ASTM E60-98(2004)
(Practice)Standard Practice for Analysis of Metals, Ores, and Related Materials by Molecular Absorption Spectrometry
Standard Practice for Analysis of Metals, Ores, and Related Materials by Molecular Absorption Spectrometry
ABSTRACT
This practice covers general recommendations for photoelectric photometers and spectrometers and for photometric practice for chemical analysis of metals, ores, and related materials. However, this practice does not include a description of every apparatus nor does it present recommendations on every detail of practice in photometric or spectrophotometric methods of chemical analysis of metals. To improve photoelectric photometers and spectrophotometers, some suggestions related to their components are mentioned, in particular, the radiation source (illuminant), filters, monochromators, absorption cells, photosensitive tubes, and current-measuring devices. In addition, prior to using photometric methods in the chemical analysis of metals, ores, and related materials, it is recommended that a complete photometric investigation of the reaction be performed. The investigation shall involve the study of the specificity of the reagent used to produce absorption; validity of Beer's law; effects of salts, solvent, pH, temperature, concentration of reagents, and the order of adding reagents; time required for absorption development and the stability of the absorption; absorption curve of the reagent and the absorbing substances; and optimum concentration range for quantitative analysis.
SCOPE
1.1 This practice covers general recommendations for photoelectric photometers and spectrophotometers and for photometric practice prescribed in ASTM methods for chemical analysis of metals, sufficient to supplement adequately the ASTM methods. A summary of the fundamental theory and practice of photometry is given. No attempt has been made, however, to include in this practice a description of every apparatus or to present recommendations on every detail of practice in ASTM photometric or spectrophotometric methods of chemical analysis of metals.
1.2 These recommendations are intended to apply to the ASTM photometric and spectrophotometric methods for chemical analysis of metals when such standards make definite reference to this practice, as covered in Section 4.
1.3 In this practice, the terms "photometric" and "photometry" encompass both filter photometers and spectrophotometers, while "spectrophotometry" is reserved for spectrophotometers alone.
1.4 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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Designation:E60–98 (Reapproved 2004)
Standard Practice for
Analysis of Metals, Ores, and Related Materials by
Molecular Absorption Spectrometry
This standard is issued under the fixed designation E60; 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.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope E169 Practices for General Techniques of Ultraviolet-
Visible Quantitative Analysis
1.1 This practice covers general recommendations for pho-
E275 Practice for Describing and Measuring Performance
toelectric photometers and spectrophotometers and for photo-
of Ultraviolet and Visible Spectrophotometers
metric practice prescribed in ASTM methods for chemical
analysis of metals, sufficient to supplement adequately the
3. Terminology Definitions and Symbols
ASTM methods. A summary of the fundamental theory and
3.1 For definitions of terms relating to absorption spectros-
practice of photometry is given. No attempt has been made,
copy, refer to Terminology E131.
however, to include in this practice a description of every
3.2 background absorption—any absorption in the solution
apparatus or to present recommendations on every detail of
duetothepresenceofabsorbingions,molecules,orcomplexes
practice inASTM photometric or spectrophotometric methods
2 of elements other than that being determined is called back-
of chemical analysis of metals.
ground absorption.
1.2 These recommendations are intended to apply to the
3.3 concentration range—the recommended concentration
ASTM photometric and spectrophotometric methods for
range shall be designated on the basis of the optical path of the
chemical analysis of metals when such standards make definite
cell, in centimetres, and the final volume of solution as
reference to this practice, as covered in Section 4.
recommended in a procedure. In general, the concentration
1.3 In this practice, the terms “photometric” and “photom-
range and path length shall be specified as that which will
etry” encompass both filter photometers and spectrophotom-
produce transmittance readings in the optimum range of the
eters, while “spectrophotometry” is reserved for spectropho-
instrument being used as covered in Section 14.
tometers alone.
3.4 initial setting— the initial setting is the photometric
1.4 This standard does not purport to address all of the
reading (usually 100 on the percentage scale or zero on the
safety concerns, if any, associated with its use. It is the
logarithmic scale) to which the instrument is adjusted with the
responsibility of the user of this standard to establish appro-
reference solution in the absorption cell. The scale will then
priate safety and health practices and determine the applica-
read directly in percentage transmittance or in absorbance.
bility of regulatory limitations prior to use.
3.5 photometric reading—the term “photometric reading”
2. Referenced Documents refers to the scale reading of the instrument being used.
Available instruments have scales calibrated in transmittance,
2.1 ASTM Standards:
T, (1) or absorbance, A, (2) (see 5.2), or even arbitrary units
E131 Terminology Relating to Molecular Spectroscopy
proportional to transmittance or absorbance.
