A new second-order derivative synchronous fluorescence spectrometry for simultaneous and rapid determination of ultratrace 1-naphthol and 2-naphthol in wastewater

Under alkaline conditions with sodium hydroxide (NaOH), both 1-naphthol (1-NAP) and 2-naphthol (2-NAP) transitioned from their molecular forms to ionic forms, resulting in redshifts of their fluorescence spectra. Thus, not only the interference of 2-NAP raman peak was eliminated, but the fluorescence intensity of two naphthols was also enhanced, thereby improving the selectivity and sensitivity of their analysis. Due to their structural similarity, the conventional fluorescence spectra of 1-NAP and 2-NAP overlapped and interfered with each other, precluding their simultaneous measurement without prior separation. In this study, the wavelength difference (Δλ) = 140 nm was selected for synchronous fluorescence spectrometry (SFS) scanning to simplify the spectra. However, the interference of 2-NAP on 1-NAP remained significant. So, the second-order derivative technique combined with SFS was adopted. The method that eliminated the severe interference between 1-NAP and 2-NAP and wastewater background by utilizing spectral parameters. Finally, a new second-order derivative SFS for simultaneous determination of 1-NAP and 2-NAP was first established. The detection limits were 0.0850 ng·mL −1 for 1-NAP and 0.1066 ng·mL −1 for 2-NAP, with linear ranges of 0.5–80 ng·mL −1 and 0.5–50 ng·mL −1 , respectively. Recoveries of two naphthols in wastewater were 87.53%–93.50% (1-NAP) and 89.85%–104.00% (2-NAP). The new SFS established in this research has been successfully applied to the analysis and detection of 1-NAP and 2-NAP residues in wastewater, achieving satisfactory results. It is expected to become a new routine detection method for 1-NAP and 2-NAP.