ASTM E60-11(2022)e1

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.
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Designation: E60 − 11 (Reapproved 2022)
Standard Practice for
Analysis of Metals, Ores, and Related Materials by
Spectrophotometry
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.
ε NOTE—Editorial changes were made throughout in July 2022.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice covers general recommendations for pho-
E131 Terminology Relating to Molecular Spectroscopy
toelectric photometers and spectrophotometers and for photo-
E135 Terminology Relating to Analytical Chemistry for
metric practice prescribed in ASTM methods for chemical
Metals, Ores, and Related Materials
analysis of metals, sufficient to supplement adequately the
E168 Practices for General Techniques of Infrared Quanti-
ASTM methods. A summary of the fundamental theory and
tative Analysis
practice of photometry is given. No attempt has been made,
E169 PracticesforGeneralTechniquesofUltraviolet-Visible
however, to include in this practice a description of every
Quantitative Analysis
apparatus or to present recommendations on every detail of
E275 PracticeforDescribingandMeasuringPerformanceof
practice inASTM photometric or spectrophotometric methods
Ultraviolet and Visible Spectrophotometers
of chemical analysis of metals.
1.2 These recommendations are intended to apply to the 3. Definitions and Symbols
ASTM photometric and spectrophotometric methods for
3.1 For definitions of terms relating to this practice, refer to
chemical analysis of metals when such standards make definite
Terminology E135.
reference to this practice, as covered in Section 4.
3.2 For definitions of terms relating to absorption
1.3 In this practice, the terms “photometric” and “photom-
spectroscopy, refer to Terminology E131.
etry” encompass both filter photometers and
3.3 Definitions of Terms Specific to this Practice:
spectrophotometers, while “spectrophotometry” is reserved for
3.3.1 background absorption—any absorption in the solu-
spectrophotometers alone.
tion due to the presence of absorbing ions, molecules, or
1.4 This standard does not purport to address all of the complexes of elements other than that being determined is
safety concerns, if any, associated with its use. It is the
called background absorption.
responsibility of the user of this standard to establish appro- 3.3.2 concentration range—the recommended concentra-
priate safety, health, and environmental practices and deter- tion range shall be designated on the basis of the optical path
mine the applicability of regulatory limitations prior to use. of the cell, in centimetres, and the final volume of solution as
recommended in a procedure. In general, the concentration
1.5 This international standard was developed in accor-
range and path length shall be specified as that which will
dance with internationally recognized principles on standard-
produce transmittance readings in the optimum range of the
ization established in the Decision on Principles for the
instrument being used as covered in Section 14.
Development of International Standards, Guides and Recom-
3.3.3 initial setting—the initial setting is the photometric
mendations issued by the World Trade Organization Technical
reading (usually 100 on the percentage scale or zero on the
Barriers to Trade (TBT) Committee.
logarithmic (absorbance) scale) to which the instrument is
adjusted with the reference solution in the absorption cell. The
scale will then read directly in percentage transmittance or in
This practice is under the jurisdiction of ASTM Committee E01 on Analytical
absorbance.
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Subcommittee E01.20 on Fundamental Practices.
CurrenteditionapprovedJune1,2022.PublishedJuly2022.Originallyapproved
in 1946. Last previous edition approved in 2016 as E60 – 11(2016). DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
E0060-11R22E01. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
For additional information on the theory and photoelectric photometry, see the Standards volume information, refer to the standard’s Document Summary page on
list of references at the end of this practice. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E60 − 11 (2022)
3.3.4 photometric reading—the term “photometric reading” will pass through the origin if the practice of cancelling out
refers to the scale reading of the instrument being used. solvent reflections and absorption and other blanks is em-
Available instruments have scales calibrated in transmittance, ployed.
T, (1) or absorbance, A, (2) (see 5.2), or even arbitrary units
5.4 In photometry it is customary to make indirect compari-
proportional to transmittance or absorbance.
son with solutions of known concentration by means of
3.3.5 reagent blank—the reagent blank determination yields
calibration curves or charts. When Beer’s law is obeyed and
a value for the apparent concentration of the element sought,
when a satisfactory instrument is employed, it is possible to
which is due only to the reagents used. It reflects both the
dispense with the curve or chart. Thus, from the transposed
amount of the element sought present as an impurity in the
form of the Bouguer-Beer law, c = A/ab, it is evident that once
reagents, and the effect of interfering species.
