text: Chromatography methods changed little after Tsvets work until the explosion of mid-20th century research in new techniques, particularly thanks to the work of Archer John Porter Martin and Richard Laurence Millington Synge.  By "the marrying of two techniques, that of chromatography and that of countercurrent solvent extraction", Martin and Synge developed partition chromatography to separate chemicals with only slight differences in partition coefficients between two liquid solvents.  Martin, who had previously been working in vitamin chemistry (including attempts to purify vitamin E), began collaborating with Synge in 1938, brought his experience with equipment design to Synges project of separating amino acids.  After unsuccessful experiments with complex countercurrent extraction machines and liquid-liquid chromatography methods where the liquids move in opposite directions, Martin hit on the idea of using silica gel in columns to hold water stationary while an organic solvent flows through the column.  Martin and Synge demonstrated the potential of the methods by separating amino acids marked in the column by the addition of methyl red.  In a series of publications beginning in 1941, they described increasingly powerful methods of separating amino acids and other organic chemicals.
  In pursuit of better and easier methods of identifying the amino acid constituents of peptides, Martin and Synge turned to other chromatography media as well.  A short abstract in 1943 followed by a detailed article in 1944 described the use of filter paper as the stationary phase for performing chromatography on amino acids: paper chromatography.  By 1947, Martin, Synge and their collaborators had applied this method (along with Fred Sangers reagent for identifying N-terminal residues) to determine the pentapeptide sequence of Gramicidin S.  These and related paper chromatography methods were also foundational to Fred Sangers effort to determine the amino acid sequence of insulin.