Fast protein liquid chromatography is a moderate-pressure chromatography system designed specifically for preparative purification of proteins and other biomolecules under conditions that preserve their native structure and activity.
Principles
FPLC operates on the same separation principles as HPLC but at lower operating pressures (typically below 5 MPa) and with biocompatible flow paths. The system consists of a pump delivering a precisely controlled mobile phase gradient, an injector for sample introduction, a chromatography column packed with separation media, detectors monitoring UV absorbance (typically 280 nm for proteins), conductivity, and pH, and a fraction collector. The biocompatible construction — inert PEEK or titanium flow paths — prevents protein denaturation and metal-catalyzed oxidation.
Columns and Media
FPLC columns range from 1 mL (analytical) to liters (process scale). Pre-packed columns such as HiTrap and HiPrep series are available in various chemistries. The media are typically agarose-based (Sepharose, Superose) or polymer-based (Superdex, Source) with controlled particle sizes optimizing resolution at moderate flow rates and pressures. Column chemistries include ion exchange (IEX), size exclusion, hydrophobic interaction, reversed-phase, and affinity chromatography including protein A, IMAC, and GST bind resins.
System Components
A dual-piston pump delivers precise flow rates from 0.001 to 50 mL/min. The gradient mixer blends up to four buffers, allowing multi-step elution protocols. UV detectors measure absorbance at 280 nm and optionally 260 nm (nucleic acids) and 214 nm (peptide bonds). Conductivity monitors buffer salt concentration, and pH electrodes track elution conditions. The fraction collector deposits eluate into tubes or microplates based on peak detection thresholds. Modern systems (ÄKTA series) are controlled by software that automates methods, data acquisition, and fraction collection.
Method Development
A typical purification begins with buffer exchange or dialysis of the sample into the starting buffer. The column is equilibrated with 5–10 column volumes of starting buffer. Sample is loaded via a loop or superloop at 0.5–2 mL/min. After loading, unbound material is washed out until the UV baseline stabilizes. Elution proceeds through a step or linear gradient, monitored continuously. Fractions are collected across eluting peaks. Column cleaning and sanitization between runs prevents carryover.
Scaling
FPLC methods scale linearly with column volume. Parameters such as linear flow rate (cm/h), sample load (mg per mL resin), gradient volume (column volumes), and fraction size (mL) are maintained constant across scales. Method development at 1 mL column volume translates directly to preparative columns of 5, 50, or 500 mL.
Applications
FPLC is the workhorse of laboratory-scale protein purification. It is used to purify recombinant proteins from bacterial, insect, or mammalian cell lysates, monoclonal antibodies from hybridoma or CHO cell culture supernatants, and native proteins from tissue extracts. Multi-step purification protocols combine orthogonal separation modes — for example, capture by IMAC, intermediate purification by ion exchange, and polishing by size exclusion — each run on the same FPLC system.
