GB/T 6913-2023 English PDF (GBT6913-2023)

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GB/T 6913-2023: Analysis of water used in boiler and cooling system -- Determination of phosphate
GB/T 6913-2023
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.040.40
CCS G 76
Replacing GB/T 6913-2008
Analysis of water used in boiler and cooling system -
Determination of phosphate
(ISO 6878:2004, Water quality - Determination of phosphorus -
Ammonium molybdate spectrometric method, NEQ)
ISSUED ON: MARCH 17, 2023
IMPLEMENTED ON: OCTOBER 01, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Ammonium molybdate spectrophotometric method ... 5
5 Continuous flow-ammonium molybdate spectrophotometric method ... 11
6 Test report ... 14
Appendix A (Normative) Things to note during the test ... 15
Appendix B (Informative) Interference judgment and elimination of coexisting ions 16
Appendix C (Normative) Continuous flow analyzer system performance check ... 18
Analysis of water used in boiler and cooling system -
Determination of phosphate
Warming: The strong acid and strong base which are used in this document are
corrosive. Avoid inhalation or contact with the skin during use. If it splashes on
the body, use plenty of water to rinse it immediately. If serious, seek medical advice
immediately.
1 Scope
This document describes methods for the determination of orthophosphate, total
inorganic phosphate, and total phosphate content in water used in boiler and cooling
system: ammonium molybdate spectrophotometric method and continuous flow-
ammonium molybdate spectrophotometric method.
This document applies to the determination of orthophosphate, total inorganic
phosphate, and total phosphate content in water used in boiler and cooling system. The
measurement range of the ammonium molybdate spectrophotometric method is 0.05
mg/L ~ 50 mg/L (based on PO43-); the measurement range of the continuous flow-
ammonium molybdate spectrophotometric method is 0.1 mg/L ~ 50 mg/L (based on
PO43-).
2 Normative references
The following documents are referred to in the text in such a way that some or all of
their content constitutes requirements of this document. For dated references, only the
version corresponding to that date is applicable to this document; for undated references,
the latest version (including all amendments) is applicable to this document.
GB/T 6682-2008, Water for analytical laboratory use - Specification and test
methods
3 Terms and definitions
No terms and definitions need to be defined in this document.
4 Ammonium molybdate spectrophotometric method
4.1 Determination of orthophosphate content
4.1.1 Method summary
In the presence of acidic media and antimonic salts, orthophosphate reacts with
ammonium molybdate solution to produce yellow phosphomolybdenum heteropoly
acid. Use ascorbic acid to reduce it to phosphomolybdenum blue, and measure it by the
spectrophotometric method at a wavelength of 710 nm.
The reaction formula is:
4.1.2 Reagents or materials
Unless otherwise specified, only use analytical reagents or above.
4.1.2.1 Water: GB/T 6682-2008, grade 3.
4.1.2.2 Ascorbic acid solution: 100 g/L. Store it in brown bottles at 4 °C, valid for 14
days.
4.1.2.3 Ammonium molybdate solution: 26 g/L. Weigh 13 g of ammonium molybdate
and 0.35 g of potassium antimony tartrate (KSbOC4H4O6·1/2H2O); dissolve in 200 mL
of water; add 230 mL of sulfuric acid solution (1+1); mix well; cool and use water to
dilute to 500 mL; shake well. Store it in brown bottles, valid for 2 months.
4.1.2.4 Phosphate standard stock solution (based on PO43-): 500 mg/L. Weigh 0.716 5
g of potassium dihydrogen phosphate that has been dried to a constant weight at 100 °C
~ 105 °C, accurate to 0.2 mg; dissolve in about 500 mL of water; transfer to a 1 000 mL
volumetric flask; use water to dilute to the mark; shake well.
4.1.2.5 Phosphate standard solution (based on PO43-): 20 mg/L. Pipette 20.00 mL of
phosphate standard stock solution into a 500 mL volumetric flask; use water to dilute
to the mark; shake well. Formulate this solution when needed.
4.1.3 Instruments and apparatuses
Spectrophotometer: Equipped with an absorption cell with a thickness of 1 cm.
4.1.4 Test procedure
4.1.4.1 Preparation of sample
Filter the water sample collected on site through medium-speed filter paper and collect
into clean and dry glass bottles for subsequent analysis. Operate things to note during
the test according to Appendix A. See Appendix B for the interference judgment and
elimination of coexisting ions in the sample.
4.3.2.3 Potassium persulfate solution: 40 g/L. Store in brown bottles, valid for 14 days.
4.3.2.4 Other reagents: Same as 4.1.2.
4.3.3 Instruments and apparatuses
Spectrophotometer: Equipped with an absorption cell with a thickness of 1 cm.
4.3.4 Test procedure
Transfer an appropriate volume of sample (4.1.4.1) to a 100 mL Erlenmeyer flask by
referring to Table 1; add water to approximately 40 mL. Add 1.0 mL of sulfuric acid
solution and 5.0 mL of potassium persulfate solution; place it on an electric furnace to
maintain a slight boil for about 30 minutes for digestion. When boiling, add water
regularly to keep the solution volume at 25 mL ~ 30 mL. After cooling, use sodium
hydroxide solution to adjust the pH to 3 ~ 10 and transfer to a 50 mL volumetric flask.
Add 2.0 mL of ammonium molybdate solution and 1.0 mL of ascorbic acid solution;
use water to dilute to the mark; shake well; leave at room temperature for 10 minutes.
Use a spectrophotometer to measure the absorbance at a wavelength of 710 nm with a
1 cm absorption cell and a blank as a reference.
Note: Other digestion methods, such as microwave digestion, can also be used.
4.3.5 Result calculation
4.3.5.1 The total phosphate (based on PO43-) content ρ3 is expressed in terms of mass
concentration, in milligrams per liter (mg/L), and is calculated according to Formula
(3):
Where:
m – the mass of PO43- found from the calibration curve (4.1.4.2) or calculated from the
regression equation, in micrograms (μg);
V – the volume of the sample transferred, in milliliters (mL).
Express the calculation result to two digits after the decimal point.
4.3.5.2 The organophosphate (based on PO43-) content ρ4 is expressed in terms of mass
concentration, in milligrams per liter (mg/L), and is calculated according to Formula
(4):
Adjust the instrument according to the instrument instruction manual to achieve optimal
usage conditions. After starting up, first replace the reagent with water to check the
tightness of the entire analysis flow path and the smoothness of the liquid flow. After
the baseline stabilizes (about 20 minutes), the system begins to take the reagent package.
After the baseline stabilizes again, proceed to the measurement of total phosphate
according to 5.4.3 ~ 5.4.4. When measuring orthophosphate, use water instead of
potassium persulfate solution; turn off the hydrolysis heating and UV digestion
functions of the total phosphate analysis module for measurement. When measuring
total inorganic phosphate, use water instead of potassium persulfate solution, and turn
off the UV digestion function of the total phosphate analysis module for measurement.
5.4.2 Preparation of calibration solutions
Respectively pipette 0.00 mL (blank), 0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL,
5.00 mL, 6.00 mL and 7.00 mL of phosphate standard solution i...