## 3 Results and Discussion
Since this descriptor represents a linear group contribution (atomic masses) for predicting the retention index property, the larger the \(MW\) for a given compound, the greater the retention index of that compound. In a recent study, the synergistic effect of \(MW\) for predicting the \(I\) property in comprehensive two-dimensional gas chromatography combined with quadrupole-mass spectrometry (GC \(\times\) GC/qMS) using a BPX5 and BP20 column coupled system was presented [25]. On the other hand, \(MDEN\)-23 is a descriptor belonging to the molecular distance-edge (MDE) vector [26]. This descriptor measures the topological distances (2D) between nitrogen atoms, in particular, type 2 for secondary (-NH-) and type 3 for ternary (-N\(<\)) nitrogen atoms. Thus, the synergistic effect on the retention time could be related to the silanophilic effect. In fact, when dealing with the \(I\) of pesticides in ultrahigh-performance liquid chromatography-electrospray ionization quadrupole-Orbitrap (UHPLC/ESI Q-Orbitrap) mass spectrometry (MS), using the Hypersil Gold selectivity column (and the guard column Accucore aQ), it was shown that the slow elution of polar molecules (pesticides) through the stationary phase was caused by the high affinity of basic amine compounds for the silica surface of the column (which was constituted by active or acidic silanol groups) [27]. The model presented here also considers a conformation-dependent descriptor belonging to the 3D-MoRSE (3D Molecule Representation of Structures based on Electron diffraction). These descriptors transform the 3D coordinates of compounds into a molecular code by applying a modified equation used in electron diffraction studies for preparing theoretical scattering curves [28; 29]. Specifically, the \(Mor13v\) descriptor considers the scattering parameter s = 12 A\({}^{-1}\) and weighs the atoms by the corresponding van der Waals volume. This weighting scheme considers a minimum effect of hydrogen atoms, decreases the contribution of nitrogen, oxygen and fluorine, and attributes significant influence to silicon, phosphorus, bromine and iodine atoms. Since the coefficient of \(Mor13v\) is negative, this descriptor could be related to the contribution of the volume of the volatile and semi-volatile compounds, expressed in terms of the van der Waals volume. Thus, higher retention indices are related to molecules having scaffolds with fragments (pairwise atoms) with high volume, which in turn interact with the stationary phase and delay the time of elution. Finally, the applicability domain of the QSPR model was analyzed in order to define the theoretical space where the model makes reliable predictions of the retention indices of new VOCs or SVOCs (i.e., interpolations). The leverage approach (Figure 2) established a threshold limit of \(h^{\star}\) = 0.1408, which indicates that predictions were reliable for only VOCs or SVOCs with a leverage value below this threshold limit; that is, predictions are the result of interpolation of the model (i.e., reliable). In this work, no test set compounds fell outside the AD of the model, indicating that Equation (1) makes reliable predictions of the retention index property and, consequently, could be useful for eliciting this property of new VOCs and SVOCs of different coffee samples.