GB/T 5750.4-2006 English PDF (GB/T5750.4-2006)

GB/T 5750.4-2006: Standard examination methods for drinking water -- Organoleptic and physical parameters
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GB/T 5750.4-2006
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 13.060
C 51
Partially replacing GB/T 5750-1985
Standard examination methods for drinking water -
Organoleptic and physical parameters
ISSUED ON: DECEMBER 29, 2006
IMPLEMENTED ON: JULY 01, 2007
Issued by: Ministry of Health of PRC;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3 
1 Chroma ... 5 
2 Turbidity ... 6 
3 Odor and taste ... 9 
4 Visible substances to the naked eye ... 10 
5 pH ... 10 
6 Conductivity ... 18 
7 Total hardness ... 21 
8 Total dissolved solids ... 25 
9 Volatile phenols ... 27 
10 Anionic synthetic detergent ... 34 
Standard examination methods for drinking water -
Organoleptic and physical parameters
1 Chroma
1.1 Platinum-cobalt standard colorimetry
1.1.1 Scope
This standard stipulates the determination of the chroma of drinking water and
its source water by platinum-cobalt standard colorimetry.
This method is applicable to the determination of the chroma of drinking water
and its source water.
The water sample is not diluted. The minimum detection chroma of this method
is 5 degrees. The measurement range is 5 degrees ~ 50 degrees.
The suspended matter in the water sample shall be removed before the
measurement.
1.1.2 Principle
The potassium chloroplatinate and cobalt chloride are used to prepare a
standard color series similar to the natural water’s yellow hue, which is used for
the visual colorimetric determination of water samples. The color of 1 mg/L
platinum [existed in the form of (PtCl6)2- is specified as a color unit, which is
called 1 degree. Even slight turbidity can interfere with the measurement, so
the turbid water sample needs to be centrifuged to make it clear before
measurement.
1.1.3 Reagents
Platinum-cobalt standard solution: Weigh 1.246 g of potassium chloroplatinate
(K2PtCl6) and 10.00 g of dry cobalt chloride (CoCl2 • 6H2O). Dissolve it in 100
mL of pure water. Add 100 mL of hydrochloric acid (ρ20 = 1.19 g/mL). Use pure
water to make the volume reach to 1000 mL. The chroma of this standard
solution is 500 degrees.
1.1.4 Instruments
1.1.4.1 Complete set of high-grade colorless plugged colorimetric tubes, 50 mL.
The minimum detection turbidity of this method is 0.5 nephelometric turbidity
unit (NTU).
Turbidity is an indicator that reflects the physical characteristics of water source
and drinking water. The turbidity of the source water is caused by optical
scattering or absorption behavior due to suspended solids or colloidal
substances, or both.
2.1.2 Principle
Under the same conditions, the intensity of the scattered light of the Formazine
standard suspension is compared with the intensity of scattered light of the
water sample. The greater the intensity of the scattered light, the higher the
turbidity.
2.1.3 Reagents
2.1.3.1 Pure water: Take distilled water and filter through a 0.2 μm membrane
filter.
2.1.3.2 Hydrazine sulfate solution (10 g/L): Weigh 1.000 g of hydrazine sulfate
[(NH2)2 • H2SO4, also known as hydrazine sulfate]. Dissolve it in pure water and
make its volume reach to the mark in a 100 mL volumetric flask.
Note: Hydrazine sulfate is carcinogenic. Avoid inhalation, ingestion, or
skin contact!
2.1.3.3 Cyclo-hexamethylenetetramine solution (100 g/L): Weigh 10.00 g of
cyclo-hexamethylenetetramine [(CH2)6N4]. Dissolve it in pure water and make
its volume reach to the mark in a 100 mL volumetric flask.
2.1.3.4 Standard suspension of Formazine: Respectively pipette 5.00 mL of
hydrazine sulfate solution and 5.00 mL of cyclo-hexamethylenetetramine
solution in a 100 mL volumetric flask. Mix it uniformly. After placing at 25 °C ±
3 °C for 24 h. Add pure water to the mark and mix it uniformly. This standard
suspension has a turbidity of 400 NTU and can be used for about one month.
2.1.3.5 Formazine turbidity standard use solution: Use pure water to dilute the
Formazine turbidity standard suspension (2.1.3.4) 10 times. The turbidity of this
suspension is 40 NTU. It shall be appropriately diluted during use according to
the need.
2.1.4 Instruments
Scattering turbidity meter.
2.1.5 Analytical procedures
5.1.1 Scope
This standard specifies the determination of the pH value of domestic drinking
water and its source water by the glass electrode method.
This method is applicable to the determination of the pH value of domestic
drinking water and its source water.
The pH value determined by this method can be accurate to 0.01.
