ASTM_E_1622_-_94_1999e1.pdf

Designation:E 1622 94(Reapproved 1999)e1Standard Practice forCorrection of Spectral Line Overlap in Wavelength-Dispersive X-Ray Spectrometry1This standard is issued under the fixed designation E 1622;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(e)indicates an editorial change since the last revision or reapproval.e1NOTEThe jurisdiction of this practice was changed from Subcommittee E01.22 to E01.20.1.Scope1.1 Procedures are given for the correction of line overlapinterferences encountered in the analysis of metallic andnonmetallic specimens in wavelength dispersive X-ray spec-trometry.1.2 Spectral interference occurs when a line of anotherelement appears at or close to the same wavelength as theanalyte line.The interfering line or lines may be from the samespectral order as the analyte line or may be from anotherspectral order.Line overlap interferences from higher orderlines are usually removed when pulse-height discrimination isused.1.3 The procedures given in this practice are applicable tomaking corrections for interferences arising from concomitantsin the sample.Interfering lines from the X-ray tube andassociated instrumental components are usually specific to thesystem and the procedure for dealing with these may be foundelsewhere.This is treated by E.P.Bertin.21.4 This practice is not generally applicable to simultaneousX-ray spectrometers if it is not possible to measure a line of theinterfering element.Correction is possible,however,if theconcentration of the interfering element is known and can beentered into the analytical program.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:E 135 Terminology Relating to Analytical Chemistry forMetals,Ores,and Related Materials3E 1361 Guide for Correction of Interelement Effects inX-Ray Spectrometric Analysis43.Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice,refer to Terminology E 135.4.Significance and Use4.1 To make accurate analytical determinations,the contri-bution of an unresolved line or lines to the measured intensityof an analyte must be subtracted before calculating its concen-tration.A correction factor determined by using this practicepermits a calculation of the amount to subtract from X-rayspectrometric data to eliminate the portion of a signal that isdue to line interference.4.2 The methods described in 5.1.1 and 5.1.2 may not beapplicable if there are severe matrix effects that change theintensity ratio between the interfering line and another line ofthe same element.For example,with reference to Fig.1,ifthere is an absorption edge of another element between P1andP2,correction for an absorption effect may be required.SeeGuide E 1361.4.3 Correcting for line overlap requires relatively precisemeasurements to avoid inaccuracy from accumulated impreci-sions(see 6.1.).Choose a counting time that reduces impreci-sion to an acceptable level.Counting error is equal to=N,and the relative error is equal to=N/N or=1/N,where N isthe total number of counts.If measurements are taken in countsper second,using R to designate this rate,the relative error isequal to=R/R=T!or=1/RT,where T is the length oftime taken for the measurement.Relative error,therefore,isreduced by increasing the measurement time,which alsoincreases total counts.4.3.1 Since background correction is needed to determinenet counts or net count rates,uncertainty in the backgroundreading contributes to the imprecision in the net count or netcount rate.The standard deviation of a net reading,SN,is theroot mean square of the standard deviations of the peak and thebackgroundreading,sPandsB,respectively,or=sP21 sB2.Variance,however,is equal to counts,whichmakes sN5=NP1 NB.Relative error of the net signal,e1This practice is under the jurisdiction of ASTM Committee E-1 on AnalyticalChemistry for Metals,Ores,and Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundamental Practices and Measurement Traceability.Current edition approved July 15,1994.Published September 1994.2Bertin,E.P.,Principles and Practice of X-Ray Spectrometric Analysis,PlenumPress,New York,NY,Second edition,1975,p.553.3Annual Book of ASTM Standards,Vol 03.05.4Annual Book of ASTM Standards,Vol 03.06.1Copyright ASTM,100 Barr Harbor Drive,West Conshohocken,PA 19428-2959,United States.N,therefore is equal to=NP1 NB/NP2 NB!.By recogniz-ing that background counts are some fractional part of peakcounts,eNcan be seen to be equal to=NP1 bNP/NP2bNP!,where b is the fractional factor.The NPcomponent canthen be factored out of the expression to m