How to solve the pressure instability in liquid chromatography analysis

1. Routine maintenance measures: Regular replacement of critical components: It is recommended to establish replacement cycles based on the instrument's usage frequency (e.g., for high-frequency use, replace the sealing ring every 3-6 months, inspect and replace the filter head monthly, and replace the guard column after 100-200 injections). Maintain records after replacement for traceability purposes.

Complete degassing: Prioritize the use of an online degasser to ensure effective degassing. If ultrasonic degassing is employed, attention must be paid to the ultrasonic duration (typically 15-20 minutes). After ultrasonication, allow a brief rest period before use to prevent re-introduction of bubbles. Buffer saline solution should be prepared and used immediately to minimize gas dissolution.

Strict sample pretreatment: All samples and mobile phases must be filtered through 0.22 μm (reverse-phase chromatography) or 0.45 μm (normal-phase chromatography) filter membranes. When analyzing complex matrix samples such as biological or environmental samples, additional pretreatment steps (e.g., solid-phase extraction, liquid-liquid extraction) should be performed to remove interfering impurities.

Proper storage of chromatographic columns: After use, the column should be rinsed with a compatible solvent (e.g., methanol or acetonitrile for reversed-phase columns) to remove residual impurities. For long-term storage, the column must be sealed at both ends and stored in a cool, dry place to prevent bed drying and filler degradation.

Regular cleaning of instrument components: Clean the injector and tubing connectors weekly, and disassemble and clean the online filter monthly to prevent impurity accumulation. Use compatible solvents (e.g., methanol, isopropanol) during cleaning to avoid component damage.

2. Baseline data recording for troubleshooting: Prior to troubleshooting, record the system pressure baseline under normal conditions (e.g., pressure value at a flow rate of 1.0 mL/min) as a comparative reference. Simultaneously, document the amplitude and frequency of pressure fluctuations, as well as whether they are synchronized with operations such as sample injection and gradient elution.

Segmental pressure inspection: Divide the system into multiple sections including pump outlet, online filter, guard column, analytical column, and detector. Disconnect each section sequentially, measure the pressure value of each section, and identify the specific section with abnormal pressure.

Begin the step-by-step backward troubleshooting from the pump: First, shut off the pump outlet pipeline, start the pump, and observe whether the pump output pressure is stable. If the pump pressure is abnormal, inspect components such as the pump head bubble, check valve, and sealing ring. If the pump pressure is normal, sequentially check the subsequent pipeline, filtration system, and chromatographic column.

Replace the faulty component for testing: For identified suspicious components (e.g., clogged online filters, contaminated protective columns), replace them with new or known functional components. Monitor whether pressure stabilizes and verify the root cause of the malfunction.

Summarize troubleshooting experience: Organize and archive information such as fault symptoms, troubleshooting process, solutions, and replaced components to create a troubleshooting manual, enabling quick resolution of similar issues in the future.

3. Professional maintenance reminder: Establish system pressure baseline records. After daily startup, record the system pressure baseline under identical conditions of flow rate, mobile phase, and column temperature to generate a pressure variation trend chart. If the pressure deviates from the baseline by more than 5%, promptly investigate the cause to prevent minor faults from escalating.

Perform regular preventive maintenance: Develop quarterly and annual preventive maintenance plans. Quarterly maintenance includes comprehensive instrument cleaning, inspection of pipeline wear, and calibration of column temperature chamber temperature. Annual maintenance may involve contacting the instrument manufacturer's engineer for in-depth maintenance such as pump accuracy calibration and detector performance testing.

Standardize operator training: Regularly organize operator training sessions to explain the working principles of the instrument, hazards of pressure abnormalities, correct operational procedures, and maintenance methods; prevent pressure-related issues caused by improper operation (e.g., rough disassembly of pipelines, shutdown without flushing the chromatographic column).

Rational selection of mobile phase and chromatographic column: Choose compatible mobile phase and chromatographic column based on sample properties, avoiding solvents that may cause degradation of the packing material; when using buffer salt mobile phase, pay attention to the pH range to prevent crystallization of buffer salts from clogging the tubing and chromatographic column.

Management of pressure challenges in specific scenarios: When analyzing high-viscosity samples, appropriately increasing column temperature and reducing flow rate can minimize the risk of pressure escalation; during gradient elution, optimizing the gradient program is essential to avoid excessively high flow rates in regions with abrupt changes in mobile phase viscosity.