ASTM D7677-11
(Test Method)Standard Test Method for the Continuous Measurement of Dissolved Ozone in Low Conductivity Water
Standard Test Method for the Continuous Measurement of Dissolved Ozone in Low Conductivity Water
SIGNIFICANCE AND USE
Dissolved Ozone is useful in many industries for water sanitization, TOC reduction, food preservation, cleaning-in-place of food and beverage systems, and pyrogen destruction. It is often necessary to know how much ozone has entered the water, how much remains, and the degree to which it has been removed before process use.
Some applications require that contact time, DO3 concentration integrated over time, be calculated, to assure disinfection.
Continuous observation of trends in these measurements are needed for continuous quality monitoring and the measurement may be used for closed loop control of ozonation.
In many pure water applications and especially where water quality is regulated by the FDA or similar enforcement agencies, ozone removal must be complete before the water is used. This test method is useful for detecting and determining dissolved ozone levels in water at the trace level as well as at process concentrations where sanitization and chemical reactions occur.
SCOPE
1.1 This test method covers the on-line and in-line determination of dissolved ozone (DO3) in low conductivity water in the range from 0.001 mg/L to 5.0 mg/L DO3 and conductivity 100 μS/cm, typical of pharmaceutical and microelectronics pure waters. DO3 is detected by correlating the response of a membrane-covered electrochemical sensor to the dissolved ozone concentration.
1.2 This test method provides a more convenient means for continuous measurement than the colorimetric methods typically used for grab sample measurements.
1.3 This test method has the advantage of high sensitivity as well as durability in the process environment and has few interferences.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D7677 − 11
StandardTest Method for the
Continuous Measurement of Dissolved Ozone in Low
Conductivity Water
This standard is issued under the fixed designation D7677; 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 3. Terminology
3.1 Definitions—For definitions of terms used in this test
1.1 This test method covers the on-line and in-line determi-
method, refer to D1129.
nation of dissolved ozone (DO ) in low conductivity water in
the range from 0.001 mg/L to 5.0 mg/L DO and conductivity
3.2 Definitions of Terms Specific to This Standard:
< 100 µS/cm, typical of pharmaceutical and microelectronics
3.2.1 dissolved ozone (DO ), n—Ozone is the tri-atomic
pure waters. DO is detected by correlating the response of a
form of oxygen and, when dissolved in water, is uniformly
membrane-covered electrochemical sensor to the dissolved
dispersed and remains in molecular form.
ozone concentration.
4. Summary of Test Method
1.2 This test method provides a more convenient means for
4.1 Dissolved ozone measurements are made on a flowing
continuous measurement than the colorimetric methods typi-
water sample containing dissolved ozone gas.
cally used for grab sample measurements.
4.2 The sensor flow housing is connected to a process-water
1.3 Thistestmethodhastheadvantageofhighsensitivityas
sample line or the sensor probe is inserted into a pipe or vessel
well as durability in the process environment and has few
with flowing water.
interferences.
4.3 The ozone gas permeates the sensor membrane and is
1.4 The values stated in SI units are to be regarded as
reduced to oxygen and hydroxide ion at the sensor’s cathode at
standard. No other units of measurement are included in this
a controlled potential of approximately +350 mV, producing a
standard.
currentflowindirectproportiontothepartialpressureofozone
1.5 This standard does not purport to address all of the in the sample outside the membrane.
safety concerns, if any, associated with its use. It is the
4.4 The current is correlated with a calibration curve in the
responsibility of the user of this standard to establish appro-
measuring instrument, accounting for temperature effects on
priate safety and health practices and determine the applica-
membrane permeation rate and on the solubility of ozone in
bility of regulatory limitations prior to use.
water. This correlation provides the conversion from ozone
partial pressure to concentration.
2. Referenced Documents
4.5 The instrument readout is provided in units of mg/L
2.1 ASTM Standards:
(ppm) or µg/L (ppb). For the purposes of this standard, the
D1129 Terminology Relating to Water paired units are considered equivalent.
D1193 Specification for Reagent Water
5. Significance and Use
D2777 Practice for Determination of Precision and Bias of
5.1 Dissolved Ozone is useful in many industries for water
Applicable Test Methods of Committee D19 on Water
sanitization, TOC reduction, food preservation, cleaning-in-
D3370 Practices for Sampling Water from Closed Conduits
place of food and beverage systems, and pyrogen destruction.
It is often necessary to know how much ozone has entered the
water, how much remains, and the degree to which it has been
This test method is under the jurisdiction of ASTM Committee D19 on Water
removed before process use.
