T h e polarographic characteristics of several gibberellins have been determined and a method for determining gibberellic acid in the presence of gibberellenic acid pro- posed. Gibberellic acid was found to possess a characteristic prewave in addition to a larger proton reduction wave shown b y all gibberellins. This prewave may be measured with an accuracy to f 2 per cent within definite concentration limits. Average recoveries of gibberellic acid from a typical formulation measured b y the method was 97 per cent. T h e main reduction wave was shown to be that of carboxyl proton but the prewave reduction mechanism is not yet clear.
HE FLUOROMPTRIC ASSAY PROCEDURES used Tfor gibberellic acid are dependent upon an effective separation of gibberellic acid from closely related compounds. Potassium carbonate chromatographic columns do not appear t o accomplish this separation and other fluorescent, biologically inactive gibberellins are detected as gibberellic acid. The use of ultraviolet irradiation to suppress the fluorescent properties of gibberellenic acid also inhibits the gibberellic acid fluorophor.
Recently, Kavanagh and Kuzel (1) have described a liquid partition system in which gibberellic acid is successfully separated from gibberellenic acid, a major interfering component.
The time-consuming biological assay (2) is absolute for plant growth activity b u t rather erratic results have been obtained.