ASTM D513-92(1996)

Designation: D 513 – 92 (Reapproved 1996)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Methods for
Total and Dissolved Carbon Dioxide in Water
This standard is issued under the fixed designation D 513; 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 age of Standard and Reagent Solutions for Chemical
Analysis
1.1 These test methods provide for the measurement of total
or dissolved carbon dioxide present as carbon dioxide (CO ),
2 3. Terminology
carbonic acid, bicarbonate ion, and carbonate ion in water:
3.1 Definitions—For definitions of terms used in these test
Range Sections
methods, refer to Terminology D 1129.
Test Method A (Gas Sensing Electrode) 2 to 800 mg/L 8 to 15
Test Method B (CO Evolution, Coulometric 5 to 800 mg/L 16 to 24
4. Significance and Use
Titration)
4.1 Carbon dioxide is a major respiration product of plants
1.2 Carbon dioxide may also be detected from carbonates
and animals and a decomposition product of organic matter and
present in particulates in samples.
certain minerals. The atmosphere averages about 0.04 vol % of
1.3 Test Method A is applicable to various natural waters
CO . Surface waters generally contain less than 10 mg/L,
and brines.
except at local points of abnormal organic or mineral decom-
1.4 Test Method B is applicable to natural waters, brines,
position; however, underground water, particularly deep wa-
and various industrial waters as delineated in 16.4.
ters, may contain several hundred mg/L.
1.5 It is the user’s responsibility to ensure the validity of
4.2 When dissolved in water, CO contributes significantly
these test methods on waters of untested matrices.
to corrosion of water-handling systems. This is particularly
1.6 Several test methods were discontinued from this stan-
troublesome in steam condensate systems. Loss of CO from
dard in 1988. Refer to Appendix X1 for historical information.
an aqueous system can disturb the carbonate equilibrium and
1.7 This standard does not purport to address all of the result in calcite encrustation of confining surfaces. Scaling of
safety concerns, if any, associated with its use. It is the water heaters is a good example. Because of the delicate
responsibility of the user of this standard to establish appro- balance between corrosion and encrustation tendencies, much
priate safety and health practices and determine the applica- care must be given to control of CO and related species in
bility of regulatory limitations prior to use. water systems. Recarbonation of municipal supplies during
final stages of softening and amine neutralization of steam
2. Referenced Documents condensate are applied for these purposes.
2.1 ASTM Standards:
5. Purity of Reagents
D 1066 Practice for Sampling Steam
5.1 Reagent grade chemicals shall be used in all tests.
D 1129 Terminology Relating to Water
Unless otherwise indicated, it is intended that all reagents shall
D 1192 Specification for Equipment for Sampling Water
conform to the specifications of the Committee on Analytical
and Steam in Closed Conduits
Reagents of the American Chemical Society. Other grades
D 1193 Specification for Reagent Water
may be used, provided it is first ascertained that the reagent is
D 1293 Test Methods for pH of Water
of sufficiently high purity to permit its use without lessening
D 2777 Practice for Determination of Precision and Bias of
the accuracy of the determination.
Applicable Methods of Committee D-19 on Water
5.2 Unless otherwise indicated, references to water shall be
D 3370 Practices for Sampling Water from Closed Con-
understood to mean water conforming to Type I of Specifica-
duits
tion D 1193. Additionally, for those test methods requiring
E 200 Practice for Preparation, Standardization, and Stor-
water free of CO , refer to 8.2 of Practice E 200.
Annual Book of ASTM Standards, Vol 15.05.
These test methods are under the jurisdiction of ASTM Committee D-19 on
Reagent Chemicals, American Chemical Society Specifications, American
Water and are the direct responsibility of Subcommittee D19.05 on Inorganic Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Constituents in Water. listed by the American Chemical Society, see Analar Standards for Laboratory
Current edition approved Oct. 15, 1992. Published December 1992. Originally Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
published as D 513 – 38. Last previous edition D 513 – 88. and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
Annual Book of ASTM Standards, Vol 11.01. MD.
D 513
6. Precautions tional to the concentration of CO . The diffusion of CO across
2 2
the membrane affects the concentration of hydrogen ions in the
6.1 Caution—Carbon dioxide is easily lost from solution
internal filling solution:
during transit and storage of samples. It is also possible for
1 2
total CO concentration to increase after sampling due to
2 CO 1 H ON H 1 HCO
2 2 3
solution of finely divided calcium carbonate as a result of
The hydrogen ion concentration of the internal solution is
temperature or pressure changes.
measured by the pH electrode located behind the membrane.
