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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 9567-1997 Melamine for industrial use. The following technical changes have been made with respect to GB/T 9567-1997 (the previous edition):
——In technical requirements, the "first-grade products" are changed to "qualified products", with indexes unchanged; the "melamine" index of superior products is changed from "≥99.8%" to "≥99.5%" (see Clause 3; Clause 3 of Edition 1997);
——The "picric acid method" is determined as the arbitration method for determination of melamine content (see 4.3.1; 5.4.1 of Edition 1997);
——Karl?Fischer method for determining moisture content is added and confirmed as arbitration method (see 4.4.2);
——"Formalin dissolution test method" is revised (see 4.7; 5.8 of Edition 1997);
——The Clause "Sampling" and part of the "Test Methods" are merged into Clause "Inspection Rules" (see Clause 5; Clause 4 and 5.2 of Edition 1997);
——The requirement of "Forbidden to be Used in Food and Related Industries" is added in Clause 6 (see 6.1).
This standard was proposed by China Petroleum and Chemical Industry Association.
This standard is under the jurisdiction of Subcommittee on Organic Chemical Industry of National Technical Committee on Chemical of Standardization Administration of China (SAC/TC 63/SC 2).
This standard was issued in 1988 as first edition, its first revision was issued in 1997, and this is the second revision.
Melamine for industrial use
1 Scope
This standard specifies the technical requirements, test methods, inspection rules, marking, packaging, transportation and storage of melamine for industrial use.
This standard is applicable to the melamine for industrial use made from urea.
Structural formula:
Molecular formula: C3H6N6
Relative molecular mass: 126.12 (according to international relative atomic mass in 2011)
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 603 Chemical reagent - Preparations of reagent solutions for use in test methods
GB/T 6283-2008 Chemical products - Determination of water - Karl·Fischer method (general method)
GB/T 6678 General principles for sampling chemical products
GB/T 6679 General rules for sampling solid chemical product
GB/T 6682 Water for analytical laboratory use - Specification and test methods
GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values
GB/T 8946-2013 General technical requirements of plastic woven sack
GB/T 10454 Flexible freight container
3 Requirements
3.1 Appearance: white or light yellow solid powder without visible impurity.
3.2 The melamine for industrial use shall comply with the technical indexes in Table 1.
Table 1 Technical indexes
Item Index
Superior product Qualified product
Melamine, ω/% ≥99.5 ≥99.0
Moisture content, ω/% ≤0.1 ≤0.2
pH 7.5~9.5
Formalin dissolution test
Chromaticity/Hazen unit (platinum-cobalt color code)
Turbidity/degree (kaolin)
≤20
≤20
≤30
≤30
Ash content, ω/% ≤0.03 ≤0.05
4 Test methods
Warning: the operator shall take appropriate safety and protective measures, for some procedures specified in test methods may cause danger.
4.1 General requirements
Unless otherwise stated, only recognized analytically pure reagents and Grade III water specified in GB/T 6682 are used for the analysis.
Unless otherwise specified, the preparations and products adopted for analysis shall be prepared according to the requirements of GB/T 603.
4.2 Appearance determination
Take appropriate amount of specimen and put it into a watch glass or sample bag, and then observe it visually under natural light or fluorescent lamp.
4.3 Determination of melamine content
4.3.1 Picric acid method (arbitration method)
4.3.1.1 Method summary
Add water into the specimen, heat it to dissolve, add picric acid solution, and weigh the mass of the generated picric acid melamine precipitate, i.e. determine the purity content of melamine.
