ASTM D4517-85(1999)
(Test Method)Standard Test Method for Low-Level Total Silica in High-Purity Water by Flameless Atomic Absorption Spectroscopy
Standard Test Method for Low-Level Total Silica in High-Purity Water by Flameless Atomic Absorption Spectroscopy
SCOPE
1.1 This test method covers the determination of total silica in water.
1.2 This test method is applicable in the range from 25 to 250 [mu]g/L of silica as SiO . Higher concentrations may be determined by decreasing the aliquot volume (see Note 6). Concentration range should not be extended by dilution.
1.3 This test method determines total silica, and does not distinguish between soluble and insoluble forms.
1.4 This test method was tested on reagent water only. It is the user's responsibility to assure the validity of the test method for waters of other matrices.
1.5 This standard does not purport to address 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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
An American National Standard
Designation: D 4517 – 85 (Reapproved 1999)
Standard Test Method for
Low-Level Total Silica in High-Purity Water by Flameless
Atomic Absorption Spectroscopy
This standard is issued under the fixed designation D 4517; 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. Summary of Test Method
1.1 This test method covers the determination of total silica 4.1 Total silica is determined using an atomic absorption
in water. spectrophotometer in conjunction with a graphite furnace. A
1.2 This test method is applicable in the range from 25 to sample is placed in a graphite tube, evaporated to dryness,
250 μg/L of silica as SiO . Higher concentrations may be charred, and atomized. Since the graphite furnace uses the
determined by decreasing the aliquot volume (see Note 6). sample much more efficiently than flame atomization, the
Concentration range should not be extended by dilution. detection of low concentrations of elements in small sample
1.3 This test method determines total silica, and does not volumes is possible. Finally, the absorption signal during
distinguish between soluble and insoluble forms. atomization is recorded and compared to standards. A general
1.4 This test method was tested on reagent water only. It is guide for the application of the graphite furnace is given in
the user’s responsibility to assure the validity of the test Practice D 3919. Pretreatment of the graphite tube may be used
method for waters of other matrices. to enhance the sensitivity and repeatability, or both, of the test.
1.5 This standard does not purport to address the safety 4.2 Total silica is determined using a freshly ultrasonically
concerns, if any, associated with its use. It is the responsibility treated and shaken aliquot of sample.
of the user of this standard to establish appropriate safety and 4.3 This test method determines low-level total silica in
health practices and determine the applicability of regulatory high purity water. Refer to Test Method D 859, Method B, for
limitations prior to use. determination of molybdate-reactive silica.
2. Referenced Documents 5. Significance and Use
2.1 ASTM Standards: 5.1 Control of silica in boiler feedwater and boiler water is
D 859 Test Method for Silica in Water necessary to minimize the formation of scale-forming silicates
D 1066 Practice for Sampling Steam which decrease heat transfer in the boiler. Volatilization and
D 1129 Terminology Relating to Water carryover of silica with the steam may cause hard, glassy
D 1192 Specification for Equipment for Sampling Water siliceous deposits to form on turbine blades which reduce
and Steam in Closed Conduits turbine efficiency.
D 1193 Specification for Reagent Water 5.2 Colloidal silica which is not removed by boiler water
D 3370 Practices for Sampling Water from Closed Con- pretreatment processes may be solubilized in the boiler and
duits thus contribute to the dissolved silica concentration in the
D 3919 Practice for Measuring Trace Elements in Water by boiler. Both dissolved and total silica are of interest.
Graphite Furnace Atomic Absorption Spectrophotometry
2 6. Interferences
D 4453 Practice for Handling of Ultra-Pure Water Samples
6.1 For a complete discussion of general interferences with
3. Terminology
furnace procedures, the analyst is referred to Practice D 3919.
3.1 Definitions—For definitions of terms used in this test 6.2 Relatively pure water such as demineralizer effluent,
method, refer to Terminology D 1129. condensate, or high-pressure boiler feedwater are of sufficient
purity to minimize potential interferences such as sodium,
orthophosphate, or sulfate.
