## 2 Basis of the QuEChERS Method
### Modifications in the Partitioning Salts  
In the original QuECHERS method, the first partitioning step via salting-out extraction was performed under unbuffered conditions, only using MgSO\({}_{4}\) and NaCl as partitioning salts in a 4:1 ratio, respectively [17]. Over time, it has been observed that under these conditions, the determination of some analytes may be affected, as they can be sensitive to degradation at high or low pH values [15; 16]. Consequently, this has led to the introduction of buffers in the QuEChERS procedure, as they can be useful to enhance the extraction efficiency of wider groups of analytes and matrices. In this sense, two main buffered procedures have been officially proposed, based on citrate or acetate buffers. Both buffered options have been extensively used and evaluated in the scientific community; thus, in consequence, they have given rise to two official methods: the CEN Standard Method EN 15,662 (the citrate buffer) [41] and the AOAC Official Method 2007.01 (the acetate buffer) [42]. The citrate buffer (relatively low buffering capacity), apart from the MgSO\({}_{4}\) and NaCl, also includes the addition of trisodium citrate dihydrate and disodium hydrogen citrate sesquihydrate. Accordingly, the four salts have to be added in a 4:1:1:0.5 ratio (\(w/w\)) [41]. In contrast, the acetate buffer (strong buffering capacity) involves the use of MgSO\({}_{4}\) and sodium acetate in a 6:1.5 ratio (\(w/w\)) [42]. Both buffered options keep the pH constant around 5-5.5 during the extraction procedure, which is a pH value that in general provides satisfactory recovery values (usually higher than 70%) for acid-sensitive compounds without degradation of base-sensitive compounds [15]. Other buffered systems, such as the phosphate buffer, have been proposed for more alkaline extractions [15]. However, they are not contemplated as official methods, and they have not been reported for the analysis of PAs by QuEChERS (Table 1). In the QuEChERS extraction of PAs, the most extended practice is the use of citrate buffer in the salting-out extraction step (50% of the works reviewed) (Table 1). Moreover, some authors have reduced the amount of the salts used in this step but maintaining the 4:1:1:0.5 proportion (\(w/w\)), achieving satisfactory recovery values [21; 24; 27; 28]. In contrast, only two works (11% of the works reviewed) carried out the QuEChERS procedure for the extraction of PAs using the acetate buffer (Table 1). [PERSON] et al. (2022) evaluated the two official buffer methods for the extraction of 28 PAs/PANOs from dried teas and herbs, and better results were achieved with the acetate buffer [25]. Likewise, [PERSON] et al. (2011) also used the acetate buffer strategy for the extraction of 11 PAs and PANOs from food supplements, feed and honey, but reducing the amount of salts employed (4 g of MgSO\({}_{4}\) and 1 g of sodium acetate), keeping the 6:1.5 ratio [30]. Conversely, 22% of the works reviewed performed the salting-out extraction step of PAs as in the original QuEChERS procedure, using 4 g of MgSO\({}_{4}\) and 1 g of NaCl, also achieving good results (Table 1). Some authors have also evaluated the amount of NaCl added [22; 23]. MgSO\({}_{4}\) can promote the distribution of analytes in the organic phase mainly by absorbing water, thus retaining some undesirable polar compounds from the sample matrix, such as sugars, improving the salting-out effect of the organic extraction solvent. However, it can also decrease the response for some water-soluble compounds, such as in the case of some PAs and mainly PANOs. Conversely, NaCl controls the polarity of the extraction solvents, increasing the selectivity of the process. Accordingly, saturated aqueous solutions of NaCl would increase the solubility of the analytes in the organic phase. With this premise, [PERSON] et al. (2019) evaluated increasing the amount of NaCl from 1 to 2 g to promote the salting out effect with the aim of improving the recovery values of the PANOs [22].