Vitamin E can be present in a formulation either as alpha-tocopherol, alpha-tocopheryl acetate, or alpha-tocopheryl acid succinate. Each of these forms of Vitamin E has somewhat different activity, as do the different stereoisomers (d or dl) of each form. The activity of any form is usually expressed in terms of the equivalent amount of d-alpha-tocopherol.

For products other than Nutritional Supplements (for example, raw materials or Vitamin E Tablets), the Vitamin E is assayed using Gas Chromatography with a Flame Ionization Detector (GC/FID). The sample is prepared by dissolution or extraction into an organic solvent which contains an internal standard (hexadecyl hexadecanoate). In order to properly prepare the sample solution, the approximate amount of Vitamin E present in the formulation must be known. This solution is analyzed by GC/FID and the amount (and form of Vitamin E present) is determined by comparison to known standards. Although this method can determine whether the formulation contains free alpha-tocopherol, the acetate or the acid succinate, it cannot distinguish the d and dl forms.

Vitamin E in Nutritional Supplements is determined using Liquid Chromatography with ultraviolet detection. Again, the sample is extracted into an organic solvent, although in this case no internal standard is used. As in the GC analyses, the form and amount of Vitamin E present is determined by comparison with known standards.

For each of these methods, Quality Control procedures require that the precision of the analysis meets certain requirements. Also, standards of potential interferences are analyzed to make sure that these compounds can be adequately resolved from the Vitamin E.

The assayed amount of Vitamin E present can then be expressed either as the mass of Vitamin E actually present in the sample, or converted to USP Units (equivalent to former International Units). This requires that we know whether the d or dl form was originally present in the formulation, since the two forms have somewhat different activity.

Please contact us to find out more about our Vitamin E Analysis capabilities.