ASTM D4517-15(2023)
(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
SIGNIFICANCE AND USE
5.1 Control of silica in boiler feedwater and boiler water is necessary to minimize the formation of scale-forming silicates that decrease heat transfer in the boiler. Volatilization and carryover of silica with the steam may cause hard, glassy siliceous deposits to form on turbine blades that reduce turbine efficiency.
5.2 Colloidal silica that is not removed by boiler water pretreatment processes may be solubilized in the boiler and thus contribute to the dissolved silica concentration in the boiler. Both dissolved and total silica are of interest.
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 μg/L to 250 μg/L of silica as SiO2. 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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4517 − 15 (Reapproved 2023)
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 D4517; 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 D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
1.1 This test method covers the determination of total silica
D1192 Guide for Equipment for Sampling Water and Steam
in water.
in Closed Conduits (Withdrawn 2003)
1.2 This test method is applicable in the range from 25 μg ⁄L
D1193 Specification for Reagent Water
to 250 μg ⁄L of silica as SiO . Higher concentrations may be
D2777 Practice for Determination of Precision and Bias of
determined by decreasing the aliquot volume (see Note 6).
Applicable Test Methods of Committee D19 on Water
Concentration range should not be extended by dilution.
D3370 Practices for Sampling Water from Flowing Process
1.3 This test method determines total silica, and does not Streams
D3919 Practice for Measuring Trace Elements in Water by
distinguish between soluble and insoluble forms.
Graphite Furnace Atomic Absorption Spectrophotometry
1.4 This test method was tested on reagent water only. It is
D4453 Practice for Handling of High Purity Water Samples
the user’s responsibility to assure the validity of the test
D5810 Guide for Spiking into Aqueous Samples
method for waters of other matrices.
D5847 Practice for Writing Quality Control Specifications
1.5 The values stated in SI units are to be regarded as
for Standard Test Methods for Water Analysis
standard. No other units of measurement are included in this
standard.
3. Terminology
1.6 This standard does not purport to address all of the
3.1 Definitions:
safety concerns, if any, associated with its use. It is the
3.1.1 For definitions of terms used in this standard, refer to
responsibility of the user of this standard to establish appro-
Terminology D1129.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
4. Summary of Test Method
1.7 This international standard was developed in accor-
dance with internationally recognized principles on standard- 4.1 Total silica is determined using an atomic absorption
ization established in the Decision on Principles for the spectrophotometer in conjunction with a graphite furnace. A
Development of International Standards, Guides and Recom- sample is placed in a graphite tube, evaporated to dryness,
mendations issued by the World Trade Organization Technical charred, and atomized. Since the graphite furnace uses the
Barriers to Trade (TBT) Committee. sample much more efficiently than flame atomization, the
detection of low concentrations of elements in small sample
2. Referenced Documents
volumes is possible. Finally, the absorption signal during
atomization is recorded and compared to standards. A general
2.1 ASTM Standards:
guide for the application of the graphite furnace is given in
D859 Test Method for Silica in Water
Practice D3919. Pretreatment of the graphite tube may be used
to enhance the sensitivity and repeatability, or both, of the test.
This test method is under the jurisdiction of ASTM Committee D19 on Water
4.2 Total silica is determined using a freshly ultrasonically
and is the direct responsibility of Subcommittee D19.03 on Sampling Water and
treated and shaken aliquot of sample.
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use,
On-Line Water Analysis, and Surveillance of Water.
Current edition approved April 1, 2023. Published April 2023. Originally
approved in 1985. Last previous edition approved in 2015 as D4517 – 15. DOI:
10.1520/D4517-15R23. The last approved version of this historical standard is referenced on
For referenced ASTM standards, visit the ASTM website, www.astm.org, or www.astm.org.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Rawa, J. A., and Henn, E. L., “Determination of Trace Silica in Industrial
Standards volume information, refer to the standard’s Document Summary page on Process Waters by Flameless Atomic Absorption Spectrometry,” Analytical
the ASTM website. Chemistry, Vol 51, March 1979.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4517 − 15 (2023)
4.3 This test method determines low-level total silica in 7.2 Silicon Light Source, silicon hollow cathode lamp.
high purity water. Refer to Test Method D859, Test Method B,
7.3 Graphite Furnace, capable of reaching temperatures
for determination of molybdate-reactive silica.
sufficient to atomize the element of interest. Atomization
temperature must be reached as rapidly as possible for maxi-
5. Significance and Use
mum sensitivity.
