GB/T 14636-2021 PDF English
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Determination of calcium and magnesium in industrial circulating cooling water and scale -- Atomic absorption spectrometric method
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| GB/T 14636-2007 | English | 319 |
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Industrial circulating cooling water -- Determination of calcium, magnesium -- Atomic absorption spectrometric method
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Industrial circulating cooling water--Determination of calcium--Atomic absorption spectrometry
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GB/T 14636-2021: PDF in English (GBT 14636-2021) GB/T 14636-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.040.40
CCS G 76
Replace GB/T 14636-2007
Determination of calcium and magnesium in industrial
circulating cooling water and scale -- Atomic absorption
spectrometric method
(ISO 7980:1986, Water quality -- Determination of calcium and magnesium --
Atomic absorption spectrometric method, NEQ)
ISSUED ON: AUGUST 20, 2021
IMPLEMENTED ON: MARCH 1, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Principles ... 6
5 Reagents or materials ... 6
6 Instruments and equipment ... 7
7 Selection of instrument conditions ... 7
8 Preparation of samples ... 8
9 Determination steps ... 10
10 Calculation of results ... 12
11 Tolerance ... 13
Appendix A (Informative) Elimination of the interference of water treatment chemicals
and coexisting elements in water ... 15
References ... 17
Determination of calcium and magnesium in industrial
circulating cooling water and scale -- Atomic absorption
spectrometric method
1 Scope
This document specifies the determination method of the content of calcium and
magnesium in industrial circulating cooling water and the content of calcium and
magnesium in the scale of the boiler water system or circulating water system - atomic
absorption spectrometry.
This document is applicable to the determination of calcium content of 0.5 mg/L~75
mg/L and magnesium content of 0.1 mg/L to 50 mg/L in industrial circulating cooling
water; it is applicable to the determination of calcium content ≥0.005% and magnesium
content ≥0.005% in scale.
This document is also applicable to the determination of calcium and magnesium
content in the scale of various other industrial water, raw water, and water systems, as
well as calcium content in phosphorus-zinc pre-film solution for industrial circulating
refrigeration.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
GB/T 602 Chemical reagent -- Preparations of standard solutions for impurity
GB/T 4470 Analytical spectroscopic methods. Flame emission, atomic absorption
and atomic fluorescence. Vocabulary
GB/T 6682-2008 Water for analytical laboratory use -- Specification and test
methods
DL/T 1151.2 Analytical methods of scale and corrosion products in power plants.
Part 2: Sampling and dissolving method for scale and corrosion products
HG/T 3530 Industrial circulating cooling water. Sampling and production for sludge
and corrosion products
3 Terms and definitions
Terms and definitions defined in GB/T 4470 are applicable to this document.
4 Principles
The sample is sprayed into air-acetylene flame or nitrous oxide-acetylene flame by
atomization, calcium and magnesium are pyrolyzed into ground state atoms; take
calcium resonance line 422.7 nm and magnesium resonance line 285.2 nm as analytical
lines to measure their absorbances, respectively. When using the air-acetylene flame to
measure calcium and magnesium, adding strontium chloride or lanthanum chloride can
inhibit the interference of water treatment chemicals and various coexisting elements
in water (see Appendix A). When using the nitrous oxide-acetylene flame to measure
calcium and magnesium, add cesium chloride to suppress interference.
5 Reagents or materials
Warning: The acetylene gas specified in this document is flammable and explosive
when mixed with air; nitrous oxide is harmful to the human body; pay attention
to safety in use, prevent leakage, and operate in strict accordance with the
specifications. Strong acids are caustic, so pay attention when using them; handle
them with care; if being splashed by them, rinse with plenty of water; avoid
inhalation or skin contact.
Unless otherwise specified, the reagents used in this document are analytical grade only.
See GB 6819 for the requirements for acetylene gas used in the test. The standard
solution for impurity used in the test shall be prepared in accordance with the provisions
of GB/T 602 unless other provisions are specified.
