Trace Level Determination of Domoic Acid in Seawater by Off-line/on-line Solid-phase Extraction Coupled to HPLC-UV
Keywords:Domoic acid, seawater, solid-phase extraction, HPLC-UV analysis.
Domoic acid (DA) is a marine neurotoxin mainly produced by microalgae of the genus Pseudo-nitzschia and is considered the main responsible for a human intoxication syndrome known as amnesic shellfish poisoning. In this work, a method for the determination of the biotoxin at low ppb or sub-ppb concentration levels in seawater was developed based on a double solid-phase extraction (SPE) followed by on-line transfer and HPLC-UV analysis of the whole extract. First, preconcentration of DA from 100-mL sample volumes and convenient sample cleanup is achieved by off-line SPE on a reversed phase C18 cartridge. Then, the extract is diluted and loaded in a polymeric reversed phase precolumn, which is further on-line eluted and analyzed. A critical condition for retaining the hydrophilic analyte in the cartridge or the precolumn is the addition of acid and an ion pairing reagent to the loading solution. Recoveries exceeded 90% for all tested seawater samples spiked with DA at 0.5-1 ng/mL. Good precision (<5%) and a limit of detection of 0.04 ng/mL were obtained with this simple method that only requires the use of conventional instrumentation existing in most analytical laboratories in Mexico.
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