Searching for Internal Standard for Chemical Routine Analysis of Lipophilic Shellfish Toxins

Abstract

The potential of using synthesized internal standards designed from phenylbenzimidazole (PBI) and the polycyclic steroid deoxycholic acid (DHO) has been assessed to reduce peak area response drift, matrix effects and unpredictable analytical events in the liquid chromatography mass spectrometry analysis of lipophilic marine toxins. A total of 15 analogues of PBIs with different chemical and physical properties were tested. Two of these were selected, based on their analytical behavior and retention time for further examination in existing methods. Quantification by the use of internal standards were compared to direct calculations from standard curves prepared from certified reference materials (CRM) fortified in methanol, and by performing standard addition of CRMs to unknown samples. Slope variations in standard curves with external and internal standard were studied in long analytical sequences where response drift is prone to happen. Preliminary results from using DHO as an internal standard for correction of matrix effect and peak area response drift in quantification of okadaic acid (OA) are promising. Corresponding results were obtained for azaspiracid-1 (AZA-1) by the use of 1-heptyl-2-phenyl-benzimidazole (Hep-PBI), although further studies are required to draw any final conclusions. The study shows the complexity of the analysis and represents a starting point with a view to improve the performance of the methods.