Liquid Chromatography–Tandem Mass Spectrometry Method for the Screening of Eight Paralytic Shellfish Poisoning Toxins, Domoic Acid, 13-Desmethyl Spirolide C, Palytoxin and Okadaic Acid in Seawater

Abstract

A quick and reproducible screening analytical method for the simultaneous determination of algal toxins, belonging to different chemical classes, was developed to provide a toxin profile in seawater, useful to assess potential risks to environment and human health. The target compounds were: gonyautoxin-1,4, gonyautoxin-2,3, decarbamoylgonyautoxin-2,3, N‐sulfocarbamoyl-gonyautoxin-1,2, neosaxitoxin, decarbamoyl-neosaxitoxin, saxitoxin, decarbamoyl-saxitoxin, domoic acid, 13-desmethyl spirolide C (SPX1), palytoxin and okadaic acid. Extraction and clean-up were carried out with a combination of Bond Elut LRC-C18 and Carbograph4 cartridges connected in series. Analyte separation was performed in gradient elution mode in 12 min with a Gemini C18 column. Compound detection was carried out in multiple reaction monitoring and in positive ionization mode for paralytic shellfish poisoning toxins, domoic acid, SPX1 and palytoxin, and in negative ionization mode for okadaic acid. The toxins were quantified with matrix-matched calibration curves constructed by spiked seawater samples (concentration levels 0.02–2 μg L−1 depending on the compound). The method was reproducible with intra-day and inter-day relative standard deviations ranging from 4 to 9% and from 8 to 16%, respectively. Good recoveries (84–105%) and good accuracy (2–20%) were obtained by spiking experiments. Limits of detection were calculated for each toxin and varied from 0.011 to 0.12 μg L−1 depending on the compound. The developed method was applied to cultured Ostreopsis cf. ovata samples. The proposed procedure may be considered a valuable alternative to existing methods for monitoring toxic microalgae, since it offers a rapid screening of target toxins, reduced organic solvent consumption, and handling of smaller sample volumes while providing good sensitivity and accuracy.