ASTM E1622-94(1999)e1
(Practice)Standard Practice for Correction of Spectral Line Overlap in Wavelength-Dispersive X-Ray Spectrometry (Withdrawn 2006)
Standard Practice for Correction of Spectral Line Overlap in Wavelength-Dispersive X-Ray Spectrometry (Withdrawn 2006)
SCOPE
1.1 Procedures are given for the correction of line overlap interferences encountered in the analysis of metallic and nonmetallic specimens in wavelength dispersive X-ray spectrometry.
1.2 Spectral interference occurs when a line of another element appears at or close to the same wavelength as the analyte line. The interfering line or lines may be from the same spectral order as the analyte line or may be from another spectral order. Line overlap interferences from higher order lines are usually removed when pulse-height discrimination is used.
1.3 The procedures given in this practice are applicable to making corrections for interferences arising from concomitants in the sample. Interfering lines from the X-ray tube and associated instrumental components are usually specific to the system and the procedure for dealing with these may be found elsewhere. This is treated by E. P. Bertin.
1.4 This practice is not generally applicable to simultaneous X-ray spectrometers if it is not possible to measure a line of the interfering element. Correction is possible, however, if the concentration of the interfering element is known and can be entered into the analytical program.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
WITHDRAWN RATIONALE
Procedures are given for the correction of line overlap interferences encountered in the analysis of metallic and nonmetallic specimens in wavelength dispersive X-ray spectrometry.
Formerly under the jurisdiction of E01 on Analytical Chemistry for Metals, Ores, and Related Materials, this practice was withdrawn in June 2006.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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e1
Designation:E1622–94 (Reapproved 1999)
Standard Practice for
Correction of Spectral Line Overlap in Wavelength-
Dispersive X-Ray Spectrometry
This standard is issued under the fixed designation E1622; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—The jurisdiction of this practice was changed from Subcommittee E01.22 to E01.20.
1. Scope X-Ray Spectrometric Analysis
1.1 Procedures are given for the correction of line overlap
3. Terminology
interferences encountered in the analysis of metallic and
3.1 Definitions—For definitions of terms used in this prac-
nonmetallic specimens in wavelength dispersive X-ray spec-
tice, refer to Terminology E135.
trometry.
1.2 Spectral interference occurs when a line of another
4. Significance and Use
element appears at or close to the same wavelength as the
4.1 To make accurate analytical determinations, the contri-
analyteline.Theinterferinglineorlinesmaybefromthesame
bution of an unresolved line or lines to the measured intensity
spectral order as the analyte line or may be from another
of an analyte must be subtracted before calculating its concen-
spectral order. Line overlap interferences from higher order
tration. A correction factor determined by using this practice
lines are usually removed when pulse-height discrimination is
permits a calculation of the amount to subtract from X-ray
used.
spectrometric data to eliminate the portion of a signal that is
1.3 The procedures given in this practice are applicable to
due to line interference.
makingcorrectionsforinterferencesarisingfromconcomitants
4.2 The methods described in 5.1.1 and 5.1.2 may not be
in the sample. Interfering lines from the X-ray tube and
applicable if there are severe matrix effects that change the
associated instrumental components are usually specific to the
intensity ratio between the interfering line and another line of
system and the procedure for dealing with these may be found
2 the same element. For example, with reference to Fig. 1, if
elsewhere. This is treated by E. P. Bertin.
thereisanabsorptionedgeofanotherelementbetween P and
1.4 Thispracticeisnotgenerallyapplicabletosimultaneous
P , correction for an absorption effect may be required. See
X-rayspectrometersifitisnotpossibletomeasurealineofthe
Guide E1361.
interfering element. Correction is possible, however, if the
4.3 Correcting for line overlap requires relatively precise
concentration of the interfering element is known and can be
measurements to avoid inaccuracy from accumulated impreci-
entered into the analytical program.
sions (see 6.1.). Choose a counting time that reduces impreci-
1.5 This standard does not purport to address all of the
sion to an acceptable level. Counting error is equal to N,
=
safety concerns, if any, associated with its use. It is the
and the relative error is equal to N/ N or 1/N, where N is
= =
responsibility of the user of this standard to establish appro-
thetotalnumberofcounts.Ifmeasurementsaretakenincounts
priate safety and health practices and determine the applica-
per second, using R to designate this rate, the relative error is
bility of regulatory limitations prior to use.
equal to R/~ R T! or 1/RT, where T is the length of
= = =
2. Referenced Documents time taken for the measurement. Relative error, therefore, is
reduced by increasing the measurement time, which also
2.1 ASTM Standards:
increases total counts.
E135 Terminology Relating to Analytical Chemistry for
3 4.3.1 Since background correction is needed to determine
Metals, Ores, and Related Materials
net counts or net count rates, uncertainty in the background
E1361 Guide for Correction of Interelement Effects in
reading contributes to the imprecision in the net count or net
count rate. The standard deviation of a net reading, S ,isthe
N
rootmeansquareofthestandarddeviationsofthepeakandthe
This practice is under the jurisdiction ofASTM Committee E-1 onAnalytical
ChemistryforMetals,Ores,andRelatedMaterialsandisthedirectresponsibilityof
background reading, s and s , respectively, or
P B
Subcommittee E01.20 on Fundamental Practices and Measurement Traceability.
