The liquid chromatography is a key instrument for precision analysis in the laboratory, composed of a high‑pressure pump, injection system, chromatographic column, detector, and other components. Correct operation and regular maintenance are fundamental to ensuring data accuracy and extending the instrument's service life. The following is a summary of precautions and systematic maintenance guidelines for your reference.
I. Core Precautions for Daily Use
Pressure stability is critical. When the mobile phase and flow rate remain unchanged, the column pressure should be stable. A sudden pressure increase usually indicates a blocked or deteriorated column. A sudden pressure drop indicates a possible leak at a fitting or air bubbles in the pump.
Proper bubble removal procedure: Stop the pump (STOP) → Open the purge valve → Press PURGE for a quick flush → After bubbles are cleared, stop the pump → Tighten the purge valve. Do not reverse the order.
It is recommended to set the pump's upper pressure limit to 200 kg and keep the flow rate generally below 1 mL/min. If the pressure is too high, reduce the flow rate accordingly; if the column has aged, replace it promptly.
Add 2–3 drops of specified lubricating oil to the pump's oil port every 15 days to ensure proper lubrication of transmission components and reduce wear.
Salt/acid-containing mobile phase: After the experiment, the system must be flushed with 95 % double‑distilled water and 5 % methanol (v/v) for 40 minutes, then with pure methanol for 30 minutes, to prevent salt crystallisation and corrosion. Before use the next day, equilibrate with the same water‑methanol ratio for 20 minutes.
Pure organic mobile phase: After the experiment, flush directly with pure methanol for 30 minutes before shutting down.
Strictly observe the column's pH tolerance range (typically pH 3–8); do not exceed the limit. Columns are consumable items; replace them promptly when abnormal peaks or excessive pressure occur.
When not in use for a long time, keep the filter immersed in methanol, and start the system every half month to circulate for a period. If liquid cannot be drawn when restarting, use the PURGE function to quickly flush out air.
Adjust only when liquid is flowing. Typically increase the pressure by 8–10 kg, then lock the nut immediately.
The detector may be turned off during flushing, but after the entire flushing procedure is complete, you must press STOP to stop the pump before turning off the power. Never cut the main power directly.
II. Systematic Periodic Maintenance Plan
Frequency: Monthly or every 500 working hours.
Procedure: Flush the pump head and flush valve with methanol‑water (1:1, v/v). Replace piston seals periodically. If the pump head leaks or pressure fluctuates significantly, inspect the seals immediately.
Frequency: Weekly or every 200 injections.
Procedure: Clean the injection port and sample loop with a lint‑free cotton swab dipped in pure water or methanol. Replace the rotor seal periodically according to usage frequency.
Frequency: Quarterly or when baseline noise increases.
Procedure: Back‑flush the flow cell sequentially with pure water, 0.1 mol/L nitric acid, pure water, and methanol (pay attention to direction to avoid damaging the lens). Hydrochloric acid is strictly prohibited.
Frequency: Monthly.
Procedure: Place the mobile phase suction filter in a beaker and sonicate in pure water for 10 minutes, then in methanol for 10 minutes. If severely clogged, soak in 20 % nitric acid for 1 hour, then clean with water and methanol. Replace in‑line filter cartridges regularly.
After each mobile phase change, degassing must be performed thoroughly. At the end of each day, the entire flow path must be thoroughly flushed with appropriate solvents to prevent any buffer salt or corrosive residue.
Keep a detailed log for the instrument, recording start/stop times, sample numbers, column pressure changes, anomalies, maintenance dates, and actions taken. This helps trace the root cause of problems and plan preventive maintenance.
Following these operational guidelines and maintenance plans will greatly reduce the failure rate of liquid chromatography, ensuring long‑term stability and reliability of analytical data across various fields such as pharmaceuticals, chemicals, and food testing.
