Fig. 6. High performance liquid chromatography (HPLC)–mass spectrometry (MS) analysis of corn root exudates. (A) Base peak chromatogram (BPC) of root exudates; (B) extracted ion chromatogram (EIC) at m/z 178 (corresponding to HMBOA-H₂O which occurs in the ion source); (C) EIC at m/z 178 of the exudates sample spiked with pure HMBOA; (D) electrospray ionization (ESI)–MS at 11.6 min of the exudates samples; (E) ESI–MS at 11.6 min of the exudates sample spiked with pure HMBOA.