ASTM E305-21

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E305 − 13 E305 − 21
Standard Practice for
Establishing and Controlling Spark Atomic Emission
Spectrochemical Analytical Curves
This standard is issued under the fixed designation E305; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers guidanceprovides direction for establishing and controlling spark atomic emission spectrochemical
analytical curves. The generation of analytical curves and their routine control are considered as separate althoughthough
interrelated operations. This practice is applicable to spark atomic emission spectrometers.
NOTE 1—X-ray emissionfluorescence spectrometric applications are no longer covered by this practice. See Guides E1361 and E1621 for discussion of
this technique.
1.1.1 Since computersoftware programs are readily available to runcompute multiple linear regressions that can be used to
generate analytical curves and since most instruments include this feature, this practice does not go into detail on the address this
procedure. However, some recommendations are given on evaluatingto evaluate the equations that are generated.
1.2 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E1329 Practice for Verification and Use of Control Charts in Spectrochemical Analysis (Withdrawn 2019)
E1361 Guide for Correction of Interelement Effects in X-Ray Spectrometric Analysis
E1621 Guide for Elemental Analysis by Wavelength Dispersive X-Ray Fluorescence Spectrometry
3. Terminology
3.1 For definitions of terms used in this practice, refer to Terminology E135.
This practice is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Subcommittee E01.20 on Fundamental Practices.
Current edition approved June 1, 2013May 15, 2021. Published July 2013June 2021. Originally approved in 1966. Last previous edition approved in 20072013 as
E305 – 07.E305 – 13. DOI: 10.1520/E0305-13.10.1520/E0305-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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NOTE 2—Spectrometer manufacturers tend to use the term “standardization” in their software. The correct technical term is “drift correction,” which is
used in this practice.
4. Summary of Practice
4.1 Systematic and random errors that occur in obtaining data are reviewed. Background corrections are considered as well as
interferences from other elements. Calibration, standardization, drift correction, and verification procedures are discussed,
including the use of reference materials and the generation of data. A basis is given for evaluating first, second, third, and higher
degree analytical curves.
5. Significance and Use
5.1 This practice is intended as ato provide fundamental guidedirection for the calibration, standardization, drift correction, and
dailyperiodic control of the analytical curves for spark atomic emission spectrometers.
5.2 It is assumed that this practice will be used by trained operators capable of performing the procedures described herein.
6. Precautions
6.1 Potential Errors:
6.1.1 Bias Because of Incorrect Calibration—In the procedure for quantitative spectrochemical analysis, the initial generation of
the analytical curve relates element composition or relative composition to spectral intensity or intensity ratio. The accuracy of the
calibration may be affected by a number of factors, such as incorrect values for element compositions, heterogeneity of the
reference materials, spectral interferences, and matrix effects. These factors may cause a shift in the analytical curve, thereby
leading to bias in the analytical data generated. It is the user’s responsibility to apply calibration models designed to evaluate the
effect of, and mathematically correct for, spectral interferences and matrix effects.
6.1.1.1 Calibration bias because of incorrect element concentrations arecompositions is minimized by the use of certified reference
materials. materials (CRMs). These calibrantsCRMs may be augmented with one or more other reference materials for which the
chemical compositions have been carefully determined by approved methods of analysis, such as ASTM or BSI (British Standards
Institute).Standard Institution). The inclusion of production materials analyzed by independent methods permits determining
whether bias exists because of differences between the metallurgical conditions of the certified reference materials CRMs and
typical samples. In the absence of certified reference materials, CRMs, it is helpful to use several reference materials from a variety
of sources to detect bias in these materials.
6.1.1.2 In general, the use of a large number of reference materials will aid in the detection and rejection of those that appear to
be inaccurate. Caution should be exercised in Exercise caution when rejecting data that appears to be inaccurate as it may be
reflecting complicated matrix effects or the impact of unknown variables.
6.1.1.3 It is advisable that analyzed materials used as calibrants calibration reference materials (RMs) be tested initially for
homogeneity.heterogeneity.
6.1.2 Bias Because of Experimental Variations—Bias may arise from experimental variations occurring within the operational
procedure (for example, change in optics, source parameters, and so forth). etc.). Such changes may result in bias because of
changes in sensitivity or background resulting in displacement of the analytical curve. The analyst may attempt to reduce bias from
experimental variations during the initial calibration procedure by replication and by measuring the reference materials in random
order; but bias may be detected later during subsequent operations, as described in 8.3.1.
