FPLC (Fast Protein Liquid Chromatography): Principle, Working, Applications and Advantages
Imagine that you have finally got that E. coli culture growing your favorite enzyme! All you have to do now is lyse them to get a nice turbid, viscous solution of proteins, DNA, lipids, salts, and cellular debris. Your enzyme is just one infinitesimal speck in this giant conglomeration. How will you isolate your protein of interest without denaturing it?
This is the problem faced by every biotechnology lab, day in and day out. From an M.Sc. dissertation to a pharma company in Hyderabad to a research institute, protein purification is one task that recurs, with slight variations, in all of them. One of the most common techniques used is FPLC (Fast Protein Liquid Chromatography).
In this article, I will be briefly discussing FPLC: the principles, the instrumentation, the working procedure, and a few comparisons. This is the kind of practical detail that I wish I had known when I was first learning about protein purification.
📑 Table of Contents
What is FPLC?
FPLC stands for Fast Protein Liquid Chromatography. It is a form of liquid chromatography, used primarily to isolate biomolecules, proteins, and peptides under gentle conditions.
The technique was developed in the early 80s by Pharmacia (Cytiva), which wanted a quicker and more reliable alternative to the traditional "gravity-flow" column chromatography, and is now used in research labs, core facilities, and biopharmaceutical companies in ÄKTA systems. Here is a brief overview of the key features:
Gentle on proteins: Uses aqueous buffers and biocompatible materials. Can operate at low pressures. Reproducible results. Sharp elution peaks. Can run at low temperatures (4°C). Can be considered an "instrumental" version of the gravity column chromatography.
Key features in one look:
- Works at low to medium pressure
- Uses aqueous buffers (water-based), which protect proteins
- Uses biocompatible materials, so proteins don’t stick to metal or get damaged
- Gives sharp separations with good reproducibility
- Can be run at cold room temperature (4°C) for sensitive proteins
Think of FPLC as the automated, upgraded version of the glass column you may have used in your practicals.
Principle of FPLC
The FPLC principle is based on the same idea as all chromatography: separation of molecules between a stationary phase and a mobile phase.
- Stationary phase: the packed resin (beads) inside the column.
- Mobile phase: the buffer that flows through the column, carrying your sample.
When your protein mixture enters the column, different proteins interact with the resin in different ways. Some stick strongly, some weakly, some barely at all. Because of these differences, proteins move through the column at different speeds and come out (elute) at different times.
What makes FPLC special is how this is done:
- A pump pushes the buffer through the column at a steady, controlled flow rate.
- The buffer composition can be changed gradually (for example, increasing salt concentration), which releases bound proteins one by one.
- A detector watches the outflow, usually at 280 nm, and records a peak whenever a protein comes out.
- A fraction collector automatically collects each portion in separate tubes.
Depending on the resin chosen, separation can be based on charge, size, hydrophobicity, or specific binding affinity. This is why FPLC is called a versatile technique, because the same instrument can run many different chromatography modes just by changing the column.
❓ Why do proteins separate on a column at all?
Because every protein has its own size, surface charge, and hydrophobic patches. The resin "feels" these differences, so each protein gets held back for a different length of time.
Instrumentation / Components of FPLC
An FPLC system is actually a number of simple pieces of equipment put together, connected by tubing. Let's go through them one by one:
1. Buffer reservoirs
These are basically the vessels that contain Buffer A and Buffer B. These are usually filtered (0.22 or 0.45 μm) and degassed.
2. Pumps
An FPLC system uses precision pumps to deliver buffers at a controlled flow rate and pressure. Depending on the instrument design, one or more pumps may be used to maintain a constant flow and generate buffer gradients during protein purification.
3. Mixer
The mixers mix the two buffer solutions in the desired ratio (using the gradient profile) so that a linear gradient is obtained. The buffer solution is then passed on to the sample injection system.
4. Sample injection system
There are a number of ways to inject a sample into an FPLC system:
Sample loop: This is a small-volume loop in which the sample is loaded. The sample loop can be of volumes ranging from 100 µL to as large as 10 mL.
- Superloop: This is an ultra-large loop, used in conjunction with the sample pump.
- Sample pump: This can be used to directly inject very large sample volumes into the column.
5. Column
The column is the heart of the FPLC system. It is made of glass or PEEK (polyetheretherketone) and has a resin of choice packed into it (HiTrap, HiLoad, Mono Q, Mono S, Superdex, Superose, etc.).
6. Detectors
UV detector at 280 nm: This detector monitors proteins as they elute from the chromatography column. Many proteins absorb UV light at 280 nm because they contain aromatic amino acids, particularly tryptophan and tyrosine. The absorbance depends on the amino acid composition of the protein.
- Conductivity monitor: Monitors the salt concentration in the running buffer.
- pH monitor: Monitors the pH of the running buffer.
7. Fraction collector
This collects the eluted protein fractions automatically, in a set of tubes or in deep-well plates, depending on the preference of the user.
