Linearity was determined by the Fischer test based on residual values, i.e.the differences between nominal and found (back-calculated) concentrations. No significant differences were observed: the function f(Nominal C-found C) exhibits significant linearity (Fisher, p-value < 0.001, R 2 = 0.999) with an intercept of about 0 (Intra-day = -0.080 and Inter-day = -0.106) and a slope of about 1 (Intraday = 1.001 and Interday =1.002). The relationship between detector responses of AS and spiked placebos was measured by analysing four calibration standards and a blank of each set. The concentrations of oleuropein were 0.4, 0.8, 1.6 and 3.2 mg/g for the spiked placebos, which, after extraction (4 ml methanol) and dilution (100 fold in 50% aqueous methanol) result in injection solutions of respectively, 5, 10, 20 and 40 mg/L oleuropein (for 100% recovery). These solutions were compared with AS solutions at the same concentrations. Five replicates of each concentration were prepared on the same day by the same operator under the same operating conditions.