Craig countercurrent extraction

We have just examined a relatively small number of Craig countercurrent extractions and seen that differences in D or Kj among solutes results in different distributions among the many Craig tubes. Most distributions are normally distributed. In the absence of systematic error, random error in analytical measurement is normally distributed and this assumption formed the basis of much of the discussion in Chapter 2. A continuous random variable x has a Normal distribution with certain parameters (mean, parameter of location) and cr (variance, parameter of spread) if its density function is given by (12) ... 

Find, in a reference book, a description of the Craig countercurrent distribution apparatus and discuss its design as it relates to the description of countercurrent extraction presented in this chapter. 

L. C. Craig and D. Craig, Laboratory extraction and countercurrent distribution . 

Craig and collaborators have extensively supplemented countercurrent extraction with gel filtration (Hill and Konigsberg, 1960 Rasmussen and Craig, 1961). Occasionally the more laborious countercurrent extraction method can be replaced by Sephadex filtration (Rasmussen and Craig, 1962). 

Camptothecin (43) was first isolated by Monroe Wall and Mansukh Wani in 1966, after ethanolic extracts of Camptotheca acuminata, a tree native to China, showed unusual and potent antitumor activity (63). Starting with 19 kg of dried wood and bark. Wall and Wani painstakingly purified the principal active component with a combination of hot solvent extraction, an 11-stage Craig countercurrent partition process, silica gel chromatography, and crystallization. Camptothecin was characterized as a novel pentacyclicalkaloid, present as j ust 0.01 % w/w of the stem bark of C ax umi-... 

Fig. 4-17. Countercurrent-extraction tube. (Courtesy of Dr. L. Craig and Interscience Publishers, Inc.)...

As shown, a considerable part of the modern separation methods of amino acids and peptides originated in Max Bergmann s laboratory at the Rockefeller Institute. A different separation technique was introduced in the same institute at the same time by Lyman C. Craig, in the laboratory of J.A. Jacobs. Here, from 1933, he worked on ergot alkaloids developing a lasting interest in separation techniques. The well-known method of extraction of substances from an aqueous into a non-water-miscible phase like chloroform or vice versa was systematically elaborated by him to a multiple extraction and re-extraction procedure, countercurrent distribution [25]. By this method, performed in a specially... 

Craig, Lyman C., 1906-1974 (p. 55, Plate 16) son of a farmer, was bom in Palmyra, Iowa. In 1932, with a fresh Ph.D. degree from the University of Iowa at Ames, he moved to Baltimore to work at the Johns Hopkins University as a National Research Council fellow. Two years later Craig joined the Rockefeller Institute in New York City to collaborate with A. Jacobs on the structure-elucidation of ergot alkaloids. Here he developed the fractionation of mixtures by repeated extraction procedures. Countercurrent distribution (CCD) turned out to be of great value in the isolation of natural and synthetic products. The definitive determination of the molecular weight of insulin, for instance, became possible through the isolation of the least substituted derivative by CCD. For the concentration of solutions recovered from CCD, he invented the rotary evaporator. 

Three steps required for multistage solvent extraction, i.e., phase mixing, phase settling, and transfer of the mobile phase, are defined clearly in the discontinuous countercurrent distribution process using the Craig apparatus. These basic requirements are essentially fulfilled by the use of a coiled tube in a continuous fashion. Solvent extraction using a coiled column is most efficiently performed with a horizontally laid coil that rotates about its own axis. In this horizontal coil orientation, the rotation induces the well known Archimedean screw force, which can be utilized for performing countercurrent solvent extraction. 

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