Four-week stability study of TTX and 4-epiTTX spiked into acetic acid extract of blank oyster matrix (stored in glass vials) or blank oyster matrix at −80, −20, 4 and 40 °C. Values represent % deviations from the average of the −80 °C reference condition. (A) TTX spiked into acetic acid oyster extract, (B) TTX spiked into blank oyster matrix, (C) 4-epiTTX spiked into acetic acid oyster extract and (D) 4-epiTTX spiked into blank oyster matrix. Error bars represent the standard deviation (n = 3), red dotted lines delineate the confidence interval (95%, 2σ) of the −80 °C reference condition (n = 12).