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,
5.2 Some applications require that contact time, DO con-
On-Line Water Analysis, and Surveillance of Water.
centration integrated over time, be calculated, to assure disin-
Current edition approved Feb. 1, 2011. Published March 2011. DOI: 10.1520/
fection.
D7677-11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.3 Continuousobservationoftrendsinthesemeasurements
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
are needed for continuous quality monitoring and the measure-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. ment may be used for closed loop control of ozonation.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7677 − 11
5.4 In many pure water applications and especially where 6.7.1 Sample lines must be short and run at high flow
water quality is regulated by the FDA or similar enforcement velocity to bring a representative sample to the sensor that has
agencies, ozone removal must be complete before the water is not had a significant decrease in ozone concentration.
used. This test method is useful for detecting and determining 6.7.2 Where grab samples are taken to establish concentra-
dissolved ozone levels in water at the trace level as well as at tion values for calibration, they must be processed quickly to
process concentrations where sanitization and chemical reac- minimize ozone decay.
tions occur.
7. Apparatus
6. Interferences
7.1 Apparatus for Dissolved Ozone Determination—Atypi-
cal installation consists of a sampling connection to a process
6.1 This technology is only effective with a flowing sample.
line, a sensor with flow housing, a cable connecting the sensor
Turbulent flow past the membrane is necessary to continuously
and electronics, and analyzer electronics.
replenish the ozone that diffuses through the membrane and is
7.1.1 Sampling—The sample can be delivered via a sensor
consumedintheprobe.Thereplenishmentoffreshliquidatthe
flow housing or cell, or accessed through direct insertion into
surface of the membrane ensures representative sampling. The
the process vessel or pipe. Flow through the flow housing must
required minimum linear velocity is dependent on membrane
be continuous during measurements and is typically controlled
material and thickness and is manufacturer specific. A flow
by a flow control valve located after the flow housing. A weir
housing designed for the sensor provides the best control of
set up is also acceptable in cases where out-gassing does not
flow velocity. Follow the manufacturer’s flow rate specifica-
occur. The weir design requires that the flow control valve be
tions for the flow housing and membrane used.
located before the flow housing. Direct insertion probes can be
6.2 Interferences are limited to gases which can permeate
mounted through a standard T-fitting connection or via an
the membrane and react at the cathode or anode. Although
extraction valve. The valve set up permits the extraction of the
many gases can pass through the membrane, only chlorine gas
probe without interrupting the process flow.
has been found to react at the applied potential. However,
7.1.2 Sensor—The sensor has a body, a membrane, a
chlorine in high purity water is typically in ionic form which
cathode, an anode, a guard ring electrode (optional), a tem-
cannot pass through the membrane and so is not usually an
perature sensor, and a cable connection to the electronics.
interference. The exception is that under acidic conditions (pH
7.1.2.1 Body—Thesensorbodyshouldbemadeofmaterials
< 6), chlorinated water can produce dissolved chlorine gas and
compatible with the process. Common materials of construc-
its presence must be minimized to avoid interference.
tion include PEEK, type 316L stainless steel, and titanium.
7.1.2.2 Membrane—Membranes are composed of a gas
6.3 Polarographicozonesensorsmusttypicallybepolarized
permeable material that is resistant to process conditions,
in the presence of ozone before they can measure reliably and
sometimes reinforced with a fine internal mesh. Common
be calibrated. The sensor must be connected to the powered
membrane materials are PFA (PerFluoroAlkoxy), PTFE
measuring instrument to apply the polarization voltage across
(PolyTetraFluoroEthylene), and Silicone rubber.
the electrodes while the sensor is in an ozonated sample.
7.1.2.3 Cathode—The cathode is the reaction center for
Lengthoftimeandozoneconcentrationsneededtoachievefull
ozone analysis and is exposed to dissolved ozone gas and
polarization are manufacturer specific.
hydroxyl radicals continuously. The cathode is constructed of
6.4 Sampletemperaturerangeisdependentonmanufacturer
high purity noble metal such as gold or platinum which resists
design and specifications but is generally limited to between 0
ozone degradation.
°C and 50 °C. Temperatures below the freezing point of water
7.1.2.4 Anode—The anode is sacrificial in this method and
can result in a disturbance of the electrolyte and an inability of
requires a metal whose oxidation products will not interfere
the sensor to function. Ozone is seldom used in hot water
with the analysis such as silver which precipitates out of
because the rate of decay to oxygen is too fast to make it
solution in the presence of halides in the electrolyte.
effective.
