WHAT IT IS
Maximum pressure is the upper pressure limit an LC instrument can safely generate and sustain during operation. It reflects the mechanical strength of pumps, seals, valves, and tubing. This parameter defines which columns and particle sizes can be used, and it sets the boundary between conventional HPLC and ultra-high-performance LC (UHPLC).
HOW IT WORKS
Pressure in LC arises from forcing the mobile phase through the packed stationary phase of the column. The smaller the particle size and the longer the column, the higher the pressure required.
System Specification - Each LC instrument lists a maximum pressure rating, above which the pump or safety valves will shut down to prevent damage.
Operating Pressure - Actual pressure during a run depends on flow rate, column dimensions, solvent viscosity, and temperature.
Safety Features - Pressure limits are monitored electronically; systems stop or alert if the threshold is exceeded.
TYPICAL RANGES
Conventional HPLC: 30–40 MPa (300–400 bar). Suitable for 3–10 µm particle columns.
UHPLC: 100–130 MPa (1000–1300 bar). Required for sub-2 µm particles and short high-efficiency columns.
Micro- and Nano-LC: Lower flows mean lower pressures, though limits are still ~70–100 MPa depending on system design.
Preparative LC: 10–40 MPa, since large-diameter columns and high flows limit pressure capacity.
IMPACT ON PERFORMANCE
Resolution and Efficiency: Higher pressures allow use of smaller particles, improving separation efficiency.
Speed: UHPLC systems run faster analyses with sharper peaks at high pressure.
Flexibility: A higher pressure limit expands column choices and method options.
Reproducibility: Stable pressure control ensures consistent retention times and peak shapes.
Limitations of Scale: Preparative LC favors lower pressures to handle high flows and large samples.
CHALLENGES AND LIMITATIONS
Hardware Stress: Operating close to maximum pressure accelerates wear of seals and pump heads.
Column Lifetime: Small-particle columns generate high backpressure, shortening column durability.
Solvent Effects: High-viscosity mobile phases increase pressure, restricting solvent choice.
System Cost: Higher pressure-rated instruments are more expensive to build and maintain.
Method Compatibility: Methods optimized for UHPLC cannot always be transferred to lower-pressure HPLC systems.