*2.3. Preparation of Positive Mock Samples*

Fresh negative pork, beef, lamb and chicken samples with fat and connective tissue removed were weighed and then homogenized by the addition of standards of amphenicols and metabolites, respectively. Where CAP was spiked at 20 μg/kg in the four kinds of livestock and poultry meat, TAP, FF and FFA were spiked at twice the MRLs specified in the Chinese standard GB 31650-2019 "National food safety standard—Maximum residue limits for veterinary drugs in foods" (Table 2) [12]. Next, the spiked and homogenized meat mash was prepared into cuboid meat blocks with a length × width × height of about 25 mm × 25 mm × 33 mm and a mass of about 18 g for subsequent cooking.


**Table 2.** Spiked concentrations of amphenicols and metabolites in positive mock samples.
