Reasons for the Pressure Variation and Fluctuation of Liquid Chromatography

1. Unstable pump operation due to plunger rod or seal ring wear: Prolonged reciprocating motion of the plunger rod or aging of the seal ring can lead to wear, resulting in poor suction and discharge of the pump, with significant pressure fluctuations. Severe wear may also cause leakage.

Air bubbles in the pump head: Incomplete removal of air bubbles within the pump head can lead to unstable pump output flow and subsequent pressure fluctuations; particularly during low-flow rate analysis, the fluctuations become more pronounced.

Uneven solvent mixing: Malfunction of the proportional valve in binary or quaternary pumps, or insufficient stirring during mobile phase mixing, can result in uneven composition of the mixed mobile phase, leading to pressure fluctuations as it passes through the chromatographic column.

2. Environmental factors cause significant temperature fluctuations in the laboratory: The absence of constant temperature equipment or direct airflow from air conditioning outlets onto instruments can lead to temperature variations in the mobile phase and chromatographic columns, subsequently affecting the viscosity of the mobile phase and column resistance, resulting in pressure changes.

Failure to use degassing equipment or suboptimal degassing effect: Dissolved gases in the mobile phase are not completely removed, leading to bubble formation during system pressure changes. The generation and rupture of bubbles can cause significant pressure fluctuations, with the impact being particularly pronounced during gradient elution due to inadequate degassing.

Unstable power supply voltage: Excessive fluctuations in laboratory power supply voltage may impair the normal operation of equipment such as pumps and column temperature chambers, resulting in unstable pump output pressure and subsequently causing system pressure fluctuations.

3. System-wide multi-component minor faults: When multiple components (e.g., slightly clogged check valves, minor pipeline leaks, or mildly contaminated protective columns) simultaneously exhibit minor malfunctions, individual troubleshooting proves challenging, but their combined effect results in persistent pressure fluctuations.

Insufficient system equilibrium: After changing the mobile phase or chromatographic column, if sufficient equilibrium time is not provided and injection analysis is initiated before system pressure stabilizes, it will lead to continuous pressure fluctuations during analysis, thereby compromising separation efficiency.

Improper software-controlled parameter settings: unreasonable gradient program configuration, excessively short ramp time for flow rate, or incorrect upper/lower pressure limit settings may cause the instrument to frequently adjust output during operation, leading to pressure fluctuations.