ASTM E1770-95(2006)
(Practice)Standard Practice for Optimization of Electrothermal Atomic Absorption Spectrometric Equipment
Standard Practice for Optimization of Electrothermal Atomic Absorption Spectrometric Equipment
SIGNIFICANCE AND USE
This practice is for optimizing the parameters used in the determination of trace elements in metals and alloys by the electrothermal atomic absorption spectrometric method. It also describes the practice for checking the spectrometer performance. The work is expected to be performed in a properly equipped laboratory by trained operators and appropriate disposal procedures are to be followed.
SCOPE
1.1 This practice covers the optimization of electrothermal atomic absorption spectrometers and the checking of spectrometer performance criteria.
1.2 The values stated in SI units are to be regarded as the standard.
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: E1770 − 95(Reapproved 2006)
Standard Practice for
Optimization of Electrothermal Atomic Absorption
Spectrometric Equipment
This standard is issued under the fixed designation E1770; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope mance. The work is expected to be performed in a properly
equipped laboratory by trained operators and appropriate
1.1 This practice covers the optimization of electrothermal
disposal procedures are to be followed.
atomicabsorptionspectrometersandthecheckingofspectrom-
eter performance criteria.
4. Apparatus
1.2 The values stated in SI units are to be regarded as the
4.1 Atomic Absorption Spectrometer with Electrothermal
standard.
Atomizer, equipped with an appropriate background corrector,
1.3 This standard does not purport to address all of the
a signal output device such as a video display screen (VDS), a
safety concerns, if any, associated with its use. It is the
digital computer, a printer or strip chart recorder, and an
responsibility of the user of this standard to establish appro-
autosampler.
priate safety and health practices and determine the applica-
4.2 Grooved Pyrolytic Graphite-Coated Graphite Tubes,
bility of regulatory limitations prior to use.
conforming to the instrument manufacturer’s specifications.
2. Referenced Documents 4.3 Pyrolytic Graphite Platforms, L’vov design, fitted to the
2 tubes specified in 4.2.
2.1 ASTM Standards:
E50 Practices for Apparatus, Reagents, and Safety Consid- 4.4 Pyrolytic Graphite-Coated Graphite Tubes,
erations for Chemical Analysis of Metals, Ores, and platformless, conforming to the instrument manufacturer’s
Related Materials specifications.
E876 Practice for Use of Statistics in the Evaluation of
4.5 Radiation Source for the Analyte—A hollow cathode
Spectrometric Data (Withdrawn 2003)
lamp or electrodeless discharge lamp is suitable.
E1184 Practice for Determination of Elements by Graphite
NOTE 1—The use of multi-element lamps is not generally
Furnace Atomic Absorption Spectrometry
recommended, since they may be subject to spectral line overlaps.
E1452 Practice for Preparation of Calibration Solutions for
4.6 For general discussion of the theory and instrumental
Spectrophotometric and for Spectroscopic Atomic Analy-
requirements of electrothermal atomic absorption spectromet-
sis (Withdrawn 2005)
ric analysis, see Practice E1184.
3. Significance and Use
5. Reagents
3.1 This practice is for optimizing the parameters used in
5.1 Purity and Concentration of Reagents—The purity and
the determination of trace elements in metals and alloys by the
concentration of common chemical reagents shall conform to
electrothermal atomic absorption spectrometric method. It also
Practices E50. The reagents should be free of or contain
describes the practice for checking the spectrometer perfor-
minimal amounts (<0.01 µg/g) of the analyte of interest.
5.2 Magnesium Nitrate Solution [2 g/L Mg(NO ) ]—
3 2
This practice is under the jurisdiction of ASTM Committee E01 on Analytical
Dissolve 0.36 6 0.01 g high-purity Mg(NO ) ·6H O in about
3 2 2
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
50 mL of water, in a 100-mL beaker, and transfer the solution
Subcommittee E01.20 Fundamental Practices.
into a 100-mL volumetric flask. Dilute to mark with water and
Current edition approved June 1, 2006. Published June 2006. Originally
approved in 1995. Last previous edition approved in 2001 as E1770 – 95 (2001).
mix. Store in polypropylene or high-density polyethylene
DOI: 10.1520/E1770-95R06.
bottle.
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
5.3 Calibration Solutions—Refer to the preparation of cali-
Standards volume information, refer to the standard’s Document Summary page on
bration solutions in the relevant analytical method for the
the ASTM website.
determination of trace elements in the specific matrix. Calibra-
The last approved version of this historical standard is referenced on
www.astm.org. tion solution S represents the calibration solution containing
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1770 − 95 (2006)
noanalyte; S theleastconcentratedcalibrationsolution; S the analyte lamp and the deuterium lamp are balanced within
1 2
calibration solution with the next highest concentration; tolerances recommended by the manufacturer.
through S , the most concentrated calibration solution. Also
8.3.2.2 If necessary, set the optical temperature sensor in
k
refer to Practice E1452. accordance with the instrument manufacturer’s recommenda-
tion.
