Ultra-rapid auxin metabolite profiling method. (A) Recoveries (%) of IAA metabolites applied to multi-StageTips using Empore sorbents in the indicated combinations (C18/C8, C18/SDB-RPS, and C18/SDB-XC). (B) Recoveries (%) of the indicated IAA metabolites with one, three, and five sorbent multilayers (C18/SDB-XC) used in the µSPE purification procedure. Values are means ±SD (n=4). (C) Plant material (10 mg) was homogenized and extracted in Na-phosphate buffer containing labelled internal standards. One portion (2 mg FW per 200 μl) of acidified supernatant was directly applied to a pre-conditioned multi-StageTip microcolumn (STop And Go Extraction Tip created by packing C18/SDB-XC sorbents in an ordinary pipette tip and inserting into a 1.5 ml microcentrifuge tube, which was then washed and eluted with methanolic solutions). The other half of the supernatant (200 μl) was derivatized using cysteamine and also purified by in-tip μSPE. The pooled eluate was evaporated to dryness, dissolved in 40 μl of 5% acidified methanol, and finally analysed using the LC-MS/MS method presented herein, affording ultra-fast chromatographic separation of 14 IAA precursors, catabolites, and conjugates (1, Trp; 2, TRA; 3, IPyA-TAZ; 4, ANT; 5, oxIAA-glc; 6, IAM; 7, IAAsp; 8, oxIAA; 9, IAA-glc; 10, IAGlu; 11, IAA; 12, trans-IAOx; 13, IAN; 14, cis-IAOx).