ASTM D513-16

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Designation: D513 − 11 D513 − 16
Standard Test Methods for
Total and Dissolved Carbon Dioxide in Water
This standard is issued under the fixed designation D513; 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.
ε NOTE—This test method was changed editorially in February 2012.
1. Scope*
1.1 These test methods cover the measurement of total or dissolved carbon dioxide present as carbon dioxide (CO ), carbonic
acid, bicarbonate ion, and carbonate ion in water:
Range Sections
Test Method A (Gas Sensing Electrode) 2 to 800 mg/L 8 to 15
Test Method B (CO Evolution, Coulometric Titration) 5 to 800 mg/L 16 to 24
Range Sections
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
Titration)
1.2 Carbon dioxide may also be detected from carbonates present in particulates in samples.
1.3 Test Method A is applicable to various natural waters and brines.
1.4 Test Method B is applicable to natural waters, brines, and various industrial waters as delineated in 16.4.
1.5 It is the user’s responsibility to ensure the validity of these test methods on waters of untested matrices.
1.6 Several test methods were discontinued from this standard in 1988. Refer to Appendix X1 for historical information.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D1293 Test Methods for pH of Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
E200 Practice for Preparation, Standardization, and Storage of Standard and Reagent Solutions for Chemical Analysis
3. Terminology
3.1 DefinitionsDefinitions:—For
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129. definitions of terms used in these test methods,
refer to Terminology D1129.
These test methods are under the jurisdiction of ASTM Committee D19 on Water and are the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
Current edition approved April 1, 2011June 15, 2016. Published April 2011June 2016. Originally approved in 1938. Last previous edition approved in 20062011 as
ɛ1
D513 – 06.D513 – 11 . DOI: 10.1520/D0513-11E01.10.1520/D0513-16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
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D513 − 16
4. Significance and Use
4.1 Carbon dioxide is a major respiration product of plants and animals and a decomposition product of organic matter and
certain minerals. The atmosphere averages about 0.04 vol % of CO . Surface waters generally contain less than 10 mg/L, except
at local points of abnormal organic or mineral decomposition; however, underground water, particularly deep waters, may contain
several hundred mg/L.
4.2 When dissolved in water, CO contributes significantly to corrosion of water-handling systems. This is particularly
troublesome in steam condensate systems. Loss of CO from an aqueous system can disturb the carbonate equilibrium and result
in calcite encrustation of confining surfaces. Scaling of water heaters is a good example. Because of the delicate balance between
corrosion and encrustation tendencies, much care must be given to control of CO and related species in water systems.
Recarbonation of municipal supplies during final stages of softening and amine neutralization of steam condensate are applied for
these purposes.
5. Purity of Reagents
5.1 Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform
to the specifications of the Committee on Analytical Reagents of the American Chemical Society. 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 accuracy of the
determination.
5.2 Unless otherwise indicated, references to water shall be understood to mean water conforming to Type I of Specification
D1193. Other reagent water types may be used provided it is first ascertained that the water is of sufficiently high purity to permit
its use without adversely affecting the bias and precision of the test method. Additionally, for those test methods requiring water
free of CO , refer to 8.2 of Practice E200.
6. Precautions
6.1 Warning—Carbon dioxide is easily lost from solution during transit and storage of samples. It is also possible for total CO
concentration to increase after sampling due to solution of finely divided calcium carbonate as a result of temperature or pressure
changes.
7. Sampling
7.1 Collect the sample in accordance with PracticesPractice D1066 and Practices D3370, as applicable.
7.2 Filter samples when they are collected if particulates are present that may contain carbonates if dissolved species only are
to be determined. When aliquots of sample are taken from sample bottles containing particulates, the bottle must be shaken or
otherwise homogenized to ensure a representative sample is taken. When particulates form in samples due to changes in
temperature, pH, etc., after the sample has been collected, these particulates must be included in tests of the sample. Care must
be used to avoid loss of CO during any homogenization of filtration of samples. Do not filter samples unless it is required to
remove potentially interfering particulates.
7.3 Use a hard, glass, chemically resistant bottle for collecting the sample.
7.4 Fill the sample bottle completely, with no air space remaining beneath the cap, and store the sample at a temperature below
that at which it was collected until the determination is made.
TEST METHOD A—GAS SENSING ELECTRODE SENSING ELECTRODE TEST METHOD
8. Scope
8.1 This test method determines total or dissolved carbon dioxide (14.3) present as CO , carbonic acid, bicarbonate ion, and
carbonate ion in water, within the interference constraints specified.
