ASTM D5997-15

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Designation: D5997 − 96 (Reapproved 2009) D5997 − 15
Standard Test Method for
On-Line Monitoring of Total Carbon, Inorganic Carbon in
Water by Ultraviolet, Persulfate Oxidation, and Membrane
Conductivity Detection
This standard is issued under the fixed designation D5997; 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
1.1 This test method covers the on-line determination of total carbon (TC), inorganic carbon (IC), and total organic carbon
(TOC) in water in the range from 0.5 μg/L to 50 000 μg/Lμg ⁄L of carbon. Higher carbon levels may be determined by suitable
on-line dilution. This test method utilizes ultraviolet-persulfate oxidation of organic carbon coupled with a CO selective
membrane to recover the CO into deionized water. The change in conductivity of the deionized water is measured and related to
carbon concentration in the oxidized sample using calibration data. Inorganic carbon is determined in a similar manner without
the requirement for oxidation. In both cases, the sample is acidified to facilitate CO recovery through the membrane. The
relationship between the conductivity measurement and carbon concentration can be described by a set of chemometric equations
− + −
for the chemical equilibrium of CO , HCO , H H , and OH OH , and the relationship between the ionic concentrations and the
2 3
conductivity. The chemometric model includes the temperature dependence of the equilibrium constants and the specific
conductances resulting in linear response of the method over the stated range of TOC. See Test Method D4519 for a discussion
of the measurement of CO by conductivity.
1.2 This test method has the advantage of a very high sensitivity detector that allows very low detection levels on relatively
small volumes of sample. Also, the use of two measurement channels allows determination of IC in the sample independently of
organic carbon. Isolation of the conductivity detector from the sample by the CO selective membrane results in a very stable
calibration with minimal interferences.
1.3 This test method was used successfully with reagent water spiked with sodium carbonate and various organic compounds.
This test method is effective with both deionized water samples and samples of high ionic strength. It is the user’s responsibility
to ensure the validity of this test method for waters of untested matrices.
1.4 This test method is applicable only to carbonaceous matter in the sample that can be introduced into the reaction zone. The
inlet system generally limits the maximum size of particles that can be introduced. Filtration may also be used to remove particles,
however, this may result in removal of organic carbon if the particles contain organic carbon.
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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits (Withdrawn 2003)
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Sampling Water and
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.
Current edition approved Oct. 1, 2009May 1, 2015. Published November 2009August 2015. Originally approved in 1996. Last previous edition approved in 20002009
as D5997 – 96 (2005).(2009). DOI: 10.1520/D5997-96R09.10.1520/D5997-15.
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.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5997 − 15
D3370 Practices for Sampling Water from Closed Conduits
D4519 Test Method for On-Line Determination of Anions and Carbon Dioxide in High Purity Water by Cation Exchange and
Degassed Cation Conductivity
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D1129.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 inorganic carbon (IC), n—carbon in the form of carbon dioxide, carbonate ion, or bicarbonate ion.
3.2.2 refractory material, n—that which cannot be oxidized completely under the test method conditions.
3.2.3 total carbon (TC), n—the sum of IC and TOC.
3.2.4 total organic carbon (TOC), n—carbon in the form of organic compounds.
4. Summary of Test Method
4.1 Fundamentals—Carbon can occur in water as inorganic and organic compounds. This test method can be used to make
independent measurements of IC and TC and can also determine TOC as the difference between TC and IC. If IC is high relative
to TOC, it is desirable to use a vacuum degassing unit to reduce the IC concentration to obtain meaningful TOC values by
difference.
4.2 The basic steps of this test method are:
4.2.1 Conversion of remaining IC to CO by action of acid,
4.2.2 Removal of IC, if desired, by vacuum degassing,
4.2.3 Split of flow into two streams to provide for separate IC and TC measurements,
4.2.4 Oxidation of TC to CO by action of acid-persulfate aided by ultraviolet (UV) radiation in the TC channel,
4.2.5 Detection of CO by passing each liquid stream over membranes that allow the specific passage of CO to high-purity
2 2
water where change in conductivity is measured, and
4.2.6 Conversion of the conductivity detector signal to a display of carbon concentration in parts per million (ppm = mg ⁄L) or
parts per billion (ppb = μg ⁄L). The IC channel reading is subtracted from the TC channel reading to give a TOC reading. A diagram
of suitable apparatus is given in Fig. 1.
5. Significance and Use
5.1 This test method is useful for detecting and determining organic and inorganic carbon impurities in water from a variety of
sources including industrial water, drinking water, and waste water.
5.2 Measurement of these impurities is of vital importance to the operation of various industries such as power, pharmaceutical,
semiconductor, drinking water treatment, and waste treatment. Semiconductor and power applications require measurement of very
low organic carbon levels (TOC < 1 μg/L). Applications in pharmaceutical industries range from USP purified water (TOC < 500
μg/L) to cleaning applications (500 μg/L < TOC < 50 000 μ g/L). μg/L). Drinking waters range from < 100 <100 μg/L to 25 000
μ g/L μg/L and higher. Some of these applications may include waters with substantial ionic impurities as well as organic matter.
