The method was validated by linearity, limit of detection (LOD), limit of quantification (LOQ), precision and accuracy. A series of standard solutions containing the four synthetic colorants in the concentration range of 0.80–500 μg L−1 were prepared for the calibration curves. LOD and LOQ were defined as the concentrations for each analyte at a signal-to-noise ratio (S/N) of 3 and 10, respectively. Three replicates of the same sample were performed to estimate the method precision. Accuracy was also evaluated by analyzing samples spiked with 0.01, 0.08 and 0.3 mg L−1 of four synthetic colorants.
The enrichment factor (EF) was calculated according to the equation