ASTM E1770-95(2001)
(Practice)Standard Practice for Optimization of Electrothermal Atomic Absorption Spectrometric Equipment
Standard Practice for Optimization of Electrothermal Atomic Absorption Spectrometric Equipment
SCOPE
1.1 This practice covers the optimization of electrothermal atomic absorption spectrometers and the checking of spectrometer performance criteria.
1.2 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 2001)
Standard Practice for
Optimization of Electrothermal Atomic Absorption
Spectrometric Equipment
This standard is issued under the fixed designation E 1770; 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 a signal output device such as a video display screen (VDS), a
digital computer, a printer or strip chart recorder, and an
1.1 This practice covers the optimization of electrothermal
autosampler.
atomicabsorptionspectrometersandthecheckingofspectrom-
4.2 Grooved Pyrolytic Graphite-Coated Graphite Tubes,
eter performance criteria.
conforming to the instrument manufacturer’s specifications.
1.2 This standard does not purport to address all of the
4.3 Pyrolytic Graphite Platforms, L’vov design, fitted to the
safety concerns, if any, associated with its use. It is the
tubes specified in 4.2.
responsibility of the user of this standard to establish appro-
4.4 Pyrolytic Graphite-Coated Graphite Tubes, platform-
priate safety and health practices and determine the applica-
less, conforming to the instrument manufacturer’s specifica-
bility of regulatory limitations prior to use.
tions.
2. Referenced Documents
4.5 Radiation Source for the Analyte—A hollow cathode
lamp or electrodeless discharge lamp is suitable.
2.1 ASTM Standards:
E 50 Practices for Apparatus, Reagents, and Safety Precau-
NOTE 1—The use of multi-element lamps is not generally recom-
tions for Chemical Analysis of Metals
mended, since they may be subject to spectral line overlaps.
E 876 Practice for Use of Statistics in the Evaluation of
4.6 For general discussion of the theory and instrumental
Spectrometric Data
requirements of electrothermal atomic absorption spectromet-
E 1184 Practice for Electrothermal (Graphite Furnance)
ric analysis, see Practice E 1184.
Atomic Absorption Analysis
E 1452 Practice for Preparation of Calibration Solutions for
5. Reagents
Spectrophotometric Atomic Analysis
5.1 Purity and Concentration of Reagents—The purity and
concentration of common chemical reagents shall conform to
3. Significance and Use
Practices E 50. The reagents should be free of or contain
3.1 This practice is for optimizing the parameters used in
minimal amounts (<0.01 µg/g) of the analyte of interest.
the determination of trace elements in metals and alloys by the
5.2 Magnesium Nitrate Solution [2 g/L Mg(NO ) ]—
3 2
electrothermal atomic absorption spectrometric method. It also
Dissolve 0.366 0.01 g high-purity Mg(NO ) ·6H O in about
3 2 2
describes the practice for checking the spectrometer perfor-
50 mL of water, in a 100-mL beaker, and transfer the solution
mance. The work is expected to be performed in a properly
into a 100-mL volumetric flask. Dilute to mark with water and
equipped laboratory by trained operators and appropriate
mix. Store in polypropylene or high-density polyethylene
disposal procedures are to be followed.
bottle.
5.3 Calibration Solutions—Refer to the preparation of cali-
4. Apparatus
bration solutions in the relevant analytical method for the
4.1 Atomic Absorption Spectrometer with Electrothermal
determination of trace elements in the specific matrix. Calibra-
Atomizer, equipped with an appropriate background corrector,
tion solution S represents the calibration solution containing
noanalyte; S theleastconcentratedcalibrationsolution; S the
1 2
1 calibration solution with the next highest concentration;
This practice is under the jurisdiction of ASTM Committee E01 on Analytical
through S , the most concentrated calibration solution. Also
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
k
Subcommittee E01.20 Fundamental Practices.
refer to Practice E 1452.
Current edition approved Nov. 10, 1995. Published January 1996.
5.4 Matrix Modifiers—Refer to the relevant analytical
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
method for the determination of trace elements in the specific
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
matrix.
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1770–95 (2001)
6. Initial Checks and Adjustments an atomization temperature of 1800°C. A large background
signal should be observed with no over-or under-correction of
6.1 Turn on power, cooling water, gas supplies, and fume
the atomic signal.
exhaust system.
6.2 Open the furnace to inspect the tube and contacts.
NOTE 2—In general, Zeeman systems should compensate for back-
Replace graphite components, if wear or contamination is
ground levels as high as 1.0 to 1.5 absorbance units. A continuum
correctionsystemshouldbeabletocorrectforthebroad-bandbackground
evident. Inspect windows and clean or replace as required.
absorbance up to 0.5 to 0.6 absorbance units.
