Small-Scale Size-Selective Fractionation

CXL fractionations can be performed in as little as 20 min for each pressurization stage such that multiple monodisperse fractions can be collected in less than 2 h as opposed to several hours for an LSAS fractionation. The CXL fractionation also produces negligible waste, as all of the solvent and C02 can be recovered at the end of the process [16, 19]. 

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In Fig. 10.15, concentration and temperature profiles along the colurim are presented for a selected experiment. The average deviation for conversion and product purity is about 2%. For the experiments with KATAPAK -S, no liquid-liquid phase separation was observed at the laboratory scale, mainly because there was still too much ethanol in the distillate fraction preventing the phase splitting. The reason is that the catalytic section is only 1 m high and the catalyst fraction of KATAPAK -S Lab is lower as compared to MULTIPAK -2 or the industrial KATAPAK -S 250.Y (see Table 10.3). It was possible to achieve the phase separation in the liquid-liquid separator with the laboratory-scale setup. On the other hand, the size of the catalytic section at the pilot scale enabled even higher conversions and thus liquid-liquid separation, due to the small ethanol fraction in the distillate. 

Details of HPLC of retinoids (4-6) can be found in Chapter 2 of this book Here we give a descnption of purification of a retinoid to be used as a standard. For HPLC purification, a concentrated solution of the retinoid is injected. How much of the solution is to be injected and appropriate concentration of the solution will depend on the impurities present in the sample, their resolution during HPLC, the column size, the solvent used, and other conditions. These can be determined by trials A reasonably volatile solvent or solvent mixture that can be removed easily under argon or nitrogen or in a rotary evaporator should be selected. Depending on the amount of the retinoid required, several injections may be performed, and the appropriate peak collected each time. Solvent is evaporated from the pooled fractions, the sample reconstituted in an appropnate solvent, and the concentration determined by recording the absorption spectrum. Small quantities of HPLC standards or retinoids for tissue culture studies may be readily purified by this procedure, using standard analytical-scale columns. 

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