mobilephase

The mobile phase in chromatography is the phase that moves relative to the stationary phase, carrying the analyte through the system and facilitating separation. The interaction between the mobile and stationary phases determines how different compounds partition between phases and thus are retained or eluted at different times.

In liquid chromatography, the mobile phase is a liquid solvent or combination of solvents. Typical constituents include water, organic solvents such as acetonitrile or methanol, and buffers. The mobile phase’s polarity, pH, and ionic strength influence sample solubility and the degree of interaction with the stationary phase. Methods may use isocratic elution (constant composition) or gradient elution (changing composition) to improve resolution. Flow rate and temperature affect pressure, retention times, and peak shapes.

In gas chromatography, the mobile phase is the carrier gas that transports vaporized analytes through a heated column. Common carriers are helium, nitrogen, and hydrogen. The carrier gas must be inert with respect to the analytes and detector, and its choice affects column efficiency, pressure, and detector response. Gas chromatography typically uses constant or controlled-flow modes, with separation achieved by differences in volatility and interaction with the column coatings.

Practical considerations include solvent purity and degassing, compatibility with the column and detector, and safety and environmental factors. Method development involves selecting mobile phase composition, gradient profile, flow rates, and buffers to balance resolution, analysis time, and robustness.