SOP for Routine and Preventive Maintenance of Agilent Gas Chromatography

To describe the procedure for preventive maintenance of Agilent GC.

Executive – Quality Control– To perform the preventive maintenance activity.
Head Quality- Quality Control – To ensure compliance against the established schedule.


Preventive Maintenance
  • Ensure that the power supply to the instrument is switched “off” before starting the preventive maintenance.
  • Clean the instrument with a clean dry cloth every day.
  • Performance checks shall be done for the following parameters before doing preventive maintenance.
  1. Flow accuracy
  2. Retention Time Reproducibility
  3. Area Ratio Reproducibility
  4. Oven Temperature
  • Enter the values in standard maintenance card as per sop

The following components of GC shall be subjected for preventive maintenance on the scheduled date.

Gas Chromatograph:
  • The instrument shall be cleaned from dust with a blower.
  • External gas leaks shall be checked with soap solution , all valves shall be tightenin case any leaks found.
  • Clean the injector port liner and change the septum
  • Clean the detector parts with DMA

Head Space:
  • Clean the system from dust.
  • Clean the HSS needle or change as and when required.
  • Check the status of rotor and stator of the HSS valve (sampling).
  • Check the contamination of transfer line.
  • Perform stream cleaning of HSS.

Enter the performance checks and preventive maintenance checks in the standard maintenance card as per SOP.
  1. Stick the under preventive maintenance label during performing.
  2. Enter the preventive maintenance status details as per SOP Preventive Maintenance Programme for Laboratory Instruments..
  3. The frequency of the schedule is every 3 months.

Routine Maintenance

1. Tank Replacement
A gas tank requires replacement when the high pressure gauge reads 500 psi or less.

A weak soap solution in a squeeze bottle (“Snoop”)
Crescent wrench that can open to at least a 2-inch diameter.

  1. Make sure no runs are currently in progress on any GC using the tank.
  2. Turn off gas tank at the valve.
  3. Using the Crescent wrench, loosen the large nut connecting the gas gauge and the tank outlet. Remove the gas gauge.
  4. Place a steel protective cap onto the empty gas tank. Remove the tank restraints and place the empty tank to one side. Label it “Empty”.
  5. Move a new, full tank into place and secure it with the tank restraints. Replace the gas gauge inlet into the tank outlet and tighten the nut using the wrench. Open the new tank.
  6. Check all joints and connections with the snoop. The presence of growing soap bubbles indicates a gas leak. Tighten or replace all joints and connections as necessary.
  7. Restore gas flow and check all affected GCs. Reset GC’s to operating conditions.
  8. As appropriate, adjust the bead power before use.
  9. Return all tools to their proper location.

2. Septa Replacement
  • A septum in the GC requires replacement when a significant change in the retention time of known peaks in any given control occurs. As a practical matter, it is recommended that the septum be changed weekly or after approximately 100 injections.

Replacement green septum (11mm diameter).
Lint-free gloves
Septum nut angled wrench

  • Set GC inlet temperature to 50°C, turn off inlet pressure. Wait until the inlet temperature falls below 100°C. The oven temperature is 120°C.
  • Remove autosampler tower and store safely.
  • Remove the septum nut with the appropriate wrench. 
CAUTION: SEPTUM NUTS MAY BE HOT! Use lint-free gloves to protect from burns.
  • Remove the old septum from the septum seat using the tweezers. Discard the old septum. If required, use the tweezers to remove old septum debris from where it sits.
  • Install a new septum using the tweezers. Replace and tighten the septum nut. Don’t over tighten the septum nut as it will expand due to injection port heating.
  • Replace the tower, restore the inlet temperature. Record this maintenance in the GC maintenance log for the GC. Initial and date the maintenance log.
  • Return all tools to their proper locations.

3. Injection Port Liner Replacement
  • Injection port liners with glass wool plugs are purchased from Supelco (or equivalent). The liners are changed when a drug contained in either a calibrator or control has a poor recovery that consists of tailing or broadening of its usual peak shape.

Clean glass liner: Split/Splitless Injection Sleeve (4mm ID) packed with deactivated glass wool
Graphite O-ring (6.35mm ID; 9.63mm OD)
Lint-free gloves
Septum nut angled wrench
Cotton swabs

  1. Set GC inlet temperature to 50°C, turn off inlet pressure. Wait until the inlet temperature falls below 100°C. The oven temperature is 120°C.
  2. Find the septum nut angled wrench; loosen the larger nut beneath the septum nut (the 22mm hexagonal injection port nut).
  3. Once the nut is free of the threading, gently move the housing aside. Be extremely careful not to snap or bend the tubing connected to the nut.
  4. Remove existing graphite O-ring. Using the tweezers, gently remove the glass liner from the injection port. Do not remove the liner at an angle as it can break and lose glass can particles can remain in the inlet.
  5. Get a clean, glass liner; using the wood end of a cotton swab, push the glass wool plug to the proper position the plug so that it is approximately 1cm from one of the ends of the glass liner.
  6. Place a new graphite O-ring on the end of the liner tube. Insert the liner with plug and O-ring back into the injection port with the plug end first (to the bottom of the injection port).
  7. Replace the injection port nut and tighten using the injection port nut wrench. Restore the inlet temperature and pressure to their routine operating values.
  8. Test runs are performed to remove possible contaminants remaining on the glass wool, inject methanol washes followed by injections of Cal Group 1 and Group 2 at 0.2 mg/L to ensure that the system is operating properly.
  9. Review the test runs: check that the chromatogram does not exhibit any signs of a leak, check the recovery of the internal standard and all the drugs in the groups, ensure that all drugs from each group are present and that there are no extraneous peaks. Consult test run with a supervisor.
  10. Record this maintenance in the GC’s maintenance log, provide all necessary documentation.
  11. Return all tools to their proper locations.

4. NPD Bead Replacement
  • NPD beads require replacement after bead voltage reaches the threshold of 4.093.

NPD replacement bead (Agilent part#G1534-60570)
Lint-free gloves
Allen wrench (1 mm)
Torx screwdriver, T-10

  1. Set bead voltage to 0.0 volts. Set detector temperature to 150°C. turn off gases to the detector. Allow cooling to 150°C. The oven will shut down once the door is opened.
  2. Remove side covers of the GC. With the Torx screwdriver, remove the 3 screws on the bead assembly (caution: these screws will be hot), gently remove the bead.
  3. Install the NPD Bead Assembly, each comes with three new screws. Review instructions included with each new bead. Do not touch the ceramic bead, and handle the bead assembly gently.
  4. Replace the three screws using the Torx screwdriver. Replace the GC’s covers that were removed.
  5. Restore all flows and temperatures to their normal operating conditions.
  6. After bead flows and temperature stabilize, use the keypad on the instrument scroll to the “adjust offset” for the replaced detector and select the “on” button. The newly installed NPD bead will adjust itself until the bead is ready to be used. Once this process is complete, the instrument will turn the “adjust offset” off, then adjust the bead voltage to 3.600 volts.
  7. The new bead is extremely sensitive and if used right away may cause carryover issues when injecting extracted cases. To lower the output of the bead, make multiple injections of methanol, followed by multiple injections of Cal Groups 1 and 2 at 0.2mg/L. Evaluate injections for the response of all the compounds, consult test runs with a supervisor.
  8. Record this maintenance on the GC maintenance log for the GC. Record this maintenance in the GC’s maintenance log, provide all necessary documentation.
  9. Return all tools to their proper locations.

SOP – Standard Operating Procedure
NMT – Not More Than
% RSD – Percentage Relative standard deviation



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