5.4 Matrix Modifiers—Refer to the relevant analytical
8.3.3 To check the performance of the background correc-
method for the determination of trace elements in the specific
tion system, measure the atomic background absorbance of 20
matrix.
µL of 2 g/L magnesium nitrate solution at a wavelength in the
200 to 250 nm region (for example, Bi 223.1 nm) using a dry
6. Initial Checks and Adjustments
temperature of 120°C, a pyrolysis temperature of 950°C, and
6.1 Turn on power, cooling water, gas supplies, and fume
an atomization temperature of 1800°C. A large background
exhaust system.
signal should be observed with no over-or under-correction of
6.2 Open the furnace to inspect the tube and contacts.
the atomic signal.
Replace graphite components, if wear or contamination is
NOTE 2—In general, Zeeman systems should compensate for back-
evident. Inspect windows and clean or replace as required.
ground levels as high as 1.0 to 1.5 absorbance units. A continuum
6.2.1 New graphite contacts or new tubes should be condi-
correctionsystemshouldbeabletocorrectforthebroad-bandbackground
tioned prior to use, in accordance with the heating program
absorbance up to 0.5 to 0.6 absorbance units.
recommended by the manufacturer.
8.4 Autosampler—Check operation of the autosampler. Pay
6.2.1.1 In the absence of manufacturer’s recommendations,
particular attention to the condition of the pipette tip and
a conditioning program for a graphite furnace is shown in
position of the tip during sample deposition. Clean the pipette
Table 1.
tip with methanol. Adjust in accordance with the manufactur-
er’s instructions.
7. Radiation Source
NOTE 3—Use of an appropriate surfactant in the rinse water may
7.1 Install and operate hollow cathode lamps or electrode-
enhance operation. If a surfactant is used, it should be checked for the
less discharge lamps in accordance with the manufacturer’s
presence of all the analytes to be determined.
instructions.
9. Optimization of the Furnace Heating Program
7.2 After the manufacturer’s prescribed warm-up time, the
signal from the radiation source should not deviate by more
9.1 Optimization of the furnace heating program is essen-
than 0.5 % from the maximum value (that is, by not more than
tial. Furnace programs recommended by the manufacturers are
0.002 absorbance units) over a period of 15 min. Significantly
often designed for samples of a completely unrelated matrix.
greater fluctuations are usually indicative of a faulty lamp or
The analyst shall optimize the furnace program for a particular
power supply.
sample matrix (for example, steel, nickel alloys, etc.) and
modifier system in accordance with the following procedure:
8. Spectrometer Parameters
Furnace Step Section
8.1 Wavelength, as specified by the appropriate procedure.
Drying 9.2
8.2 Slit Width, as recommended by the manufacturer.Where
Pyrolysis 9.3
Atomization 9.4
two slit height settings are available, select the shorter height.
Clean-out 9.5
8.3 Background Correction:
9.2 Drying Step:
8.3.1 Zeeman Background Correction System:
9.2.1 Select the graphite tube type (L’vov or platformless)
8.3.1.1 Ensure that the poles of the magnet are clean and
and measurement mode (peak height or integrated peak area).
securely tightened.
Then select the same heating parameters used in 8.3.3. Opti-
8.3.1.2 If necessary, set the optical temperature sensor in
mize the drying parameters using any of the calibration
accordance with the instrument manufacturer’s instructions.
solutions (see 5.3) and the procedure given in either 9.2.2 or
8.3.2 Continuum Background System:
9.2.3.
8.3.2.1 Select the background correction option and allow
9.2.2 Samples Deposited on the Tube Wall—For wall-
lamps to stabilize for 30 min. Verify that the energies of the
deposited samples, a drying temperature of 120°C is satisfac-
tory. To avoid spattering, a 20 s ramping time should be used
to reach the 120°C temperature and then held at that tempera-
TABLE 1 Program for Graphite Furnace Conditioning
ture.Theholdingtimewilldependonthevolumeofthesample
Gas flow, mL/
introduced. Typical holding times are as follows:
Step Temperature, °C Ramp, s Hold, s
min
Injected Volume, µL Holding Time, s
1 1500 60 20 300
2 20 1 10 300
10 15
3 2000 60 20 300
40 30
4 20 1 10 300
5 2600 60 10 300
9.2.3 Samples Deposited on the L’vov Platform:
6 20 1 10 300
9.2.3.1 When using a L’vov platform, a two-stage drying
7 2650 2 5 0
process is beneficial to prevent spattering.