Since the hydrogen ion concentration is directly related to CO
7. Sampling 2
concentration, the electrode response is Nernstian.
7.1 Collect the sample in accordance with Practices D 1066
9.2 Samples are treated prior to measurement with a buffer
and D 3370 and Specification D 1192, as applicable.
solution that sets the pH between 4.8 and 5.2. At this pH,
7.2 Filter samples when they are collected if particulates are
interferences are minimized and the various ionic forms are
present that may contain carbonates if dissolved species only
converted to CO (see Section 10).
are to be determined. When aliquots of sample are taken from
sample bottles containing particulates, the bottle must be
10. Interferences
shaken or otherwise homogenized to ensure a representative
10.1 Volatile weak acids are potential positive electrode
sample is taken. When particulates form in samples due to
interferences. Concentrations of these interfering species that
changes in temperature, pH, etc., after the sample has been
cause a 10 % error at 44 mg/L CO or 100 mg/L (as CaCO )
2 3
collected, these particulates must be included in tests of the
and at pH 4 and 5, are listed below:
sample. Care must be used to avoid loss of CO during any
Interferences, mg/L pH 5 pH 4
homogenization of filtration of samples. Do not filter samples
HS10 7
unless it is required to remove potentially interfering particu-
−
NO (NO ) 161 24
2 2
−
lates.
HSO (SO ) 320 (as SO ) 48 (as SO )
3 2 2 2
HOAc (acetic acid) 372 216
7.3 Use a hard, glass, chemically resistant bottle for collect-
HCOOH (formic acid) 1841 345
ing the sample.
10.2 Samples containing sulfide can be treated with dilute
7.4 Fill the sample bottle completely, with no air space
solutions of potassium dichromate (or the like), since sulfur is
remaining beneath the cap, and store the sample at a tempera-
not an interference for this test method. However, it is possible
ture below that at which it was collected until the determination
that some organic material could be oxidized to CO by this
is made.
treatment, resulting in falsely high results. The suitability of the
TEST METHOD A—GAS SENSING ELECTRODE
test method for samples containing sulfide should be
TEST METHOD
determined individually.
10.3 Water vapor is a potential electrode interference. Water
8. Scope
can move across the membrane as water vapor, changing the
8.1 This test method determines total or dissolved carbon
concentration of the internal filling solution under the
dioxide (9.2) present as CO , carbonic acid, bicarbonate ion,
membrane. Such changes will be seen as electrode drift. Water
and carbonate ion in water, within the interference constraints
vapor transport is not a problem if (1) the total concentration of
specified.
dissolved species in solution (Note 1) is approximately equal to
8.2 Samples containing 2 to 800 mg/L total CO can be
that of the internal filling solution, and (2) electrode and
analyzed by this test method. The concentration range may be
sample temperatures are the same.
extended by dilution of an appropriate aliquot.
NOTE 1—The osmotic strength of a solution is related to the total
8.3 Samples should be analyzed immediately. If this is not
concentration of dissolved species in the solution. For example, the
possible, preserve by making them slightly alkaline (pH
osmotic strength of a solution containing 0.1 M hydrochloric acid, 0.1 M
between 8 and 9) using carbonate-free NaOH solution and
acetic acid, and 0.1 M sucrose is determined as follows: Hydrochloric acid
store them in a tightly capped vessel. The latter step prevents
dissociates to give 0.1 M hydrogen ion and 0.1 M chloride ion. The acetic
absorption of CO from the air. acid, because of the concentration of free hydrogen ion, is essentially
undissociated; thus giving 0.1 M of species. Likewise, the concentration of
8.4 The precision and bias were obtained on reagent water
sucrose species is 0.1 M. Therefore, the total osmotic strength is 0.4
and a water matrix of choice that included natural waters and
osmolar.
brines. It is the responsibility of the analyst to determine the
10.4 Addition of carbon dioxide buffer (12.1) to samples of
acceptability of this test method for the water being analyzed.
low osmotic strength automatically adjusts them to the correct
9. Summary of Test Method
level. Samples with osmotic strength greater than
9.1 Carbon dioxide is liberated by acidification of the approximately 1 M should be diluted before measurement to
sample to pH 5.0. The carbon dioxide electrode uses a avoid drifting associated with water vapor transport. Dilution
gas-permeable membrane to separate the sample solution from should not reduce the carbon dioxide level below 2.5 mg/L.
the electrode internal solution. Dissolved carbon dioxide in the Samples with osmotic strengths above 1 M that cannot be
sample solution diffuses through the membrane until an equi- diluted can be measured by adjusting the osmotic strength of
librium is reached between the partial pressure of CO in the the internal filling solution. To adjust the total concentration of
sample solution and the CO in the internal filling solution. In dissolved species in the internal filling solution, add 0.425 g of
any given sample, the partial pressure of CO will be propor- reagent-grade NaNO to 10 mL of internal filling solution.
