Ultra-trace determination of domoic acid in the Ebro Delta estuary by SPE-HILIC-HRMS

Marine phytoplankton, such as diatoms, are responsible for a considerable part of carbon fixation and form the basis of the marine food web. However, different factors, such as eutrophication, can affect their population growth and induce the production of toxins. During the last few years, the presence of domoic acid (DA) has increased worldwide in coastal areas. Its toxic properties and capacity to bioaccumulate through the food chain have reinforced the need for developing monitoring strategies to ensure the safety and quality of marine resources. In this work, a highly sensitive analytical method has been developed to be used as an early detection and quantification tool for DA in seawater. The method is based on a sample pre-treatment step by solid-phase extraction (SPE) and an instrumental analysis by hydrophilic interaction liquid chromatography coupled with high-resolution mass spectrometry (HILIC-HRMS). The method has been validated, showing good results in terms of sensitivity and repeatability. Limits of detection and quantification were 0.25 and 0.75 ng L−1 respectively, and acceptable recovery was in the range of 48–69%. Then, the method was applied to study a real scenario in the Ebro Delta where mariculture activities are relevant for the economy of the area. A total of 34 samples were collected in different campaigns during three seasons covering the two main delta bays (Alfacs and Fangar) and four lagoons (La Tancada, Illa de Buda, l'Encanyissada and Canal Vell). 65% of the samples had concentrations of DA at the ng L−1 level, ranging from 0.90 to 69.6 ng L−1. The highest levels were found in samples from Alfacs bay and the summer campaign. In the case of the lagoons, DA was detected only in La Tancada at 8.78 ng L−1 in the winter campaign. This study proves the prevalence of DA in highly eutrophic areas, during all seasons, often at trace level concentrations.