Chromatographic stationary phase

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Below are the requirements for fixing agents (from Baidu). What is the principle behind how fixing agents separate substances? Is it to selectively slow down the flow rate of the material, or is it about achieving separation of the materials? Requirements for stationary phases: 1. Low volatility, with a low vapor pressure at the operating temperature, to prevent loss. 2. Good thermal stability; no decomposition or polymerization reactions occur at the operating temperature, and it remains in liquid form, preserving the original properties of the stationary phase. 3. Sufficient solvating power for the sample, so that the components being analyzed are not carried away and thus the separation function can be maintained. 4. Good selectivity, meaning that under operating conditions, it should have the highest possible separation capability for different substances with similar boiling points or properties. 5. Good chemical stability, without reacting chemically with the components being analyzed, the support material, or the carrier gas. Selection of stationary phases: The principle of like dissolves like is generally followed. 1. For separating non-polar substances, use a non-polar stationary phase; those with higher polarity elute later, while those with lower polarity elute first. 2. For separating polar substances, use a polar stationary phase; those with higher polarity elute later, while those with lower polarity elute first. 3. For mixed polar and non-polar substances, use a polar stationary phase; those with higher polarity elute later, while those with lower polarity elute first. 4. For substances that form hydrogen bonds, use a polar or hydrogen-bonding stationary phase; those that do not easily form hydrogen bonds elute first from the chromatography column, and vice versa. 5. For separating complex substances that are difficult to separate, a mixture of two or more stationary phases can be used.