Do’s & Don’ts Regarding Operation of Gas Chromatography

Do’s

Before starting the instrument, verify the volume of gas in cylinder.If the primary gas pressure is less than 4 psi, replace it.
Purity of carrier gas should be maintained to prevent degradation of chromatographic hardware.
Purity of gases should be 99.999% and cylinder should be supplied with a purity certificate.
Gases should be passed through a gas panel containing Hydrocarbon and Oxygen traps to ensure no impurity or moisture enters the Inlet or Column.

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Immediately change the expired oxygen and moisture traps (when blue colour changes to white) to avoid gas contamination.
During cartridge replacement, check valves and close off the system to the atmosphere, further minimizing the entry of contaminants.
Start the Instrument (GC-HS) first then Load the software from the system.
Once the Instrument is “On”, always start the machine by running ‘Conditioning’ method for half hour.
Samples and Standards should be clearly marked and labelled, to avoid error.
Always use fresh, clean and sterile vials for sample preparation and storage.
Septa with a PTFE face down, should be used to seal the headspace vial to eliminate bleed from the septa.
Shaking or vibrating the vial containing high viscosity sample matrices during heating can assist in achieving equilibrium faster.
Adjust the temperature of the sample to change the solubility of the analyte as well as to drive the equilibrium in towards the gaseous phase.
To minimize matrix problems and prevent water condensation from aqueous samples, use a higher transfer line temperature, usually 100 higher than sample heating temperature.
Heat the syringe to a temperature comparable to the sample vial temperature to minimise pressure differences, when using gas tight syringes.
Ensure the septum of the GC injection port is well maintained to decrease the possibility of a leak.
In Headspace, septa can be changed after 500 injections.
Use injection port liners of small internal diameters and lower buffer volumes to maintain a narrow bandwidth.
Use an on-column syringe when injecting into an on-column inlet so that the injector, syringe and column are not damaged.
Inject standards and samples in order from low to high concentrations to help minimize carryover.
For high concentration samples in a sequence of samples, run a blank after the suspected samples to reduce carryover contamination.
Increase the oven temperature after the samples are completely transferred to the column to increase the movement of compounds inside the column.
Built sufficient time into the sample cycle to achieve constant state of equilibrium.
GC instrument maintenance should include checking fittings and connections with a gas leak detector.
To prevent stationary phase decomposition, the oven and inlet should be at room temperature when not in use and when changing the septum.
After running the samples, condition the system at least 30min before shut down.
Always ensure Detector temperature reaches 500°C and lower, before switching “Off” the GC Instrument.

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Don'ts

Constant exposure of capillary columns to oxygen and moisture should be avoided especially at high temperatures as it may produce rapid and severe column damage.
Improper handling or installation of gas lines should be avoided as moisture introduced by this can be a common cause of column stationary phase degradation.
Do not use sample matrices containing high molecular weight compounds to avoid incomplete or inefficient transfer into the GC injection port.
Transfer line temperature should not be kept low than sampler oven as water from the sample matrix can cause problems by condensing in the transfer line.
Avoid using high-concentrated samples lest they produce ghost peaks in subsequent analyses due to carryover of sample from previous injections.
Do not use reuse unclean or unpacked vials.
Septa with punctured PTFE face should not be reused.
Do not use transfer line having smaller internal diameter than the injection port liner to avoid broader peaks, tailing peaks, lower sensitivity, and loss of resolution.
Use company recommended regulator materials and tubing. These should only be changed by an company engineer.
Non-metallic types of tubing such as polyethylene and Teflon are not recommended for GC applications due to their gas permeability and difficulty in cleaning.
Unclean or improperly cleaned tubing can lead to contamination of the system with disastrous results.
Never open the GC door if oven temperature is more than 1000°C or during running conditions.
Do not inject air into the vials to prevent the vacuum. This often damages the cap seal.
Avoid cleaning agents that are alkaline, contain phosphates, or are strongly acidic for syringes or glassware.