ASTM E60-98

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E 60 – 98
Standard Practice for
Analysis of Metals, Ores, and Related Materials
by Molecular Absorption Spectrometry
This standard is issued under the fixed designation E 60; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology Definitions and Symbols
1.1 This practice covers general recommendations for pho- 3.1 For definitions of terms relating to absorption spectros-
toelectric photometers and spectrophotometers and for photo- copy, refer to Terminology E 131.
metric practice prescribed in ASTM methods for chemical 3.2 background absorption—any absorption in the solution
analysis of metals, sufficient to supplement adequately the due to the presence of absorbing ions, molecules, or complexes
ASTM methods. A summary of the fundamental theory and of elements other than that being determined is called back-
practice of photometry is given. No attempt has been made, ground absorption.
however, to include in this practice a description of every 3.3 concentration range—the recommended concentration
apparatus or to present recommendations on every detail of range shall be designated on the basis of the optical path of the
practice in ASTM photometric or spectrophotometric methods cell, in centimetres, and the final volume of solution as
of chemical analysis of metals. recommended in a procedure. In general, the concentration
1.2 These recommendations are intended to apply to the range and path length shall be specified as that which will
ASTM photometric and spectrophotometric methods for produce transmittance readings in the optimum range of the
chemical analysis of metals when such standards make definite instrument being used as covered in Section 14.
reference to this practice, as covered in Section 4. 3.4 initial setting— the initial setting is the photometric
1.3 In this practice, the terms “photometric” and “photom- reading (usually 100 on the percentage scale or zero on the
etry” encompass both filter photometers and spectrophotom- logarithmic scale) to which the instrument is adjusted with the
eters, while “spectrophotometry” is reserved for spectropho- reference solution in the absorption cell. The scale will then
tometers alone. read directly in percentage transmittance or in absorbance.
1.4 This standard does not purport to address all of the 3.5 photometric reading—the term “photometric reading”
safety concerns, if any, associated with its use. It is the refers to the scale reading of the instrument being used.
responsibility of the user of this standard to establish appro- Available instruments have scales calibrated in transmittance,
priate safety and health practices and determine the applica- T, (1) or absorbance, A, (2) (see 5.2), or even arbitrary units
bility of regulatory limitations prior to use. proportional to transmittance or absorbance.
3.6 reagent blank— the reagent blank determination yields
2. Referenced Documents
a value for the apparent concentration of the element sought,
2.1 ASTM Standards: which is due only to the reagents used. It reflects both the
E 131 Terminology Relating to Molecular Spectroscopy
amount of the element sought present as an impurity in the
E 168 Practices for General Techniques of Infrared Quanti- reagents, and the effect of interfering species.
tative Analysis
3.7 reference solution—photometric readings consist of a
E 169 Practices for General Techniques of Ultraviolet- comparison of the intensities of the radiant energy transmitted
Visible Quantitative Analysis
by the absorbing solution and the radiant energy transmitted by
E 275 Practice for Describing and Measuring Performance the solvent. Any solution to which the transmittance of the
of Ultraviolet, Visible, and Near Infrared Spectrophotom-
absorbing solution of the substance being measured is com-
eters pared shall be known as the reference solution.
4. Reference to This Practice in Standards
This practice is under the jurisdiction of ASTM Committee E-1 on Analytical
4.1 The inclusion of the following paragraph, or a suitable
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
equivalent, in any ASTM test method (preferably after the
Subcommittee E01.20 on Fundamental Practices and Measurement Traceability.
Current edition approved May 10, 1998. Published July 1998. Originally
published as E60 – 46 T. Last previous edition E60 – 93.
For additional information on the theory and photoelectric photometry, see the
list of references at the end of this practice. The boldface numbers in parentheses refer to the list of references appended to
Annual Book of ASTM Standards, Vol 03.06. this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E60
section on scope) shall constitute due notification that the APPARATUS
photometers, spectrophotometers, and photometric practice
6. General Requirements for Photometers and
prescribed in that test method are subject to the recommenda-
Spectrophotometers
tions set forth in this practice.
