## Materials and Methods  
### Chemicals, Standards and Consumables  
Ultrapure water (UPW) (18.2 M\(\Omega\)cm) was generated in house using a Millipore water purification system (Cork, Ireland). Romil \"SpS\" (super purity solvent) grade methanol (MeOH) 215, acetonitrile (MeCN) 200 far UV and propan-2-ol (IPA) were sourced from Romil Ltd. (Cambridge, UK). Acetone puriss was purchased from Honeywell Research Chemicals (Honeywell Riedel-de Haen; Seelze, Germany). Dimethyl sulfoxide (DMSO), 99.5% d-MeOH, ammonium formate puriss p.a. (puriss pro analysis), formic acid (HCOOH) 98-100%, methyl tert-Butyl ether (MTBE) (Fluka for GC) and sodium meta-bisulphite (\(>\)97%) were sourced from Sigma-Aldrich (Dublin, Ireland). Glacial Acetic acid (CH\({}_{3}\)COOH) (100%) and ammonia solution (25% \(w/v\)) were obtained from Merck (Darmstadt, Germany). Concentrated hydrochloric acid (HCI) (36%) was sourced from BDH Chemicals Ltd. (Poole, UK).  
Neat analytical standards of abandectin (ABA), albendazole (ABZ), bithionol (BITH), clorsulon (CLOR), closantel (CLOS), coumaphos (COUMA), doramectin (DORA), Emamectin benzoate (EMA), eprimometcin (EPRINO), fenbendazole (FBZ), haloxon (HALOX), ivermectin (IVER), levamisole hydrochloride (LEV), morantel-tartrate-hydrate (MOR), moxidectin (MOXI) niclosamide (NIC LOS), nitroxyl (NITROX), oxfendazole (OXF), oxyclozanide (OXY), rafoxanide (RAFOX), thiabendazole (TBZ), trichalendazole (TCB) and salicanilide (SAL) were purchased from Sigma-Aldrich Ireland (Dublin, Ireland). Albendazole-sulphoxide (ABZ-SO), albendazole-sulphone (ABZ-SO\({}_{2}\)), albendazole-amino-sulphone hydrochloride (ABZ-NH\({}_{2}\)-SO\({}_{2}\)), cambedazole (CAM), fenbendazole-sulphone (FBZ-SO\({}_{2}\)), 5-hydroxy-thiabendazole (5-OH-TBZ), trichalendazole sulphoxide (TCB-SO), trichalendazole sulphone (TCB-SO\({}_{2}\)) and amino-triclabendazole (TCB-NH\({}_{2}\)) were purchased from Witega (Berlin, Germany). Coumaphos-oxon (COUM-O) was purchased from Greyhound Chromatography and Allied Chemicals, (Merseyside, UK). Flubendazole (FLU), amino-flubendazole (FLU-NH\({}_{2}\)), hydroxy-flubendazole (FLU-OH), mebendazole (MBZ), amino-mebendazole (MBZ-NH\({}_{2}\)) and hydroxy-mebendazole (MBZ-OH) were obtained from Janssen Animal Health (Beerse, Belgium). Oxibendazole (OXI) was purchased from QMX Laboratories (Essex, UK), while selametectin (SEL) was acquired from Pfizer (Kent, UK). Monepantel (MONE) and monepantel-sulphone (MONE-SO\({}_{2}\)) were purchased from Novartis Pharmaceuticals (Dublin, Ireland). All deuterated or isotopically labelled internal standards (specified for each compound in Table 2) were purchased from Witega (Berlin, Germany), except for flubendazole-d\({}_{3}\) (FLU-d\({}_{3}\)) which was purchased from Sigma-Aldrich Ireland (Dublin, Ireland).  
Duran style (GL45) glass amber bottles (1000 mL) were purchased from Scientific and Chemical Supplies Ltd. (Cork, Ireland). Analytical grade glass wool (silanised and unsilanised) were purchased from Sigma-Aldrich (Dublin, Ireland). Polypropylene tubes (15 mL, conical) were obtained fromSarstedt Ltd. (Wexford, Ireland). Isolute 150 mL frittless SPE reservoirs were purchased from Biotage (Uppsala, Sweden). Reservoirs were connected to the SPE cartridge using adapter caps for 1-6 mL cartridges, provided by Agilent Technologies Ltd. (Cork, Ireland). Captiva Econo PTFE 0.2 \(\upmu\)m filters were also purchased from Agilent Technologies Ltd., as were the glass inserts (400 \(\upmu\)L) used in the Waters HPLC vials (Waters; Dublin, Ireland) The different SPE sorbents evaluated as part of method development included: Bond Elut ENV (200 mg, 6 mL) and Bond Elut PLEXA (200 mg, 6 mL) from Agilent technologies Ltd. (Cork, Ireland), Oasis HLB (200 mg, 6 mL) from Waters (Dublin, Ireland) and UCT Enviro Clean HL DVB (200 mg, 6 mL) and UCT Enviro Clean HL DVB (500 mg, 6 mL) from United Chemical Technologies Ireland Ltd.