a has been determined for any system, c can be obtained, since
3.3.6 reference solution—photometric readings consist of a
b is known and A can be measured.
comparison of the intensities of the radiant energy transmitted
5.5 The value for a can be obtained from the equation
bytheabsorbingsolutionandtheradiantenergytransmittedby
a = A/cb by substituting the measured value of A for a given b
the solvent. Any solution to which the transmittance of the
and c. Theoretically, in the determination of a for an absorbing
absorbing solution of the substance being measured is com-
system, a single measurement at a given wavelength on a
pared shall be known as the reference solution.
solution of known concentration will suffice. However, it is
better to use the average value obtained with three or more
4. Reference to This Practice in Standards
concentrations, covering the range over which the determina-
4.1 The inclusion of the following paragraph, or a suitable
tionsarelikelytobemadeandmakingseveralreadingsateach
equivalent, in any ASTM test method (preferably after the
concentration. The validity of the Bouguer-Beer law for a
section on scope) shall constitute due notification that the
particular system can be tested by showing that a remains
photometers, spectrophotometers, and photometric practice
constant when b and c are changed.
prescribed in that test method are subject to the recommenda-
tions set forth in this practice.
APPARATUS
“Photometers, Spectrophotometers, and Photometric
6. General Requirements for Photometers and
Practice—Photometers, spectrophotometers, and photometric
Spectrophotometers
practice prescribed in this test method shall conform toASTM
Practice E60, Practice for Analysis of Metals, Ores, and 6.1 A photoelectric photometer consists essentially of the
Related Materials by Spectrophotometry.
following:
NOTE 1—The choice of an instrument may naturally be based on price
5. Theory
considerations, since there is no point in using a more elaborate (and,
incidentally, more expensive) instrument than is necessary. In addition to
5.1 Photoelectric photometry is based on Bouguer’s and
satisfactory performance from the purely physical standpoint, the instru-
Beer’s (or the Lambert-Beer) laws which are combined in the
ment should be compact, rugged enough to stand routine use, and not
following expression:
require too much manipulation. The scales should be easily read, and the
2abc
absorption cells should be easily removed and replaced, as the clearing,
P 5 P 10
o
refilling, and placing of the cells in the instrument consume a major
portion of the time required. It is advantageous to have an instrument that
where:
permits the use of cells of different depth (see Practice E275).
P = transmitted radiant power,
6.1.1 An illuminant (radiant energy source),
P = incident radiant power, or a quantity proportional to it,
o
6.1.2 A device for selecting relatively monochromatic radi-
as measured with pure solvent in the beam,
a = absorptivity, a constant characteristic of the solution ant energy (consisting of a diffraction grating or a prism with
and the frequency of the incident radiant energy, selection slit, or a filter),
b = internal cell length (usually in centimetres) of the 6.1.3 One or more absorption cells to hold the sample,
column of absorbing material, and
calibration, reagent blank, or reference solutions, and
c = concentration of the absorbing substance, g/L.
6.1.4 An arrangement for photometric measurement of the
intensity of the transmitted radiant energy, consisting of one or
5.2 Transmittance, T, and absorbance, A, have the following
more photocells or photosensitive tubes, and suitable devices
values:
for measuring current or potential.
T 5 P/P
o
6.2 Precision instruments that employ monochromators ca-
A 5 log 1/T 5 log P /P
~ ! ~ !
10 10 o
pable of supplying radiant energy of high purity at any chosen
where P and P have the values given in 5.1.
o
wavelength within their range are usually referred to as
spectrophotometers. Instruments employing filters are known
5.3 From the transposed form of the Bouguer-Beer
as filter photometers or abridged spectrophotometers, and
equation, A = abc, it is evident that at constant b, a plot of A
usually isolate relatively broad bands of radiant energy. Fre-
versus cgivesastraightlineifBeer’slawisfollowed.Thisline
quently the absorption peak of the compound being measured
is relatively broad, and sufficient accuracy can be obtained
using a fairly broad band (10 nm to 75 nm) of radiant energy
The boldface numbers in parentheses refer to a list of references at the end of
this standard. for the measurement (Note 2). Other times the absorption
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E60 − 11 (2022)
peaksarenarrow,andradiantenergyofhighpurity(1nmto10 read directly in transmittance. It is important that both photo-
nm) is required. This applies particularly if accurate values are cells show linear response, and that they have identical
to be obtained in those systems of measurement based on the radiation sensitivity if the light is not monochromatic.
