ASTM E1832-96e2

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
e2
Designation: E 1832 – 96
Standard Practice for
Describing and Specifying a Direct-Current-Plasma Optical
Emission Spectrometer
This standard is issued under the fixed designation E 1832; 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.
e NOTE— Figs. 1 and 2 were added editorially in August 1997.
e NOTE—Section 5, Theory, was deleted editorially in August 1998.
1. Scope E 1097 Guide for Direct Current Plasma Emission Spec-
trometry Analysis
1.1 This practice describes the components of a direct-
current-plasma (DCP) optical emission spectrometer. This
3. Terminology
practice does not attempt to specify component tolerances or
3.1 For terminology relating to emission spectrometry, refer
performance criteria. This practice does, however, attempt to
to Terminology E 135.
identify critical factors affecting bias, precision, and sensitivity.
A prospective user should consult with the vendor before
4. Significance and Use
placing an order to design a testing protocol for demonstrating
4.1 This practice describes the essential components of the
that the instrument meets all anticipated needs.
DCP spectrometer. This description allows the user or potential
1.2 This standard does not purport to address all of the
user to gain a basic understanding of this system. It also
safety concerns, if any, associated with its use. It is the
provides a means of comparing and evaluating this system with
responsibility of the user of this standard to establish appro-
similar systems, as well as understanding the capabilities and
priate safety and health practices and determine the applica-
limitations of each instrument.
bility of regulatory limitations prior to use. Specific hazards
statements are give in in Section 9.
5. Overview
5.1 A DCP spectrometer is an instrument for determining
2. Referenced Documents
concentration of elements in solution. It typically is comprised
2.1 ASTM Standards:
of several assemblies including a direct current (dc) electrical
E 135 Terminology Relating to Analytical Chemistry for
2 source, a sample introduction system, components to form and
Metals, Ores, and Related Materials
contain the plasma, an entrance slit, elements to disperse
E 158 Practice for Fundamental Calculations to Convert
radiation emitted from the plasma, one or more exit slits, one
Intensities into Concentrations in Optical Emission Spec-
or more photomultipliers for converting the emitted radiation
trochemical Analysis
into electrical current, one or more electrical capacitors for
E 172 Practice for Describing and Specifying the Excitation
storing this current as electrical charge, electrical circuitry for
Source in Emission Spectrochemical Analysis
measuring the voltage on each storage device, and a dedicated
E 406 Practice for Using Controlled Atmospheres in Spec-
computer with printer. The liquid sample is introduced into a
trochemical Analysis
spray chamber at a right-angle to a stream of argon gas. The
E 416 Practice for Planning and Safe Operation of a Spec-
3 sample is broken up into a fine aerosol by this argon stream and
trochemical Laboratory
carried into the plasma produced by a dc-arc discharge between
E 520 Practice for Describing Detectors in Emission and
3 a tungsten electrode and two or more graphite electrodes.
Absorption Spectroscopy
When the sample passes through the plasma, it is vaporized
E 528 Practices for Grounding Basic Optical Emission
3 and atomized, and many elements are ionized. Free atoms and
Spectrochemical Equipment
ions are excited from their ground states. When electrons of
E 876 Practice for Use of Statistics in the Evaluation of
3 excited atoms and ions fall to a lower-energy state, photons of
Spectrometric Data
specific wavelengths unique to each emitting species are
emitted. This radiation, focussed by a lens onto the entrance slit
This practice is under the jurisdiction of ASTM Committee E-1 on Analytical of the spectrometer and directed to an echelle grating and
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
quartz prism, is dispersed into higher orders of diffraction.
Subcommittee E01.20 on Fundamental Practices.
Control on the diffraction order is accomplished by the
Current edition approved Oct. 10, 1996. Published December 1996.
Annual Book of ASTM Standards, Vol 03.05.
Annual Book of ASTM Standards, Vol 03.06.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1832
low-dispersion, echelle grating. Radiation of specific wave-
length or wavelengths passes through exit slits and impinges on
a photomultiplier or photomultipliers. The current outputs
charge high-quality capacitors, and the voltages thus generated
are measured and directed to the computer. Using calibration
solutions, a calibration curve is generated for each element of
interest. The computer compares the signals arising form the
many elements in the sample to the appropriate calibration
curve and then calculates the concentration of each element.
