ASTM E1770-95
(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: E 1770 – 95
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 4.3 Pyrolytic Graphite Platforms, L’vov design, fitted to the
tubes specified in 4.2.
1.1 This practice covers the optimization of electrothermal
4.4 Pyrolytic Graphite-Coated Graphite Tubes, platform-
atomic absorption spectrometers and the checking of spectrom-
less, conforming to the instrument manufacturer’s specifica-
eter performance criteria.
tions.
1.2 This standard does not purport to address all of the
4.5 Radiation Source for the Analyte—A hollow cathode
safety concerns, if any, associated with its use. It is the
lamp or electrodeless discharge lamp is suitable.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
NOTE 1—The use of multi-element lamps is not generally recom-
bility of regulatory limitations prior to use. mended, since they may be subject to spectral line overlaps.
4.6 For general discussion of the theory and instrumental
2. Referenced Documents
requirements of electrothermal atomic absorption spectromet-
2.1 ASTM Standards:
ric analysis, see Practice E 1184.
E 50 Practices for Apparatus, Reagents, and Safety Precau-
tions for Chemical Analysis of Metals
5. Reagents
E 876 Practice for Use of Statistics in the Evaluation of
5.1 Purity and Concentration of Reagents—The purity and
Spectrometric Data
concentration of common chemical reagents shall conform to
E 1184 Practice for Electrothermal Atomic Absorption
Practices E 50. The reagents should be free of or contain
Analysis
minimal amounts (<0.01 μg/g) of the analyte of interest.
E 1452 Practice for Preparation of Calibration Solutions for
5.2 Magnesium Nitrate Solution [2 g/L Mg(NO ) ]—
3 2
Spectrophotometric Atomic Analysis
Dissolve 0.366 0.01 g high-purity Mg(NO ) ·6H O in about
3 2 2
50 mL of water, in a 100-mL beaker, and transfer the solution
3. Significance and Use
into a 100-mL volumetric flask. Dilute to mark with water and
3.1 This practice is for optimizing the parameters used in
mix. Store in polypropylene or high-density polyethylene
the determination of trace elements in metals and alloys by the
bottle.
electrothermal atomic absorption spectrometric method. It also
5.3 Calibration Solutions—Refer to the preparation of cali-
describes the practice for checking the spectrometer perfor-
bration solutions in the relevant analytical method for the
mance. The work is expected to be performed in a properly
determination of trace elements in the specific matrix. Calibra-
equipped laboratory by trained operators and appropriate
tion solution S represents the calibration solution containing
disposal procedures are to be followed.
no analyte; S the least concentrated calibration solution; S the
1 2
calibration solution with the next highest concentration;
4. Apparatus
through S , the most concentrated calibration solution. Also
k
4.1 Atomic Absorption Spectrometer with Electrothermal
refer to Practice E 1452.
Atomizer, equipped with an appropriate background corrector,
5.4 Matrix Modifiers—Refer to the relevant analytical
a signal output device such as a video display screen (VDS), a
method for the determination of trace elements in the specific
digital computer, a printer or strip chart recorder, and an
matrix.
autosampler.
4.2 Grooved Pyrolytic Graphite-Coated Graphite Tubes,
6. Initial Checks and Adjustments
conforming to the instrument manufacturer’s specifications.
6.1 Turn on power, cooling water, gas supplies, and fume
exhaust system.
6.2 Open the furnace to inspect the tube and contacts.
This practice is under the jurisdiction of ASTM Committee E-1 on Analytical
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Replace graphite components, if wear or contamination is
Subcommittee E01.20 Fundamental Practices.
evident. Inspect windows and clean or replace as required.
Current edition approved Nov. 10, 1995. Published January 1996.
2 6.2.1 New graphite contacts or new tubes should be condi-
Annual Book of ASTM Standards, Vol 03.05.
Annual Book of ASTM Standards, Vol 03.06. tioned prior to use, in accordance with the heating program
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1770
recommended by the manufacturer. position of the tip during sample deposition. Clean the pipette
6.2.1.1 In the absence of manufacturer’s recommendations, tip with methanol. Adjust in accordance with the manufactur-
a conditioning program for a graphite furnace is shown in er’s instructions.
Table 1.
NOTE 3—Use of an appropriate surfactant in the rinse water may
enhance operation. If a surfactant is used, it should be checked for the
7. Radiation Source
presence of all the analytes to be determined.
7.1 Install and operate hollow cathode lamps or electrode-
less discharge lamps in accordance with the manufacturer’s 9. Optimization of the Furnace Heating Program
instructions.