6.2 Random Errors:
6.2.1 Measurement Error—Measurement repeatability may be assessed using an estimate of standard deviation of repeated
measurements. While the true standard deviation is designated σ, an estimate of standard deviation calculated from a limited
number of values is designated by the symbol s,
where:
s =
= x 2x¯ / n21
~ ! ~ !
( i
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and where:
x = are individual values
i
x¯ = average x , and
i
n = number of measurements.
6.2.1.1 Errors in determining the average signal intensity or intensity ratio from reference materials occur because of statistical
variation, less than optimum excitation parameters, and elevated specimen inhomogeneity.heterogeneity. Increasing the number of
replicate measurements and using the average of the values will reduce the effect of statistical variation and minor elevated
specimen inhomogeneity.heterogeneity. The use of optimum excitation conditions, including sufficient preburn and integration
times, will also reduce statistical variations and increase accuracy.
7. Calibration
7.1 Spectral Background—Background intensities vary throughout the spectral regions. Correcting for the background in
measurements of weak spectral line intensities (those slightly more intense than background) can improve the measurements.
However, the effectiveness of the correction must be evaluated. The need for background correction varies with the type of material
being analyzed. Ensure that background correction is necessary and can be accomplished consistently before proceeding.
NOTE 2—The need for background correction varies with the type of material being analyzed. Ensure that background correction is necessary and can
be accomplished consistently before proceeding.
7.1.1 Background Correction—Methods of background correction may use either a dynamic correction or a shifting of spectra
through exit slits to read background near a line.
7.1.1.1 In a dynamic background correction, a selected portion of the background of a spectrum is integrated simultaneously with
analytical signals. When this integrated measurement is strong and broad enough to give a consistent sampling, it can be used to
subtract out background. A background area signal may be made to have a strong signal strengthened by using a wide exit slit or
by using an extra-sensitive detector, or by a combination of these. Because the dynamic approach is difficult to control and may
depend on maintaining consistent response from two detectors, it is rarely used in photomultiplier systems. It can be used more
effectively with solid-state detector systems.
NOTE 3—Measurement of spectral intensity may not be truly simultaneous even with solid-state detectors. Some spectrometer designs read multiple
regions of a detector in rapid succession, not in true simultaneity. Such a design can be subject to instrument drift.
7.1.1.2 Shifting to read background has validity only if the generation of background intensity shows little variation from
burnmeasurement to burn.measurement.
7.2 Generation of the Analytical Curve:
7.2.1 Calibrants, Calibration Reference Materials (RMs), preferably certified reference materials CRMs as described in 6.1.1.1,
should span the composition ranges and types of materials expected. Extrapolation should be avoided. It is recommended that the
number of calibrants to be calibration RMs used for each curve be twice the number of coefficients to be determined by regression.
This includes the curve parameters and any correction coefficients. If the composition range exceeds one order of magnitude or
if several calibrants are close to each other in composition, the use of more calibrants is recommended, preferable at least three
per order of magnitude, spaced as equally apart as possible.
7.2.1.1 Minimally, there should be at least one more data point than the number of coefficients or constants in the equation. If this
minimum is not met, the calculation of a supposed regression fit will merely make the resulting curve go through each data point
as if each was absolutely correct, negating the purpose of making a least square fit of data. In fact, reputable curve fitting software
will reject such an attempt to calculate the parameters, citing that there is insufficient data.
7.2.1.2 If the composition range exceeds one order of magnitude or if several calibration RMs are close to each other in
composition, the use of more calibration RMs is recommended, preferably at least three per order of magnitude, spaced as equally
apart as possible.
7.2.2 Drift Correction Samples and Verifiers—All materials that may be useful in monitoring and normalizing calibrations should
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be burnedmeasured in a random order along with calibrants. calibration RMs. Control and drift correction samples shall be
homogeneous such that they give have reasonably low heterogeneity that provide repeatable measurements over time. The
repeatability standard deviation for suitable material shall be less than or equal to the interlaboratory repeatability goal for the test
method. In general, calibrants calibration RMs should not be used as drift correction samples or verifier
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