5.1 Water: it shall be grade 2 specified in GB/T 6682-2008.
5.2 Hydrochloric acid.
5.3 Nitric acid.
5.4 Perchloric acid.
5.5 Hydrochloric acid solution: 1+1.
5.6 Hydrochloric acid solution: 1+99.
5.7 Nitric acid solution: 1+99.
min~10 min before measurement can be performed.
8 Preparation of samples
8.1 Collection of water sample and preparation of sample solutions
Collect a certain amount of water sample from the flowing water to be tested;
immediately, add the hydrochloric acid solution (5.5) to acidify the water sample to pH
≈1 [generally, add 2.0 mL of hydrochloric acid solution (5.5) per 100 mL of water
sample] to prepare a sample solution, and record the volume of the collected water
sample and the volume of the added hydrochloric acid solution (5.5). The collected and
acidified water sample shall be clear and transparent, otherwise, it shall be filtered with
medium-speed quantitative filter paper. The sample solution is sealed and stored in the
sampling container and can be placed stably for 14 days.
8.2 Preparation of scale sample and sample solutions
8.2.1 Collect and prepare scale sample according to the requirements of HG/T 3530 or
DL/T 1151.2, and then dissolve the scale sample according to the steps of 8.2.2 or 8.2.3.
to prepare the scale sample solution.
8.2.2 Use the electric heating method to dissolve the scale sample, and operate
according to the following requirements:
a) Weigh about 0.2 g~0.3 g of the prepared scale sample, and the weight shall be
accurate to 0.1 mg; place it in a 250 mL glass beaker.
b) Add a small amount of water to the beaker to fully wet the scale sample; slowly
add 15 mL of hydrochloric acid and 5 mL of nitric acid, cover with a watch glass,
and shake well; slowly heat and boil the solution on an electric hot plate or
adjustable electric furnace for 20 min. If there is still brown or tan residue, add
10 mL of hydrochloric acid and boil until the solution is clear.
c) Remove the beaker, add 10 mL of perchloric acid after the solution cools slightly,
then heat until thick white smoke begins to emit; remove the watch glass slightly,
and continue to slowly heat for 15 min~20 min; must not evaporate the solution
to dryness.
d) Remove the beaker, add 10 mL of the nitric acid solution while it is still hot, and
stir well to dissolve the salts on the wall of the beaker.
e) If the scale sample is completely dissolved, transfer the solution to a 100 mL
volumetric flask; use a pipette to absorb the nitric acid solution to wash the inner
wall of the beaker (no less than 3 times), and collect the washing solution in the
100 mL volumetric flask; add nitric acid solution to dilute to the Scale, and shake
well; it is the scale sample solution. If the dissolved solution contains white
suspended solids, filter it with medium-speed quantitative filter paper; wash the
beaker wall, the precipitation attached to the wall, and filter paper with the nitric
acid solution (about 10 mL each time) several times; wash them no less than 5
times; collect the filtrate and the washing solution in a volumetric flask, add nitric
acid solution to dilute to the Scale, and shake well; it is the scale sample solution.
8.2.3 Use microwave digestion to dissolve scale sample, and operate according to the
following requirements:
a) Weigh 0.2 g~0.3 g of the prepared scale sample, and the weight shall be accurate
to 0.1 mg; put it into the digestion inner tank of the microwave digestion apparatus,
add a few drops of water to wet it, and slowly add 6 mL hydrochloric acid and 2
mL nitric acid; shake the digestion inner tank, and let the gas run out (if a large
amount of gas is generated, the inner tank can be pre-digested at 100 °C for 20
min on the electric hot plate, and then add the same proportion of digestion
solution to about 10 mL); cover the tank tightly and put it into the vessel. Put the
digestion vessel into the microwave digestion apparatus, and digest the scale
sample according to the instrument instructions.
b) After the digestion is completed, transfer the solution in the tank to a 250 mL glass
beaker, wash the digestion tank and the lid with a small amount of nitric acid
solution, and pour the washing solution into the beaker together; add 10 mL
perchloric acid; place the beaker on an electric hot plate or adjustable electric
furnace, and slowly heat until white smoke emits for 15 min~20 min; do not
evaporate the solution to dryness; remove the beaker from the electric hot plate
or adjustable electric furnace, add 10 mL of the nitric acid solution while it is still
hot, and stir well to dissolve the salts on the wall of the beaker.
