ASTM E406-81(2008)
(Practice)Standard Practice for Using Controlled Atmospheres in Spectrochemical Analysis
Standard Practice for Using Controlled Atmospheres in Spectrochemical Analysis
SIGNIFICANCE AND USE
An increasing number of optical emission spectrometers are equipped with enclosed excitation stands and plasmas which call for atmospheres other than ambient air. This practice is intended for users of such equipment.
SCOPE
1.1 This practice covers general recommendations relative to the use of gas shielding during and immediately prior to specimen excitation in optical emission spectrochemical analysis. It describes the concept of excitation shielding, the means of introducing gases, and the variables involved with handling gases.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E406 − 81(Reapproved 2008)
Standard Practice for
Using Controlled Atmospheres in Spectrochemical
Analysis
This standard is issued under the fixed designation E406; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 5. Reference to this Practice in ASTM Standards
5.1 The inclusion of the following paragraph, or suitable
1.1 This practice covers general recommendations relative
to the use of gas shielding during and immediately prior to equivalent, in any ASTM spectrochemical method, preferably
in the section on excitation, shall constitute due notification
specimenexcitationinopticalemissionspectrochemicalanaly-
sis. It describes the concept of excitation shielding, the means that this practice shall be followed:
X.1 Gas Handling—Store and introduce the gas in accor-
of introducing gases, and the variables involved with handling
gases. dance with Practice E406.
1.2 This standard does not purport to address all of the
6. Concepts of Excitation Shielding
safety concerns, if any, associated with its use. It is the
6.1 Control of Excitation Reactions:
responsibility of the user of this standard to establish appro-
6.1.1 Nonequilibriumreactionsinvolvingvariableoxidation
priate safety and health practices and determine the applica-
rates and temperature gradients in the analytical gap produce
bility of regulatory limitations prior to use.
spurious analytical results. The use of artificial gas mixtures
can provide more positive control of excitation reactions than
2. Referenced Documents
is possible in air, although air alone is advantageous in some
2.1 ASTM Standards:
instances.
E135Terminology Relating to Analytical Chemistry for
6.1.2 Methods of introducing the gas require special con-
Metals, Ores, and Related Materials
sideration.Temperature gradients in both the specimen and the
E416Practice for Planning and Safe Operation of a Spec-
excitationcolumncanbecontrolledbythecoolingeffectofthe
trochemical Laboratory (Withdrawn 2005)
gasflow.Also,currentdensitycanbeincreasedbyconstricting
the excitation column with a flow of gas.
3. Terminology
6.1.3 Control of oxidation reactions is possible by employ-
3.1 For definitions of terms used in this practice, refer to ing nonreactive or reducing atmospheres. For example, argon
Terminology E135. can be used to preclude oxidation reactions during excitation.
A gas may be selected for a particular reaction, such as
4. Significance and Use nitrogentoproducecyanogenbandsasameasureofthecarbon
content of a specimen. Oxygen is used in some instances to
4.1 Anincreasingnumberofopticalemissionspectrometers
ensure complete oxidation or specimen consumption. In point-
are equipped with enclosed excitation stands and plasmas
to-planesparkanalysis,areducingatmospherecanbeprovided
which call for atmospheres other than ambient air. This
by the use of carbon or graphite counter electrodes in combi-
practice is intended for users of such equipment.
nation with an inert gas or by the use of special circuit
parameters in ambient air.
6.2 Effects of Controlled Atmospheres:
This practice is under the jurisdiction ofASTM Committee E01 on Analytical
6.2.1 Numerous analytical advantages can be realized with
Chemistry for Metals, Ores and Related Materials and is the direct responsibility of
Subcommittee E01.20 on Fundamental Practices. controlled atmospheres:
Current edition approved May 1, 2008. Published June 2008. Originally
6.2.1.1 The elimination of oxidation during point-to-plane
approved in 1970. Last previous edition approved in 2003 as E406–81(2003).
sparkexcitationcansignificantlyreducetheso-called“matrix”
DOI: 10.1520/E0406-81R08.
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 Schreiber, T. P., and Majkowaki, R. F., “Effect of Oxygen on Spark Excitation
the ASTM website. and Spectral Character,” Spectrochimica Acta,Vol 15, 1959, p. 991.
