Targeted and untargeted approaches using liquid chromatography with high-resolution mass spectrometry for the determination of lipophilic marine biotoxins in seawater and mussel samples

Marine biotoxins are naturally occurring compounds produced around the world by various species of microalgae, whose presence increases significantly due to harmful algal blooms. This phenomenon is a major public health concern, as a large amount of marine fauna is exposed to these biotoxins. The aim of this study was the improvement and application of dispersive liquid-liquid microextraction and liquid chromatography coupled to high-resolution mass spectrometry for the determination of eight lipophilic marine biotoxins, okadaic acid (OA), dinophysistoxin 1 (DTX-1), dinophysistoxin 2 (DTX-2), 16:0 7-O-acyl okadaic acid (DTX-3a), gambierone (GAM), 44-methylgambierone (44-GAM), yessotoxin (YTX), and homoyessotoxin (hYTX), and their derivatives in seawaters and mussels by targeted and untargeted approaches. The proposed method provided detection limits ranging from 0.0004 to 1.7 ng mL^-1 in seawater and 0.06 to 119 ng g^-1 in mussel samples, depending on the biotoxin. A total of 23 seawater samples collected in the Mar Menor lagoon between 2021 and 2023 were analyzed and several of them were found to contain OA and DTX-3a at concentration levels in the 0.006-1.5 ng mL^-1 range. OA and DTX-2 were also found at maximum levels of 8.0 and 1.2 ng g^-1, respectively, in several mussel samples from commercial origin. In addition, a suspect screening was developed in the untargeted approach to investigate the presence of other derivatives of the target marine biotoxins in the samples using a home-made database covering 93 compounds. An unsaturated ester derivative of OA/DTX-2 was detected in the seawater samples collected during a red tide.