  3. 3Keep a low carrier gas flow through the column at all times, or cool fully before switching the carrier off, to protect the stationary phase.
  4. 4Close cylinder valves if the instrument will be idle for a long period, as per site procedure, and complete the usage log.
  • Never switch off carrier gas while the column is hot: oxygen diffusing in will strip the stationary phase.
In LimsPulse · Calibration Management

Keep every GC in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.

See how