Visual quantitative determination of lead ions in tobacco flavor samples using a ratiometric fluorescent probe

To find a convenient, rapid and accurate measurement of lead (Pb²⁺) content in tobacco flavors, blue carbon dots (CDs) were used as a signal probe due to their fluorescence response to Pb²⁺. At the same time, a fluorescent material that does not react with Pb²⁺ and exhibits different fluorescence color was used as a reference probe. By adjusting the mixing ratio of the above two materials, a ratiometric fluorescence probe was constructed and used for visual quantitative analysis of Pb²⁺ mass frations in tobacco flavor samples. The results showed that: 1) Under ultraviolet irradiation, as the mass fraction of Pb²⁺ increased from 0 to 20 mg/kg, there was a distinct color transition of the probe solution from blue to pink. The mass fraction of Pb²⁺ showed on a good linear relationship with the fluorescence intensity ratio (I₄₆₀/I₅₈₀) with a limit of detection (LOD) as low as 1.32 μg/L. 2) The probe demonstrated rapid response capability with detection completed within 5 min, and showed an excellent selectivity and interference resistance. 3) The fluorescence color change could be identified by the Red/Green/Blue (RGB value) color mode by smartphones, then a standard working curve corresponding to RGB values and Pb²⁺ mass fraction was established to simplify the analysis process and realize rapid detection of Pb²⁺ with LOD of 7.04 μg/L. 4) The average recoveries ranged from 91.14% to 103.80%, and the relative standard deviations (RSDs) were from 3.01% to 5.23%. This method is simple, fast and accurate, and realizes the rapid visual quantitative detection of Pb²⁺ mass fraction in tobacco flavor samples.