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A simple microwave-assisted synthesis of nitrogen-doped carbon dots with high oxygen content (O-N-CDs) was carried out with citric acid as a carbon source and 2,4-diamino-6-methyl-1,3,5-triazine as a nitrogen source in triethylene glycol (TEG) media. It was determined by SEM analysis that O-N-CDs consisted of particles of different sizes and shapes. Transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction (XRD) analysis confirmed that O-N-CDs have a graphitic structure. Moreover, they showed a high fluorescence property based on the excitation wavelength. Therefore, a new fluorometric method was developed for the determination of banned food dye Sudan II by using the O-N-CDs. The proposed method was used in the determination of Sudan II in spiked spice samples. The detection limit was 0.6 mg L−1 and the linear range was 0–8 mg L−1. [ABSTRACT FROM AUTHOR]

• The synthetic procedures and spectrofluorimetric studies of new MPcs described. • The new procedure suggests detecting the banned food colorant Sudan II dye. • The new simpler, cheaper, and faster fluorimetric method was described instead of HPLC. • MPcs were used for the first time as spectrofluorimetric agents to detect Sudan II dye. The structural elucidation and syntheses methods of new peripherally tetra-substituted MPcs [CuII (6) , CoII (7) , MnCIIII (8), and NiII (9) phthalocyanines] carrying 4-methyl- N -(3-morpholinopropyl)benzenesulfonamide moieties were reported in the present study. The corroboration of the prepared compounds (3 , 5 , and 6 to 9) was made by LC–TOF/MS, UV–Vis, Fourier Infrared, 1H NMR, 13C NMR, and MALDI–TOF mass spectral data. Herein, we submit a new procedure that uses metallophthalocyanine complexes for the first time as spectrofluorimetric agents to detect and determine health-threatening food additive, Sudan II dye, with a new simpler, cheaper, and faster spectrofluorimetric method instead of time-consuming and expensive HPLC processes. Furthermore, the sensitivities of the proposed methods are good enough to determine the amount of dye at a concentration of 0.1 mg/L. The methods have LOD values between 0.035 and 0.050 mg/L. The linear ranges are found to be between 0 and 8.3 mg/L. The precision of the methods is determined to be between 1.1 and 2.4 as % RSD. Therefore, this study would make a good contribution to the food industry and phthalocyanine chemistry by detecting and determining the hazardous food colorant Sudan II with metal phthalocyanines. [ABSTRACT FROM AUTHOR]