6.2.1 New graphite contacts or new tubes should be condi-
tioned prior to use, in accordance with the heating program
8.4 Autosampler—Check operation of the autosampler. Pay
recommended by the manufacturer.
particular attention to the condition of the pipette tip and
6.2.1.1 In the absence of manufacturer’s recommendations,
position of the tip during sample deposition. Clean the pipette
a conditioning program for a graphite furnace is shown in
tip with methanol. Adjust in accordance with the manufactur-
Table 1.
er’s instructions.
NOTE 3—Use of an appropriate surfactant in the rinse water may
7. Radiation Source
enhance operation. If a surfactant is used, it should be checked for the
7.1 Install and operate hollow cathode lamps or electrode-
presence of all the analytes to be determined.
less discharge lamps in accordance with the manufacturer’s
instructions. 9. Optimization of the Furnace Heating Program
7.2 After the manufacturer’s prescribed warm-up time, the
9.1 Optimization of the furnace heating program is essen-
signal from the radiation source should not deviate by more
tial. Furnace programs recommended by the manufacturers are
than 0.5 % from the maximum value (that is, by not more than
often designed for samples of a completely unrelated matrix.
0.002 absorbance units) over a period of 15 min. Significantly
The analyst shall optimize the furnace program for a particular
greater fluctuations are usually indicative of a faulty lamp or
sample matrix (for example, steel, nickel alloys, etc.) and
power supply.
modifier system in accordance with the following procedure:
Furnace Step Section
8. Spectrometer Parameters
Drying 9.2
8.1 Wavelength, as specified by the appropriate procedure.
Pyrolysis 9.3
8.2 Slit Width, as recommended by the manufacturer.Where
Atomization 9.4
Clean-out 9.5
two slit height settings are available, select the shorter height.
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-
analyte lamp and the deuterium lamp are balanced within
tory. To avoid spattering, a 20 s ramping time should be used
tolerances recommended by the manufacturer.
to reach the 120°C temperature and then held at that tempera-
8.3.2.2 If necessary, set the optical temperature sensor in
ture.Theholdingtimewilldependonthevolumeofthesample
accordance with the instrument manufacturer’s recommenda-
introduced. Typical holding times are as follows:
tion.
Injected Volume, µL Holding Time, s
8.3.3 To check the performance of the background correc-
10 15
tion system, measure the atomic background absorbance of 20
40 30
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
9.2.3 Samples Deposited on the L’vov Platform:
temperature of 120°C, a pyrolysis temperature of 950°C, and 9.2.3.1 When using a L’vov platform, a two-stage drying
process is beneficial to prevent spattering.
9.2.3.2 In the first stage, heat the sample rapidly to 80°C,
TABLE 1 Program for Graphite Furnace Conditioning
usinga1s ramp and then hold the temperature at 80°C for a
Gas flow, mL/
short time. The holding time depends upon the volume of the
Step Temperature, °C Ramp, s Hold, s
min
solution injected. Typical holding times are shown in 9.2.2.
1 1500 60 20 300
9.2.3.3 Forthesecondstage,thetemperatureisrampedover
2 20 1 10 300
a period of 20 to 30 s, to a value 20 to 40°C above the boiling
3 2000 60 20 300
point of the solvent. The holding times should be the same as
4 20 1 10 300
5 2600 60 10 300
given in 9.2.3.2.
6 20 1 10 300
9.2.4 In both cases, select a preliminary set of drying
7 2650 2 5 0
conditions and monitor the drying process visually with the aid
E1770–95 (2001)
of a dental mirror, to ensure that it proceeds without spattering. 9.4.1 This step involves the production of gaseous analyte
Hold the mirror directly above the sample introduction port atoms inside the graphite tube.
(avoid touching the magnet), or near the end windows of the 9.4.2 The analyst should determine the optimum atomiza-
graphite tube. Observe vapor formation on the mirror as drying tion temperature and integration time experimentally, using the
proceeds. Vapor evolution should cease at approximately 10 s same“GasInterruptoption,”graphitetubetype,andmeasuring
before the end of the drying step. Adjust the hold times mode combination selected before the optimization of the
accordingly to accomplish this. drying step.
9.2.4.1 Warning:To prevent serious eye injury, do not view
NOTE 8—Although it is possible to optimize the L’vov platform using
the tube directly during the atomization or clean-out steps.
the peak height measurement mode, the atomization step shall be
9.3 Pyrolysis Step:
optimized in such a manner that the conditions required for stabilized
9.3.1 Duringthisstep,volatilecomponentsoft
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