8. Control software
This is computer software (UNICORN for ÄKTA systems) that controls all operations and monitors the entire FPLC run.
❓ Why is FPLC made of inert materials and not stainless steel?
High-salt buffers can corrode steel and release metal ions, and these can damage or inactivate sensitive proteins. Inert plastics keep your protein safe.
Working / Procedure (Step-by-Step)
Here is how a typical FPLC run goes. Don’t worry if the details change a little between experiments, because the logic stays the same.
Step 1: Prepare buffers and sample.
Prepare fresh buffers (appropriate for the type of chromatography to be performed) and adjust the pH. The buffers must be filtered (0.22 or 0.45 µm) and degassed. Clarify the sample by centrifugation and filtration (0.45 µm pore size).
Step 2: Wash the system.
Rinse the pumps and tubing with water and then with your starting buffer. This removes air bubbles and storage solution (often 20% ethanol).Step 3: Equilibrate the column
Pass 5 to 10 column volumes (CV) of starting buffer through the column. Wait until the UV baseline and conductivity are stable. This tells you the resin is ready.Step 4: Inject the sample
Load the sample through the loop or sample pump. In binding modes (ion-exchange, affinity), your target protein sticks to the resin while unwanted proteins pass through.Step 5: Wash
Continue with the starting buffer until the UV signal returns to baseline. This washes away unbound material (the “flow-through”).Step 6: Elution
Now release the bound protein. This can be done by:- Gradient elution: slowly increasing salt (or imidazole, etc.), which separates proteins in order of binding strength
- Step elution: a sudden jump to a higher concentration, which releases the protein in one sharp peak
Step 7: Collect fractions
The fraction collector fills tubes as peaks appear on the chromatogram.Step 8: Analyze fractions.
Check fractions by SDS-PAGE, activity assays, or Bradford or BCA assays. Pool the pure fractions.Step 9: Clean and store the column.
Wash with cleaning solution (for example, 1 M NaCl or 0.5 M NaOH, as the manufacturer recommends), then store in 20% ethanol.Types of Chromatography Used in FPLC
One of the best things about FPLC is that it supports many separation modes. Here are the main ones.
1. Ion Exchange Chromatography (IEX)
Separates proteins based on net charge.
- Anion exchange (e.g., Q resin): positively charged resin binds negatively charged proteins.
- Cation exchange (e.g., S resin): negatively charged resin binds positively charged proteins.
The pH of the buffer decides the protein’s charge, so choosing the correct pH relative to the protein’s isoelectric point (pI) is important.
2. Size Exclusion Chromatography (SEC) / Gel Filtration
Separates proteins by size (molecular weight). Large proteins can’t enter the pores of the beads, so they travel faster and elute first. Small proteins enter the pores, take a longer path, and elute later.
3. Affinity Chromatography
Uses a specific interaction between the protein and a ligand on the resin. Examples:
- His-tag proteins bind to Ni²⁺-NTA resin and are eluted with imidazole.
- GST-tagged proteins bind to glutathione resin.
- Antibodies bind to Protein A or Protein G.
4. Hydrophobic Interaction Chromatography (HIC)
Separates proteins by surface hydrophobicity. Proteins bind in high salt and elute as salt decreases.
5. Reversed Phase Chromatography (RPC)
Used mainly for peptides and small proteins and for final analytical polishing. It uses organic solvents, so it is harsher and not always suitable for native proteins.
6. Chromatofocusing
Separates proteins by their isoelectric point using a pH gradient on the column.
Quick summary table:
| Technique | Basis of Separation: | Typical Elution Method |
|---|---|---|
| Ion Exchange (IEX) | Net Surface Charge: | Increasing salt or change in pH |
| Size Exclusion (SEC) | Molecular Size | Isocratic (same buffer throughout) |
| Affinity | Specific Binding to a Ligand | Competitor (e.g., imidazole) or pH change |
| Hydrophobic Interaction (HIC) | Surface hydrophobicity | Decreasing salt gradient |
| Reversed Phase (RPC) | Hydrophobicity (stronger): | Increasing organic solvent |
Applications of FPLC
FPLC is used almost everywhere proteins are studied or produced.
- Recombinant protein purification: Purifying His-tagged, GST-tagged, or other tagged proteins expressed in E. coli, yeast, or mammalian cells.
- Enzyme studies: Getting pure enzymes for kinetics, structure and inhibitor studies.
- Structural biology: X-ray crystallography, cryo-EM and NMR all need highly pure, homogeneous protein. Size exclusion is often the final polishing step before crystallisation trials.
- Biopharmaceutical industry: Purification of monoclonal antibodies, vaccines, hormones and other therapeutic proteins, and process development.
- Antibody purification: Protein A or G affinity columns capture antibodies from serum or cell culture supernatant.
- Studying protein complexes and oligomeric state: SEC can tell you whether your protein is a monomer, dimer or larger assembly.