2 3
D 513
11. Apparatus 14. Procedure
11.1 pH Meter, with expanded mV scale, or a selective ion 14.1 Bring samples to the same temperature as the electrode
and standards.
meter.
14.2 Place a known volume, V , (100 mL is convenient) of
11.2 CO Gas-Sensing Electrode .
s
sample in 150-mL beaker and stir slowly. Immerse the
11.3 Mixer, magnetic with TFE-fluorocarbon-coated stirring
electrode in the solution.
bar or equivalent.
14.3 Add 1 mL of buffer, V , for each 10 mL of sample.
b
Allow the potential reading to stabilize and record the value.
12. Reagents
Read the concentration measured, C , directly from the
m
12.1 Buffer Solution— Dissolve 294 g of sodium citrate in
calibration curve.
approximately 700 mL of water in a 1-L volumetric flask.
14.4 Determine the sample concentration, C , as follows:
s
Acidify the solution to pH 4.5 with concentrated HCl
V 1 V
(approximately 90 mL) and dilute to the mark with water.
s b
C 5 C
s m
V
s
12.2 Sodium Bicarbonate Solution, Standard (0.1 M)—
Dissolve 8.40 g of sodium bicarbonate in water and dilute to 1
15. Precision and Bias
L.
15.1 Precision—The overall and single operator precision
12.3 Sodium Bicarbonate Solution, Standard (0.01 M)—
of this test method, within its designated range, varies with the
Dilute 10.0 mL of sodium bicarbonate standard solution (0.1
quantity tested as shown in Fig. 1 for reagent water and Fig. 2
M) to 100 mL.
for selected water matrices. These matrices included natural
waters and brines.
13. Calibration and Standardization
15.2 Bias—Recoveries of known amounts of total CO
13.1 Assemble and check the electrode in accordance with
from reagent water and selected water matrices were as shown
the manufacturer’s instructions.
in Table 1.
13.2 Dilute 10 mL of the buffer solution to 100 mL with
15.3 The information in 15.1 and 15.2 is derived from
water using a volumetric flask. Transfer the contents of the
round-robin testing in which eight laboratories, including
flask to a 150-mL beaker and add a stirring bar. Immerse the
twelve independent operators, participated. Of twelve data sets
electrode in the solution. Stir at a slow rate using the magnetic
ranked as described in Practice D 2777, four were rejected in
stirrer.
the case of reagent water and three were rejected in the case of
13.3 Using a volumetric pipet, add 0.5 mL of the 0.01 M
selected water matrices. Four outlier data points were also
NaHCO standard solution and mix slowly. Allow the potential
rejected. Four sample levels were run on three days, and blanks
reading to stabilize (approximately 10 min) and record the
were obtained for the waters used.
potential (corresponds to 2.2 mg/L CO or 5.0 mg/L (as
CaCO )).
TEST METHOD B—CO EVOLUTION,
13.4 Using a volumetric pipet, add 0.5 mL of the 0.01 M
COULOMETRIC TITRATION TEST METHOD
NaHCO standard solution and mix slowly. Allow the potential
16. Scope
reading to stabilize (approximately 5 min) and record the
potential (corresponds to 4.4 mg/L CO or 10.0 mg/L (as
16.1 This test method determines total or dissolved carbon
CaCO )).
dioxide present as carbon dioxide, carbonic acid, bicarbonate
13.5 Using a volumetric pipet, add 0.9 mL of the 0.1 M
ion, and carbonate ion in water within the interference
NaHCO standard solution and mix slowly. Allow the potential
constraints specified.
reading to stabilize (approximately 2 min) and record the
16.2 Carbon dioxide will also be detected from carbonates
potential (corresponds to 43.2 mg/L CO or 98.1 mg/L (as
present in particulates in samples.
CaCO )).
16.3 Samples containing between 5 and 800 mg/L total CO
13.6 Using a volumetric pipet, add 10 mL of the 0.1 M
can be analyzed by this test method. The concentration range
NaHCO standard solution and mix slowly. Allow the potential may be extended upward by use of smaller samples or dilution
reading to stabilize (approximately 2 min) and record the
of an appropriate aliquot. The range may be extended lower by
po
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