ASTM D5462-93(2001)

Standard Test Method for On-Line Measurement of Low-Level Dissolved Oxygen in Water

SCOPE
1.1 This test method covers the on-line determination of dissolved oxygen (DO) in water samples primarily in ranges from 0 to 500 µg/L (ppb), although higher ranges may be used for calibration. On-line instrumentation is used for continuous measurements of DO in samples that are brought through sample lines and conditioned from high-temperature and high-pressure sources when necessary.
1.2 This standard does not purport to address all of the safety problems, 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. For specific hazards statements, see 6.5.

General Information

• Status: Historical
• Publication Date: 09-Jun-2001
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.03 - Sampling Water and Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water

Relations

• Referred By: ASTM D5127-13(2018) - Standard Guide for Ultra-Pure Water Used in the Electronics and Semiconductor Industries
• Effective Date: 10-Jun-2001

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 5462 – 93 (Reapproved 2001)
Standard Test Method for
On-Line Measurement of Low-Level Dissolved Oxygen in
Water
This standard is issued under the fixed designation D 5462; 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 tration. Oxygen consumption and regeneration balance each
other within the probes under stable conditions, and the net flux
1.1 This test method covers the on-line determination of
through the membrane is insignificant.
dissolved oxygen (DO) in water samples primarily in ranges
3.2.3 galvanic systems—sensing probes and measuring in-
from 0 to 500 μg/L (ppb), although higher ranges may be used
struments that develop an electrical current from two elec-
for calibration. On-line instrumentation is used for continuous
trodes inside the probe from which the final measurement is
measurements of DO in samples that are brought through
derived.
sample lines and conditioned from high-temperature and high-
3.2.4 partial pressure (of oxygen)—the volume fraction of
pressure sources when necessary.
oxygen multiplied by the total pressure. The partial pressure of
1.2 This standard does not purport to address all of the
oxygen is the actual parameter detected by DO probes, whether
safety concerns, if any, associated with its use. It is the
in air or dissolved in water.
responsibility of the user of this standard to establish appro-
3.2.5 polarographic systems—sensing probes and measur-
priate safety and health practices and determine the applica-
ing instruments that include circuitry to control the operating
bility of regulatory limitations prior to use. For specific hazards
voltage of the system, usually using a third (reference) elec-
statements, see 6.5.
trode in the probe.
2. Referenced Documents
4. Summary of Test Method
2.1 ASTM Standards:
4.1 Dissolved oxygen is measured by means of an electro-
D 1066 Practice for Sampling Steam
2 chemical cell separated from the sample by a gas-permeable
D 1129 Terminology Relating to Water
membrane. Behind the membrane and inside the probe, elec-
D 1192 Specification for Equipment for Sampling Water
trodes immersed in an electrolyte develop an electrical current
and Steam in Closed Conduits
proportional to the oxygen partial pressure of the sample.
D 1193 Specification for Reagent Water
4.2 The partial pressure signal is temperature compensated
D 2777 Practice for Determination of Precision and Bias of
automatically to account for variations with temperature of the
Applicable Methods of Committee D-19 on Water
following: oxygen solubility in water; electrochemical cell
D 3370 Practices for Sampling Water from Closed Con-
output; and, when necessary, diffusion rate of oxygen through
duits
the membrane. This yields a direct readout in concentration of
D 3864 Practice for Continual On-Line Monitoring Systems
μg/L (ppb) or mg/L (ppm).
for Water Analysis
4.3 Diffusion-type probes rely on a continuous diffusion of
3. Terminology oxygen through the membrane. Immediately inside the mem-
brane, oxygen is reduced at the noble metal cathode, usually
3.1 Definitions—For definitions of terms used in this test
platinum or gold. An electrical current is developed that is
method, refer to Terminology D 1129.
directly proportional to the arrival rate of oxygen molecules at
3.2 Definitions of Terms Specific to This Standard:
the cathode, which is in turn dependent on the diffusion rate
3.2.1 diffusion-type probes—galvanic or polarographic sen-
through the membrane. The less noble anode, usually silver or
sors that depend on the continuous influx of oxygen through
lead, completes the circuit and is oxidized in proportion to the
the membrane to develop the measurement signal.
current flow. At steady state, the resulting current signal is then
3.2.2 equilibrium-type probes—modified polarographic
proportional to the oxygen partial pressure of the sample.
sensing probes that have a negligible influx of oxygen through
Thorough descriptions of diffusion-type probes are given by
the membrane except during changes of sample DO concen-
