## 2 Materials and Methods  
### Reagents, Instruments and Samples  
Analytical standards were obtained from LGC Standards (Teddington, Middlesex, UK). Stock solutions (1 mg/mL) were prepared and stored according to pesticide databases [25]. A working standard mixture solution containing 480 pesticides for calibration and spiking purpose was prepared at 10 ug/mL in acetonitrile and was stored at \(-\)20 \({}^{\circ}\)C for half a year. For screening purposes, a 100 ng/mL working standard mixture was freshly diluted in acetonitrile.  
Methanol, acetonitrile, ammonium formate (either LC-MS or HPLC grade), and the Ascents Express C18 HPLC column (100 mm \(\times\) 3 mm, 2.7 \(\upmu\)m) were purchased from the Merck-Sigma group (Schnelldorf, Germany). EN 15662:2018 QuEChERS (Quick Easy Cheap Effective Rugged Safe) extraction salt was obtained from Agilent Technologies (Waldbronn, Germany; containing 4.0 g MgSO\({}_{4}\), 1.0 g NaCl, 1.0 g Na-citrate \(\times\) 2H\({}_{2}\)O, and 0.5 g Na-hydrogenictrate sesquihydrate). HPLC gradient grade water was obtained from VWR International Ltd. (Debrecen, Hungary). HPLC pre-column holders and C18 pre-column cartridges (4 mm \(\times\) 3 mm; 5 \(\upmu\)m), dispersive solid-phase extraction (dSPE) cartridges and graphitized carbon black (GCB) were obtained from Phenomenex (Torrance, CA, USA).  
LC-MS/MS analyses were carried out on a Shimadzu Nexera LC-30 AD liquid chromatographic system (Shimadzu Corporation, Kyoto, Japan), coupled to a QTRAP 6500+ triple quad MS detector equipped with an IonDrive Turbo V Source (Sciex; Warrington, Cheshire, UK). Data acquisition and evaluation were performed with the Analyst software version 1.7.1 and MultiQuant software version 3.0.3, respectively (Sciex).  
Proficiency test samples were purchased from FAPAS (Food Analysis Performance Assessment Scheme, Fera Science Ltd., Sand Hutton, York, UK) and from Test Veritas S.r.l. (Test Veritas s.r.l., Via Svizzera, Padova, Italia). They included blueberry purcee (FAPAS, sample: FCPM2-FRU31, proficiency test: 19258), virgin olive oil (FAPAS, sample: FCPM2-OIL34, proficiency test: 5147), apple purcee (FAPAS, sample: FCPM2-FRU2, proficiency test: 19307), green bean purcee (FAPAS, sample: FCPM2-VEG106, proficiency test: 19310), milk powder (FAPAS, sample: FCPX10-DRY14, proficiency test: 05161) and lettuce (Test Veritas s.r.l., sample: VF1700, proficiency test: VF1700P).  
Customer-derived samples were received for pesticide screening analysis with the EN 15662:2018 standard method and they comprised of date seed coffee (_Coffa Phoenix dactylifera_), white peppercorn (_Piper nigrum_), herb extract (1.0 mL of the ethanolic herb extract (1:5) contained 80.0 mg _Epilobium parviform Schreb_, herba and 53.4 mg _Utrica dioica L._ and _Utrica urens L._; folium, 40.0 mg _Utrica dioica L._ and _Utrica urens L._; radix, and 40.0 mg _Solidago canadensis L. et Solidago gigante Ait._, herba, and 13.4 mg _Foeniculum vulgarz miller subsp. vulgarz var. dulce ([PERSON]) [PERSON]_, fructus), elderberry (_Sambuucus_), dried ginger (_Zingiber officinal_) and fennel (_Foeniculum vulgarz_).  
The validated sample matrices included cereals, olive oil, carrot, peas, lettuce, tomato and bell pepper that were either purchased in local stores or were formerly received for analysis.