QUANTITATIVE-ANALYSIS OF GIBBERELLINS BY ISOTOPE-DILUTION MASS-SPECTROMETRY - A COMPARISON OF THE USE OF CALIBRATION CURVES, AN ISOTOPE-DILUTION FIT PROGRAM AND ARITHMETICAL CORRECTION OF ISOTOPE RATIOS

The quantitative analysis of gibberellin A1 (GA1) in apices of 19-day- old seedlings of Pisum sativum L. cultivar Alaska is described using i sotope dilution mass spectrometry. Three methods are compared for dete rmining the dilution of isotope in the internal standards, [17-H-2(2)] GA1 and [2beta-H-2(1)]GA1. Similar results were obtained with each met hod. The use of calibration curves gave the most precise determination with [H-2(2)]GA1 as internal standard irrespective of the amount adde d. The use of an isotope dilution fit program was more precise using [ H-2(1)]GA1 as internal standard. A simpler arithmetical correction pro cedure gave consistently higher estimates with both internal standards . The relative merits of the methods are discussed and the requirement s for reliable quantification by isotope dilution gas chromatography-m ass spectrometry are presented.