ASTM E663-86(1991)E01

Practice for Flame Atomic Absorption Analysis (Withdrawn 1997)

General Information

• Status: Withdrawn
• Withdrawal Date: 09-Oct-1997
• Technical Committee: E01 - Analytical Chemistry for Metals, Ores, and Related Materials
• Drafting Committee: E01.20 - Fundamental Practices

Standards Content (Sample)

-
ASTM Ebb3*EL 86 S 87595E0 O076545 4
AMERICAN SOCIETY FOR TESTING AND MATERIALS
41)) Designation: E 663 - 86 (Reapproved 1991)''
1916 Race St Philadelphia, Pa 19103
Reprinted from the Annwl Book of ASTM Standards. Copyright ASTM
if not listed in the current combined bide><; wl appear in the next editon
Standard Practice for
Flame Atomic Absorption Analysis'
This standard is issued under the fixed designation E 663; 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.
NOTE-Section 12 was added editorially in July 1991.
1. Scope solution by flame atomization. It includes the preparation of
curves (Figs. 1 and 2) to establish the useful calibration range
1,l This practice covers the use of an atomic absorption
for the instrument and analytical method to be used. With
spectrophotometer (AAS) for determining the concentration
these curves the operator can objectively determine the
of elements in solution by flame atomization. Recommenda-
useful concentration range of a particular instrument. Once
tions are provided for preparing the instrument for making
the useful concentration range is established for a specific
measurements, measuring the sensitivity, establishing criteria
atomic absorption procedure and instrument, repetition of
which should result in satisfactory instrument performance,
the work is not required unless the performance of the
determining the useful calibration concentration range, and
instrument changes. These operations are common to and
measuring and calculating the test solution analyte concen-
are a part of some basic atomic absorption methods.
tration.
1.2 This standard does not purport to address all of the
5. Atomic Absorption Theory and Practice
safeiy problems, if any, associated with its use. It is ihe
5.1 In atomic absorption, a test solution is aspirated into a
responsibility of the user of this standard to establish appro-
flame through which passes radiation from a line emission
priate safety and health practices and determine the applica-
source of the element sought. The radiation of the element
bility of regulatory limitations prior to use. Specific precau-
sought is absorbed in proportion to the concentration of its
tionary statements are given in Section 6 and specific
neutral atoms present in the flame. The concentration of the
warning statements are given in Note 4.
analyte is obtained by comparison to calibration solutions.
5.2 A theoretical basis for using atomic absorption to
2. Referenced Documents
determine analyte concentration is described by Walsh
2. I ASTM Standards:
A broader more practical background can be found in a
E 50 Practices for Apparatus, Reagents, and Safety Pre-
modern text on instrumental analysis such as that by Willard
cautions for Chemical Analysis of Metals2
et al (2). A detailed discussion of atomic absorption theory
E 13 1 Terminology Relating to Molecular Spectroscopy3
and practice can be found in Dean and Rains (3).
E 135 Terminology Relating to Analytical Atomic
6. Safety Precautions
Spectroscopy4
E 863 Practice for Describing Flame Atomic Absorption 6.1 Operating personnel should adhere to the manufactur-
Spectroscopy Equipment4 er's recommended practice for igniting and extinguishing the
burner on the atomic absorption spectrophotometer, to
3. Terminology
avoid an explosion which could cause physical injury. See
Note 4. Also see Practices E 50 for further general safety
3.1 For definitions of terms used in this practice, refer to
precautions.
Terminology E 13 1 and E 135.
3.2 Description of Term Specific to This Standard:
7. Preparation of Reference, Blank, and Calibration Solu-
3.2.1 useful concentration range-the useful concentra-
tions
tion range is the range in analyte concentrations through
7.1 Reference Solution-Combine all acids, reagents, and
which the precision of the method or the AAS, or both, are
other additions present in the test solution and dilute to the
acceptable.
same concentrations. This solution is used to set the zero
4. Significance and Use
absorbance or 100 % transmittance of the AAS.
7.2 Blank Solution-Incorporate in the reference solution
4.1 This practice describes how to prepare and calibrate
all the specimen matrix elements of significant concentra-
an AAS for the quantitative determination of elements in
tion, except the analyte, in the same concentrations as in the
test solution.
I This practice is under the jurisdiction of ASTM Committee E-I on Analytical
NOTE I-In practice it may not always be possible to obtain matrix
Chemistry for Metals, Ores and Related Materials and is the direct responsibility of
