Nuijs, Alexander L. N. vanLai, Foon YinBeen, FredericAndrés-Costa, María JesúsBarron, LeonBaz-Lomba, Jose AntonioBerset, Jean-DanielBenaglia, LisaBijlsma, LubertusBurgard, Daniel A.Castiglioni, SaraChristophoridis, Christophoros E.Covaci, AdrianVoogt, Pim deEmke, ErikFatta-Kassinos, DespoFick, JerkerHernández, FélixGerber, CobusGonzález Mariño, IriaGrabic, RomanGunnar, TeemuKannan, KurunthachalamKarolak, SaraKasprzyk-Hordern, BarbaraKokot, ZenonKrizman-Matasic, IvonaLi, AngelaLi, XiqingLöve, Arndís S.C.López de Alda, MirenMcCall, Ann-KathrinMeyer, Markus R.Oberacher, HerbertO'Brien, JakeQuintana Álvarez, José BenitoReid, Malcolm J.Schneider, SergeSadler Simoes, SusanaThomaidis, Nikolaos S.Thomas, Kevin V.Yargeau, VivianeOrt, Christoph2018-11-282020-03-222018-03-22Van Nuijs et al. Multi-year interlaboratory exercises for the analysis of illicit drugs and metabolites in wastewater: development of a quality control system Trends in Analytical Chemistry, 2018, 103, 34-43. Doi: 10.1016/j.trac.2018.03.0090165-9936http://hdl.handle.net/10347/17857This is the postprint (accepted manuscript) version of the article published in Trends in Analytical Chemistry. https://doi.org/10.1016/j.trac.2018.03.009Thirty-seven laboratories from 25 countries present the development of an inter-laboratory testing scheme for the analysis of seven illicit drug residues in standard solutions, tap- and wastewater. Almost 10 000 concentration values were evaluated: triplicates of up to five samples and 26 laboratories per year. The setup was substantially improved with experiences gained across the six repetitions (e.g. matrix type, sample conditions, spiking levels). From this, (pre-)analytical issues (e.g. pH adjustment, filtration) were revealed for specific analytes which resulted in formulation of best-practice protocols for inter-laboratory setup and analytical procedures. The results illustrate the effectiveness of the inter-laboratory setup to assess laboratory performance in the framework of wastewater-based epidemiology. The exercise proved that measurements of laboratories were of high quality (>80% satisfactory results for six out of seven analytes) and that analytical follow-up is important to assist laboratories in improving robustness of wastewater-based epidemiology resultseng© Elsevier 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/http://creativecommons.org/licenses/by-nc-nd/4.0/Illicit drugsWastewaterInter-laboratory testingWastewater-based epidemiologyQuality assurancejournal article10.1016/j.trac.2018.03.009open access