## 2 Results and Discussion
### Polyphenols Analysis  
The polyphenolic fraction of _R. coriaria_ fruits has been so far carried out by HPLC coupled with a photodiode array (PDA) and/or MS detection [17; 18]. A comprehensive work on the phytochemical components of sumac fruit epicarp from Palestine by using HPLC-PDA-ESI-MS was reported by [PERSON] et al. [14], where a tentative identification of 211 phenolic and other phyto-constituents, most of which never reported before in _R. coriaria_ fruits, were described. However, in none of these works was a quantification of the individual polyphenolic content reported due to the presence of overlapping peaks and matrix interferences. In this work the analysis of the polyphenolic compounds in _R. coriaria_ samples was carried out by HILIC\(\times\)RP-LC-PDA-ESI/MS. So far, most of the applications on polyphenols in food and natural products have been carried out on RP-LC\(\times\)RP-LC [19; 20; 21; 22; 23; 24; 25; 26; 27], despite applications of HILIC\(\times\)RP-LC also being reported [28; 29; 30]. Prior to either RP-LC\(\times\)RP-LC or HILIC\(\times\)RP-LC analysis, an optimization of the single separations must be carried out [31; 32; 33; 34; 35]. Normally a low mobile phase flow rate is used in the \({}^{1}\)D separation to decrease the fraction volume onto the \({}^{2}\)D and increase the \({}^{1}\)D sampling rate; as a consequence, a microcolumn is used in the \({}^{1}\)D. Since most commercial LC pumps are not capable of delivering a stable and repeatable flow rate, a higher flow rate is commonly employed and split up before entering the \({}^{1}\)D column. In this work, an easy-to-use micropump with a completely new direct-drive engineering was employed and was capable of delivering stable micro- to semi-micro flow rates [25]. Notably when HILIC is hyphenated to RP, such coupling is not straightforward due to solvent incompatibility. To overcome such an issue, a modulation procedure called \"active modulation\" was reported [36; 37]. Such an approach is based on the introduction of a make-up flow of a weaker solvent (water) after the \({}^{1}\)D separation and before the entrance to the valves. In such a way, a reduction in the solvent strength is achieved, increasing the retention of the trap columns towards the compounds separated in the \({}^{1}\)D. Afterwards, when the valve is  
Figure 2: GC-MS analysis of the volatile profile for Sample 3 (fresh, collected in October) and Sample 4 (fresh and air-dried, collected in October). actuated, the retained analytes are eluted in narrow bands thanks to the \({}^{2}\)D mobile phase. Figure 3 reports the HILIC\(\times\)RP-LC-PDA-ESI/MS plots of the polyphenolic fraction of \(R\). _coriaria_ for Samples 3 and 4. For MS detection, a triple quadruple MS analyzer was used, equipped with an electrospray interface working on both positive and negative ionization mode. The list of the compounds identified is reported in Table S2. A total of 83 polyphenolic compounds were positively identified in the investigated samples by combining the information coming from PDA absorption (\(\lambda_{\text{max}}\)), mass-to-charge ratio (\(m/z\)), and literature data [17; 18]. Among them, the majority were represented by gallic acid and derivates (37), as well as quercetin derivates (11). The rest were represented by cyanidin, luteolin, myricetin, and apigenin derivates. Concerning the performance of the developed HILIC\(\times\)RP-LC system, Table 1 reports the values attained for both peak capacity and orthogonality [38]. Figure 3: HILIC\(\times\)RP-LC-PDA contour plots (280 nm) of the polyphenolic profile for Sample 3 (fresh, collected in October) and Sample 4 (fresh and air-dried, collected in October). The highest theoretical peak capacity values, resulting from the product of the peak capacity, \(\rm n_{c}\) of the two single dimensions ([PERSON] and [PERSON], 2018), were attained for Sample 4 (3381), whereas the lowest one was attained for Sample 5 (2673). The orthogonality, \(\rm A_{O}\), values ranged from 0.72 to 0.90% for Sample 6 and Sample 3, respectively.