elements containing nonmeasurable quantities of analyte. In such
Subcommittee E01 -20 on Fundamental Practices.
situations a correction must be applied as directed in 7.3 or 8.2.
Current edition approved Aug. 29, 1986. Published October 1986. Originally
published as E 663 - 78. Last previous edition E 663 - 78.
Annirai Book ofASTM Standards, Vol 03.05.
Anniral Book of ASTM Standards, Vol 14.0 I. The boldface numbers in parentheses refer to the list of references at the end
Anniral Book ofASTM Slandards, Vol 03.06.
of this practice.
ASTM Ebb3*El 8b-r Ö7Ci5lÖ 007bSYb b
10.0
8.0
Useful Range RCE
-
Inst 1 5 to 130 1X
I Inst 2 15 to 85 2%
6.0
w
4.0
2.0
-
.-
I
I. I I
O 20 40 60 80 100 120 140
Concen era tion, vg/mL
FIG. 1 RCE Versus Concentration (Lead in 2 % Nitric Acid, 283.3.nm Line)
io( ‘10.0
O( -8.0
6Q 6.0
F
A*
fi
.’.f
H
N
W
bo b . Q
20 2.0
I II I Il
1 2 3 4 6 810 20 30 40 60 DO 100 200
Cuiiceiitrntion, 1ig/iiii.
PIG. 2 Typical Curves (Lead In 2 % Nitric Acid, 283.3-nm Line)
7.3 Colìúration Soliitions-Using the manufacturer’s data
twelve calibration solutions to cover the absorbance range
as r? guide and some triai and error, prepare a minimum of
ASTM Ebb3*E1 Bb 0759510 0076547 B 0
4m E663
solution between each measurement. In the same way, make
0.005 to 1.5, or greater if needed. At least three of these
solutions should be in the range 0.005 to O. 1 absorbance and three measurements of the blank solution. Average each of
these measurement sets and use the average to calculate the
three in the range 0.9 to 1.5. The remaining six solutions
blank and the sensitivity as directed in 8.2 and 8.3, respec-
should be approximately equally spaced in terms of concen-
tration between O. 1 and 0.9 absorbance. These calibration tively,
solutions should, as closely as possible, match the composi-
NOTE 4: Warning-Follow the manufacturer’s recommended prac-
tion of the test solution. If the composition of the test
tice for igniting and extinguishing the burner to avoid an exploslon
which will damage the burner chamber or cause physical harm to
solution is unknown to the extent that matching calibration
operating personnel.
solutions cannot be prepared, for example, other matrix
impurities are concentrated along with the analyte, refer to
8.2 Blank-Calculate an analyte concentration for the
the method of standard additions described in 10.4. If a
blank as follows:
measurable amount of the analyte is present in the blank
c, = AB(G/Al) (1)
solution, its absorbance reading must be converted to
where: .
concentration and this amount must be added to the
concentration of the analyte in these calibration solutions,
C, = concentration of analyte in the blank,
when these solutions are used to establish the useful calibra-
Cl = concentration of analyte in the calibration solution,
tion range, When the calibration solutions are used to
A, = average absorbance of CE, and
construct a working curve to measure the analyte in the test
A = average absorbance of Cl.
solution, the blank concentration may be subtracted from The concentration of analyte in the blank is added to the
the analyte concentration or added to the calibration concen- concentration of analyte in the calibration solutions as
trations as directed by the basic method.
directed in 7.3.
NOTE 2-The twelve solutions described here are used for preparing
NOTE 5-The blank solution may be substituted for the reference
a precalibration curve to establish the useful range of the AAS. The
solution when the respective absorbances are essentially the same,
working or calibration curve uscd to measure the test solution will
analyte concentration is not measurable with an AAS, and errors in
usually contain fewer calibration solutions, but may include some of
operation cancel.
these twelve solutions.
8.3 Sensitivity-The sensitivity (S) is the concentration of
NOTE 3-Matching the chemical composition of calibration and test
analyte that gives an absorption of 1 % or an absorbance of
solutions to eliminate matrix effects may not be necessary if the weight
0.0044. The smaller this sensitivity value the more sensitive
of the sample in the solution is less than 0.1 % on a weight per unit
volume basis. For test specimens of this type the analysis of standard
is the AAS. To determine if the AAS has adequate response,
or of test solutions to which further additions of the
reference materials,
calculate from the data obtained in 8.1 the sensitivity as
analyte have been made, will reveal the presence of a matrix effect as
follows:
evidenced by a significant difference in results. If a matrix effect is
absent the calibration solutions need contain nothing more than known S = 0.0044 (C,/A,) (2)
amounts of the analyte in the same solvent as the sample.
where Cl and A, have the same meaning as in Eq 1.
Determine if sensitivity is adequate by reference to the