E1770 − 95 (2006)
9.2.3.2 In the first stage, heat the sample rapidly to 80°C, 9.3.9 Calculate the mean of the three absorbance measure-
usinga1s ramp and then hold the temperature at 80°C for a ments. There should be no evidence of analyte loss (indicated
short time. The holding time depends upon the volume of the by lower absorbances for the longer hold times).
solution injected. Typical holding times are shown in 9.2.2. 9.3.10 Provided the pyrolysis condition in 9.3.7 is satisfied,
select the shortest time in which the background signal returns
9.2.3.3 Forthesecondstage,thetemperatureisrampedover
to the baseline and add 10 s to this value to obtain the optimum
a period of 20 to 30 s, to a value 20 to 40°C above the boiling
hold time.
point of the solvent. The holding times should be the same as
given in 9.2.3.2.
NOTE 7—A slow ramp time of 30 s and a hold time of 30 s is usually
9.2.4 In both cases, select a preliminary set of drying
sufficient for all pretreatment reactions to occur. Short ramp times may
conditions and monitor the drying process visually with the aid provoke explosive loss of sample in the tube.
of a dental mirror, to ensure that it proceeds without spattering.
9.4 Atomization Step:
Hold the mirror directly above the sample introduction port
9.4.1 This step involves the production of gaseous analyte
(avoid touching the magnet), or near the end windows of the
atoms inside the graphite tube.
graphite tube. Observe vapor formation on the mirror as drying
9.4.2 The analyst should determine the optimum atomiza-
proceeds. Vapor evolution should cease at approximately 10 s
tion temperature and integration time experimentally, using the
before the end of the drying step. Adjust the hold times
same“GasInterruptoption,”graphitetubetype,andmeasuring
accordingly to accomplish this.
mode combination selected before the optimization of the
9.2.4.1 Warning:To prevent serious eye injury, do not view
drying step.
the tube directly during the atomization or clean-out steps.
NOTE 8—Although it is possible to optimize the L’vov platform using
9.3 Pyrolysis Step:
the peak height measurement mode, the atomization step shall be
optimized in such a manner that the conditions required for stabilized
9.3.1 Duringthisstep,volatilecomponentsofthematrixare
temperatureplatformfurnace(STPF)operationaresatisfied.Inadditionto
driven off and precursory reactions occur (for example, reduc-
the use of “Gas Interrupt” and matrix modification (inherent in certain
tion of the analyte oxide to the elemental state and the
procedures),thefollowingadditionalconditionsaretobesatisfied:(1)The
formation of matrix refractory oxides and carbides).
temperaturedifferencebetweenthepyrolysisstepandtheatomizationstep
should be as small as possible (less than 1000°C). This allows the furnace
NOTE 4—Because of the low volatility of most metal alloy matrices,
to approach the near isothermal conditions quickly and reduces the
most of the matrix will remain in the furnace after the pyrolysis.
amountofmatrixvolatilized;(2)Peakareaintegrationmeasurementmode
shall be used; and (3) There shall be zero ramping time between the
9.3.2 Use the optimum drying conditions as determined in
pyrolysis and the atomization steps. The “Gas Interrupt” will interrupt the
9.2.
flow of inert gas through the graphite tube from a few seconds prior to the
start of the atomization cycle to the end of the atomization cycle.
NOTE 5—At this stage, both the optimum pyrolysis and atomization
temperatures are unknown. An estimate of the suitable atomization
9.4.3 Use the optimum drying and pyrolysis conditions.
temperature shall be made and entered into the instrument prior to
9.4.4 Select an atomization temperature of 1200°C and an
optimization of the pyrolysis temperature.
integration time of 20 s.
9.3.3 Set atomizing temperature according to the manufac-
9.4.5 Obtain three absorbance measurements with the cali-
turer’s instructions. Select the “Gas Interrupt” (or “Gas Stop”)
bration solution used in 9.3.5.
option. Select an atomization integration time of 10 s.
9.4.6 Repeat varying the atomization temperature in 100°C
9.3.4 Select a pyrolysis time of 30 s ramp and 30 s hold.
incrementsupto2500°C.Itisnotnecessarytocontinueraising
9.3.5 Select a calibration solution (see 5.3) which will give
the atomization temperature once the absorbance reaches a
an absorbance reading of 0.2 to 0.4 absorbance units. plateau.
9.3.6 Vary the pyrolysis temperature in increments of 9.4.7 Plot the mean of the three absorbance measurements
obtained for each step against the atomization temperature.
100°C, throughout the range from 500 to 1400°C, taking three
absorbance measurements at each step for the calibration 9.4.8 Examine the graph and determine the lowest atomiza-
solution selected in accordance with 9.3.5.
tion temperature where maximum absorbance was obtained.
Add 200°C to this value to obtain the optimum atomization
9.3.7 Calculate the mean of the three absorbance measure-
ments obtained for each temperature step. Plot a graph relating temperature.
the pyrolysis temperature to the mean absorbance. Note the
NOTE 9—At the lowest atomization temperature that gives maximum
temperature at which the absorbance starts to decline. Subtract
absorbance when using the peak area integr
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