additive nature of absorbance values. 7.2.2 Thesecondtypeoftwo-photocellinstrumentissimilar
to the first, but part of the radiant energy from the source is
NOTE 2—One nanometre (nm) equals one millimicron (mµ).
passed through an absorption cell to the first photocell; the
remainder is impinged on the second photocell without,
7. Types of Photometers and Spectrophotometers
however,passingthroughanabsorptioncell.Adjustmentofthe
7.1 Single-Photocell Instruments—In most single-photocell
calibrated slide wire to read 100 on the percentage scale, with
instruments, the radiant energy passes from the monochroma-
the reference solution in the cell, is accomplished by rotating
tor or filter through the reference solution to a photocell. The
the second photocell. The reference solution is then replaced
photocurrent is measured by a galvanometer or a microamme-
by the sample and the slide wire is turned until the galvanom-
ter and its magnitude is a measure of the incident radiant
eter again reads zero.
power, P .An identical absorption cell containing the solution
o
of the absorbing component is now substituted for the cell 8. Radiation Source
containing the reference solution and the power of the trans-
8.1 In most of the commercially available instruments the
mitted radiant energy, P, is measured. The ratio of the current
illuminant is an incandescent lamp with a tungsten filament.
corresponding to P to that of P gives the transmittance, T,of
o
This type of illuminant is not ideal for all work. For example,
the absorbing solution, provided the illuminant and photocell
when an analysis calls for the use of radiant energy of
are constant during the interval in which the two photocurrents
wavelengths below 400 nm, it is necessary to maintain the
are measured. It is customary to adjust the photocell output so
filament at as high a temperature as possible in order to obtain
that the galvanometer or microammeter reads 100 on the
sufficient radiant energy to ensure the necessary sensitivity for
percentage scale or zero on the logarithmic (absorbance) scale
the measurements. This is especially true when operating with
when the incident radiant power is P , so that the scale will
o
a photovoltaic cell, for the response of the latter falls off
read directly in percentage transmittance or absorbance. This
quickly in the near ultraviolet. The use of high-temperature
adjustment is usually made in one of three ways. In the first
filament sources may lead to serious errors in photometric
method, the position of the cross-hair or pointer is adjusted
work if adequate ventilation is not provided in the instrument
electrically by means of a resistance in the photocell-
inordertodissipatetheheat.Anotherimportantsourceoferror
galvanometer circuit. In the second method, adjustment is
results from the change of the shape of the energy distribution
made with the aid of a rheostat in the source circuit (Note 3).
curve with age. As a lamp is used, tungsten will be vaporized
The third method of adjustment controls the quantity of radiant
and deposited on the walls. As this condensation proceeds,
energy striking the photocell with the aid of a diaphragm
there is a decrease in the radiation power emitted and, in some
somewhere in the path of radiant energy.
instances, a change in the composition of the radiant energy.
This change is especially noticeable when working in the near
NOTE 3—Kortüm (3) has noted on theoretical grounds this method of
controls is faulty, since the change in voltage applied to the lamp not only
ultraviolet range and will lead to error (unless frequent
changes the radiant energy emitted but also alters its chromaticity.
calibration is performed) in all except those cases where
However, instruments employing this principle are giving good service in
essentially monochromatic radiant energy is used.
industry, so the errors involved evidently are not excessive.
NOTE 4—The errors discussed in 8.1 have been successfully overcome
7.2 Two-Photocell Instruments—To eliminate the effect of
in commercially available instruments. One instrument has been so
fluctuation of the source, many types of two-photocell instru-
designed that a very low-current lamp (approximately 200 mA) is
ments have been proposed. Most of these are good, but some
employed as the source. This provides for long lamp life, freedom from
have poorly designed circuits and do not accomplish the
line fluctuations (since a storage battery is employed), stability of energy
distribution,reproducibility,andlow-costoperation.Inaddition,thestable
purpose for which they are designed. Following is a brief
illuminant permits operation for long periods of time without need for
description of two types of two-photocell photometers and
repeated calibrations against known solutions.
spectrophotometers that have been found satisfactory:
8.2 In most of the commercially available instruments
7.2.1 In the first type of two-photocell instrument, beams of
where relatively high-wattage lamps are used, the power is
radiant energy from the same source are passed through the
derived from the ordinary electric mains with the aid of a
reference solution and the sample solution and are focused on
constant-voltage transformer. Where the line voltages vary
their respective photocells. Prior to insertion of the sample, the
markedly,itisnecessarytoresorttotheuseofbatteriesthatare
reference solution is placed in both absorption cells, and the
under continuous charge, or to a stable constant voltage
photocells are balanced with the aid of a potentiometric bridge
regulator.