2 2
s 1s . Variance, however, is equal to counts, which
=
P B
Current edition approved July 15, 1994. Published September 1994.
Bertin,E.P., Principles and Practice of X-Ray Spectrometric Analysis,Plenum
Press, New York, NY, Second edition, 1975, p. 553.
3 4
Annual Book of ASTM Standards, Vol 03.05. Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1622
system, the factor causing an increase in imprecision is
1 1 b/~1 2 b !. It can then be seen that if background is
=
40% of the peak reading, the imprecision of the net reading
will be increased by almost two-fold.
4.4 The following methods of correction are based on
intensities in terms of total counts. The equations may also be
used for intensities in terms of count rates. If total counts are
used, it is imperative that the counting time for any one
intensity reading is not changed, since such a change would
invalidate the correcting factor being used.
5. Methods of Correction
5.1 When the measured intensity of an analyte includes
counts from an interfering line, the contribution of the inter-
ference may be inferred and eliminated by measuring another
line of the interfering element. The alternate line, however,
must be free of interferences. In Fig. 1, P is the analyte line
that is being measured at the angular position Q , P is an
1 3
interferinglinewhichcontributessomeofitsintensityto P . P
1 2
is another line of the interfering element appearing at angular
position Q . The observed measurement is:
I 5 I 1 I8 1 B (1)
Q1 1 1 1
where:
I 5 total intensity, in counts, measured at Q ,
Q1 1
I 5 net intensity, in counts, of the analyte at Q ,
1 1
I8 5 net contribution, in counts, of the interfering line,
P , appearing at Q , and
3 1
B 5 intensity, in counts, of the background at Q .
1 1
5.1.1 Use of Pure Elements—Determineafactor, F,relating
the relative intensity of the overlapping line at Q to another
line, P , of the same interfering element at Q by using a pure
2 2
specimen of the interfering element. The specimen may be a
metalfoiloranoxidepowder.Correctingallmeasurementsfor
background, the determination is as follows:
F 5 I8 /I (2)
1 2
where:
I 5 net intensity, in counts, of the fully resolved line, P ,
2 2
of the interfering element measured at Q,(I − B ),
2 Q2 2
where B istheintensityincounts,ofthebackground
at Q .
5.1.1.1 Calculate the corrected net intensity of the analyte
using:
I 5 I 5 B 5 F~I ! (3)
1 Q1 1 2
NOTE 1—When measuring pure elements it is important to verify that
FIG. 1 Typical Line Overlap
thecountratedoesnotexceedthelinearityofthedetectionsystem.Aplot
ofcountversustubecurrentwillestablishthelimitoflinearity.Ifbending
is observed, the X-ray power must be reduced.The reduction can be done
makes s 5 N 1 N . Relative error of the net signal, e
=
N P B
by reducing the current of the X-ray tube, but do not reduce the voltage
N, therefore is equal to N 1 N /~N 2 N !. By recogniz-
=
P B P B
applied to the X-ray tube.
ing that background counts are some fractional part of peak
counts, e can be seen to be equal to N 1 bN /~ N 2 5.1.2 Use of Synthetic Specimens—Prepare specimens con-
=
N
P P P
bN !, where b is the fractional factor. The N component can taining increasing amounts of the interfering element. The
P P
then be factored out of the expression to make e 5 contribution of the interfering element to the intensity of the
N
1/N @ 1 1 b/~1 2 b !#. In a similar fashion, e can be analytical wavelength can be established graphically. The net
= =
P N
seen to be equal to 1/ R T@ 1 1 b/~1 2 b !#, when intensity, the reading corrected for background, measured at
= =
N
readings are taken in terms of counts per second and R is the the analytical wavelength is plotted against the net intensity
N
count rate observed over T seconds. In either measurement measured for a line of the interfering element that is free of
E1622
interference. The slope will be equal to the overlap correction calculatedbymultiplelinearregressionasdescribedintextson
5,6
factor, F, in Eq 2. See Fig. 2. statistics, or by use of a computer program (Note 3). In this
5.1.3 Use of Regression Analysis—Frequently it is not case, two regressions on the concentration variable are deter-
possible to prepare specimens specifically for the determina- mined:theprimaryrelationshiptotheintensitymeasuredatthe
tion of line overlap correction factors. It is possible, however, analyte wavelength; and a secondary relationship to an inten-
to use a series of specimens with varying amounts of both the sity measured for another reading of the interfering element.
analyte and the interfering element to determine the overlap Thelinecorrectionfactora /a iscalculatedandsubstitutedfor
2 1
correction factor through the use of multiple linear regression F in Eq 3, after changing its sign.The computer program used
using the following relationship: for the X-ray spectrometer may permit a regression to deter-
mine the correction factor.
C 5a 1a I 1a I (4)
0 1 n 2 2
NOTE 3—Standard spreadsheet programs often are able to determine
where:
regression coefficients.
C
...
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