7.1.2.5 Guard Ring Electrode—The optional guard ring
6.5 Sample pressure must be within manufacturer specifi- electrode surrounding the cathode is charged at the same
cations. In some cases varying process pressure can cause potential as the cathode and prevents the migration of silver
instability. ions back over to the cathode. As the silver passes over the
cathode it has a tendency to plate out, causing an increase in
6.6 Response time can vary from as little as a few seconds
maintenance frequency as well as a background interference.
to a few minutes depending on membrane and sensor design
The guard ring electrode can improve stability and response
and materials. Time for full response must be allowed, espe-
time but does not serve a direct measurement function.
cially when calibrating.
Platinum is typically used since it is resistant to ozone
degradation.
6.7 Although not a true interference in the measurement
itself, the rapid decay of ozone to oxygen makes sampling and 7.1.2.6 Temperature sensor—Changes in water temperature
calibration especially time dependent. The decay rate is in- affect permeation rates through the membrane and require
creased greatly at higher temperatures and to some degree at temperature compensation. Temperature is also used to com-
higher pH. The half-life of ozone in neutral water is approxi- pensate for changing ozone solubility with temperature in the
mately 20 minutes at 25 °C. conversion of the partial pressure signal to concentration. An
D7677 − 11
accurate temperature sensor, typically embedded in the head of react, producing a color inversely proportional to the ozone
the sensor, is required for proper compensation. concentration. Store these ampoules in accordance with manu-
7.1.3 Cable—The sensor cable must withstand the environ- facturer’s instructions, as they are light, time and heat sensi-
mental conditions of the installation and provide continuous tive.
high impedance insulation and shielding to carry the low,
8.3.5 N,N-diethyl-p-phenylenediamine (DPD) reagent—
nanoampere level signal. Installation in dedicated dc signal
This reagent is used with other spectrophotometer or colorim-
conduit is recommended, with proper shielding from electrical
eter systems and is supplied in manufacturer-specific formula-
interference. Refer to the manufacturer’s requirements.
tions.
7.1.4 Analyzer electronics—The measuring circuit applies a
8.4 Calibration and Verification using air as a reference—A
controlled polarization voltage between the anode and cathode
certified thermometer and a certified barometer are used to
(and optional guard ring electrode) to promote the ozone
perform a traceable air calibration.
reduction reaction.The sensor’s ozone and temperature signals
are combined with stored calibration data to compute and
9. Hazards
display concentration, as mg/L (ppm) or µg/L (ppb) of DO .
Data may be accumulated in internal nonvolatile memory, or 9.1 Ozone gas at high enough concentration is a health
exported via analog or digital signals to printer, data acquisi- hazard.Areas where dissolved ozone is measured are typically
tion or control systems. near ozone generators and holding tanks that could potentially
leak ozone gas into the ambient atmosphere. Ozone is gener-
8. Reagents and Materials
ally detectable by its characteristic odor at 0.02 to 0.05 ppm by
weight in air although prolonged exposure may cause some
8.1 Purity of Water—Reference to water that is used for
desensitization. The OSHA (U. S. Occupational Safety and
reagent preparation, rinsing or dilution shall be understood to
HealthAdministration) limit is 0.1 ppm averaged over 8 hours.
mean water that conforms to the quantitative specifications of
Atleastoneambientozonegasalarmmustbeonsiteforsafety
Type II reagent water of Specification D1193
of personnel working in the area.
8.2 Sensor Electrolyte—A manufacturer-specific electrolyte
bathes the anode and cathode to enable the electrochemical 9.2 Hazardous materials may be used in manufacturer-
recommended sensor maintenance procedures. Sensor and
reaction reducing the ozone.
material supplier safety precautions should be observed.
8.3 Calibration and Verification Using a Colorimetric
Method—Materials or reagents are required for verification or
10. Sampling
calibration using a colorimetric method. This method uses a
spectrophotometer or colorimeter and either indigo trisulfonate
10.1 Connect the sensor to the sample source in accordance
or N,N-diethyl-p-phenylenediamine (DPD) reagent. Indigo
with Practice D3370 and the instrument manufacturer’s in-
color is bleached by ozone; DPD develops a pink color in the
structions. If any conflict exists in these instructions, give
presence of ozone.
priority to the manufacturer’s requirements, as they may be
8.3.1 Containers—Containers used for blanks and samples
specific to a particular sensor.
must be clean and free of contaminants. The typical container
10.2 When sampling with dissolved gases present, take
is a beaker or flask with large opening at the top for access to
special care to use a connection or insertion location that will
the water sample. Reference D3370 for proper container
result in representative sampling. DO , or dissolved oxygen
preparation. After the container has been cleaned and before
from its decay, in a circulating system, can easily out-gas and
being used, it should be rinsed thoroughly with the water
form bubbles in the water which can affect stability of
sample.
measurement. Often these bubbles are temporary in pressur-
8.3.2 Blank—Choose a blank water sample which is repre-
ized water. Choose
...
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