Sensitive determination of domoic acid in shellfish by on-line coupling of weak anion exchange solid-phase extraction and liquid chromatography-diode array detection-tandem mass spectrometry.

An automated method based on the use of on-line solid-phase extraction (SPE) coupled to liquid chromatography with diode array detection and tandem mass spectrometry (LC-DAD-MS/MS) has been developed for the determination of domoic acid in shellfish. The on-line coupling of SPE and liquid chromatography was accomplished by a column switching approach. A weak anion exchange (WAX) sorbent was selected for the SPE procedure, allowing a selective cleanup of shellfish extracts. High sensitivity was achieved by on-line pre-concentration of large volume injections (50-1000μL). A simple protein precipitation cleanup with acetone was used to efficiently remove proteins from shellfish extracts, preventing possible column clogging during chromatographic separation. The proposed method showed good performance in terms of linearity, limits of detection (LODs), precision and accuracy. Quantitative recovery and satisfactory inter-day precision (RSD ⩽7%) was achieved. LODs in the in the sub-nanogram per gram level (0.23-0.32ngg) were obtained with MS/MS detection. Matrix effects were assessed by post-extraction addition method and no signal enhancement or suppression was observed during MS detection. This method was successfully applied to the determination of domoic acid in several shellfish samples, including scallops, oysters, mussels, Manila clams, common cockles and razor clams.