Polarized absorption recovery after

Silicic acid absorption chromatography has also been used fairly extensively in the past for the separation of retinoids. Heat-activated silicic acid will separate retinol, retinaldehyde, and retinoic acid and its more polar metabolites, with recoveries reported to range from 60 to 100% (Dunagin et al., 1966 Zile and DeLuca, 1965, 1968 Garry et al., 1970 Pollack et al., 1973 J. A. Olson, personal communication). In contrast, however, retinyl esters show only a 10-15% recovery after chromatography on silicic acid with the production of various oxidation products (Zile and DeLuca, 1968 Pollack et al., 1973). The... 

Zou et al. have described an MSPD procedure for the extraction of eight sulfonamides from honey samples using C18 as solid support. After the MSPD, the sulfonamides were derivatized with 9-lluorenylmethylchloroformate (EMOC-Cl). The derivatives required further purification by silica gel SPE, prior to LC-UV determination. Average recoveries for most sulfonamides were >70%. Other polar sorbents, such as silica gel, CN- or NH2-bonded silica resulted in a strong absorption of the polar sulfonamides, providing very low recoveries. 

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