Do’s
- Before starting the instrument, verify the volume of gas in the cylinder. If the primary gas pressure is less than 4 psi, replace it.
- The purity of carrier gas should be maintained to prevent the degradation of chromatographic hardware.
- The purity of gases should be 99.999% and the 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.
- Immediately change the expired oxygen and moisture traps (when the blue color 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 the ‘Conditioning’ method for half an hour.
- Samples and Standards should be clearly marked and labeled, to avoid errors.
- 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 bleeding 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 toward the gaseous phase.
- To minimize matrix problems and prevent water condensation from aqueous samples, use a higher transfer line temperature, usually 100 higher than the sample heating temperature.
- Heat the syringe to a temperature comparable to the sample vial temperature to minimize 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 a 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 the 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 the 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 the carryover of samples from previous injections.
- Do not use reuse unclean or unpacked vials.
- Septa with punctured PTFE face should not be reused.
- Do not use a transfer line having a 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 a 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 the 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.
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Tags
Chromatography
