In the field of transformer insulation oil detection, gas chromatography relies on packed columns to achieve component separation. When problems such as peak distortion and decreased separation occur, it is necessary to replace the packed column in a timely manner to ensure the accuracy of the detection results. The following are the standardized operating procedures and technical points:

Preliminary preparation

1. Power off and cool down: Turn off the power of the gas chromatograph and wait for the column temperature to drop below room temperature to avoid high temperature burns and residual pressure hazards.

2. Tool materials: Prepare specialized wrenches (compatible with both ends of the column joint), newly filled columns (same model as the original column), silicone rubber gaskets, anhydrous ethanol, degreased cotton, nitrogen gas cylinders, and pipelines.

3. Safety protection: Wear chemical resistant gloves and goggles, lay oil absorbing paper on the experimental platform to prevent oil droplets.

Dismantle the old pillar

1. Cut off the airflow: Close the main valve of the carrier gas and slowly release the residual pressure in the system to zero gauge pressure to prevent sudden pressure relief shock.

2. Separate the pipeline: Use two wrenches to fix the nuts at both ends of the column, apply symmetrical force counterclockwise to loosen them, remove the old column and mark the inlet and outlet directions.

3. Cleaning the interface: Use a degreased cotton dipped in anhydrous ethanol to repeatedly wipe the inner and outer walls of the column interface, remove residual particles, and then blow with dry air.

4. Waste disposal: Seal the old columns in dedicated containers and dispose of them according to hazardous waste standards. Direct disposal is prohibited.

Install a new column

1. Direction identification: Check the new column label identification, and the arrow generally points in the direction of the carrier gas flow (the inlet end is connected to the sample inlet, and the outlet end is connected to the detector).

2. Pre assembly: Connect the two ends of the new column to the corresponding interface of the chromatograph, manually tighten the nut 3-5 turns, and keep the column naturally straight without distortion.

3. Sealing reinforcement: Use a torque wrench to gradually tighten the nut in a diagonal alternating manner, with a single rotation angle of ≤ 90 °, and refer to the instrument manual for the final torque.

4. Leak detection verification: Introduce low-pressure nitrogen gas (0.2MPa), soak in soapy water at each interface, observe for the generation of bubbles, and focus on checking the nut gaps and gasket edges.

System activation

1. Segmented heating: Set the program heating mode, with the initial temperature below the lower limit of column temperature by 20 ℃, and raise it to the maximum operating temperature at a rate of 5 ℃/min for 30 minutes.

2. Carrier gas flushing: Maintain the high-purity nitrogen flow rate at 1.5 times the set value throughout the entire process, continuously flush for at least 4 hours, and remove adsorbed impurities from the column.

3. Aging assessment: Inject a small amount of n-hexadecane standard substance, and observe that the peak time deviates from the theoretical value by less than 5%. If tailing or splitting occurs, the aging time should be extended.

Precautions

1. Environmental control: Avoid dusty environments throughout the operation, and use dehumidification equipment when the humidity exceeds 70% on rainy days.

2. Material matching: It is strictly prohibited to mix chromatography columns with different polarity fillers, and the quartz fiber filter must be replaced with the column.

3. Performance verification: After replacement, the calibration curve needs to be redrawn, with a focus on verifying the resolution of the characteristic peaks of polycyclic aromatic hydrocarbons.

By standardizing operations, column efficiency loss can be minimized to the greatest extent possible. When using a new column, it is recommended to inject samples continuously for at least 3 times until the baseline is stable before conducting formal sample analysis. Regularly recording column life data helps optimize preventive replacement cycles.