INVESTIGATIONS INTO THE EPIMERIZATION OF TIPREDANE ETHYLSULPHOXIDE DIASTEREOISOMERS DURING CHROMATOGRAPHIC ANALYSIS ON REVERSED-PHASE SILICA .2. THE INVOLVEMENT OF METALS IN COMMERCIALLY AVAILABLE C-18 SILICAS

The degree of sulphoxide epimerisation (and concomitant ethylsulphenic acid elimination) of the alpha-ethylsulphoxide epimers of tipredane showed no direct correlation with measured chromatographic parameters for a wide range of commercially available octadecylsilyl stationary phases. Correlation was however established with the metal content (i.e. iron(II) and titanium) of these phases. Low metal content stationary phases have been shown to cause epimerisation (in addition to poor chromatography for analytes with chelating properties) via contamination of the top of the column with metal ions extracted from the stainless-steel or titanium frits when the column had been shipped in neat acetonitrile or methanol. The total metal content of packed columns could be conveniently assessed using the highly sensitive 2,3- and 2,7-dihydroxynaphthalene efficiency ratio test.