Hitchman (1) and Fatt (2).
4.4 Equilibrium-type probes rely on oxygen diffusion
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
Water-Formed Deposits, Surveillance of Water, and Flow Measurement of Water.
Current edition approved Sept. 15, 1993. Published November 1993. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 11.01. this test method.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 5462
through the membrane only until equilibrium between the spheric conditions that deviate from a nominal range of 745 to
inside and outside is achieved. Oxygen is reduced at the noble 775 mmHg. See Table 1 for altitude corrections. Calibration
metal cathode, as with diffusion-type probes. However, the under low-pressure conditions without compensation would
measuring circuit forces electrical current to flow through the result in positive measurement errors.
noble metal anode equal and opposite to that at the cathode, 6.5 The growth of bacteria in sample lines and flow cham-
and the resulting oxidation reaction produces bers and on probe membranes can consume oxygen and cause
oxygen. This is the exact reverse of the reaction at the cathode, negative errors. Chemical sterilization with hydrochloric acid
so there is no net consumption of oxygen by the probe. It (1 + 44) or sodium hypochlorite solution (10 mg/L) should be
reaches equilibrium in constant DO samples, and no net performed if errors from bacteria growth are suspected.
oxygen diffuses through the membrane. Accuracy is not
NOTE 1—Warning: Do not mix hydrochloric acid and sodium hy-
dependent on membrane surface condition or sample flow-
pochlorite since hazardous chlorine gas would be released rapidly.
rate.
6.6 The passage of high-temperature samples containing
both DO and an oxygen scavenger through hot sample lines
5. Significance and Use
can allow continued reaction of the two. With long sample
5.1 DO may be either a corrosive or passivating agent in
lines, the DO measured at the probe may be significantly below
boiler/steam cycles and is therefore controlled to specific
that at the sample point. Short sample lines and cooling near
concentrations that are low relative to environmental and
the source are recommended.
wastewater treatment samples. Out-of-specification DO con-
6.7 Volatile oxygen scavengers or suppressants, such as
centrations may cause corrosion in boiler systems, which leads
hydrazine, amines, and hydrogen, that pass through the probe
to corrosion fatigue and corrosion products—all detrimental to
membrane may cause unwanted reactions at the electrodes and
the life and efficient operation of a power unit. The efficiency
negative errors. The magnitude of errors depends on the
of DO removal from boiler feedwater by mechanical or
relative concentrations of DO and the oxygen scavenger or
chemical means, or both, may be monitored by continuously
suppressant as well as the type of electrochemical cell used.
measuring the DO concentration before and after the removal
The probe manufacturer’s cautions and limitations should be
process with on-line instrumentation. DO measurement is also
considered.
a check for air leakage into the boiler water cycle.
6.8 New sample lines require conditioning to achieve equi-
5.2 Guidelines for feedwater to high-pressure boilers with
librium conditions. See Practices D 3370 to avoid sampling
all volatile treatment generally require a feedwater DO con-
interferences.
centration below 5 μg/L (3).
6.9 Iron oxides and other deposits accumulate in slow-
5.3 Boiler feedwater with oxygenated treatment is main-
flowing horizontal sample lines and can develop
tained in a range of 50 to 300 μg/L DO (4).
chromatograph-like retention of dissolved species, resulting in
5.4 In microelectronics production, DO can be detrimental
very long delay times. Precautions are described in Section 9.
in some manufacturing processes, for example, causing unde-
6.10 The response time can be slow for large decreases in
sirable oxidation on silicon wafers.
DO. This is especially true of measurements below 10 μg/L
following air calibration, which corresponds to a concentration
6. Interferences
6.1 The leakage of atmospheric air into samples is some-
TABLE 1 Solubility of Oxygen (mg/L) at Various Temperatures
times difficult to avoid and detect. Although sample line fittings
and Elevations (Based on Sea Level Barometric Pressure of
and connections to flow chambers may be water tight, it is still
760 mmHg) (5)
possible for air to diffuse through the water film of a joint to
Temperature, Elevation, ft above Sea Level
contaminate a low-μg/L sample. Section 9 provides further
°C
0 1000 2000 3000 4000 5000 6000
details on this non-obvious interference.
6.2 Diffusion-type probes consume oxygen and will deplete 0 14.6 14.1 13.6 13.2 12.7 12.3 11.8
2 13.8 13.3 12.9 12.4 12.0 11.6 11.2
it from the sample in immediate contact with the membrane
4 13.1 12.7 12.2 11.9 11.4 11.0 10.6
surface unless an adequate, turbulent sample flow is main-
6 12.4 12.0 11.6 11.2 10.8 10.4 10.1
tained. The manufacturer’s minimum flowrate recommenda- 8 11.8 11.4 11.0 10.6 10.3 9.9 9.6
