ASTM_D_7783_-_13.pdf

Designation:D778313Standard 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.NoteBalloted information was included and the year date changed on March 28,2013.1.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 the developing the study data provide a represen-tative and fair evaluation of the scope and applicability of thetest method,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 wouldinclude,but are not limited to,modifications to the sample,modifications to the measurement procedure,modifications tothe measurement equipment of the validated method,and grossand easily discernible transcription errors(provided there wasa way 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 quantiation estimates in general.Therefore,the WQE procedure is appropriate when the domi-nant source of variation is not instrument calibration,but isperhaps 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 lowest%RSD possible for anygiven data set.Thus,if possible,WQE10%would be computed.If the data indicated that the method was too noisy,one mighthave to compute instead WQE20%,or possibly WQE30%.Inany case,a WQE with a higher%RSD level(such asWQE50%)would not be considered,though a WQE with RSD10%(such as WQE1%)would be acceptable.The appropriatelevel of%RSD is based on the data-quality objective(s)for aparticular use or uses.This practice allows for calculation ofWQEs with user selected%RSDs less than 30%.1This 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 March 28,2013.Published April 2013.Originallyapproved in 2012.Last previous edition approved in 2012 as D7783 12.DOI:10.1520/D778313.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 2.Referenced Documents2.1 ASTM Standards:3D1129 Terminology Relating to WaterD2777 Practice for Determination of Precision and