8. Preparation of Apparatus
manufacturer’s handbook or to the basic analytical method.
8.1 Alomic Absorption Spectrophotometer-Select the in-
Sensitivity should not be less than 75 % of the required
strument operating parameters including wavelength of the
value.
analyte element line emission source, support and fuel gases,
8.4 Precision of Measurements-Use the following proce-
and slit width for the element being determined by referring
dure to determine if the instrument precision is acceptable:
to the instrument manufacturer’s instructions or by referring
Set the absorbance to zero while aspirating a reference
to the basic analytical method that is being used (see Practice
solution prepared as specified in 7.1. Obtain an absorbance
E 863). Turn on the appropriate support and fuel gases, and
or concentration measurement on the calibration solution
ignite the burner. Aspirate water until a stable signal is
used in 8.1. Repeat the measurement sequence for the
obtained (that is, until the absorbance or transmittance
reference and the calibration solutions, alternating with
reaches a plateau value). Adjust the readout system to obtain
solvent flushing between measurements to obtain six read-
zero absorbance of 100 % transmittance while aspirating the
ings of absorbance for the calibration solution. Calculate the
reference solution prepared as directed in 7.1. Continue the
standard deviation of the readings made on this calibration
aspiration until a stable signal is obtained. Aspirate a
solution by applying acceptable statistical methods. If the
calibration solution, prepared as described in 7.3, containing
standard deviation is greater than 1 % of the average
the analyte at a concentration that will yield an absorbance
absorbance of the calibration solution, determine the cause
of 0.2 to 0.4, and at a concentration that is expected to be
of the variability (for example, deposits in the burner or
within the linear absorbance range of the method. Refer to
clogged capillaxy), and make the appropriate changes. If
the instrument manufacturer’s instruction manual for guid-
unacceptable precision is caused by a large amount of
ance to determine an approximation of the linear concentra-
dissolved solids in the calibration and test solutions, make an
tion range for the analyte, and for the following mechanical
appropriate dilution to prevent an erratic flame or clogging
adjustments: Adjust iteratively the zero absorbance using the
of the nebulizer.
reference solution, the burner height and its horizontal
NOTE 6-An approximation of the sfandard deviation (s) can be
position, the flow rate of the fuel gases, and the nebulizer
obtained with less calculation as follows:
position for maximum absorbance of the selected calibration
s = (A - E) X 0.40
(3)
solution. Obtain three measurements of the absorbance of
the calibration solution, washing with solvent or reference
ASTM Ebb38Eli 8b Y 875951i13 8076548 T
measurements and will have a useful range of 15 to 85
w liere:
A = the highest of the six readings, and
WmL.
I3 = the lowest of the six readings.
NOTE 7-If a conservative cross check on this approach to the uaful
range is desired, process the average absorbances as directed in 9.3.
9.3 Conservative Determinatiori of UseJiil Concenrralion
9, Dcterminntion of Useful Concentration Range
Range-If a rigorous determination of the high and low
9.1 General Cotisiderations-The useful concentration
limits of the useful concentration range is not required, this
range for a particular analytical system must be determined
conservative approach may be used and will require substan-
experimentally because the useful range will depend on the
tialIy fewer measurements (6,7,8). Make a single measure.
operation and characteristics of the individual AAS, Three
ment of transmittance for each of the calibration solutions as
dift’erent approaches to the determination of this useful range
described in 9.1.1. If only absorbance can be measured on
are described in 9.2, 9.3, and 9.4. Selection of the approach
the instrument or is available from other measurements,
to be used depends on the precision requirements of the
convert each absorbance measurement to percent transmit-
analytical method, or the limitations of the AAS used, or the
tance by means of the relationship:
concentration range of the analyte in the material to be
A loglo( 100/% T) (5)
analyzed, or all three.
9,l.I For any of the three approaches prepare reference
where:
and calibration solutions as directed in 7. i and 7.3. Prepare
A = absorbance, and
the AAS and adjust the readout system to zero absorbance or
T = transmittance.
100 % transmittance as directed in 8.1 using the reference
Make two plots, one of % T against the loglo concentration
solution. Aspirate the calibration solutions in the order
of the analy
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