5.3 Measurement of inorganic carbon as well as total organic carbon is highly important to some applications, such as in the
power industry.
5.4 Continuous monitoring and observation of trends in these measurements are of interest in indicating the need for equipment
adjustment or correction of water purification procedures.
5.5 Refer to Annex A1the Bibliography section for additional information regarding the significance of this test method.
6. Interferences and Limitations
6.1 The oxidation of dissolved carbon to CO is brought about at relatively low temperatures by the chemical action of reactive
species produced by UV-irradiated persulfate ions. Not all suspended or refractory material may be oxidized under these
conditions; analysts should take steps to determine what recovery is being obtained. This may be done by several methods: (1) by
rerunning the sample under more vigorous reaction conditions; (2) by analyzing the sample by an alternative method known to
result in full recovery; or (3) by spiking samples with known refractories and determining recovery.
6.2 Interferences have been investigated and found to be minimal under most conditions. Chloride ions above 250 000 μg/L may
cause low results. Follow the manufacturer’s instructions for dealing with high-chloride interference. Other interferences have been
investigated and found to be minimal under most conditions. The membrane is hydrophobic in nature and passes only gaseous
materials. Potential interferences are nitrite, sulfide, and high levels of hypochlorite or iodine. Refer to Annex A1the Bibliography
section for more information.
6.3 Note that error will be introduced when the method of difference is used to derive a relatively small level from two large
levels. For example, a water high in IC and low in TOC will give a less precise TOC value as (TC-IC) than by direct measurement.
D5997 − 15
FIG. 1 Schematic Diagram of TOC Analyzer System
In this case the vacuum degassing unit on the instrument should be used to reduce the concentration of IC prior to measurement,
or another method of inorganic carbon removal should be employed.
6.4 Use of the vacuum degassing unit or sparging the sample renders the IC reading meaningless and may cause loss of volatile
organic compounds, thus yielding a value lower than the true TOC level. At low TOC levels, the degassing unit may introduce a
measurable TOC and IC background. The user should characterize the background and performance of the degassing module for
their applications. Table 1 provides typical IC removal performance and background levels of the vacuum degassing unit.
6.5 The membrane conductivity detection technique may experience positive interference in the presence of low molecular
weight, reduced, inorganic acid species such as H S or HNO . Such interferences can be eliminated by oxidation or removal of
2 2
the gas.
7. Apparatus
7.1 Apparatus for Carbon Determination—A typical instrument consists of reagent and sample introduction mechanism,
reaction vessel, detector, control system, and a display. Fig. 1 shows a diagram of such an arrangement.
D5997 − 15
TABLE 1 Blank Contribution and IC Removal Efficiency of
Vacuum Degassing Unit
TOC Background, IC Background, IC Level with
Unit No.
A A
μg/L μg/L 25 000 μg/L Input
1 3.2 8.2 55
2 3.2 22 61
3 2.4 8.0 105
4 4.2 13 89
5 2.8 13 30
6 3.0 8.0 70
7 4.8 8.9 67
8 4.7 8.3 63
9 4.6 11 62
10 4.7 2.9 72
A
Values are the difference between, before, and after addition of the degasser to
a high-purity (<5 μg/L) water stream.
7.1.1 Vacuum degassing requires the manufacturer’s module, which includes a vacuum pump and a hollow fiber membrane
assembly. Use of this vacuum degasser will remove essentially all IC as part of the analysis. The membrane module consists of
a tube and shell arrangement of microporous polypropylene hollow fibers. Sample flows along the inside of the fibers while air
is passed on the shell side, counterflow to the sample flow. The shell side pressure is reduced by means of a vacuum pump on the
air outlet. The sample is acidified before introduction into the degasser to facilitate CO transport through the hollow fibers.
7.1.2 Reaction—The sample flow is split after the addition of reagents. Half the flow passes to the delay coil while the other
half passes into the oxidation reactor. The effluent from both streams passes over individual membranes that allow CO to pass
through the membrane into prepurified water for detection.
7.1.3 Detector—The CO that has passed through the membrane into the purified water is measured by conductivity sensors.
The temperature of the conductivity cell is also automatically monitored so the readings can be corrected for changes in
temperature.
7.1.4 Membrane—The membrane is a CO selective fluoropolymer that is hydrophobic and non-porous. Refer to the
bibliography inBibliography section Annex A1for additional details.
7.1.5 Internal Purified Water—Water on the conductivity side of the membrane is purified by continual pumping through a
mixed bed ion exchange resin as shown in Fig. 1. On power up, the instrument automatically delays for a period of at least 5 min
to allow the water in the internal loop to be fully deionized. The mixed bed ion exchange resin has an expected life of several years.
See 14.3 for details on monitoring the resin.
7.1.6 Presentation of Results—The conductivity detector output is related to stored calibration data and then displayed as parts
per million (ppm = mg ⁄L of carbon) or parts per billion (ppb = μg ⁄L of carbon). Values are given for TC, IC, and TOC by
difference. Data can be maintained on internal nonvolatile RAM, printer tape, or computer storage.
8. Reagents and Materials
8.1 Purity of Reagents—Use reagent grade chemicals in all tests. Unless otherwise indicated, it is intended that all reagents
conform to the specifications 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
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