ASTM_D_7783_-_21.pdf

Designation:D778321Standard Practice forWithin-laboratory Quantitation Estimation(WQE)1This standard is issued under the fixed designation D7783;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice establishes a uniform standard for com-puting the within-laboratory quantitation estimate associatedwith Z%relative standard deviation(referred to herein asWQEZ%),and provides guidance concerning the appropriateuse and application.1.2 WQEZ%is computed to be the lowest concentration forwhich a single measurement from the laboratory will have anestimated Z%relative standard deviation(Z%RSD,based onwithin-laboratory standard deviation),where Z is typically aninteger multiple of 10,such as 10,20,or 30.Z can be less than10 but not more than 30.The WQE10%is consistent with thequantitation approaches of Currie(1)2and Oppenheimer,et al.(2).1.3 The fundamental assumption of the WQE is that themedia tested,the concentrations tested,and the protocolfollowed in developing the study data provide a representativeand fair evaluation of the scope and applicability of the testmethod,as written.Properly applied,the WQE procedureensures that the WQE value has the following properties:1.3.1 Routinely Achievable WQE ValueThe laboratoryshould be able to attain the WQE in routine analyses,using thelaboratorys standard measurement system(s),at reasonablecost.This property is needed for a quantitation limit to befeasible in practical situations.Representative data must beused in the calculation of the WQE.1.3.2 Accounting for Routine Sources of ErrorThe WQEshould realistically include sources of bias and variation thatare common to the measurement process and the measuredmaterials.These sources include,but are not limited to intrinsicinstrument noise,some typical amount of carryover error,bottling,preservation,sample handling and storage,analysts,sample preparation,instruments,and matrix.1.3.3 Avoidable Sources of Error ExcludedThe WQEshould realistically exclude avoidable sources of bias andvariation(that is,those sources that can reasonably be avoidedin routine sample measurements).Avoidable sources include,but are not limited to,modifications to the sample,modifica-tions to the measurement procedure,modifications to themeasurement equipment of the validated method,and grossand easily discernible transcription errors(provided there is away to detect and either correct or eliminate these errors inroutine processing of samples).1.4 The WQE applies to measurement methods for whichinstrument calibration error is minor relative to other sources,because this practice does not model or account for instrumentcalibration error,as is true of most quantitation estimates ingeneral.Therefore,the WQE procedure is appropriate whenthe dominant source of variation is not instrument calibration,but is perhaps one or more of the following:1.4.1 Sample Preparation,and especially when calibrationstandards do not go through sample preparation.1.4.2 Differences in Analysts,and especially when analystshave little opportunity to affect instrument calibration results(as is the case with automated calibration).1.4.3 Differences in Instruments(measurement equipment),such as differences in manufacturer,model,hardware,electronics,sampling rate,chemical-processing rate,integra-tion time,software algorithms,internal signal processing andthresholds,effective sample volume,and contamination level.1.5 Data Quality ObjectivesFor a given method,onetypically would compute the WQE for the lowest RSD forwhich the data set produces a reliable estimate.Thus,ifpossible,WQE10%would be computed.If the data indicatedthat the method was too noisy,so that WQE10%could not becomputed reliably,one might have to compute insteadWQE20%,or possibly WQE30%.In any case,a WQE with ahigher RSD level(such as WQE50%)would not be considered,though a WQE with RSD 10%(such as WQE5%)could beacceptable.The appropriate level of RSD is based on the dataquality objective(s)for a particular use or uses.This practiceallows for calculation of WQEs with user selected RSDs lessthan 30%.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for the1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.02 on Quality Systems,Specification,and Statistics.Current edition approved Nov.15,2021.Published March 2022.Originallyapproved in 2012.Last previous edition approved in 2013 as D7783 13.DOI:10.1520/D7783-21.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Consho