Figure 2. (a) Representative UPLC ESI+ chromatogram of the polar extract of mussel samples. (b) OPLS-DA scores plot representing AZA non-contaminated controls (blue squares; n = 92) vs. azaspiracid (AZA) contaminated samples (red circles; n = 56). Explained variance (R2) was 98.7%, the predictive ability (Q2) was 98.3% and RMSECV was 7.56%. (c) The s-plot which corresponds to Fig. 1c. Highlighted in red represent features which are at significantly higher concentrations in AZA samples when compared with controls. Highlighted in blue are features which are at significantly lower concentrations in AZA samples when compared with controls (non-contaminated mussel specimens).