Comparison of three chromatographic techniques for the detection of indole and oxindole alkaloids in Mitragyna speciosa

Leaves of the Southeast Asian plant Mitragyna speciosa are used to suppress pain and mitigate opioid withdrawal syndromes. The potential threat of abuse and ready availability of this uncontrolled psychoactive plant have led to the need for improved analytical techniques for the detection of the major, active components, mitragynine and 7-hydroxymitragynine. Three independent chromatographic methods coupled with two detection systems, GC/MS, SFC/DAD, and HPLC/MS/DAD, were compared for the analysis of mitragynine and other indole and oxindole alkaloids in speciosa plants. The indole alkaloids included two sets of diastereoisomers, i) paynantheine and 3-isopaynantheine, and ii) mitragynine, speciogynine, and speciociliatine. Two oxindole alkaloid diastereoisomers, corynoxine and corynoxine B, were also studied. The HPLC and SFC methods successfully resolved the major components with slightly different elution orders. The GC method was less satisfactory because it was unable to resolve mitragynine and speciociliatine. Without derivatization, this separation was difficult by GC with a liquid stationary phase because these diastereoisomers differ only in the orientation of an interior hydrogen. The observed lack of resolution of the indole alkaloid diastereoisomers coupled with the likeness of the MS and MS² spectra, calls into question proposed GC methods for the analysis of mitragynine based on solely GC/MS separation and identification.