The pH value is the logarithm of the reciprocal of hydrogen ion’s activity in water.
The chroma, turbidity, free chlorine, oxidant, reducing agent, higher salt content
of water does not interfere with the measurement. However, in a strong alkaline
solution, when a large amount of sodium ions is present, an error will occur,
which will make the reading relatively low.
5.1.2 Principle
The glass electrode is used as the indicator electrode, the saturated calomel
electrode is used as the reference electrode, which are inserted into the solution
to form a primary battery. When the hydrogen ion’s concentration changes, the
electromotive force between the glass electrode and the calomel electrode also
changes. At 25 °C, each unit of the pH scale is equivalent to 59.1 mV
electromotive force’s change, directly represented by the pH reading on the
instrument. There is a temperature difference compensation device on the
instrument.
5.1.3 Reagents
5.1.3.1 Potassium hydrogen phthalate standard buffer solution: Weigh 10.21 g
of potassium hydrogen phthalate (KHC8H4O4) which had been dried at 105 °C
for 2 h. Dissolve it in pure water and dilute to 1000 mL. The pH value of this
solution is 4.00 at 20 °C.
5.1.3.2 Mixed phosphate standard buffer solution: Weigh 3.40 g of potassium
dihydrogen phosphate (KH2PO4) which had been dried at 105 °C for 2 h and
3.55 g of disodium hydrogen phosphate (Na2HPO4). Dissolve it in pure water
and dilute it to 1000 mL. The pH of this solution is 6.88 at 20 °C.
5.1.3.3 Sodium tetraborate standard buffer solution: Weigh 3.81 g of sodium
tetraborate (Na2B4O7 • 10H2O). Dissolve it in pure water. Dilute it to 1000 mL.
The pH value of this solution is 9.22 at 20 °C.
mixed phosphate standard buffer solution for repositioning. If the water
sample’s pH is > 7.0, use sodium tetraborate standard buffer solution for
positioning; use potassium bi-phthalate or mixed phosphate standard buffer
solution for repositioning.
Note: If the positioning values of the three buffers are found to be non-linear, it
shall check the quality of the glass electrode.
5.1.5.4 Use the washing bottle to slowly rinse the two electrodes several times
by pure water. Then use water sample to rinse it for 6 ~ 8 times. Then insert it
into the water sample. After 1 min, directly read the pH value from the
instrument.
Note 1: In the calomel electrode, it is a saturated solution of potassium chloride.
When the room temperature rises, the solution may change from a saturated
state to an unsaturated state, so a certain amount of potassium chloride crystals
shall be maintained.
Note 2: For solutions with a pH value greater than 9, the pH value shall be
measured using a high-alkali glass electrode.
5.2 Standard buffer solution colorimetry
5.2.1 Scope
This standard specifies the standard buffer solution colorimetric method for
measuring the pH of drinking water and its source water.
This method is applicable to the determination of the pH value of drinking water
and its source water with very low chroma and turbidity.
Using this method to determine the pH can be accurate to 0.1.
Water samples are colored, turbid, or contain more free residual chlorine,
oxidants, reducing agents, it has interference.
5.2.2 Principle
Different acid-base indicators show different colors in a certain pH range. Add
the same indicator to a series of standard buffer solutions and water samples
with known pH values. Compare the measured pH values of the water samples
after color development.
5.2.3 Reagents
5.2.3.1 Potassium hydrogen phthalate solution [c(KHC8H4O4) = 0.10 mol/L]:
Place potassium hydrogen phthalate (KHC8H4O4) in an oven at 105 °C for 2 h
and place it in a silica gel dryer to cool it for 30 min. Weigh 20.41 g and dissolve
(mol/L);
m - The mass of potassium hydrogen phthalate, in grams (g);
V - The volume of sodium hydroxide solution used for titration of potassium
hydrogen phthalate, in milliliters (mL);
V0 - The volume of the sodium hydroxide solution used for titrating the blank
solution, in milliliters (mL);
0.2042 - The mass of potassium hydrogen phthalate equivalent to 1.00 mL
of sodium hydroxide standard solution [c(NaOH) = 1.000 mol/L].
According to the concentration of the sodium hydroxide stock solution, calculate
the volume of the stock solution required to prepare 0.1000 mol/L sodium
hydroxide solution according to formula (3). Use pure water to make the volume
reach the required value.
Where:
V1 - The volume of the stock solution, in milliliters (mL);
V2 - The volume after dilution, in milliliters (mL);
c1 (NaOH) - Concentration of stock solution.
5.2.3.5 Chlorophenol red indicator: Weigh 100 mg of chlorophenol red
(C19H12C12O5S). Put it in an agate mortar. Add 23.6 mL of sodium hydroxide
solution (5.2.3.4). Grind until completely dissolving it. Use pure water to make
its volume reach to 250 mL. The applicable pH range of this indicator is 4.8 ~
6.4.