8.2 Samples containing 2 to 800 mg/L total CO can be analyzed by this test method. The concentration range may be extended
by dilution of an appropriate aliquot.
8.3 Samples should be analyzed immediately. If this is not possible, preserve by making them slightly alkaline (pH between 8
and 9) using carbonate-free NaOH solution and store them in a tightly capped vessel. The latter step prevents absorption of CO
from the air.
8.4 The precision and bias were obtained on reagent water and a water matrix of choice that included natural waters and brines.
It is the responsibility of the analyst to determine the acceptability of this test method for the water being analyzed.
Reagent Chemicals, American Chemical Society Specifications , American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed by
the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D513 − 16
9. Summary of Test Method
9.1 Carbon dioxide is liberated by acidification of the sample to pH 5.0. The carbon dioxide electrode uses a gas-permeable
membrane to separate the sample solution from the electrode internal solution. Dissolved carbon dioxide in the sample solution
diffuses through the membrane until an equilibrium is reached between the partial pressure of CO in the sample solution and the
CO in the internal filling solution. In any given sample, the partial pressure of CO will be proportional to the concentration of
2 2
CO . The diffusion of CO across the membrane affects the concentration of hydrogen ions in the internal filling solution:
2 2
→
1 2
CO 1H O H 1HCO
2 2 3
←
9.2 The hydrogen ion concentration of the internal solution is measured by the pH electrode located behind the membrane. Since
the hydrogen ion concentration is directly related to CO concentration, the electrode response is Nernstian.
9.3 Samples are treated prior to measurement with a buffer solution that sets the pH between 4.8 and 5.2. At this pH,
interferences are minimized and the various ionic forms are converted to CO (see Section 10).
10. Interferences
10.1 Volatile weak acids are potential positive electrode interferences. Concentrations of these interfering species that cause a
10 % error at 44 mg/L CO or 100 mg/L (as CaCO ) and at pH 4 and 5, are listed below:
2 3
Interferences, mg/L pH 5 pH 4
H S 10 7
−
NO (NO ) 161 24
2 2
−
HSO (SO ) 320 (as SO ) 48 (as SO )
3 2 2 2
HOAc (acetic acid) 372 216
HCOOH (formic acid) 1841 345
10.2 Samples containing sulfide can be treated with dilute solutions of potassium dichromate (or the like), since sulfur is not
an interference for this test method. However, it is possible that some organic material could be oxidized to CO by this treatment,
resulting in falsely high results. The suitability of the test method for samples containing sulfide should be determined individually.
10.3 Water vapor is a potential electrode interference. Water can move across the membrane as water vapor, changing the
concentration of the internal filling solution under the membrane. Such changes will be seen as electrode drift. Water vapor
transport is not a problem if (1) the total concentration of dissolved species in solution (Note 1) is approximately equal to that of
the internal filling solution, and (2) electrode and sample temperatures are the same.
NOTE 1—The osmotic strength of a solution is related to the total concentration of dissolved species in the solution. For example, the osmotic strength
of a solution containing 0.1 M hydrochloric acid, 0.1 M acetic acid, and 0.1 M sucrose is determined as follows: Hydrochloric acid dissociates to give
0.1 M hydrogen ion and 0.1 M chloride ion. The acetic acid, because of the concentration of free hydrogen ion, is essentially undissociated; thus giving
0.1 M of species. Likewise, the concentration of sucrose species is 0.1 M . Therefore, the total osmotic strength is 0.4 osmolar.
10.4 Addition of carbon dioxide buffer (12.1) to samples of low osmotic strength automatically adjusts them to the correct level.
Samples with osmotic strength greater than approximately 1 M should be diluted before measurement to avoid drifting associated
with water vapor transport. Dilution should not reduce the carbon dioxide level below 2.5 mg/L. Samples with osmotic strengths
above 1 M that cannot be diluted can be measured by adjusting the osmotic strength of the internal filling solution. To adjust the
total concentration of dissolved species in the internal filling solution, add 0.425 g of reagent-grade NaNO to 10 mL of internal
filling solution.
11. Apparatus
11.1 pH Meter, with expanded mV scale, or a selective ion meter.
11.2 CO Gas-Sensing Electrode.
11.3 Mixer, magnetic with TFE-fluorocarbon-coated stirring bar or equivalent.
12. Reagents and Materials
12.1 Buffer Solution—Dissolve 294 g of sodium citrate in approximately 700 mL of water in a 1-L volumetric flask. Acidify the
solution to pH 4.5 with concentrated HCl (approximately 90 mL) and dilute to the mark with water.