Over seventy elements may be determined. Detection limits in
a simple aqueous solution are less than 1 mg/L for most of
these elements. Mineral acids or organic liquids also may be
used as solvents, and detection limits are usually within an
order of magnitude of those obtained with water. Detection
limits may be improved by using preconcentration procedures.
Solid samples are dissolved before analysis.
6. Description of Equipment
6.1 Echelle Spectrometer—Components of the equipment
shown in Fig. 1 and described in this section are typical of a
commercially available spectrometer. Although a specific spec-
trometer is described herein, other spectrometers having equal
or better performance may be satisfactory. The spectrometer is
a Czerny-Turner mount and consists of a condensing lens in
front of an entrance slit, a collimating mirror, combined
FIG. 1 Echelle Grating Spectrometer
dispersing elements (grating and prism), focus mirror, exit slits,
photomultipliers, control panel, and wavelength selector
mechanism.
Select the specific exit slit width before installation. Provide a
6.1.1 Condensing Lens, placed between the DCP source and
single channel cassette with one exit slit variable from 0.025 to
the entrance slit. It should have a focal length capable of
0.200 mm in width and from 0.100 to 0.500 mm in length.
focusing an image of the source on the entrance slit and with
6.1.7 Photomultipliers, up to twenty end-on tubes, are
sufficient diameter to fill the aperture of the spectrometer with
mounted behind the focal plane in a fixed pattern. Consider
radiant energy.
6.1.2 Entrance Slit, although available with fixed width and sensitivity at specific wavelength and dark current in the
selection of appropriate photomultipliers. Provide variable
height, a slit variable in both width and height provides greater
flexibility. Typical values are 0.025 to 0.500 mm in width and voltage to each photomultiplier to change its response as
required by the specific application. A typical range is from 550
0.100 to 0.500 mm in height. Adjustable slit widths and heights
to 1000 V in 50-V steps. A survey of the properties of
are useful in obtaining optimal spectral band width and radiant
photomultipliers is given in Practice E 520.
energy entering the spectrometer for the requirements of the
analytical method. 6.1.8 Control Panels, are provided to perform several func-
6.1.3 Collimating Mirror, renders all rays parallel after tions and serve as input to microprocessors to control the
entering the spectrometer. These parallel rays illuminate the operation of the spectrometer. Provide a numeric keyboard to
combined dispersing elements. The focal length and f number enter high and low concentrations of reference materials for
should be specified. Typical focal length and f number are 750 calibration and standardization of each channel and to display
mm and f/13. entered values for verification. Provide a switch on this panel
6.1.4 Combined Dispersing Components, positioned so that to set the mode either to integrate during analysis or to measure
the radiant energy from the collimating mirror passes through instantaneous intensity. The latter mode is required to obtain
the prism, is refracted and reflected by a plane grating and back the peak position for a specific channel by seeking maximum
intensity by wavelength adjustment and verifying by wave-
through the prism. Specify the ruling on the grating (for
example, 79 grooves/mm). length scanning. Conduct interference and background inves-
tigations with this mode. Scanning is required if automatic
6.1.5 Focus Mirror, placed to focus the radiant energy from
the combined dispersing elements on a flat two-dimensional background correction is to be performed. Provide other
focal plane where the exit slits are located. necessary switches for the following purposes: to calibrate or
6.1.6 Fixed Exit Slits, mounted in a removable fixture called standardize the spectrometer, start analysis, interrupt the func-
an optical cassette for multielement capability. A two-mirror tion being performed, set integration time and the number of
periscope behind each exit slit directs the radiant energy to a replicate analyses, and direct the output to a printer, display, or
corresponding photomultiplier. For single element capability, storage medium. Impose a fixed time delay of 10 s before
energy for one wavelength usually passes through its exit slit integration can begin to ensure that the solution being analyzed
directly to the photomultiplier without the need for a periscope. is aspirated into the DCP discharge. Provide digital and analog
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1832
voltmeters for displaying the instantaneous or integrated inten-
sities during peaking, scanning, or analysis. If a computer is an
integral part of the spectrometer, most of the control functions
are accomplished with software.
