Designation:D7783−21StandardPracticeforWithin-laboratoryQuantitationEstimation(WQE)1ThisstandardisissuedunderthefixeddesignationD7783;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thispracticeestablishesauniformstandardforcom-putingthewithin-laboratoryquantitationestimateassociatedwithZ%relativestandarddeviation(referredtohereinasWQEZ%),andprovidesguidanceconcerningtheappropriateuseandapplication.1.2WQEZ%iscomputedtobethelowestconcentrationforwhichasinglemeasurementfromthelaboratorywillhaveanestimatedZ%relativestandarddeviation(Z%RSD,basedonwithin-laboratorystandarddeviation),whereZistypicallyanintegermultipleof10,suchas10,20,or30.Zcanbelessthan10butnotmorethan30.TheWQE10%isconsistentwiththequantitationapproachesofCurrie(1)2andOppenheimer,etal.(2).1.3ThefundamentalassumptionoftheWQEisthatthemediatested,theconcentrationstested,andtheprotocolfollowedindevelopingthestudydataprovidearepresentativeandfairevaluationofthescopeandapplicabilityofthetestmethod,aswritten.Properlyapplied,theWQEprocedureensuresthattheWQEvaluehasthefollowingproperties:1.3.1RoutinelyAchievableWQEValue—ThelaboratoryshouldbeabletoattaintheWQEinroutineanalyses,usingthelaboratory’sstandardmeasurementsystem(s),atreasonablecost.Thispropertyisneededforaquantitationlimittobefeasibleinpracticalsituations.RepresentativedatamustbeusedinthecalculationoftheWQE.1.3.2AccountingforRoutineSourcesofError—TheWQEshouldrealisticallyincludesourcesofbiasandvariationthatarecommontothemeasurementprocessandthemeasuredmaterials.Thesesourcesinclude,butarenotlimitedtointrinsicinstrumentnoise,sometypicalamountofcarryovererror,bottling,preservation,samplehandlingandstorage,analysts,samplepreparation,instruments,andmatrix.1.3.3AvoidableSourcesofErrorExcluded—TheWQEshouldrealisticallyexcludeavoidablesourc...
