Transient isotachophoresis-capillary zone electrophoresis for the analysis of paralytic shellfish toxins in mussel sample

Accumulation of paralytic shellfish toxins (PSTs) in contaminated shellfish is a serious health risk making early detection important to improve shellfish safety and biotoxin management. Capillary electrophoresis (CE) has been proven as a high resolution separation technique compatible with miniaturization, making it an attractive choice in the development of portable instrumentation for early, on-site detection of PSTs. In this work, capillary zone electrophoresis (CZE) with capacitively coupled contactless conductivity detector (C⁴D) was compared with UV detection because of its small footprint. To improve sensitivity and deal with the high conductivity sample matrix, counter-flow transient isotachophoresis (tiTP) was used, exploiting the high sodium levels in the matrix as leading ion while L-alanine was used as the background electrolyte (BGE) and terminating electrolyte (TE). Careful optimization of the injected sample volume and duration of the counter-flow resulted in limit of detections (LODs) ranging from 74.2- 1020 ng/ml for tiTP-CZE-C⁴D and 141-461 ng/ml for tiTP-CZE-UV, an 8-97 fold over reduction compared to conventional CZE. The LODs were adequate for the analysis of PSTs in shellfish samples close to the regulatory limit (800 ng/ml). The developed method was applied to the analysis of a contaminated mussel sample and validated against results from Association of Official Analytical Chemists (AOAC)-approved method for PSTs analysis using pre-column oxidation of the sample prior to analysis by high performance liquid chromatography (HPLC) with fluorescence detection (FLO). The method presented has potential for incorporation into field-deployable devices for the early detection of PSTs on-site.