c) If the scale sample is completely dissolved, transfer the solution to a 100 mL
volumetric flask, use a pipette to suck the nitric acid solution to wash the inner
wall of the beaker (no less than 3 times), and collect the washing solution in the
100 mL volumetric flask; add nitric acid solution to dilute to the Scale, and shake
well; it is the scale sample solution. If the dissolved solution contains white
suspended solids, filter it with medium-speed quantitative filter paper; wash the
beaker wall, the precipitate attached to the wall, and the filter paper with the nitric
acid solution (about 10 mL each time) several times; wash them no less than 5
times; collect the filtrate and the washing solution in the volumetric flask, add
nitric acid solution to dilute to the Scale, and shake well; it is the scale sample
solution.
8.2.4 Except for not adding the scale sample, follow the same operation as preparation
of the scale sample solution in 8.2.2 or 8.2.3 to prepare the blank solution.
zero-setting with the reagent blank, and respectively measure the absorbances of the
blank solution and the scale sample solution after dilution; then, obtain the
corresponding calcium content (mg/L) from the calcium calibration curve. If the
calcium content is lower than the detection limit or exceeds the range of the calibration
curve, the dilution factor can be adjusted and then re-measured.
9.2 Determination of the content of magnesium
9.2.1 Drawing of the magnesium calibration curve
Accurately pipette 0.00 mL (blank), 0.50 mL, 1.00 mL, 2.00 mL, and 3.00 mL of
magnesium standard solution II into 50 mL volumetric flasks respectively, and add 5.0
mL strontium chloride solution or 2.0 mL lanthanum chloride solution (if using nitrous
oxide-acetylene flame, then add 5.0 mL cesium chloride solution); dilute to the Scale
with the hydrochloric acid solution (5.6), and shake well. The mass concentrations of
magnesium in this series of calibration solutions are 0.00 mg/L, 0.10 mg/L, 0.20 mg/L,
0.40 mg/L, and 0.60 mg/L, respectively. Under the best working conditions of the
instrument, at the wavelength of 285.2 nm, carry out zero-setting with the reagent blank
and then measure the absorbance. Taking the measured absorbance as the ordinate and
the corresponding magnesium content (mg/L) as the abscissa, draw the calibration
curve or calculate the regression equation. The linear correlation coefficient of the
calibration curve shall be greater than 0.999, otherwise, it shall be redrawn.
9.2.2 Determination of water sample
Pipette an appropriate volume of the acidified sample solution (8.1) accurately, put it
into a 50 mL volumetric flask, and add 5.0 mL of strontium chloride solution or 2.0 mL
lanthanum chloride solution (if using nitrous oxide-acetylene flame, then add 5.0 mL
cesium chloride solution); dilute to the Scale with the hydrochloric acid solution (5.6),
and shake well. According to the same instrument conditions as that is in the preparation
of the calibration curve, carry out zero-setting with the reagent blank and measure the
absorbance; then, obtain the corresponding magnesium content (mg/L) from the
magnesium calibration curve. If the magnesium content is lower than the detection limit
or exceeds the range of the calibration curve, the dilution factor can be adjusted and
then re-measured.
9.2.3 Determination of scale sample
Accurately pipette appropriate volumes of the scale sample solution (8.2.2 or 8.2.3) and
the blank solution (8.2.4) respectively, and place them in a 50 mL volumetric flask.
