Approaches to the evaluation of matrix effects in the liquid chromatography-mass spectrometry (LC-MS) analysis of three regulated lipophilic toxin groups in mussel matrix (Mytilus edulis).

Liquid chromatography coupled to mass spectrometry (LC-MS) is seen as an integral part of methods of choice for the replacement of animal tests in the determination of lipophilic shellfish toxins. However, these techniques are prone to matrix effects that need to be considered when developing and validating methods. The analysis of shellfish is a challenging task due to the complexity of the shellfish matrix and the number of shellfish species encountered in monitoring laboratories. Therefore, it is crucial that the cause and the extent of matrix effects is fully understood in order to apply corrective measures to the analytical method and to develop efficient sample clean-up steps. This paper presents different approaches to evaluate matrix effects associated with the analysis of okadaic acid (OA), azaspiracid-1 (AZA1) and pectenotoxin-2 (PTX2) in cooked and raw mussel flesh. Post-extraction addition and standard addition experiments were carried out and analysed using various LC-MS methods. Gradient and isocratic elution were compared and ultra-performance liquid chromatography (UPLC), using C8 and C18 Acquity BEH columns, was evaluated for the extent of matrix effects. When matrix effects were observed, OA and PTX2 were always prone to signal enhancement and AZA1 to signal suppression. For all the toxins studied, matrix effects were dependent on chromatographic conditions. UPLC separation using a C8 column significantly reduced matrix effects compared to the other conditions assessed. Furthermore, sample dilution has proven to be an efficient way of reducing matrix effects associated with OA analysis.