After the optimisation of the analytical conditions, the linearity of the analytical curves was studied. Five standard solutions in the concentration range of 10–80 mg L−1 for 5-HMF using IS (caffeine) were analysed, with triplicate injections at each concentration level.
A linear relationship between the ratio of the peak area values (5-HMF/caffeine) and ratio of concentration (HMF/caffeine) was obtained with a satisfactory coefficient of determination (>0.99) and intercepts close to the origin. The method indicates a significant degree of selectivity, since the main peak is separated from caffeine (IS). The purity of 5-HMF was assessed check details with the aid of the PDA detector. The peak slicing technique was employed with the aid of the PDA detector to check for peak purity. Detection was carried out at 284 nm, and the overlaid UV spectra obtained for the 5-HMF peak in the honey samples analysed were identical, indicating the purity of the peak and lack of interference from potentially interfering substances. Moreover, samples without 5-HMF (below LOD) were analysed and did not show any peak that might interfere in the analyses, verifying the selectivity of the method. The repeatability of the injection system
was examined by injecting 20 mg L−1 of 5-HMF and IS with learn more 20 injections of the same solution. All determinations were carried out on the same day and under the same experimental conditions. The electropherograms were evaluated considering the migration time and the ratio of the peak area values (5-HMF/caffeine) and the calculated concentration. The RSD values were 2.40%, 4.91% and 4.55% for migration time, peak area ratio and calculated concentration, respectively, which verifies the acceptable repeatability L-NAME HCl of the method. Repeatability (intra-day precision) was established by six consecutive injections of 5-HMF at 20 mg L−1and the caffeine (IS) standard solution. The repeatability of the migration time, the peak area ratio and the calculated concentration were better than
0.60%, 1.07% and 0.91% RSD, respectively. Intermediate precision (inter-day precision) was established for the analysis of three preparations of standard solutions, over 3 days with six consecutive injections. The results ranged from 1.61% to 5.41% RSD. The data evaluated are summarised in Table 3. The obtained RSD values obtained indicate an acceptable level of inter-day and intra-day precision. The method accuracy was investigated by analysing two final concentrations of 5-HMF (20 and 40 mg L−1) added to honey samples not containing previously detectable concentrations of this substance (within the calibration range) which was been prepared as previously described (Table 4). Table 4 shows the results for the recovery tests. The recovery ranged from 96.37–99.56% for the analyte, demonstrating the good reliability of the method for the analysis of 5-HMF in honey samples.