## 3 Results
### FFF Spectral Profiles of Honey of Different Botanic Origin  
A selection of FFF emission spectra of the twelve monofloral honey samples produced in Tuscany (Italy) is reported in Figure 2. The most significant emission bands are observed by fixing the excitation wavelength at 280 nm (Figure 2a), 340 nm (Figure 2b), and 420 nm (Figure 2c), respectively [23; 24; 25; 35; 36]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Honey Sample Label*** & \(\mathbf{\lambda_{\max}}\) **(nm)** \\ \hline AC1 & 270 (326) \\ SU1 & 286 (451, 690) \\ CL1 & 277 (326) \\ CL2 & 277 (325) \\ CL3 & 276 (326) \\ MA1 & 276 (329) \\ MA2 & 275 (330) \\ MA3 & 275 (329) \\ L1 & 282 (327) \\ AR1 & 285 (335) \\ IN1 & 282 (326) \\ FH1 & 278 (325) \\ AA1 & 277 (334) \\ C1 & 243 (318–355, 607) \\ H1 & 272 (334) \\ S1 & 269 (425–450–485, 692) \\ \hline \hline \end{tabular}  
* _labels are defined in Table 2._  
\end{table} 
Table 3: Maximum UV-Vis absorption wavelengths of honey samples investigated in this work. Minor peaks are indicated between parentheses, as explained in the text. Figure 2: Front-face flourescense (FFF) emission spectra of honey samples in the bulk obtained with excitation wavelength (\(\lambda_{\rm ex}\)) fixed at 280 nm (**a**), 340 nm (**b**), and 420 nm (**c**). Twelve honey samples of different botanic origins are reported here, as indicated in the legend on the right. The intensity of the emission spectra is normalized (arbitrary units, a.u.). In (a) the sharper peaks from 440 to 500 nm are due to the xenon lamp. To help in the discussion of typical spectral profiles of honey of different botanic origin, the wavelengths of the maximum emission at the three selected excitation wavelengths, namely \(\lambda_{\rm ex}\) = 280, 340, and 420 nm, are summarized in Table 4.  
As a general comment, the emission/excitation profiles of honey are quite complex due to the contemporary presence of several fluorophores with different concentrations and to the presence of eventual quenching phenomena. However, the comparison among emission spectra recorded at different wavelengths can be used to underline differences and analogies among honey samples of different botanic origin and to support the identification of possible markers. As discussed in detail in Section 4, significant information can be obtained by simulating the emission spectra, in particular those obtained by exciting the sample at 280-290 nm (Figure 2a) and at 330-340 nm (Figure 2b). On the contrary, at higher exciting wavelengths (\(\lambda_{\rm ex}\) > 420 nm) the emission spectra are quite similar among different honey samples (Figure 2c). In particular, chestnut honey presents very peculiar emission spectra at \(\lambda_{\rm ex}\) = 280 nm and 340 nm (Figure 2a,b), while sunflower honey differentiates from others for the emission spectrum at \(\lambda_{\rm ex}\) = 420 nm (Figure 2c) and for the absorption in the visible interval (Table 3). The other honey samples are grouped into three sub-classes:  
* the first group (lavender, clover, acacia, and marruca honeys) is characterized by emission spectra with a maximum emission around 330-360 nm (at \(\lambda_{\rm ex}\) = 280 nm);
* the second group (sulla and heather honeys) presents similar emission spectra with a maximum emission around 410-440 nm (at \(\lambda_{\rm ex}\) = 280 nm);
* the third group (arbutus, inula, alfalfa honey, and forest honeybee honeys) is characterized by different emission spectra (at \(\lambda_{\rm ex}\) = 280 nm), but similar emission spectra are obtained exciting the sample at \(\lambda_{\rm ex}\) = 340 nm, with a typical shoulder around 360-385 nm. In Section 4, these spectral features are correlated with the presence of specific fluorophores. The complexity of the honey matrix in terms of fluorescent molecules is also evident by observing the synchronous spectra. For simplicity, we are reporting only synchronous spectra obtained by fixing the wavelength interval, \(\Delta\lambda\), equal to 20 nm (see Figure 3).