4.1 Carbon dioxide is a respiration product of plants and animals and a decomposition product of organic matter and certain minerals. The atmosphere averages about 0.04 vol % of CO₂. 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, CO₂ contributes significantly to corrosion of water-handling systems. This is particularly troublesome in steam condensate systems. Loss of CO₂ 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 CO₂ 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.

1.1 These test methods cover the measurement of total or dissolved carbon dioxide present as carbon dioxide (CO₂), 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 (CO₂ Evolution, Coulometric Titration)

5 to 800 mg/L

16 to 24

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.