3.1.2.2. Calibration curves. Calibration curves were determined for five different concentrations of standard solutions for each organic acid analysed. Each calibration standard was injected three times. The calibration test was performed in triplicate. Calibration curves were calculated applying the least-squares method to concentration versus peak area. Table 4 lists the parameters and correlation coefficients of the calibration plots. Each plot was linear over a wide interval from LOD to at least 200mg/L for formic, pyruvic and quinic acid, 300mg/L for citric acid, 900mg/L for succinic acid, 1500mg/L for acetic acid and 15mg/L for malic acid. R2 values were always above 0.9909 (except malic acid, 0.9890).