(Select an appropriate dilution factor according to the source of the scale sample and
the type of scale. Generally, the scale sample mainly composed of calcium and
magnesium scale is diluted about 50 times to 200 times; the scale sample mainly
composed of iron oxide scale is diluted about 10 times to 50 times. Adopt the same
dilution factor to dilute the blank solution and the scale sample solution.) Add 5.0 mL
strontium chloride solution or 2.0 mL lanthanum chloride solution (if using nitrous
oxide-acetylene flame, then add 5.0 mL cesium chloride solution), dilute with the
hydrochloric acid solution (5.6) to the Scale, and shake well. According to the same
instrument conditions as that is in the preparation of the calibration curve, carry out
zero-setting with the reagent blank, and respectively measure the absorbances of the
blank solution and the scale sample solution after dilution; then, obtain the
corresponding magnesium content (mg/L) from the magnesium calibration curve. If the
magnesium content is lower than the detection limit or exceeds the range of the
calibration curve, the dilution factor can be adjusted and then re-measured.
10 Calculation of results
10.1 Calculation of calcium and magnesium content in water sample
The content of calcium and magnesium is expressed by mass concentration ρ and in
milligram per liter (mg/L), calculated according to formula (1):
Where:
ρ1 --- The value of calcium and magnesium content obtained from the calibration
curves of calcium and magnesium, in milligrams per liter (mg/L);
f --- The ratio of the acidulated sample volume (mL) to the volume of the collected
water sample (mL) (see 8.1);
V1 --- The value of the constant volume of the sample solution after dilution during
measurement, in milliliters (mL) (V1=50);
V --- The value of the volume of the collected sample solution during dilution, in
milliliters (mL).
The calculation results shall be rounded to two decimal places.
10.2 Calculation of calcium and magnesium content in scale sample
The content of calcium and magnesium is expressed by mass fraction w, and the value
is expressed in %; calculate it according to formula (2):
Appendix A
(Informative)
Elimination of the interference of water treatment chemicals and
coexisting elements in water
A.1 Interference in calcium measurement
Calcium is one of the easily interfered elements in atomic absorption analysis. In
industrial circulating cooling water, there are usually some coexisting inorganic ions
and the added water treatment chemicals; When there are still some ions, such as Al3+,
Si, SO42-, PO43-, in the water, the sensitivity of the calcium determination will be
reduced. After the addition of strontium chloride or lanthanum chloride, the following
ions and agents will not interfere with the determination when their concentrations are
less than or equal to the following specified values:
a) Inorganic ions in water: Fe2+ 50 mg/L; Al3+ 50 mg/L; Mg2+ 80 mg/L; Si 60 mg/L;
Na+ 500 mg/L; K+ 50 mg/L; Cl- 500 mg/L; SO42- 100 mg/L; Cu2+ 20 mg/L; PO43-
60 mg/L; Zn2+ 50 mg/L.
b) Water treatment chemicals: polyol phosphonate 10 mg/L; sodium
hexametaphosphate 10 mg/L; sodium polyacrylate 10 mg/L; polyacrylic acid 10
mg/L; acrylic acid-acrylate copolymer 10 mg/L; tripolyphosphoric acid Sodium
10 mg/L; HEDP 20 mg/L; EDTMPS 10 mg/L; ATMP 10 mg/L; polyquaternium
100 mg/L; mercaptobenzothiazole 3 mg/L; benzotriazole 3 mg/L.
A.2 Interference in magnesium measurement
Magnesium is an alkaline earth metal with a low ionization potential and is prone to
ionization interference in flames. In circulating cooling water, there are usually some
coexisting inorganic ions and added water treatment chemicals. When there are some
ions, such as Al3+, Si, PO43-, Fe2+, they will form difficult-to-dissociate compounds with
magnesium, and the sensitivity of the magnesium will be reduced. After the addition of
a release agent, such as lanthanum chloride or strontium chloride, it will form stable
compounds with the ions; then, magnesium will be released from the compounds of
interfering elements. The following ions and agents will not interfere with the
determination when their concentrations are less than or equal to the following specified
values:
a) Inorganic ions in water: Al3+ 50 mg/L; Fe2+ 50 mg/L; Si 40 mg/L; Na+ 500 mg/L;
K+ 50 mg/L; Cl- 500 mg/L; SO42- 100 mg/L; Cu2+ 20 mg/L; PO43- 60 mg/L; Zn2+
50 mg/L.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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