9.1 Optimization of the furnace heating program is essen-
7.2 After the manufacturer’s prescribed warm-up time, the
tial. Furnace programs recommended by the manufacturers are
signal from the radiation source should not deviate by more
often designed for samples of a completely unrelated matrix.
than 0.5 % from the maximum value (that is, by not more than
The analyst shall optimize the furnace program for a particular
0.002 absorbance units) over a period of 15 min. Significantly
sample matrix (for example, steel, nickel alloys, etc.) and
greater fluctuations are usually indicative of a faulty lamp or
modifier system in accordance with the following procedure:
power supply.
Furnace Step Section
8. Spectrometer Parameters
Drying 9.2
Pyrolysis 9.3
8.1 Wavelength, as specified by the appropriate procedure.
Atomization 9.4
8.2 Slit Width, as recommended by the manufacturer. Where
Clean-out 9.5
two slit height settings are available, select the shorter height.
9.2 Drying Step:
8.3 Background Correction:
9.2.1 Select the graphite tube type (L’vov or platformless)
8.3.1 Zeeman Background Correction System:
and measurement mode (peak height or integrated peak area).
8.3.1.1 Ensure that the poles of the magnet are clean and
Then select the same heating parameters used in 8.3.3. Opti-
securely tightened.
mize the drying parameters using any of the calibration
8.3.1.2 If necessary, set the optical temperature sensor in
solutions (see 5.3) and the procedure given in either 9.2.2 or
accordance with the instrument manufacturer’s instructions.
9.2.3.
8.3.2 Continuum Background System:
9.2.2 Samples Deposited on the Tube Wall—For wall-
8.3.2.1 Select the background correction option and allow
deposited samples, a drying temperature of 120°C is satisfac-
lamps to stabilize for 30 min. Verify that the energies of the
tory. To avoid spattering, a 20 s ramping time should be used
analyte lamp and the deuterium lamp are balanced within
to reach the 120°C temperature and then held at that tempera-
tolerances recommended by the manufacturer.
ture. The holding time will depend on the volume of the sample
8.3.2.2 If necessary, set the optical temperature sensor in
introduced. Typical holding times are as follows:
accordance with the instrument manufacturer’s recommenda-
Injected Volume, μL Holding Time, s
tion.
8.3.3 To check the performance of the background correc-
10 15
40 30
tion system, measure the atomic background absorbance of 20
μL of 2 g/L magnesium nitrate solution at a wavelength in the
9.2.3 Samples Deposited on the L’vov Platform:
200 to 250 nm region (for example, Bi 223.1 nm) using a dry
9.2.3.1 When using a L’vov platform, a two-stage drying
temperature of 120°C, a pyrolysis temperature of 950°C, and
process is beneficial to prevent spattering.
an atomization temperature of 1800°C. A large background
9.2.3.2 In the first stage, heat the sample rapidly to 80°C,
signal should be observed with no over-or under-correction of
usinga1s ramp and then hold the temperature at 80°C for a
the atomic signal.
short time. The holding time depends upon the volume of the
solution injected. Typical holding times are shown in 9.2.2.
NOTE 2—In general, Zeeman systems should compensate for back-
ground levels as high as 1.0 to 1.5 absorbance units. A continuum
9.2.3.3 For the second stage, the temperature is ramped over
correction system should be able to correct for the broad-band background
a period of 20 to 30 s, to a value 20 to 40°C above the boiling
absorbance up to 0.5 to 0.6 absorbance units.
point of the solvent. The holding times should be the same as
8.4 Autosampler—Check operation of the autosampler. Pay
given in 9.2.3.2.
particular attention to the condition of the pipette tip and
9.2.4 In both cases, select a preliminary set of drying
conditions and monitor the drying process visually with the aid
of a dental mirror, to ensure that it proceeds without spattering.
TABLE 1 Program for Graphite Furnace Conditioning
Hold the mirror directly above the sample introduction port
Gas flow, mL/
Step Temperature, °C Ramp, s Hold, s
min (avoid touching the magnet), or near the end windows of the
graphite tube. Observe vapor formation on the mirror as drying
1 1500 60 20 300
2 20 1 10 300
proceeds. Vapor evolution should cease at approximately 10 s
3 2000 60 20 300
before the end of the drying step. Adjust the hold times
4 20 1 10 300
accordingly to accomplish this.
5 2600 60 10 300
6 20 1 10 300
NOTE 4—Warning: To prevent serious eye injury, do not view the tube
7 2650 2 5 0
directly during the atomization or clean-out steps.
E 1770
9.3 Pyrolysis Step: optimized in such a manner that the conditions required for stabilized
temperature platform furnace (STPF) operation are satisfied. In addition to
9.3.1 During this step, volatile components of the matrix are
the use of “Gas Interrupt” and matrix modification (inherent in certain
driven off and precursory reactions occur (for example, reduc-
procedures), the following additional conditions are to be satisfied: (1) The
tion of the analyte oxide to the elemental state and the
temperature difference between the pyrolysis step and the atomization step
formation of matrix refractory oxides and carbides).
should be as small as possible (less than 1000°C). This allows the furnace
to approach the near i
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