Separation Shave/recycle

A commercial customer had four compounds to recover from a synthesis mixture they separated as two pairs of compounds. They injected and collected each pair together, then diluted each pair with water, reinjected onto the reverse-phase column, and ran shave/recycle. Using this technique they purified 50gm of each compound in the two injections of the pair fractions on the 3-in column. 

Shave-recycling A mode of recycling in which a large sample is injected and incompletely resolved bands are eluted. The zones containing the prue components in the front and rear of the mixed band are collected separately and the incompletely resolved mixture is recycled through the same coliurm, rmtil the sample is exhausted. 

FIGURE 10-3. Recycle-shaving technique. Mobile phase 10% CH2CI2 in isooctane (50% water saturated). Flow rate 2 mL/min. Detector UV, 254 nm, 1.0 AUFS. Sample mixture of aromatics. Column Porasil A, 2 mm ID x 122 cm. (Note Actual separation will depend upon quality of mobile phase and column packing.)... 

The recycling techniques have been used for preparative chromatography using lower-resolution columns packed with larger particle sizes. The application is usually a binary separation. In this case, it is possible to extract the sides of the bands during each run to obtain the pure compounds. This technique is called peak shaving. The center of the band is recycled as usual. Thus the load on the column continuously decreases, and the width of the band can be controlled. With this method it is possible to obtain high-resolution prepara-... 

An additional example of the technique of recycling, which includes a procedure called peak shaving, is the preparative separation of the enantiomers of 5-methyl-5-phenylhydantoin. The recycling and peak shaving procedure is depicted in figure 12.8. The column was 30 cm long, 2 in. I.D., packed with 10 m particles carrying Vancomycin as the chiral stationary phase. The mobile phase was ethanol and the flow rate 100 ml/minute. The sample load was 400 mg dissolved in 5 ml of ethanol. 

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