E168 Practices for General Techniques of Infrared Quanti-
3.6 reagent blank— the reagent blank determination yields
tative Analysis
a value for the apparent concentration of the element sought,
which is due only to the reagents used. It reflects both the
This practice is under the jurisdiction of ASTM Committee E01 on Analytical
amount of the element sought present as an impurity in the
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
reagents, and the effect of interfering species.
Subcommittee E01.20 on Fundamental Practices.
3.7 reference solution—photometric readings consist of a
Current edition approved May 1, 2004. Published June 2004. Originally
approved in 1946. Last previous edition approved in 1998 as E60 – 98. DOI:
comparison of the intensities of the radiant energy transmitted
10.1520/E0060-98R04.
bytheabsorbingsolutionandtheradiantenergytransmittedby
For additional information on the theory and photoelectric photometry, see the
the solvent. Any solution to which the transmittance of the
list of references at the end of this practice.
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 boldface numbers in parentheses refer to a list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E60–98 (2004)
absorbing solution of the substance being measured is com- each concentration.The validity of the Bouguer-Beer law for a
pared shall be known as the reference solution. particular system can be tested by showing that a remains
constant when b and c are changed.
4. Reference to This Practice in Standards
APPARATUS
4.1 The inclusion of the following paragraph, or a suitable
equivalent, in any ASTM test method (preferably after the
6. General Requirements for Photometers and
section on scope) shall constitute due notification that the
Spectrophotometers
photometers, spectrophotometers, and photometric practice
6.1 A photoelectric photometer consists essentially of the
prescribed in that test method are subject to the recommenda-
following:
tions set forth in this practice.
“Photometers, Spectrophotometers, and Photometric
NOTE 1—The choice of an instrument may naturally be based on price
Practice—Photometers, spectrophotometers, and photometric
considerations, since there is no point in using a more elaborate (and,
practice prescribed in this test method shall conform toASTM
incidentally, more expensive) instrument than is necessary. In addition to
Practice E60, Photometric and Spectrophotometric Methods satisfactory performance from the purely physical standpoint, the instru-
ment should be compact, rugged enough to stand routine use, and not
for Chemical Analysis of Metals.”
require too much manipulation. The scales should be easily read, and the
absorption cells should be easily removed and replaced, as the clearing,
5. Theory
refilling, and placing of the cells in the instrument consume a major
5.1 Photoelectric photometry is based on Bouguer’s and
portion of the time required. It is advantageous to have an instrument that
Beer’s (or the Lambert-Beer) laws which are combined in the
permits the use of cells of different depth (see Recommended Practice
following expression: E275).
2abc
6.1.1 An illuminant (radiant energy source),
P 5 P 10
o
6.1.2 A device for selecting relatively monochromatic radi-
where:
ant energy (consisting of a diffraction grating or a prism with
P = transmitted radiant power,
selection slit, or a filter),
P = incidentradiantpower,oraquantityproportionaltoit,
o
6.1.3 One or more absorption cells to hold the sample,
as measured with pure solvent in the beam,
standards, reagent blank, or reference solution, and
a = absorptivity, a constant characteristic of the solution
6.1.4 An arrangement for photometric measurement of the
and the frequency of the incident radiant energy,
intensity of the transmitted radiant energy, consisting of one or
b = internal cell length (usually in centimetres) of the
more photocells or photosensitive tubes, and suitable devices
column of absorbing material, and
for measuring current or potential.
c = concentration of the absorbing substance, g/L.
6.2 Precision instruments that employ monochromators ca-
5.2 Transmittance,T, and absorbance,A, have the following
pable of supplying radiant energy of high purity at any chosen
values:
wavelength within their range are usually referred to as
T 5 P/P
o
spectrophotometers. Instruments employing filters are known
as filter photometers or abridged spectrophotometers, and
A 5 log ~1/T! 5 log ~P /P!
10 10 o
usuallyisolaterelativelybroadbandsofradiantenergy.Inmost
where P and P have the values given in 5.1.
o
cases the absorption peak of the compound being measured is
5.3 From the transposed form of the Bouguer-Beer equa-
relatively broad, and sufficient accuracy can be obtained using
tion, A = abc, it is evident that at constant b, a plot of Aversus
a fairly broad band (10 to 75 nm) of radiant energy for the
c gives a straight line if Beer’s law is followed. This line will
measurement (Note 2). In other cases the absorption peaks are
pass through the origin if the usual practice of cancelling out
narrow, and radiant energy of high purity (1 to 10 nm) is
solvent reflections and absorption and other blanks is em-
required. This applies particularly if accurate values are to be
ployed.
