The approximately 5 kDa exclusion limit determines which solutes can enter the dextran gel pores. Proteins and other molecules above this size are largely excluded from the internal volume, whereas smaller compounds can penetrate it. This difference in pore access creates the separation and allows high-molecular-weight protein samples to be resolved from salts and other low-molecular-weight substances.
Proteins elute earlier because their larger size prevents substantial entry into the gel pores, so they travel mainly through the space between the gel particles. Salts, free nucleotides, and related small solutes enter the pores and follow a longer effective path. Their delayed elution makes it possible to separate these components during passage through the column.
Retention depends primarily on molecular size relative to the gel’s pore-access limit. Molecules that can enter the pores experience a delayed path through the packed medium, while larger species remain mostly outside that internal space. Consequently, the degree of pore access, rather than a specific chemical interaction, governs the order in which components emerge.
A sample is applied to a column packed with Sephadex G-25, and its components move through the gel as they pass along the column. Larger protein molecules emerge ahead of smaller solutes that enter the pores. The resulting separation enables collection of a protein-containing fraction with reduced amounts of salts, free nucleotides, or other small reagents.
Sephadex G-25 is useful when a protein solution contains low-molecular-weight substances that must be removed before the next experimental step. Typical purposes supported by the medium include desalting, buffer exchange, and removal of small reagents. These applications help produce a protein preparation more suitable for subsequent purification or biochemical analysis.
By separating proteins from smaller solutes, Sephadex G-25 can change the chemical environment surrounding a protein without targeting the protein itself for a separate binding interaction. Removing salts, free nucleotides, or other low-molecular-weight reagents can prepare the sample for later purification or analysis, where those substances might otherwise remain in the preparation.