Step 1: Why is the pump critical in HPLC?
In High Performance Liquid Chromatography (HPLC), the mobile phase must be pushed through a column packed with very fine particles. These fine particles create high resistance, so high pressure is needed to maintain flow.
Step 2: What type of flow is required?
The pump must deliver the mobile phase at high constant pressure without pulsations. Constant (pulse-free) flow ensures reproducible retention times and accurate peak areas. Pulsating flow creates noise in the detector baseline and affects accuracy.
Step 3: Types of HPLC pumps.
Reciprocating piston pumps are most common. They have pulse dampeners to convert pulsatile mechanical action into a steady, constant flow. Operating pressures can reach 400 bar or more.
Step 4: Eliminate wrong options.
Pulsatile flow causes baseline noise and poor reproducibility. Low pressure is used in gravity-based chromatography, not HPLC. Intermittent flow would ruin column efficiency and peak shape.
Step 5: Confirm.
HPLC pumps must deliver mobile phase at high constant pressure to maintain column integrity and detector accuracy.
Answer: Option (3) — High constant pressure