obtained in those systems of measurement based on the
5.4 In photometry it is customary to make indirect compari-
additive nature of absorbance values.
son with solutions of known concentration by means of
calibration curves or charts. When Beer’s law is obeyed and
NOTE 2—One nanometre (nm) equals one millimicron (mµ).
when a satisfactory instrument is employed, it is possible to
7. Types of Photometers and Spectrophotometers
dispense with the curve or chart. Thus, from the transposed
form of the Bouguer-Beer law, c = A/ab, it is evident that once 7.1 Single-Photocell Instruments—In most single-photocell
a has been determined for any system, c can be obtained, since instruments, the radiant energy passes from the monochroma-
b is known and A can be measured. tor or filter through the reference solution to a photocell. The
5.5 The value for a can be obtained from the equation photocurrent is measured by a galvanometer or a microamme-
a = A/cb by substituting the measured value of A for a given b ter and its magnitude is a measure of the incident radiant
and c. Theoretically, in the determination of a for an absorbing power, P .An identical absorption cell containing the solution
o
system, a single measurement at a given wavelength on a of the absorbing component is now substituted for the cell
solution of known concentration will suffice. Actually, how- containing the reference solution and the power of the trans-
ever, it is safer to use the average value obtained with three or mitted radiant energy, P, is measured. The ratio of the current
more concentrations, covering the range over which the deter- corresponding to P to that of P gives the transmittance, T,of
o
minations are likely to be made and making several readings at the absorbing solution, provided the illuminant and photocell
E60–98 (2004)
are constant during the interval in which the two photocurrents This type of illuminant is not ideal for all work. For example,
are measured. It is customary to adjust the photocell output so when an analysis calls for the use of radiant energy of
that the galvanometer or microammeter reads 100 on the wavelengths below 400 nm, it is necessary to maintain the
percentage scale or zero on the logarithmic scale when the filament at as high a temperature as possible in order to obtain
incident radiant power is P , in order that the scale will read sufficient radiant energy to ensure the necessary sensitivity for
o
directly in percentage transmittance or absorbance. This ad- the measurements. This is especially true when operating with
justment is usually made in one of three ways. In the first a photovoltaic cell, for the response of the latter falls off
method, the position of the cross-hair or pointer is adjusted quickly in the near ultraviolet. The use of high-temperature
electrically by means of a resistance in the photocell- filament sources may lead to serious errors in photometric
galvanometer circuit. In the second method, adjustment is work if adequate ventilation is not provided in the instrument
made with the aid of a rheostat in the source circuit (Note 3). inordertodissipatetheheat.Anotherimportantsourceoferror
The third method of adjustment is to control the quantity of results from the change of the shape of the energy distribution
radiant energy striking the photocell with the aid of a dia- curve with age. As a lamp is used, tungsten will be vaporized
phragm somewhere in the path of radiant energy. and deposited on the walls. As this condensation proceeds,
there is a decrease in the radiation power emitted and, in some
NOTE 3—Kortüm (3) has pointed out on theoretical grounds this
instances, a change in the composition of the radiant energy.
method of controls is faulty, since the change in voltage applied to the
This change is especially noticeable when working in the near
lamp not only changes the radiant energy emitted but also alters its
chromaticity.Actually, however, instruments employing this principle are ultraviolet range and will lead to error (unless frequent
giving good service in industry, so the errors involved evidently are not
standardization is resorted to) in all except those cases where
too great.
essentially monochromatic radiant energy is used.
7.2 Two-Photocell Instruments—In order to eliminate the
NOTE 5—The errors discussed in 8.1 have been successfully overcome
effect of fluctuation of the source, a great many types of
in commercially available instruments. One instrument has been so
two-photocell instruments have been proposed. Most of these
designed that a very low-current lamp (of the order of 200 mA) is
are good, but some have poorly designed circuits and do not
employed as the source. This provides for long lamp life, freedom from
accomplishthepurposeforwhichtheyaredesigned.Following line fluctuations (since a storage battery is employed), stability of energy
distribution,reproducibility,andlow-costoperation.Inaddition,thestable
isabriefdescriptionoftwotypesoftwo-photocellphotometers
illuminant permits operation for long periods of time without need for
and spectrophotometers that have been found satisfactory:
restandardization against known solutions.
7.2.1 In the first type of two-photocell instrument, beams of
8.2 In most of the commercially available instruments
radiant energy from the same source are passed through the
where relatively high-wattage lamps are used, the power is
reference solution and the sample solution and are focused on
derived from the ordinary electric mains with the aid of a
their respective photocells. Prior to insertion of the sample, the
constant-voltage transformer. Where the line vo
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