- Peptide and nucleic acid separation: Some FPLC setups are also used for oligonucleotides and plasmid DNA purification.
- Quality control and research: Checking purity and aggregation of protein preparations.
❓ Why is gel filtration so popular before crystallisation?
Crystals form only when all protein molecules are alike. SEC removes aggregates and leftover contaminants, giving a uniform sample.
Advantages of FPLC
- Gentle on proteins: aqueous buffers and mild conditions keep proteins folded and active.
- High resolution: sharp peaks and good separation, much better than manual gravity columns.
- Reproducibility: automated flow and gradients give consistent results run after run.
- Fast: much quicker than traditional open-column methods.
- Versatile: many chromatography modes on a single system.
- Scalable: from small analytical runs to larger preparative runs.
- Reusable columns: many columns can be cleaned and reused many times.
- Automation: programmable methods, fraction collection and data recording save time and reduce human error.
- Cold-room compatible: can be used at 4 °C for unstable proteins.
Limitations of FPLC
No technique is perfect, so let’s be honest about the downsides.
- High cost: the instrument, columns and software are expensive, which can be a challenge for smaller institutions.
- Lower pressure capacity than HPLC: this limits the use of very fine particles and ultra-high-resolution analysis.
- Sample preparation needed: samples must be clarified and filtered, or the column can clog.
- Column maintenance: resins need careful cleaning and storage, and improper handling reduces column life.
- Limited for small molecules: it is designed mainly for large biomolecules.
- Skill required: method development (choosing resin, pH, gradient) takes experience.
- Dilution of sample: proteins often elute in larger volumes and may need concentrating afterwards.
❓ Why can't we just use higher pressure to make FPLC faster and sharper?
The soft agarose-based beads used for proteins can compress or collapse under very high pressure, which blocks flow and ruins the separation.
Difference Between FPLC and HPLC
Students often mix these two up, because FPLC is really a type of liquid chromatography closely related to HPLC. The main difference is the target and operating conditions.
| Feature | FPLC | HPLC |
|---|---|---|
| Full form | Fast Protein Liquid Chromatography | High Performance (Pressure) Liquid Chromatography |
| Main use | Protein and biomolecule purification | Analysis of small molecules, drugs, vitamins, etc. |
| Operating pressure | Low to medium | High to very high |
| Column material | Glass or inert polymers (e.g., PEEK) | Usually stainless steel |
| Stationary phase | Soft, porous resins (agarose, dextran, etc.) | Rigid silica or polymer particles |
| Mobile phase | Aqueous buffers, mild conditions | Often organic solvents (e.g., methanol, acetonitrile) |
| Effect on proteins | Keeps native structure and activity | May denature proteins (especially reversed phase) |
| Scale | Preparative (collecting protein) | Mostly analytical |
| Resolution | Good | Very high |
Simple way to remember: FPLC is gentle and built for proteins, while HPLC is powerful and built for speed and analytical precision.
❓ Why is FPLC better for active proteins while HPLC is better for small molecules?
Proteins are fragile and can lose shape in harsh solvents or high pressure, whereas small molecules are tough and can easily handle those conditions.
References
- Wilson K, Walker J (eds.). Principles and Techniques of Biochemistry and Molecular Biology. Cambridge University Press.
- Nelson DL, Cox MM. Lehninger Principles of Biochemistry. W.H. Freeman.
- Berg JM, Tymoczko JL, Gatto GJ, Stryer L. Biochemistry. W.H. Freeman.
- Scopes RK. Protein Purification: Principles and Practice. Springer.
- Janson J-C (ed.). Protein Purification: Principles, High Resolution Methods, and Applications. Wiley.
- Burgess RR, Deutscher MP (eds.). Guide to Protein Purification, 2nd ed. Methods in Enzymology, Vol. 463. Academic Press, 2009.
- Deutscher MP (ed.). Guide to Protein Purification. Methods in Enzymology, Vol. 182. Academic Press, 1990.
- Rosenberg IM. Protein Analysis and Purification: Benchtop Techniques. Birkhäuser.
- Hage DS (ed.). Handbook of Affinity Chromatography. CRC Press.
- Coligan JE, et al. (eds.). Current Protocols in Protein Science. Wiley.
- Cytiva (formerly GE Healthcare). Protein Purification Handbook.
- Cytiva. Ion Exchange Chromatography: Principles and Methods.
- Cytiva. Gel Filtration: Principles and Methods.
- Cytiva. Affinity Chromatography: Principles and Methods.
- Cytiva. Hydrophobic Interaction and Reversed Phase Chromatography: Principles and Methods.
About the Author
Aftab Baig is a biotechnology student, science writer, and founder of BioTechyEdu. He is passionate about biotechnology, genetics, molecular biology, microbiology, and biomedical sciences. Through BioTechyEdu, he publishes research-based and student-friendly articles that simplify complex scientific concepts for students, educators, and science enthusiasts.
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