ASTM D3868-15(2023)

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: D3868 − 15 (Reapproved 2023)
Standard Test Method for
Fluoride Ions in Brackish Water, Seawater, and Brines
This standard is issued under the fixed designation D3868; 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 D5847 Practice for Writing Quality Control Specifications
for Standard Test Methods for Water Analysis
1.1 This test method covers the determination of soluble
fluoride ions in brackish water, seawater and brines by use of
3. Terminology
a fluoride selective electrode.
3.1 Definitions—For definitions of terms used in this test
1.2 Samples containing from 1.0 to 25 mg/L can be ana-
method, refer to Terminology D1129.
lyzed by this test method.
1.3 The values stated in SI units are to be regarded as
4. Summary of Test Method
standard. No other units of measurement are included in this
4.1 A fluoride selective electrode, reference electrode, and
standard.
millivoltmeter are used to determine fluoride in brine samples
1.4 This standard does not purport to address all of the
by a standard addition method.
safety concerns, if any, associated with its use. It is the
4.2 The fluoride selective electrode consists of a lanthanum
responsibility of the user of this standard to establish appro-
fluoride crystal that develops an electrode potential corre-
priate safety, health, and environmental practices and deter-
sponding to the level of fluoride ion in solution.
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor-
5. Significance and Use
dance with internationally recognized principles on standard-
5.1 Identification of a brackish water, seawater, or brine is
ization established in the Decision on Principles for the
determined by comparison of the concentrations of their
Development of International Standards, Guides and Recom-
dissolved constituents. The results are used to evaluate the
mendations issued by the World Trade Organization Technical
origin of the water, determine if it is a possible pollutant, or if
Barriers to Trade (TBT) Committee.
it is related to a potential source of a valuable mineral. For
2. Referenced Documents
example, in geochemical studies some correlation data indicate
3 that fluoride is an indirect indicator of the presence of lithium.
2.1 ASTM Standards:
D1129 Terminology Relating to Water
6. Interferences
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of 6.1 Metal ions such as aluminum and iron (III) interfere
Applicable Test Methods of Committee D19 on Water with the fluoride determination by forming complexes with
D3370 Practices for Sampling Water from Flowing Process fluoride ions. The buffer solution contains a complexing agent
Streams that preferentially complexes these metal ions. This solution
also contains a pH buffer to reduce electrode interference from
hydroxide ions and to prevent the formation of HF. Sodium
This test method is under the jurisdiction of ASTM Committee D19 on Water
chloride is added as ionic strength adjustor. Increasing amounts
and is the direct responsibility of D19.05 on Inorganic Constituents in Water.
of aluminum, iron (III), and borate ions were added to
Current edition approved April 1, 2023. Published April 2023. Originally
1.5 mg ⁄L fluoride solutions and were found not to interfere up
approved in 1979. Last previous edition approved in 2015 as D3868 – 15. DOI:
10.1520/D3868-15R23. to 5, 350, and 250 mg/L (as boron), respectively.
Additional information is contained in the following references: Hoke, S. H.,
Fletcher, G. E., and Collins, A. G., “Fluoride and Iodide Selective Electrodes
7. Apparatus
Applied to Oilfield Brine Analysis,” U.S. Department of Energy, Report of
Investigations, BETC/RI-78/7.Rix, C. J., Bond, A. M., and Smith, J. D., “District
7.1 Millivoltmeter (accurate to 60.1 mV), specific ion
Determination of Fluoride in Sea Water with a Fluoride Selective Ion Electrode by
meter.
a Method of Standard Additions,” Analytical Chemistry, Vol 48, 1976, p. 1236.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
NOTE 1—A specific ion meter that directly reads concentration may be
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
used.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 7.2 Fluoride Selective Electrode, reference electrode.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3868 − 15 (2023)
TABLE 1 Determination of Precision and Bias
7.3 Microlitre Pipets.
Amount Added Amount Found S S
t o
Bias%
8. Reagents mg/L mg/L mg/L mg/L
3.03 3.68 1.051 0.439 + 21.4
8.1 Purity of Reagents—Reagent grade chemicals shall be
4.09 5.89 1.208 0.253 + 44.1
19.4 12.14 1.596 0.972 −37.4
used in all tests. Unless otherwise indicated, it is intended that
20.5 23.42 2.383 1.570 + 14.2
all reagents shall conform to the specification of the Committee
on Analytical Reagents of the American Chemical Society,
where such specifications are available. Other grades may be
used, provided it is first ascertained that the reagent is of
sufficiently high purity to permit its use without lessening the
where:
accuracy of the determination.
A and B = two fluoride solutions of known concentration,
8.2 Purity of Water—Unless otherwise indicated, reference mg/L,
E = electrode potential of Solution A mV, and
to water shall be understood to mean reagent water conforming
A
E = electrode potential of Solution B, mV.
to Specification D1193, Type I. Other reagent water types may B
NOTE 2—The slope of the electrode should meet the manufacturer’s
be used provided it is first ascertained that the water is of
specifications.
sufficiently high purity to permit its use without adversely
11.2 Calculate the concentration of fluoride in the sample as
affecting the precision and bias of the test method. Type III
follows:
water was specified at the time of round robin testing of this
test method.
Xf
A 5 mg/L 5 × 1000 (2)
ΔE
8.3 Buffer Solution —Dissolve 58 g of NaCl, 4 g of CDTA
antilog 2 1
S D
slope
complexing agent (cyclohexylene dinitrilo tetraacetic acid),
and 57 mL of glacial acetic acid in 500 mL of water. Slowly
where:
add NaOH solution (200 g/L) to adjust the pH of the solution
X = change in concentration upon addition of standard
to 5.0 to 5.5 while cooling in a water bath. Transfer solution to
−
(mg F added per 80 mL of solution),
a 1-L volumetric flask and dilute to the mark with water.
f = dilution factor (80 mL/mL of sample), and
−
8.4 Fluoride Solution, Standard (1 mL = 2 mg F )— ΔE = change in potential resulting from addition of
Dissolve 4.420 g of NaF in water and dilute to 1 L and store in standard.
a polyethylene bottle. This solution will contain 2000 mg of
From the above procedure, two A values can be calculated
−
F /L. Alternatively, certified fluoride stock solutions are com-
and averaged for each sample.
mercially available through chemical supply vendors and may
be used.
12. Precision and Bias
12.1 The precision of the test method within its designated
9. Sampling
range may be expressed as follows:
9.1 Collect the sample in accordance with Practices D3370.
S 5 0.08X10.73 (3)
T
10. Procedure
S 5 0.063X10.097
c
10.1 Pipet an aliquot of a brine sample containing 0.01 to
where:
0.03 mg of fluoride into a 125-mL polyethylene beaker and if
S = overall precision,
necessary add water to make the total volume equal 40 mL. T
S = single-operator precision, and
o
Add 40 mL of buffer solution. Place electrodes in the solution
X = concentration of fluoride determined, mg/L.
to a depth of 30 mm. Stir solution for 5 min or until equilibrium
is reached. Stop the stirrer and record the potential. Add 20 μL
12.2 The bias
...