In 1949, Lyman Craig improved the separation of analytes with similar distribution ratios through countercurrent liquid-liquid extraction, offering a foundational understanding of chromatographic sepa...In 1949, Lyman Craig improved the separation of analytes with similar distribution ratios through countercurrent liquid-liquid extraction, offering a foundational understanding of chromatographic separations. Unlike sequential extractions, countercurrent extraction involves serial extraction of both sample and extracting phases. While outdated due to chromotography's efficiency, it remains instructive theoretically.