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HJ 506-2009 PDF in English

HJ 506-2009 (HJ506-2009) PDF English
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HJ 506-2009: PDF in English

HJ 506-2009
Replacing GB 11913-89
Water Quality - Determination of Dissolved Oxygen -
Electrochemical Probe Method
Issued by: Ministry of Environmental Protection of the People’s Republic
of China
Table of Contents
Announcement of the Ministry of Environmental Protection of the People’s
Republic of China ... 3
Foreword ... 5
1 Scope ... 7
2 Normative References ... 7
3 Terms and Definitions ... 7
4 Method and Principle ... 7
5 Reagents and Materials ... 8
6 Instruments and Equipment ... 8
7 Analytical Procedures ... 9
8 Result Calculation ... 10
9 Inspection Report ... 13
10 Precautions ... 13
Appendix A (normative) Relations between Solubility of Oxygen in Water, and
Temperature, Air Pressure and Salinity ... 16
Appendix B (informative) A Comparison of Chapter No. between this Standard
and ISO 5814:1990 ... 22
Water Quality - Determination of Dissolved Oxygen -
Electrochemical Probe Method
1 Scope
This Standard specifies the electrochemical probe method for the determination of
dissolved oxygen in water.
This Standard is applicable to the determination of dissolved oxygen in surface water,
underground water, domestic sewage, industrial wastewater and saline water.
This Standard can determine dissolved oxygen with a saturation percentage of 0% ~
100% in water and can also determine supersaturated dissolved oxygen above 100%
(20 mg/L).
2 Normative References
The content of this Standard takes the clauses in the following documents as a
reference. In terms of reference documents without a specified date, their valid
versions are applicable to this Standard.
GB 7489 Water Quality - Determination of Dissolved Oxygen - Iodometric Method
ISO 7888 Water Quality - Determination of Electrical Conductivity
3 Terms and Definitions
Dissolved Oxygen
Dissolved oxygen refers to molecular oxygen dissolved in water, which is usually
recorded as DO, and expressed in milligrams and saturation percentage of oxygen per
liter of water. The saturation content of dissolved oxygen is closed related to the partial
pressure of oxygen in the air, the air pressure, water temperature and water quality.
4 Method and Principle
The electrochemical probe for dissolved oxygen is a small chamber enclosed by a
selective membrane, which contains two metal electrodes and is filled with electrolyte.
Oxygen, and a certain amount of other gases and lyophilic substances can penetrate
through this membrane, but water and soluble substance ions can hardly penetrate
through this membrane. When the probe is immersed in water for the determination of
dissolved oxygen, due to the effect of battery or the potential difference between the
type (for example, silver / gold); there should be a temperature compensation device
attached to the probe.
6.1.2 Meter: directly display the mass concentration or saturation percentage of
dissolved oxygen.
6.2 Magnetic stirrer.
6.3 Electrical conductivity meter: with a measuring range of 2 ~ 100 mS/cm.
6.4 Thermometer: with a minimum division value of 0.5 °C.
6.5 Barometer: with a minimum division value of 10 Pa.
6.6 Dissolved oxygen bottle.
6.7 Commonly used glass instruments in the laboratory.
7 Analytical Procedures
When using the measuring instruments, strictly comply with the instructions of the
7.1 Calibration
7.1.1 Zero-point check and adjustment
When the mass concentration level of dissolved oxygen being determined is lower than
1 mg/L (or 10% saturation), or when the dissolved oxygen membrane cover or the
internally filled electrolyte is replaced, zero-point check and adjustment are required. If
the instrument has a zero-point compensation function, then, it is unnecessary to
adjust the zero-point.
Zero-point adjustment: immerse the probe into the zero-point check solution (5.3), after
the reaction is stable, read the reading; adjust the instrument to the zero point.
7.1.2 Calibration near saturation value
At a certain temperature, aerate the distilled water, so that the oxygen content in the
water reaches saturation or approaches saturation. At this temperature, maintain for
15 min; adopt the method specified in GB 7489 to determine the mass concentration
of dissolved oxygen.
Immerse the probe in the bottle. The bottle is completely filled with the sample prepared
and determined in accordance with the above-mentioned steps. After the probe is
stable in the stirred solution for 2 ~ 3 min, adjust the instrument reading to the already-
known dissolved oxygen mass concentration of the sample.
10.2 Linearity Check
Before a new instrument is put into use, and after electrode or electrolyte is replaced,
the linearity of the instrument shall be checked. Generally speaking, linearity check
shall be performed once every 2 months.
Method of linearity check: by determining the concentration of dissolved oxygen in a
series of distilled water samples with different concentrations, check the linearity of the
instrument. Slowly flow nitrogen bubbles into three to four 250 mL narrow-necked
bottles that are completely filled with distilled water, so as to remove oxygen in the
water; use the probe to measure the remaining dissolved oxygen content at all times,
until the approximate mass concentration of the required dissolved oxygen is obtained,
then, immediately stop the nitrogen flow; use GB 7489 to determine the accurate mass
concentration of dissolved oxygen in the water.
If there is no significant difference between the dissolved oxygen concentration value
determined by the probe method and the iodometric method at the significance level
of 5%, then, it is deemed that the response of the probe is linear. Otherwise, the cause
for the deviation from linearity shall be found.
10.3 Maintenance and Regeneration of Electrodes
10.3.1 Maintenance of electrodes
At any time, DO NOT touch the active surface of the membrane with your hands.
Electrode and membrane cleaning: if there are pollutants on the membrane and
electrode, they would cause measurement errors. Generally speaking, the electrode
and membrane shall be cleaned once every 1 ~ 2 weeks. Be careful when cleaning.
Put the electrode and membrane in clean water and rinse them; be careful not to
damage the membrane.
It is recommended that frequently used electrodes shall be stored in a container with
distilled water, so as to maintain the membrane moist. Before use, dried membrane
shall be moistened and activated with distilled water.
10.3.2 Regeneration of electrode
When the linearity of an electrode fails, the electrode needs to be regenerated. The
regeneration of electrode is performed about once a year.
The regeneration of electrode includes replacement of dissolved oxygen membrane
cover and electrolyte, and electrode cleaning.
Every certain time, or when the membrane is damaged and contaminated, it is
necessary to replace the dissolved oxygen membrane cover and replenish new filling
electrolyte. If the membrane is not damaged or contaminated, it is recommended that
Appendix A
Relations between Solubility of Oxygen in Water, and Temperature, Air
Pressure and Salinity
The solubility of oxygen in water changes with the temperature at a given air pressure;
similarly, it changes with the air pressure at a given temperature. In addition, the
solubility of oxygen decrease with the increase of salinity.
A.1 Functional Relations between Oxygen Solubility in Water and Water
Temperature and Salinity
A.1.1 Influence of temperature
Table A.1-1 provides the solubility ρ(O)s of oxygen in pure water under the standard air
pressure (101.325 kPa) in the presence of water vapor-saturated air with an oxygen
volume fraction of 20.94%, expressed in milligrams of oxygen per liter of pure water.
A.1.2 Influence of salinity
The solubility of oxygen in water decreases with the increase of salinity. When the total
salinity is below 35 g/kg, the two are in a linear relation.
Table A.1-1 provides the correction factor ∆ρ(O)s of dissolved oxygen in the water when
the water temperature is t °C (0 ~ 39 °C, at the interval of 1 °C) and the salt content in
the water (calculated as NaCl) changes by 1 g/kg. This correction factor is applicable
to sea water or harbor water. Using the above correction value can bring about 1%
error to the calculation result of dissolved oxygen in saline water.
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.