6.1.9 Wavelength Adjustment, provided to adjust the wave-
length range and diffraction order for peaking the spectrometer
because a two-dimensional spectrum is produced. Both coarse
and final control of these adjustments are required. To maintain
optical alignment, the spectrometer should be thermally iso-
lated from the DCP source or heated. A heated base on which
the spectrometer rests has been satisfactory for this purpose.
6.1.10 Dispersion and Spectral Band Pass—Typical disper-
sion and spectral band pass with a 0.025-mm slit width vary
from 0.061 nm/mm and 0.0015 nm at 200 nm to 0.244 nm/mm
and 0.0060 nm at 800 nm, respectively.
6.2 DCP Source, composed of several distinct parts, namely
the electrode, direct current power supply, gas flow, sample
introduction, exhaust, water cooling, and safety systems. Refer
to Practice E 172 for a list of the electrical source parameters
that should be specified in a DCP method.
FIG. 2 DCP Source
6.2.1 Electrode System, Fig. 2, consists of two graphite
anodes fixed in a vertical plane and at a typical angle of 60° to
one another, and a tungsten cathode fixed in a horizontal plane
symmetrical discharge and a triangular- or arrowhead-shaped
at an angle of 45° to the optic axis. In their operating position,
excitation region where the specimen’s spectrum is generated.
the tips of the two anodes are separated by a distance of 1 ⁄16
6.2.3.4 Providing isolation of the gas flow system from the
in., (3.0 cm), and the tungsten cathode is 1 ⁄8 in., (4.1 cm),
ambient atmosphere. For good analytical performance, ensure
above the anode tips. Each electrode is recessed in a ceramic
that all tubing connections are tight and O-rings are in good
sleeve fitted into water-cooled anode and cathode blocks.
condition.
Because the electrodes are of special design to fit into and be
6.2.4 Sample Introduction System is required to control the
held by these blocks, the user must follow the manufacturer’s
flow of sample solution. This typically involves placing a
recommendations for these electrodes. The electrode system
flexible tube in the sample container, which aspirates the
shall provide mechanism to adjust the electrodes vertically and
sample solution into a nebulizer, usually a cross-flow design. A
horizontally across the optic axis to properly project the image
peristaltic pump is used to pump the sample solution to the
of the excitation region onto the entrance slit and obtain a
nebulizer. As a specimen drop is formed at the nebulizer orifice
maximum signal-to-noise ratio. Sometimes a visible excitation
(0.02 in. or 0.05 cm), it is removed by the argon stream and
region is not produced when some specimens are aspirated into
broken into several smaller drops. Most of these impinge on
this source. Iron solutions, as well as solutions of several other
the walls of the spray chamber running down to collect in a
elements, however, are satisfactory for this purpose.
waste reservoir. Typically, about 20 % of the nebulized speci-
6.2.2 Direct Current Power Supply, capable of maintaining
men is carried by the argon stream as an aerosol into the
a constant current of 7 A dc in the discharge with a voltage of
plasma. The liquid in the waste reservoir is removed continu-
40 to 50 V dc between the anodes and cathodes. The resulting
ously by the same peristaltic pump used to feed the nebulizer,
discharge has the shape of an inverted letter Y with a luminous
and passes the waste through a second tube to be safely
zone in the crotch of the Y.
disposed. If this is not done, the volume of liquid waste in the
6.2.3 Gas Flow System, (Refer to Practice E 406) shall be
reservoir and the spray chamber is increased, increasing the gas
capable of the following:
pressure and volume of the specimen injected into the plasma,
6.2.3.1 Providing argon gas delivered at a pressure of 80 psi
thus extinguishing the plasma. Because this pump crushes
(5.62 kg/cm ) to the discharge sustaining gas and sample
these tubes with use, daily damage inspection is required for
nebulization.
optimum performance.
6.2.3.2 Providing a pneumatic system to extend the anode
6.2.5 Exhaust System—Provide a small hood connected to
and cathode out of their sleeves and move the cathode block
an exhaust fan
...