“Photometers, Spectrophotometers, and Photometric
6.1 A photoelectric photometer consists essentially of the
Practice—Photometers, spectrophotometers, and photometric following:
practice prescribed in this test method shall conform to ASTM
NOTE 1—The choice of an instrument may naturally be based on price
Practice E 60, Photometric and Spectrophotometric Methods
considerations, since there is no point in using a more elaborate (and,
for Chemical Analysis of Metals.”
incidentally, more expensive) instrument than is necessary. In addition to
satisfactory performance from the purely physical standpoint, the instru-
5. Theory
ment should be compact, rugged enough to stand routine use, and not
require too much manipulation. The scales should be easily read, and the
5.1 Photoelectric photometry is based on Bouguer’s and
absorption cells should be easily removed and replaced, as the clearing,
Beer’s (or the Lambert-Beer) laws which are combined in the
refilling, and placing of the cells in the instrument consume a major
following expression:
portion of the time required. It is advantageous to have an instrument that
2abc
permits the use of cells of different depth (see Recommended Practice
P 5 P 10
o
E 275).
where:
6.1.1 An illuminant (radiant energy source),
P = transmitted radiant power,
6.1.2 A device for selecting relatively monochromatic radi-
P = incident radiant power, or a quantity proportional to it,
o
ant energy (consisting of a diffraction grating or a prism with
as measured with pure solvent in the beam,
selection slit, or a filter),
a = absorptivity, a constant characteristic of the solution
6.1.3 One or more absorption cells to hold the sample,
and the frequency of the incident radiant energy,
standards, reagent blank, or reference solution, and
b = internal cell length (usually in centimetres) of the
6.1.4 An arrangement for photometric measurement of the
column of absorbing material, and
intensity of the transmitted radiant energy, consisting of one or
c = concentration of the absorbing substance, g/L.
more photocells or photosensitive tubes, and suitable devices
5.2 Transmittance, T, and absorbance, A, have the following
for measuring current or potential.
values:
6.2 Precision instruments that employ monochromators ca-
T 5 P/P
o
pable of supplying radiant energy of high purity at any chosen
A 5 log ~1/T! 5 log ~P /P!
wavelength within their range are usually referred to as
10 10 o
spectrophotometers. Instruments employing filters are known
where P and P have the values given in 5.1.
o
as filter photometers or abridged spectrophotometers, and
5.3 From the transposed form of the Bouguer-Beer equa-
usually isolate relatively broad bands of radiant energy. In most
tion, A = abc, it is evident that at constant b, a plot of A versus
cases the absorption peak of the compound being measured is
c gives a straight line if Beer’s law is followed. This line will
relatively broad, and sufficient accuracy can be obtained using
pass through the origin if the usual practice of cancelling out
a fairly broad band (10 to 75 nm) of radiant energy for the
solvent reflections and absorption and other blanks is em-
measurement (Note 2). In other cases the absorption peaks are
ployed.
narrow, and radiant energy of high purity (1 to 10 nm) is
5.4 In photometry it is customary to make indirect compari-
required. This applies particularly if accurate values are to be
son with solutions of known concentration by means of
obtained in those systems of measurement based on the
calibration curves or charts. When Beer’s law is obeyed and
additive nature of absorbance values.
when a satisfactory instrument is employed, it is possible to
dispense with the curve or chart. Thus, from the transposed
NOTE 2—One nanometre (nm) equals one millimicron (mμ).
form of the Bouguer-Beer law, c = A/ab, it is evident that once
7. Types of Photometers and Spectrophotometers
a has been determined for any system, c can be obtained, since
b is known and A can be measured.