10 11.3 10.9 10.5 10.2 9.8 9.5 9.2
tions must be met or exceeded in order to prevent erroneously
12 10.8 10.4 10.1 9.7 9.4 9.1 8.8
low readings.
14 10.3 9.9 9.6 9.3 9.0 8.7 8.3
6.3 Diffusion-type probes are subject to negative errors 16 9.9 9.7 9.2 8.9 8.6 8.3 8.0
18 9.5 9.2 8.7 8.6 8.3 8.0 7.7
from the buildup of coatings such as iron oxides, which impede
20 9.1 8.8 8.5 8.2 7.9 7.7 7.4
the diffusion rate of oxygen. (Equilibrium-type probes are not
22 8.7 8.4 8.1 7.8 7.7 7.3 7.1
24 8.4 8.1 7.8 7.6 7.3 7.1 6.8
subject to errors from flowrate or coating.)
26 8.1 7.8 7.6 7.3 7.0 6.8 6.6
6.4 Calibration must be corrected for barometric pressure
28 7.8 7.5 7.3 7.0 6.8 6.6 6.3
according to the manufacturer’s recommendations at atmo-
30 7.5 7.2 7.0 6.8 6.5 6.3 6.1
32 7.3 7.1 6.8 6.6 6.4 6.1 5.9
34 7.1 6.9 6.6 6.4 6.2 6.0 5.8
36 6.8 6.6 6.3 6.1 5.9 5.7 5.5
Leeds & Northrup, North Wales, PA, Model 7931 dissolved oxygen analyzer
38 6.6 6.4 6.2 5.9 5.7 5.6 5.4
and probe have been found to provide satisfactory equilibrium-type probe perfor-
40 6.4 6.2 6.0 5.8 5.6 5.4 5.2
mance.
D 5462
decrease of 3 to 4 orders of magnitude. Hours may be required where such specifications are available. Other grades may be
for all traces of oxygen to diffuse out of the probe and to used, provided it is first ascertained that the reagent is of
sufficiently high purity to permit its use without lessening the
achieve accurate measurements at low μg/L levels.
accuracy of the determination.
8.2 Purity of Water— Unless otherwise indicated, refer-
7. Apparatus
ences to water shall be understood to mean reagent water as
7.1 Measuring Instrument:
defined by Type I of Specification D 1193.
7.1.1 The instrument should have both μg/L (ppb) and mg/L
8.3 Hydrochloric Acid (1 + 44)—Add 1 volume of concen-
(ppm) range capability. It must have a span calibration adjust-
trated HCl (sp gr 1.19) to 44 volumes of water and mix.
ment to match the readout to the sensitivity of a particular
8.4 Sodium Hypochlorite (10 mg/L)—Add approximately
probe.
0.05 mL (1 drop) of 5 % NaOCl solution (commercial bleach
7.1.2 The direct readout of DO concentration requires is satisfactory for this purpose) to 250 mL of water.
8.5 Cobalt Chloride Solution, Saturated—Dissolve 4.5 g of
temperature compensation for effects of the following: ( 1)
cobalt chloride (CoCl ) in 10 mL of water.
oxygen solubility in water; (2) electrochemical cell output; and
8.6 Sodium Sulfite Zero Solution (10 g/200 mL)—Dissolve
(3) when necessary, diffusion rate of oxygen through the
10 g of sodium sulfite (Na SO ) in 200 mL of water.
membrane. During air calibration, the instrument must disable
2 3
the oxygen solubility portion of the compensation to respond
NOTE 2—To attain zero DO more rapidly, add two drops of saturated
only to partial pressure.
cobalt chloride solution to the sodium sulfite zero solution.
7.1.3 If included, electrical output signal(s) from the instru-
9. Sampling
ment must be isolated from the probe measuring circuit and
9.1 Design and operate the sample lines to maintain sample
from earth ground in order to prevent ground loop problems
integrity and fast response. Follow the applicable sampling
when the instrument is connected to grounded external devices.
precautions in Practices D 1066, D 3370, and D 3864 and
7.2 Probe:
Specification D 1192.
7.2.1 Diffusion-type probes use galvanic or polarographic
9.2 Use sample lines of compatible materials. Do not use
systems, with a noble metal cathode and oxidizable anode
copper because it can oxidize and consume oxygen. Do not use
immersed in an electrolyte and separated from the sample with
plastic or rubber since they are gas permeable and would allow
a polyethylene or fluorocarbon gas-permeable membrane.
air contamination.
7.2.2 Equilibrium-type probes are similar to polarographic
9.3 Maintain a continuous, stable flowrate to enable the
probes, except that both the anode and cathode are platinum
sample line to reach equilibrium with the sample conditions.
and the anode is not oxidized.
Measurements following changes to the sample flowrate or
temperature may not represent actual process conditions during
7.2.3 A sealed flow-through probe configuration must be
the period of time required to recover from transient effects.
used to prevent contamination from the atmosphere, as de-
9.4 Seal the sample from the atmosphere to prevent oxygen
scribed in 6.1. The flowrate must be maintained within the
absorption. Leakage of the equivalent of only one 2-mm-
manufacturer’s recommendations. The probe must be capable
diameter air bubble/min into a sample flowing at 100 mL/min
of withstanding the flowrate, temperature, and pressure condi-
adds approximately 11 μg/L oxygen to the sample. Test the
tions of the installation. The probe must incorporate an integral
sample line integrity by observing the measurement under
precision temperature sensor to ensure that it senses the sample
steady state conditions of DO and increasing the sample
temperature at which the DO is being detected in order to
flowrate approximately 50 %, but not exceeding the m
...