1Liquid Chromatograph5 Core Techniques for Daily Maintenance

Mobile phase management: dual insurance of degassing and filtration

Degassing: The mobile phase needs to be pre treated with ultrasonic degassing or online degassing devices to avoid pressure fluctuations or baseline noise caused by bubbles entering the pump system. For example, the helium degassing method can remove 80% of dissolved oxygen, but online degassing modules (low-cost, low failure rate) are more commonly used in domestic laboratories.

Filtration: All mobile phases (especially solutions containing buffer salts) need to be filtered through a 0.45 μ m microporous membrane to prevent particle blockage of the one-way valve or chromatographic column inlet sieve plate. If HPLC grade solvents are used, the filtration step can be omitted, but the buffer salt solution must be filtered.

Pump system maintenance: Sealing rings and check valves are key

Sealing ring maintenance: Worn pump sealing rings can cause leakage or pressure fluctuations. It is recommended to replace them every 6 months. If gray black sediment (gasket wear) or yellow/green stains (microbial contamination) are found, the replacement cycle should be shortened.

Cleaning of one-way valve: Use isopropanol ultrasonic cleaning for 10-15 minutes to remove salt precipitation or impurities blocking the one-way valve. If the pressure is still unstable after cleaning, the one-way valve needs to be replaced.

Column protection: Backwash and preservation specifications

Backwash operation: Only chromatography columns explicitly allowed by the manufacturer (such as the ChromCore series for nanophotonic analysis) are allowed to be backwashed to remove impurities from the column head. The flow velocity during recoil should be lower than the conventional analysis flow velocity to avoid damage to the packing structure.

Long term storage: The chromatographic column should be filled with acetonitrile or methanol, and both ends should be sealed with plugs to prevent solvent evaporation from causing the packing to dry. Do not leave the buffer solution overnight in the column, otherwise salt precipitation will permanently damage the chromatographic column.

Detector Cleaning: Flow Pool and Light Source Management

Cleaning of circulation pool: After daily analysis, rinse the detection pool with isopropanol or 6M nitric acid solution to avoid salt precipitation or sample residue blockage. If there is a regular fluctuation in the baseline, it may be due to bubbles entering the flow cell, and the detector needs to be rinsed with isopropanol.

Lamp source lifespan: The lifespan of ultraviolet lamps is about 2000 hours, and when approaching the time limit, the lamp energy (low, medium, and high wavelength bands) needs to be tested through instrument software. If there is insufficient energy in a certain wavelength range, the light source needs to be replaced.

Anti contamination of injection system: cross contamination and maintenance of needle sealing gasket

Automatic sampler: Enable needle washing function, clean the inner and outer surfaces of the injection needle with initial proportion mobile phase to avoid high concentration or adsorbed sample residue. If the reproducibility of peak area is poor, check whether the liquid level of the sample bottle is sufficient or whether the bottle cap is too tight (resulting in inaccurate sample aspiration).

Manual sampler: Use LC dedicated injection needle, clean the inner and outer surfaces of the needle immediately after injection to avoid sample deposition on the needle seat or flow valve.

2、 Troubleshooting and Solutions

Abnormal column pressure: fluctuation, increase or decrease

Pressure fluctuations:

Reason: There are bubbles inside the pump, the one-way valve is blocked, and the sealing ring is worn.

Solution: Re exhaust (high flow flushing pump), ultrasonic cleaning of one-way valve, replacement of sealing ring.

Pressure increase:

Reason: Blockage of chromatographic column, failure of protective column, high viscosity of mobile phase.

Solution: Backwash chromatography column (if allowed), replace the protective column, and use low viscosity solvents (such as acetonitrile instead of methanol).

Pressure reduction:

Reason: System leakage, low flow rate setting, improper selection of chromatographic column.

Solution: Check the connector connection, adjust the flow rate, and replace the appropriate chromatographic column.

Baseline noise and drift

Baseline noise:

Reason: Bubbles entering the circulation pool, insufficient energy of the detector lamp, and contamination of the mobile phase.

Solution: Rinse the detector with isopropanol, replace the light source, filter or replace the mobile phase.

Baseline drift:

Reason: Column temperature fluctuation, uneven mobile phase, and contamination of the flow pool.

Solution: Stabilize the room temperature, use a mixer to ensure uniform mobile phase, and clean the flow cell.

Spectral anomaly: retention time drift or peak shape deformation

Retention time drift:

Reason: Indoor temperature changes, changes in mobile phase composition, and chromatographic column imbalance.

Solution: Control room temperature, use freshly prepared mobile phase, and extend column equilibrium time.

Peak deformation (tailing or broadening):

Reason: Column contamination, excessive injection volume, improper pH of mobile phase.

Solution: Clean or replace the chromatography column, reduce the injection volume, adjust the pH of the mobile phase to the tolerance range of the packing (such as pH 2-9 for silica gel matrix columns).

IIILiquid ChromatographLong term maintenance recommendations

Record maintenance history: Establish instrument logs to record each maintenance date, content, replacement consumables model, and abnormal situations, for easy tracking of performance changes.

Regular calibration: Calibrate the detector sensitivity, pump flow rate accuracy, and column temperature every quarter to ensure data accuracy.

Spare parts management: Reserve commonly used consumables (such as sealing rings, one-way valves, chromatographic column inlet sieve plates) to avoid downtime caused by waiting for spare parts.