Upper panel: correlation between total absolute magnitude and the interquartile range of the [O/Na] ratio for GC in our FLAMES survey. Lower panel: relation between cluster concentration and the residual around the best-fit relation IQR[O/Na] – M_V(tot). M 80 is indicated by a filled star symbol. In each panel the Spearman rank correlation coefficient r_s and the Pearson linear correlation coefficient r_p are listed.