Which of the following techniques is least likely to be used for GFP purification?

Gas chromatography is the least likely technique to be used for GFP purification because it is primarily designed for the separation and analysis of volatile and thermally stable compounds. It operates by vaporizing a sample and separating its components based on their respective boiling points and affinities for the stationary phase within the column. In contrast, GFP is a large, water-soluble protein that does not fit the criteria for effective analysis via gas chromatography.

On the other hand, affinity chromatography is highly effective for purifying proteins like GFP due to its ability to exploit specific binding interactions, often involving tags such as polyhistidine or other affinity tags engineered into the protein. Size-exclusion chromatography allows for the separation of proteins based on their size, which is useful for isolating GFP from smaller contaminating molecules. Ion-exchange chromatography can separate proteins based on their charge, making it another viable method for purifying GFP in the context of protein purification workflows.