Rapid enrichment coupled with liquid chromatography–tandem mass spectrometry for the analysis of marine algal toxins

C18 (up)-graphitized carbon (down) solid-phase extraction disks were used for the first time to simultaneously and rapidly enrich 35 dissolved marine algal toxins (MATs) from seawater, with a maximum difference in log K_ow values of 12.3. The enriched MATs were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The flow rate of the pretreatment process was 100 mL/min, and a 2000-fold enrichment was achieved for seawater, with recoveries of the target MATs exceeding 65.9%. The developed method demonstrated high sensitivity and excellent precision, with limits of detection as low as 2.0 × 10^-4 ng/L and average relative standard deviations ≤12.8%. Real seawater samples from Liaodong Bay and Beibu Bay were analyzed using this method to detect dissolved MATs. Nine MATs, including gymnodimine, pectenotoxin-2, okadaic acid (OA), 19-epi-OA, dinophysistoxin-1 (DTX1), 19-epi-DTX1, homo-yessotoxin, gonyautoxin-2 (GTX2), and GTX3, were detected in seawater samples from the selected research areas. Notably, 19-epi-OA and 19-epi-DTX1 were identified for the first time in China. The concentrations of dissolved ∑MATs in Liaodong Bay and Beibu Bay ranged from 26.12 to 56.95 ng/L and 28.12 to 51.98 ng/L, respectively. This study proposes a potential technique for exploring the distribution characteristics of multiple MATs across large-scale coastal seawater.