Introduction
Ciguatoxins (CTXs) are marine toxins produced by microalgae of the genera Gambierdiscus and Fukuyoa that cause harmful algal blooms. These blooms are a threat to food safety due to the consumption of fish or shellfish containing CTXs. Liquid chromatography combined with tandem mass spectrometry (LC-MS/MS) allows the identification of CTXs congeners. Instrument sensitivity can be affected by sample matrix effects; however, sample purification could prevent erroneous results.
Methods
Different samples of Gambierdiscus have been analyzed by LC-MS/MS after suspension and column-cleaning protocols were tested with seven resins (Florisil, C18, Diaion® γ-CD-HDI, γ-CD-EPI, β-CD-HDI and β-CD-EPI). Firstly, solid-phase extraction (SPE) was performed on suspension and columns using established standards to test the efficacy of each resin. Secondly, SPE was performed on the column using the four most effective resins from the first phase for one Gambierdiscus sample. Thirdly, all Gambierdiscus samples were subjected to the four resins used in the second phase.
Results and conclusion
The performances of all resins and two SPE formats were evaluated using gambierone and 44-methylgambierone standards at different concentrations (2.5 ng/mL, 12.5 ng/mL and 200 ng/mL). The recovery rates obtained with 12.5 ng/mL of C18, Diaion, and γ-CD-EPI in the column were very good. Florisil was associated with the lowest number of recoveries, while β-CD-HDI and β-CD-EPI did not perform well. The clean-up in suspension worked well, but the recovery rates were lower.
The performance of C18, Diaion, γ-CD-EPI and γ-CD-HDI was evaluated by SPE in column with the addition of gambierone, 44-methylgambierone and CTX1B to a G. excentricus extract. Recoveries were similar for C18, Diaion and γ-CD-EPI. Gambierone had a greater recovery with C18, while 44-methylgambierone and CTX1B achieved greater recovery with diaion. Finally, all Gambierdiscus samples were passed through the four resins and analyzed. To compare the matrix effect and establish a toxin profile, these samples were also analyzed without SPE.
