Marine biotoxins are a diverse range of naturally occurring compounds with various groups of structurally related toxin families exhibiting very different solubilities and mechanisms of toxicity. This chapter focuses on detection methods, specifically those conventional methods incorporating fluorescence and ultraviolet detection. The toxin isomers are generally low in proportion to the parent compound and not always present in contaminated Shellfish. High performance-liquid chromatography (HPLC) with pre-column oxidation (Pre-COX) involves the derivatization of Shellfish extracts with chemical oxidants prior to chromatographic analysis. HPLC with post-column oxidation (PCOX) involves the chromatographic analysis of non-derivatized toxins, with the separated toxins oxidized online through a continuous flow reaction system. The PCOX method theoretically provides more accurate results in terms of determining pro le and quantifying toxicity, given the overestimation of toxicity provided by the Pre-COX analysis resulting from its inability to separate epimeric pairs.