AbstractTwo new solvent systems, n‐hexane + propionic acid (26:5, v/v) and chloroform + acetone (29:3, v/v), for the rapid resolution and identification of an 18‐component mixture of phenylthiohydantoin amino acids are reported. Using these systems certain difficult combinations of phenylthiohydantoin amino acids are resolved. Two more solvent systems, viz chloroform+acetic acid (27:3, v/v) and chloroform + methanol (30:4, v/v), are developed to resolve phenylthiodantoin derivatives of aspartic and glutamic ac