circuit. Since b is defined as the internal cell length, the
cancellation of radiant energy lost at the glass-liquid interfaces
9. Filters and Monochromators
and within the glass must be accomplished by inserting the
reference solution in the absorption cells. The reference solu- 9.1 Filters—Relatively inexpensive instruments employing
tion and sample are then inserted and the balance reestablished filters are adequate for a large proportion of photometric
by manipulation of the potentiometer until the galvanometer methods, since most absorbing systems show broad absorption
againreadszero.Bychoosingsuitableresistancesandbyusing bands. In general, filters are designed to isolate as narrow a
a graduated slide wire, the scale of the latter can be made to band of the spectrum as possible. It is usually necessary,
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E60 − 11 (2022)
especially when the filters are used in conjunction with an The measures which improve linearity of response also tend to
instrument employing photovoltaic cells, to sacrifice spectral reduce fatigue. With most commercial instruments, the errors
purity to obtain sufficient sensitivity for measurement with a due to reversible fatigue are usually less than 1 %.
rugged galvanometer or a microammeter. Glass filters are most
12. Current-Measuring Devices
often used because of their stability to light and heat, but
gelatin filters and even aqueous solutions are sometimes used.
12.1 The usual types of photometers and spectrophotom-
etersemployphotovoltaiccellsinconjunctionwithamicroam-
9.2 Monochromators—Spectrophotometric methods call for
meteroramoderatelyhigh-sensitivitygalvanometer,asmaybe
theisolationoffairlynarrowwavebandsofradiantenergy.Two
appropriate for the illumination level employed. The scales for
typesofmonochromatorsareincommonuse:theprismandthe
thegalvanometersaresometimesdesignedtopermitreadingof
diffraction grating. Prisms have the disadvantage of exhibiting
absorbance values but more often yield only the more conve-
a dependence of dispersion upon wavelength. However, the
niently read T or percentage T values. Some photometers and
elimination of stray radiation energy is less difficult when a
spectrophotometers are designed so that the current is mea-
prism is used. In a well-designed monochromator, stray radiant
sured potentiometrically, using the galvanometer as a null
energy resulting from reflections from optical and mechanical
instrument. It is stated that the error due to nonlinearity of the
members is reduced to a minimum, but some radiant energy,
galvanometer under load is eliminated. However, this error is
caused by nonspecular scatterings by the optical elements, will
usually small and many instruments provide individual cali-
remain. This unwanted radiant energy can be reduced through
bration of the galvanometer.
the use of a second monochromator or a filter in combination
with a monochromator. Unfortunately, any process of mono-
12.2 When photoemission cells are used, current amplifica-
chromatization is accompanied by a reduction of the radiant
tion is usually performed before the galvanometer or meter is
power, and the more complex the monochromator the greater
used.
the burden upon the measuring system.
PHOTOMETRIC PRACTICE
10. Absorption Cells
13. Principle of Test Method
10.1 Some photometers and spectrophotometers provide for
the use of several sizes and shapes of absorption cells. Others
13.1 Photometric methods are generally based on the mea-
aredesignedforasingletypeofcell.Itisadvantageoustohave
surement of the transmittance or absorbance of a solution of an
an instrument that permits the use of cells of different depths.
absorbing salt, compound, or reaction product of the substance
In some single-photocell instruments there is only one recep-
to be determined. It is usually desirable to perform a rather
tacle for the cell; in others (and this is especially desirable in
complete photometric investigation of the reaction before
those instruments where the illuminant is unstable) a sliding
attempting to employ it in quantitative analysis (see Practices
carriage is provided so that two cells can be interchangeably
E168 and E169). The investigation should include a study of
inserted into the beam of radiant energy coming from the
the following:
monochromator.
13.1.1 The specificity of any reagent employed to produce
absorption,
11. Photocells and Photosensitive Tubes
13.1.2 The validity of Beer’s law,
11.1 In photometry, the measurement of radiant energy is
13.1.3 The effect of salts, solvent, pH, temperature, concen-
usually accomplished with the aid of either photoemission or
tration of reagents, and the order of adding the reagents,
photovoltaic cells.
13.1.4 The time required for absorption development and
11.2 The spectral response of a photoemission cell will the stability of the
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