3 5
The last approved version of this historical standard is referenced on Bartel, R., and Goldblatt, A., “The Direct Reading Spectrometric Analysis of
www.astm.org. Alloy Cast Iron,” Spectrochimica Acta,Vol 9, 1957, p. 227.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E406 − 81 (2008)
effects and compositional differences. This can result in im- Frequently, these same devices are also suitable for use with
proved precision and accuracy. arc excitation provided they can withstand the associated high
6.2.1.2 The use of argon or nitrogen atmospheres in point- temperatures.
to-plane procedures can increase instrument response so that a 7.3.2 Effectiveshieldingforpoint-to-planesparkanalysisin
wide range of concentrations can be covered with one set of conventional excitation stands can be accomplished by the use
excitation parameters, but because of the increased of a chamber around the counter electrode. The gas is directed
background, small losses in the detection limit can result from into the chamber and its outward flow envelops the counter
oscillatory high voltage spark excitation. Which effect occurs electrode, analytical gap, and excited area of the specimen.
depends on wavelengths used. Several variations of such a device are commercially avail-
6 8
6.2.1.3 Various forms of the Stallwood jet are used in d-c able.
arcprocedures.Onegasoramixtureofgasescanbeusedwith 7.3.3 Optical and excitation shielding is necessary with
this device depending on the particular analytical problem. vacuum emission instruments for spectra below 2000 Å.Air is
Mixtures of 70% argon and 30% oxygen, or 80% argon and opaque to radiation in this region and must be replaced, for
20% oxygen are routinely used to eliminate cyanogen bands, example, by argon, to permit transmission of these wave-
reduce background intensity, and promote more favorable lengths. Commercial vacuum spectrometers are equipped with
volatilization.Certaingasesenhanceintensityatvariouswave-
gas-shielded excitation stands. In these instruments, a flat
lengths. The precision and accuracy achieved for most ele- specimen often is used to seal the excitation chamber. Other
ments with d-c arc procedures employing controlled atmo-
shapes can be accommodated if a special holder is constructed
spheres are significantly better than when ambient air is used. to also seal the chamber. Such holders are commercially
Such improvement is of particular value in trace analysis.
available.
6.2.1.4 Self-absorptionofanalyticallinescanbereducedby
employing a suitable gas flow around or across the excitation
8. Variables Concerned with Gas Handling
column; the flow of gas sweeps away the cooler clouds of
8.1 Gas Purity—Gases used in excitation shielding must be
excited vapor which cause the self-absorption. In argon, the
of consistent purity. While total impurities as high as 50 ppm
diffusion of ions out of the excitation column is comparatively
may not affect analytical results when nitrogen is used, most
slow, and this also decreases self-absorption.
supplierscanfurnishinertgaseswithtotalimpuritylevelsof30
ppm or less.
7. Means of Introducing Atmospheres
8.1.1 Gases that have been packaged by means of water or
7.1 Design Considerations—Design of a device for excita-
oil-lubricated compressors are to be avoided because of pos-
tion shielding involves the following: (1) degree of shielding
sible contamination by moisture, organic species, or both.
needed, (2) type of excitation to be employed, (3) speed of
Industry practice is to produce and store the major inert gases,
specimen handling, (4) constructional simplicity, and (5) cost.
forexample,argonandnitrogen,inliquidform.Ingeneral,the
terms “water pumped” and “oil pumped” are only classifica-
7.2 The purpose of the shield dictates its complexity; a
tions and do not relate to the types of compressor lubrication.
totallyenclosedsystemwouldbesuperfluouswhenasimplejet
The major inert gases are usually packaged directly from the
would suffice. The excitation employed dictates the choice of
liquid phase through impeller pumps and head exchangers.
materials.Withsparkexcitation,aplasticshieldcanfrequently
However, helium is not liquefied and is packaged under
be used, but a more refractory material, such as alumina or
pressure immediately after purification.Additional pressure, if
heat-resistant glass, is usually necessary when employing an
needed,isfurnishedbynonlubricateddiaphragmpumps.Some
arc.Speedandeaseofspecimenhandlingareimportantdesign
small producers using gaseous liquefaction plants still employ
considerations for routine operation. Construction should be
oil or water compressors for packaging under pressure.
simple, employing easily obtainable
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