7.1 Single-Photocell Instruments—In most single-photocell
5.5 The value for a can be obtained from the equation
instruments, the radiant energy passes from the monochroma-
a = A/cb by substituting the measured value of A for a given b
tor or filter through the reference solution to a photocell. The
and c. Theoretically, in the determination of a for an absorbing
photocurrent is measured by a galvanometer or a microamme-
system, a single measurement at a given wavelength on a
ter and its magnitude is a measure of the incident radiant
solution of known concentration will suffice. Actually, how-
power, P . An identical absorption cell containing the solution
o
ever, it is safer to use the average value obtained with three or
of the absorbing component is now substituted for the cell
more concentrations, covering the range over which the deter-
containing the reference solution and the power of the trans-
minations are likely to be made and making several readings at
mitted radiant energy, P, is measured. The ratio of the current
each concentration. The validity of the Bouguer-Beer law for a
corresponding to P to that of P gives the transmittance, T,of
o
particular system can be tested by showing that a remains
the absorbing solution, provided the illuminant and photocell
constant when b and c are changed.
are constant during the interval in which the two photocurrents
are measured. It is customary to adjust the photocell output so
that the galvanometer or microammeter reads 100 on the
Annual Book of ASTM Standards, Vol 03.05. percentage scale or zero on the logarithmic scale when the
E60
incident radiant power is P , in order that the scale will read filament at as high a temperature as possible in order to obtain
o
directly in percentage transmittance or absorbance. This ad- sufficient radiant energy to ensure the necessary sensitivity for
justment is usually made in one of three ways. In the first the measurements. This is especially true when operating with
method, the position of the cross-hair or pointer is adjusted a photovoltaic cell, for the response of the latter falls off
electrically by means of a resistance in the photocell- quickly in the near ultraviolet. The use of high-temperature
galvanometer circuit. In the second method, adjustment is filament sources may lead to serious errors in photometric
made with the aid of a rheostat in the source circuit (Note 3). work if adequate ventilation is not provided in the instrument
The third method of adjustment is to control the quantity of in order to dissipate the heat. Another important source of error
radiant energy striking the photocell with the aid of a dia- results from the change of the shape of the energy distribution
phragm somewhere in the path of radiant energy. curve with age. As a lamp is used, tungsten will be vaporized
and deposited on the walls. As this condensation proceeds,
NOTE 3—Kortüm (3) has pointed out on theoretical grounds this
there is a decrease in the radiation power emitted and, in some
method of controls is faulty, since the change in voltage applied to the
instances, a change in the composition of the radiant energy.
lamp not only changes the radiant energy emitted but also alters its
chromaticity. Actually, however, instruments employing this principle are This change is especially noticeable when working in the near
giving good service in industry, so the errors involved evidently are not
ultraviolet range and will lead to error (unless frequent
too great.
standardization is resorted to) in all except those cases where
essentially monochromatic radiant energy is used.
7.2 Two-Photocell Instruments—In order to eliminate the
effect of fluctuation of the source, a great many types of
NOTE 5—The errors discussed in 8.1 have been successfully overcome
two-photocell instruments have been proposed. Most of these
in commercially available instruments. One instrument has been so
are good, but some have poorly designed circuits and do not designed that a very low-current lamp (of the order of 200 mA) is
employed as the source. This provides for long lamp life, freedom from
accomplish the purpose for which they are designed. Following
line fluctuations (since a storage battery is employed), stability of energy
is a brief description of two types of two-photocell photometers
distribution, reproducibility, and low-cost operation. In addition, the stable
and spectrophotometers that have been found satisfactory:
illuminant permits operation for long periods of time without need for
7.2.1 In the first type of two-photocell instrument, beams of
restandardization against known solutions.
radiant energy from the same source are passed through the
8.2 In most of the commercially available instruments
reference solution and the sample solution and are focused on
where relatively high-wattage lamps are used, the power is
their respective photocells. Prior to insertion of the sample, the
derived from the ordinary electric mains with the aid of a
reference solution is placed in both absorption cells, and the
constant-voltage transformer. Where the line voltages vary
photocells are balanced with the aid of a potentiometric bridge
markedly, it is necessary to resort to the use of batteries that are
circuit (Note 4). The reference solution and sample are then
under continuous charge, or to a very good constant voltage
inserted and the
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