This test method is under the jurisdiction of ASTM Committee D-19 on Water
and is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
Water-Formed Deposits, Surveillance of Water, and Flow Measurement of Water. Rawa, Judith A. and Earl L. Henn, “Determination of Trace Silica in Industrial
Current edition approved Aug. 30, 1985. Published October 1985. Process Waters by Flameless Atomic Absorption Spectrometry,” Analytical Chem-
Annual Book of ASTM Standards, Vol 11.01. istry, Vol 51, March 1979.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4517 – 85 (1999)
6.3 Graphite tube pretreatment with the calcium/lanthanum 7.8 Flasks, volumetric, 100 and 1000-mL polyethylene.
reagent has been found to improve the silica response with
8. Reagents and Materials
some graphite tube materials or designs. Since response
8.1 Purity of Reagents—Reagent grade chemicals shall be
problems may include memory effects as well as poor sensi-
tivity, the following procedure must be used to determine used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the Commit-
whether pretreatment is needed.
6.3.1 Following instrument set-up and blank determination tee on Analytical Reagents of the American Chemical Society
where such specifications are available. Other grades may be
as described in 10.1-10.3, inject 10 to 12 replicates of a
standard containing 100 to 150 μg/L of SiO . Treat the tube in used, provided it is first ascertained that the reagent is of
sufficiently high purity to permit its use without lessening the
accordance with 6.4, and repeat. Note whether the response of
the two sets is constant, indicating no memory effect, or accuracy of the determination.
8.2 Purity of Water— All references to reagent water in this
whether the first set shows increasing response. Note also
whether the response of the second set is greater than that of method shall be understood to conform to Specification
D 1193, for reagent water Type II. In addition, the reagent
the first. If either sensitivity of repeatability is improved, tube
pretreatment is recommended. water shall be made silica-free and determined as such in
6.4 Pretreatment may be accomplished as follows: accordance with this method. The collecting apparatus and
6.4.1 Inject into the furnace the diluted calcium/lanthanum storage containers for the reagent water must be made of
reagent using the maximum aliquot recommended by the suitable materials that will not contaminate the reagent water
manufacturer of the tube, and start the atomization program. with silica (see Section 9).
Repeat three times, or more if necessary. Run blank atomiza-
NOTE 4—Silica-free water may be prepared by distillation, demineral-
tion cycles until the furnace blank is constant.
ization, and passage through a 0.22 μm filter. Total removal of colloidal
6.4.2 Proceed to calibrate the furnace and analyze samples
silica may be done by treating the above water with hydrofluoric acid,
in accordance with Sections 10 and 11. The absorbance letting it stand for 24 h, and then processing it through strong base
ion-exchange resin in the hydroxide form.
enhancement may deteriorate after numerous injections, in
which case retreatment will be required. Refer to Practice
8.3 Calcium/Lanthanum Reagent—Wet 2.90 g of lanthanum
D 3919.
oxide (La O 99.99 % pure) with about 50 mL of water in a
2 3
100 mL volumetric flask. Carefully add 5.5 mL of concentrated
7. Apparatus
nitric acid (HNO sp gr 1.42) and swirl to dissolve. Add 0.100
7.1 Atomic Absorption Spectrophotometer, for use at 251.6
g of calcium oxide (CaO) and swirl to dissolve. Dilute to
nm.
volume with water. This solution contains 100 mg/L CaO and
2500 mg/L La. Dilute 1:100 for injection. The diluted reagent
NOTE 1—A wavelength other than 251.6 nm may be used if it has been
determined to be equally suitable. is needed only for pretreatment of the graphite tube as
NOTE 2—The manufacturer’s instructions should be followed for all
described in 6.4.
instrument parameters.
8.4 Silica Stock Solution (1 mL = 1 mg SiO )— Dissolve
7.2 Silicon Light Source, silicon hollow cathode lamp. 4.7 g of sodium metasilicate (Na SiO ·9H O) and dilute to 1
2 3 2
L with water. Determine the silica concentration of this
7.3 Graphite Furnace, capable of reaching temperatures
sufficient to atomize the element of interest. Atomization solution in accordance with Test Method D 859, Method A.
8.5 Silica Working Solution (1 mL = 0.05 mg SiO )—Dilute
temperature must be
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.