12.2 Sodium Bicarbonate Solution, Standard (0.1 M)—Dissolve 8.40 g of sodium bicarbonate in water and dilute to 1 L.
12.3 Sodium Bicarbonate Solution, Standard (0.01 M)—
Dilute 10.0 mL of sodium bicarbonate standard solution (0.1 M) to 100 mL.
12.4 Filter Paper—Purchase suitable filter paper. Typically the filter papers have a pore size of 0.45-μm membrane. Material
such as fine-textured, acid-washed, ashless paper, or glass fiber paper are acceptable. The user must first ascertain that the filter
paper is of sufficient purity to use without adversely affecting the bias and precision of the test method.
There are currently several manufacturers of the gas-sensing electrodes for carbon dioxide.
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13. Calibration and Standardization
13.1 Assemble and check the electrode in accordance with the manufacturer’s instructions.
13.2 Dilute 10 mL of the buffer solution to 100 mL with water using a volumetric flask. Transfer the contents of the flask to
a 150-mL beaker and add a stirring bar. Immerse the electrode in the solution. Stir at a slow rate using the magnetic stirrer.
13.3 Using a volumetric pipette, add 0.5 mL of the 0.01 M NaHCO standard solution and mix slowly. Allow the potential
reading to stabilize (approximately 10 min) and record the potential (corresponds to 2.2 mg/L CO or 5.0 mg/L (as CaCO )).
2 3
13.4 Using a volumetric pipette, add 0.5 mL of the 0.01 M NaHCO standard solution and mix slowly. Allow the potential
reading to stabilize (approximately 5 min) and record the potential (corresponds to 4.4 mg/L CO or 10.0 mg/L (as CaCO )).
2 3
13.5 Using a volumetric pipette, add 0.9 mL of the 0.1 M NaHCO standard solution and mix slowly. Allow the potential reading
to stabilize (approximately 2 min) and record the potential (corresponds to 43.2 mg/L CO or 98.1 mg/L (as CaCO )).
2 3
13.6 Using a volumetric pipette, add 10 mL of the 0.1 M NaHCO standard solution and mix slowly. Allow the potential reading
to stabilize (approximately 2 min) and record the potential (corresponds to 433 mg/L CO or 983 mg/L (as CaCO )).
2 3
13.7 Plot Follow manufacturer instructions for calibrating selective-ion meters with a direct reading of concentration
capabilities. For pH meters, generate a calibration curve by creating a calibration curve by plotting potential values (on the linear
scale) versus concentration (on the logarithmic scale) on semilogarithmic graph paper to obtain a calibration curve. The curve may
be extended down to 2 mg/L and up to 800 mg/L CO . Commercially available meters may be used.
14. Procedure
14.1 Bring samples to the same temperature as the electrode and standards.
14.2 Place a known volume, V , (100 mL is convenient) of sample in 150-mL beaker and stir slowly. Immerse the electrode in
s
the solution.
14.3 Add 1 mL of buffer, V , for each 10 mL of sample. Allow the potential reading to stabilize and record the value. Read the
b
concentration measured, C , directly from the calibration curve.
m
14.4 Determine the sample concentration, C , as follows:
s
V 1V
s b
C 5 C
s m
V
s
15. Precision and Bias
15.1 Precision—The overall and single operator precision of this test method, within its designated range, varies with the
quantity tested as shown in Fig. 1 for reagent water and Fig. 2 for selected water matrices. These matrices included natural waters
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:XXX-XXX RR:D19-1069. Contact ASTM
Customer Service at service@astm.org.
FIG. 1 Interlaboratory Precision for Total CO Found in Reagent Water—Test Method A
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FIG. 2 Interlaboratory Precision for Total CO Found in Selected Water Matrices—Test Method A
and brines.
15.2 Bias—Recoveries of known amounts of total CO from reagent water and selected water matrices were as shown in Table
1.
15.3 The information in 15.1 and 15.2 is derived from round-robin testing in which eight laboratories, including twelve
independent operators, participated. Of twelve data sets ranked as described in Practice D2777, four were rejected in the case of
reagent water and three were rejected in the case of selected water matrices. Four outlier data points were also rejected. Four
sample levels were run on three days, and blanks were obtained for the waters used.
15.4 Precision and bias for this test method conforms to Practice D2777 – 77, which was in place at the time of collaborative
testing. Under the allowances made in 1.4 of Practice D2777 – 08,13, these precision and bias data do meet existing requirements
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