Detection, occurrence and monthly variations of typical lipophilic marine toxins associated with diarrhetic shellfish poisoning in the coastal seawater of Qingdao City, China

•A new method was developed for the determination of OA, YTX, and PTX2 in seawater.•OA and PTX2 commonly existed in the seawater along the coastline of Qingdao City.•OA and PTX2 were present almost every month in the coastal seawater of Qingdao.•The highest concentrations of OA and PTX2 occurred in August and July respectively. In recent years, related research has mainly examined lipophilic marine toxins (LMTs) in contaminated bivalves or toxic algae, whereas the levels of LMTs in seawater remain largely unexplored. Okadaic acid (OA), yessotoxin (YTX), and pectenotoxin-2 (PTX2) are three typical LMTs produced by certain marine algae that are closely linked to diarrhetic shellfish poisoning. In this study, a new method of solid phase extraction combined with liquid chromatography – electrospray ionization ion trap tandem mass spectrometry was developed to determine the presence of OA, YTX, and PTX2 in seawater simultaneously. Satisfactory sensitivity, repeatability (RSD