5.2.3.6 Bromothymol blue indicator: Weigh 100 mg bromothymol blue
(C27H28Br2O5S, also known as thymol blue). Place it in an agate mortar. Add
16.0 mL of sodium hydroxide solution (5.2.3.4). The following operations are
the same as (5.2.3.5). The applicable pH range of this indicator is 6.2 ~ 7.6.
5.2.3.7 Phenol red indicator: Weigh 100 mg of phenol red (C19H14O5S). Put it in
an agate mortar. Add 28.2 mL of sodium hydroxide solution (5.2.3.4). The
following operations are the same as (5.2.3.5). The applicable pH range of this
indicator is 6.8 ~ 8.4.
5.2.3.8 Thymol blue indicator: Weigh 100 mg of thymol blue (C27H30O5S, also
known as thymol blue). Put it in an agate mortar. Add 21.5 mL of sodium
hydroxide solution (5.2.3.4). The following operations are the same as (5.2.3.5).
Potassium chloride standard solution [c (KCL) = 0.01000 mol/L]: Weigh 0.7456
g of superior grade pure potassium chloride which had been dried at 110 °C.
Dissolve it in freshly boiled and cooled distilled water (conductivity is less than
1 μS/cm). Dilute it to 1000 mL in a volumetric flask at 25 °C. The conductivity of
this solution at 25 °C is 1413 μS/cm. The solution shall be stored in a plastic
bottle.
6.1.4 Instruments
6.1.4.1 Conductivity meter.
6.1.4.2 Constant temperature water bath.
6.1.5 Analytical procedures
6.1.5.1 Pour the potassium chloride standard solution (6.1.3) into 4 test tubes.
Then inject the water sample into 2 test tubes. Put 6 test tubes into 25 °C ±
0.1 °C constant temperature water bath at the same time. Heat it for 30 min, to
make the temperature of the solution in the tube reach 25 °C.
6.1.5.2 Use three tubes of potassium chloride solution to rinse the conductivity
electrode and conductivity cell in sequence. Then pour the potassium chloride
solution in the fourth tube into the conductivity cell. Insert the conductivity
electrode to measure the conductivity GKCl or resistance RKCl of potassium
chloride.
6.1.5.3 Use one tube of water sample to fully rinse the electrode. Measure the
conductivity Gs, or resistance Rs, of the other tube of water sample.
Measure other water samples in turn. If the temperature change is less than
0.2 °C during the measurement, the conductivity or resistance of the potassium
chloride standard solution does not need to be measured again. However, when
measuring in different batches (days), it shall measure the conductivity or
resistance of potassium chloride solution again.
6.1.6 Calculation
6.1.6.1 Conductivity cell constant C: Equal to the conductivity (1413 μS/cm) of
the potassium chloride standard solution divided by the measured conductivity
GKCL of the potassium chloride standard solution. The temperature during
measurement shall be 25 °C ± 0.1 °C, then:
6.1.6.2 At 25 °C ± 0.1 °C, the conductivity γ of water sample is equal to the cell
constant C multiplied by the measured conductivity of the water sample (μS)
Since the reaction of calcium ion and chrome black T indicator at the end of the
titration cannot show a significant color change, so when the magnesium
content in the water sample is very small, it needs adding a known amount of
magnesium salt to make the color change at the end of the titration clear. When
calculating the results, subtract the amount of magnesium salt added, or add a
small amount of MgEDTA to the buffer solution, to ensure a clear end point.
7.1.2 Principle
The calcium and magnesium ions in the water sample form a purplish red
chelate with the chrome black T indicator. The instability constants of these
chelates are greater than the instability constants of calcium ethylenediamine
tetraacetate and magnesium chelates. When pH = 10, disodium
ethylenediaminetetraacetic acid first forms a chelate with calcium ions and then
magnesium ions. When titrated to the end, the solution appears pure blue with
chrome black T indicator.
7.1.3 Reagents
7.1.3.1 Buffer solution (pH = 10).
7.1.3.1.1 Weigh 16.9 g of ammonium chloride and dissolve it in 143 mL of
ammonia water (ρ20 = 0.88 g/mL).
7.1.3.1.2 Weigh 0.780 g of magnesium sulfate (MgSO4 • 7H2O) and 1.178 g of
ethylenediaminetetraacetic acid disodium (Na2EDTA • 2H2O). Dissolve it in 50
mL of pure water. Add 2 mL of chlorination ammonium-amine hydroxide solution
(7.1.3.1.1) and 5 drops of chrome black T indicator (the solution shall be purple
red. If it is pure blue, a small amount of magnesium sulfate shall be added to
make it purple red). Use Na2EDTA standard solution...