Table 6.

List of the MRM transitions (m/z) for the four MTXs known to date (LC-LRMS/MS, API 4000 QTrap). MRM transitions of MTX and MTX4 were chosen according to HRMS data provided in this study. Quantification of MTX and MTX4 was operated using the MRM transition [M − 2H]²⁻ → [M − 2H]²⁻ (in bold). In the absence of MS/MS data on maitotoxin-2 (MTX2) and maitotoxin-3 (MTX3), putative MRM transitions were chosen based on their MS spectral peaks reported in literature and assuming that they share the same fragmentation behavior as that of MTX and MTX4. * = M refers to the free acid form, i.e., without the sodium salt(s) on sulfate ester group(s), e.g., M = C₁₆₄H₂₅₈O₆₈S₂ for MTX.

Compound	MRM Transitions (m/z) *		CE (eV)	CXP (eV)
MTX	[M − 2H]2−/[M − 2H]2−	1689.8/1689.8	−40	−15
	[M − 2H]2−/[HOSO3]−	1689.8/96.9	−125	−21
	[M + Na − 3H]2−/[HOSO3]−	1700.8/96.9	−125	−21
	[M + 2Na − 3H]2−/[HOSO3]−	1711.8/96.9	−125	−21
	[M − 3H]3−/[M − 3H]3−	1126.2/1126.2	−40	−15
	[M − 3H]3−/[HOSO3]−	1126.2/96.9	−125	−21
	[M − 4H]4−/[HOSO3]−	844.4/96.9	−125	−21
MTX2	[M − 2H]2−/[HOSO3]−	1637.5/96.9	−125	−21
	[M + Na − 3H]2−/[HOSO3]−	1648.2/96.9	−125	−21
	[M + K − 3H]2−/[HOSO3]−	1656.0/96.9	−125	−21
	[M − 3H]3−/[HOSO3]−	1091.5/96.9	−125	−21
	[M + Na − 4H]3−/[HOSO3]−	1098.6/96.9	−125	−21
	[M + K − 4H]3−/[HOSO3]−	1103.8/96.9	−125	−21
MTX3	[M − H]−/[HOSO3]−	1015.5/96.9	−125	−21
	[M + Na − 2H]−/[HOSO3]−	1037.6/96.9	−125	−21
	[M + 2Na − 3H]−/[HOSO3]−	1057.5/96.9	−125	−21
	[M − 2H]2−/[HOSO3]−	507.3/96.9	−125	−21
MTX4	[M − 2H]2−/[M − 2H]2−	1646.2/1646.2	−40	−15
	[M − 2H]2−/[HOSO3]−	1646.2/96.9	−125	−21
	[M + Na − 3H]2−/[HOSO3]−	1657.2/96.9	−125	−21
	[M + 2Na − 3H]2−/[HOSO3]−	1668.2/96.9	−125	−21
	[M − 3H]3−/[M − 3H]3−	1097.1/1097.1	−40	−15
	[M − 3H]3−/[HOSO3]−	1097.1/96.9	−125	−21