Macro- and Micromethods for the Determination of Serum Vitamin A using Trifluoroacetic Acid

A new method for the determination of plasma or serum vitamin A levels which uses trifluoroacetic acid (TFA) as the chromogen is described. This reagent produces a typical Carr-Price color but does not exhibit the turbidity or film-forming properties of SbCl3 in the presence of moisture. The new procedure gives values that agree well with those obtained by the Carr-Price method when rat, porcine, or human sera are analyzed. Significantly higher values are obtained with TFA, however, when bovine sera were analyzed. A micro- modification of the method permitting the analysis of 50 µl of serum is described and its advantages over existing methods are discussed.