Analysis and Quantitation of Insect Juvenile Hormones Using Chemical Ionization Ion-Trap Mass Spectrometry

Abstract

A method for identification and quantitation of insect juvenile hormones (JH) has been developed using capillary gas chromatography–chemical ionization (isobutane)–ion-trap mass spectroscopy. The method does not require derivatization of samples or use of selected ion monitoring. Analysis over a mass range of 60–350 u allowed for identification of as little as 0.01 pmol of individual JH homologs. Quantitative analysis was based on the ion intensities of six diagnostic ions and the summed intensities of these ions for each homolog. The ratio of diagnostic ions did not vary significantly over a range of concentrations from 2.7 to 200 pg. The technique was used to identify and quantify the amounts of JH homologs secreted by individual retrocerebral complexes from the moth Manduca sexta maintained in tissue culture and to identify JH III from hexane extracts of hemolymph of the Caribbean fruit fly. No discrimination due to disparate abundance ratios of the individual homologs was found when analyzing natural product samples differing in concentration by at least fivefold. The technique allows for facile, concrete identification and quantitation of biologically relevant amounts of JH. The ability to analyze samples without derivatization or fractionation by chromatographic methods, coupled with data acquisition over a broad mass range, provides levels of accuracy and confidence greater than those of other methods.