Inventors: Lyman Craig and Otto Post
How it began: During World War II the introduction of complex drugs for preventing and treating malaria created a need to determine their chemical purity. The large molecular weight and instability of these compounds made this a difficult task.
What it does: This extraction apparatus has a series of glass tubes (five in this photo and up to 1,000 in the laboratory) that mix and then separate complex chemical mixtures based on their different solubility in two known immiscible liquids. It worked by means of an ingenious connection of the tubes (a tribute to the glassblower’s art) and a tilting frame. On repeated tilts, shakes, and settling times, the heavier liquid phase remains stationary while the lighter phase transfers stepwise from one tube to the next, ultimately isolating the pure components in the mixture. Some compounds can be separated by a few transfers while others require hundreds of cycles.
Impact on medical science: Until the development of simpler modern-day chromatographic techniques, countercurrent distribution was the only effective procedure for the isolation of many antibiotics, insulin and other hormones, and vitamins in pure form.
Reference: Craig, L. Identification of small amounts of organic compounds by distribution studies. Journal of Biological Chemistry, 1944, 155:519-534.
Photo by Lubosh Stepanek
Lyman Craig, Otto Post, countercurrent distribution machine, malaria drugs