5.1 Control of silica in boiler feedwater and boiler water is
NOTE 3—Special furnace accessories are commercially available to
necessary to minimize the formation of scale-forming silicates
provide a means of accelerating atomization temperature.
that decrease heat transfer in the boiler. Volatilization and
7.4 Graphite Tubes, compatible with furnace device. Stan-
carryover of silica with the steam may cause hard, glassy
dard graphite tubes are preferred, particularly when tube
siliceous deposits to form on turbine blades that reduce turbine
pretreatment is practiced. Pyrolytic graphite tubes may be used
efficiency.
if it has been determined by the analyst that the precision, bias,
5.2 Colloidal silica that is not removed by boiler water
and sensitivity of the determination are not compromised.
pretreatment processes may be solubilized in the boiler and
7.5 Pipets:
thus contribute to the dissolved silica concentration in the
7.5.1 Microlitre, with disposable, polypropylene tips. Sizes
boiler. Both dissolved and total silica are of interest.
may range from 1 μL to 1000 μL, as required.
7.5.2 Millilitre, 50.0 mL.
6. Interferences
7.6 Data System—Fast transient signal data are collected
6.1 For a complete discussion of general interferences with
and processed using an internal microprocessor or external
furnace procedures, the analyst is referred to Practice D3919.
desktop computer systems. Data can be stored on disks,
6.2 Relatively pure waters such as demineralizer effluent,
transmitted to central servers, or printed in hard copy. Data
condensate, or high-pressure boiler feedwater are of sufficient
may be evaluated and processed using the instrument’s dedi-
purity to minimize potential interferences such as sodium,
cated systems to determine analyte concentrations. Users of
orthophosphate, or sulfate.
this practice may use a strip chart recorder to obtain sample and
6.3 Graphite tube pretreatment with the calcium/lanthanum
calibration data, if desired.
reagent has been found to improve the silica response with
7.7 Ultrasonic Cleaner, operable at >20 KHz.
some graphite tube materials or designs. Since response
7.8 Flasks, volumetric, 100 mL and 1000 mL polyethylene.
problems may include memory effects as well as poor
sensitivity, the following procedure must be used to determine
8. Reagents and Materials
whether pretreatment is needed.
6.3.1 Following instrument set-up and blank determination
8.1 Purity of Reagents—Reagent grade chemicals shall be
as described in 10.1 – 10.3, inject 10 to 12 replicates of a
used in all tests. Unless otherwise indicated, it is intended that
standard containing 100 μg ⁄L to 150 μg ⁄L of SiO . Treat the
2 all reagents shall conform to the specifications of the Commit-
tube in accordance with 6.4, and repeat. Note whether the
tee on Analytical Reagents of the American Chemical Society
response of the two sets is constant, indicating no memory
where such specifications are available. Other grades may be
effect, or whether the first set shows increasing response. Note
used, provided it is first ascertained that the reagent is of
also whether the response of the second set is greater than that
sufficiently high purity to permit its use without lessening the
of the first. If either sensitivity of repeatability is improved,
accuracy of the determination.
tube pretreatment is recommended.
8.2 Purity of Water—All references to reagent water in this
6.4 Pretreatment may be accomplished as follows:
method shall be understood to conform to Specification D1193,
6.4.1 Inject into the furnace the diluted calcium/lanthanum
for reagent water Type II. In addition, the reagent water shall
reagent using the maximum aliquot recommended by the
be made silica-free and determined as such in accordance with
manufacturer of the tube, and start the atomization program.
this method. The collecting apparatus and storage containers
Repeat three times, or more if necessary. Run blank atomiza-
for the reagent water must be made of suitable materials that
tion cycles until the furnace blank is constant.
will not contaminate the reagent water with silica (see Section
6.4.2 Proceed to calibrate the furnace and analyze samples
9).
in accordance with Sections 10 and 11. The absorbance
NOTE 4—Silica-free water may be prepared by distillation,
enhancement may deteriorate after numerous injections, in
demineralization, and passage through a 0.22 μm filter. Total removal of
which case retreatment will be required. Refer to Practice
colloidal silica may be done by treating the above water with hydrofluoric
D3919.
acid, letting it stand for 24 h, and then processing it through strong base
ion-exchange resin in the hydroxide form.
