Impact of pH on 4,9-ah-TTX, 4-epiTTX and TTX. (Top) Plot of mass spectrometry results comparing peak area/internal standard ratio based on peak integration corresponding to 4,9-ah-TTX, 4-epiTTX, and TTX. (Inset) Zoomed-in graph of represented data. (Below) Reaction conditions used in analysis. ER: external recording solution used in electrophysiology experiments. 1XP: binding buffer used in competition binding experiments.