Laboratory evaluation reveals significant impurities and oxidation in commercial cholesterol primary standards, highlighting the need for strict quality verification.
Cholesterol preparations recommended for use as primary standards were studied in 1968 (three samples) and 1969 (seven samples). Two lots of one preparation, one studied each year, contained only 97% cholesterol, as shown by gas-liquid chromatography or colorimetry. Three other products studied in 1969 contained oxidized products. Other preparations (two in 1968, three in 1969) were identical as judged by melting point, infrared spectra, qualitative thin-layer and gas-liquid chromatography, and their cholesterol content as determined by gas-liquid chromatography and the Lieberman-Burchard color reaction.
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Williams et al. (1970) studied this question.
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