DETERMINATION OF IAA AND ABA IN THE SAME PLANT-SAMPLE BY A WIDELY APPLICABLE METHOD USING GC-MS WITH SELECTED ION MONITORING

A method for the purification and subsequent quantification of indole-3-acetic acid (IAA) and abscisic acid (ABA) from the same sample of highly pigmented green tissue has been developed and tested in several species. Solvent partitioning and high-performance liquid chromatography (HPLC) were used for purification. Separate fractions from HPLC-containing IAA and ABA were analyzed by gas chromatography-mass spectrometry (GC-MS) using selected-ion monitoring (SIM). Isotope dilution was used to correct for incomplete recovery. Results are presented for tissue samples from 11 different species and five different plant organs. The method can be completed, for both IAA and ABA, for two samples in 8 h by an experienced technician. IAA and ABA were the dominant peaks in the gas chromatograms from HPLC-purified samples, and amounts of about 1 ng can be detected. The extract was partitioned into an aqueous solution of pH 9.5, a step suspected of ester hydrolysis. By analyzing samples known to contain esters of IAA and ABA and comparing the results with methods which excluded this step, we have shown that this partitioning does not result in erroneously high values due to ester hydrolysis. A direct comparison of the method with one in which HPLC was not employed indicates that our method measures IAA and ABA in samples in which these compounds are not detectable when HPLC is omitted. Thus, HPLC is an essential purification step for samples where contaminating compounds co-purify with IAA and ABA through the solvent-partitioning steps.