4.3.1.2 Reagents and solutions
4.3.1.2.1 Sulfuric acid solution: 1+200.
4.3.1.2.2 Phenolphthalein indicating liquid: 10g/L.
4.3.1.2.3 Picric acid solution: 10g/L.
4.3.1.2.4 Saturated solution of picric acid melamine: weigh 1g specimen, put it into a 500mL conical flask, add 400mL water, and heat it to dissolve. After cooling, add 3 drops of phenolphthalein indicating liquid, if color develops, add sulfuric acid solution till the color of solution disappears; the insoluble substance (if any) shall be filtered and washed with water. Mix the filter liquor with washing liquor to realize a total volume of 500mL, and then transfer them into a 2000mL beaker; heat the solution to 80℃ in water bath, add 500mL picric acid solution already heated to 80℃, cool to room temperature, and keep it below 15℃ for about 8h; filter it with glass sand filter, wash with 50mL water, dry the washed precipitate at 100~105℃ for 2h, and cool it for later use. Take 3~4g of such precipitate (or the picric acid melamine precipitate collected after analysis), add 2L water, boil them for 5min, filter the waste liquid after cooling, take the precipitate and dry for standby, and the precipitate namely is the picric acid melamine precipitate. Take 1g picric acid melamine precipitate, add 2L water, heat and dissolve, and then keep it still for storage.
Filter the saturated solution of picric acid melamine as it is used, and the temperature is consistent with that of washing.
4.3.1.3 Instruments and equipment
4.3.1.3.1 Common laboratory instruments and equipment.
4.3.1.3.2 Glass sand filter (crucible shape): G4.
4.3.1.4 Analysis steps
Weigh 1g specimen (accurate to 0.0002g), put it into a 500mL conical flask, add 400mL water, and heat them to dissolve. After cooling, add 3 drops of phenolphthalein indicating liquid, if color develops, add sulfuric acid solution till the color of solution disappears; the insoluble substance (if any) shall be filtered and washed with water. Mix the filter liquor with washing liquor, transfer them into a 500mL volumetric flask, add water to the scale, carefully shake and mix them, accurately pipet 100mL of such solution and place it in a 500mL beaker; heat the solution to 80℃ in water bath and add 100mL picric acid solution already heated to 80℃; cool to room temperature, and keep it below 15℃ for about 8h; filter it with a constant-weight glass sand filter, then wash it with about 100mL saturated solution of picric acid melamine, and then wash it with 10mL water; dry the glass sand filter at 100~105℃ for 2h, then place it in a dryer, cool it, and weigh it (accurate to 0.0002g) to calculate the precipitate mass.
4.3.1.5 Calculation of analysis result
The mass fraction ω1 of melamine is calculated using Equation (1):
(1)
Where,
m1——the mass of precipitate, g;
m——the mass of specimen, g;
0.355 0——the relative molecular mass ratio of melamine to picric acid melamine precipitate.
The arithmetic mean of two parallel determination results is taken as the determination result, and the difference between two parallel determination results shall not be greater than 0.2%.
4.3.2 Sublimation method
4.3.2.1 Method summary
Heat the specimen under negative pressure in a sublimation apparatus to completely sublimate the melamine, then weigh the amount of residue, i.e. determine the purity of melamine.
4.3.2.2 Test apparatus
The structure of pressure reducing and sublimation apparatus for specimen is shown in Figure 1, and shall meet the following conditions:
a) The specimen container is made of platinum, glass, porcelain, etc. and has the shape of a disk or a tube, so that the specimen contained is easy to sublimate and will not splash during the pressure reducing and sublimation;
b) For the pressure reducing and sublimation apparatus, the heating apparatus and vacuum apparatus with controlled internal temperature of (305±10)℃ and internal pressure kept below 4.00kPa shall be adopted.
4.3.2.3 Analysis steps
Weigh about 2g specimen (accurate to 0.0002g) and put it into a pre-dried specimen container of known mass; put the specimen container into a pressure reducing and sublimation apparatus, open the vacuum apparatus to slowly suck after the pressure reducing and sublimation apparatus is completely sealed, and reduce the pressure to 0.67~4.00kPa; adjust the temperature of apparatus to reach (305±10)℃ within about 20min from the start of suction; then, continue the sublimation under 0.67~4.00kPa at (305±10)℃, and finish the sublimation after 1h; stop heating and suction to ensure that the pressure of apparatus slowly returns to normal pressure, then take out the specimen container. Cool to room temperature in a dryer, then weigh the mass (accurate to 0.0002g) of specimen container to calculate the residual amount.
Foreword i
1 Scope
2 Normative references
3 Requirements
4 Test methods
5 Inspection rules
6 Marking, packaging, transportation and storage
Annex A (Normative) Determination of turbidity and chromaticity in formalin dissolution test
