1. High-Performance Liquid Chromatography (HPLC)
HPLC is the most common LC technique, using high pressure to push the mobile phase through a tightly packed column. It provides excellent resolution, speed, and reproducibility.
- Normal-Phase HPLC (NP-HPLC) : Uses a polar stationary phase (e.g., silica) and a nonpolar mobile phase. Ideal for separating polar compounds.
- Reverse-Phase HPLC (RP-HPLC) : Employs a nonpolar stationary phase (e.g., C18) with a polar mobile phase (e.g., water-methanol). Preferred for separating hydrophobic compounds.
- Gradient HPLC : The composition of the mobile phase changes over time, improving separation for complex mixtures.
- Isocratic HPLC : Uses a constant mobile phase composition, suitable for simpler separations.
2. Ultra-High-Performance Liquid Chromatography (UHPLC)
UHPLC is an advanced version of HPLC that operates at even higher pressures (>15,000 psi), allowing for faster analysis, improved resolution, and reduced solvent consumption.
3. Size Exclusion Chromatography (SEC)
Also known as Gel Filtration Chromatography (GFC), SEC separates molecules based on size. Larger molecules elute faster as they do not penetrate the porous stationary phase, while smaller molecules take longer to pass through.
4. Ion Exchange Chromatography (IEC)
IEC separates charged molecules based on their interaction with oppositely charged stationary phase materials. It is widely used for proteins, peptides, and ionic compounds.
- Cation Exchange Chromatography : Retains and separates positively charged ions.
- Anion Exchange Chromatography : Separates negatively charged ions.
5. Affinity Chromatography
This technique exploits highly specific interactions between biomolecules (e.g., enzyme-substrate, antigen-antibody, receptor-ligand). It is commonly used for protein purification and biomarker detection.
6. Hydrophilic Interaction Liquid Chromatography (HILIC)
HILIC is useful for separating highly polar compounds. It operates similarly to normal-phase HPLC but with an aqueous-organic mobile phase.
7. Chiral Liquid Chromatography
Chiral chromatography is designed to separate enantiomers of chiral molecules using a chiral stationary phase. It is crucial in pharmaceutical research to differentiate between drug isomers.