7. Apparatus
7.1 Atomic Absorption Spectrophotometer, for use at
251.6 nm. ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, American Chemical Society, Washington,
NOTE 1—A wavelength other than 251.6 nm may be used if it has been
DC. For suggestions on the testing of reagents not listed by the American Chemical
determined to be equally suitable.
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
NOTE 2—The manufacturer’s instructions should be followed for all U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
instrument parameters. copeial Convention, Inc. (USPC), Rockville, MD.
D4517 − 15 (2023)
NOTE 6—While sample size and furnace programming vary among
8.3 Calcium/Lanthanum Reagent—Wet 2.90 g of lanthanum
instruments, the following analytical conditions have generally been
oxide (La O 99.99 % pure) with about 50 mL of water in a
2 3
found to be suitable. It is up to the analyst to optimize analytical
100 mL volumetric flask. Carefully add 5.5 mL of concentrated
conditions for the instrument used.
nitric acid (HNO sp gr 1.42) and swirl to dissolve. Add
Aliquot—An aliquot size of 10 μL to 100 μL, depending on tube size
0.100 g of calcium oxide (CaO) and swirl to dissolve. Dilute to
and concentration of sample. The same aliquot size must be used for all
volume with water. This solution contains 100 mg/L CaO and standard, sample, and blank injections.
2500 mg/L La. Dilute 1:100 for injection. The diluted reagent
Function Temperature, °C Time, s
Dry 100 1 s/μL
is needed only for pretreatment of the graphite tube as
Char 1000 30
described in 6.4.
Atomize 2800 7
8.4 Silica Stock Solution (1 mL = 1 mg SiO )—Dissolve
10.4 Determine the furnace blank by initiating the atomiza-
4.7 g of sodium metasilicate (Na SiO ·9H O) and dilute to 1 L
2 3 2
tion program without making an injection. Repeat until the
with water. Determine the silica concentration of this solution
furnace blank reproduces within 10 %.
in accordance with Test Method D859, Test Method A.
NOTE 7—Determination of the furnace blank is a mechanism for
8.5 Silica Working Solution (1 mL = 0.05 mg SiO )—Dilute
evaluating the acceptability of the graphite tube for silica determination.
50.0 mL of the silica stock solution (see 8.4) to 1 L with water
in a volumetric flask. The concentration of this diluted standard
10.5 Inject a measured aliquot of the 100 μg/L of SiO
is calculated after confirming the concentration of the stock
standard solution (see 10.1) into the furnace, and initiate the
solution.
present atomization program. Repeat this analysis until the
response reproduces within 10 %.
8.6 Argon, standard, welder’s grade, commercially avail-
able.
10.6 Determine the acceptability of the water by injecting a
measured aliquot of the “0” standard solution into the furnace
9. Sampling
and initiating the preset atomization program. Repeat this
9.1 Collect the sample in accordance with the applicable analysis until the response reproduces within 10 %.
ASTM standards: Practice D1066, Guide D1192, Practices
10.7 Inject a measured aliquot of each of the remaining
D3370, and Practice D4453.
standard solutions as described in 10.5.
9.2 Since silica is such a ubiquitous material, meticulous
10.8 Prepare a calibration curve by plotting absorbance or
sample collection, handling, and injection into the furnace are
peak height versus concentration as micrograms per litre of
necessary to avoid contamination.
SiO on linear paper if direct readout in terms of concentration
9.2.1 Collect samples only in plastic or TFE-fluorocarbon 2
is not possible with the instrument.
containers. Polystyrene, polypropylene, linear polyethylene,
and TFE-fluorocarbon have been found to be generally
suitable, but tests should be conducted on sample containers 11. Procedure
before use to determine their suitability.
11.1 Rinse the microlitre pipet with water and inject an
9.2.2 Sample containers must be ultrasonically cleaned
aliquot of water to test pipet and furnace cleanliness before
before use. Fill the sample containers with water and immerse
sample analysis. After samples containing a high concentration
in an operating ultrasonic cleaner for at least 1 min. Remove,
of silica are analyzed, additional atomization cycles may be
shake vigorously, and drain. Additional cycles of cleaning may
needed to reduce the furnace blank to prior level.
be found necessary.
9.2.3 Before actual sample collection, rinse sample con-
11.2 Ultrasonicate for at least 1 min and then vigorously
tainer with the sample it is to contain three times with vigorous
shake sample. Immediately withdraw an aliquot (refer to 10.3
shaking, then fill. Do not allow any object to touch the insid
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