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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard was proposed by China Petroleum and Chemical Industry Federation.
This standard is under the jurisdiction of National Technical Committee 5 on Paints & Pigments of Standardization Administration of China (SAC/TC 5).
Determination of formaldehyde content in water-borne coatings — High performance liquid chromatographic method
Warning: the personnel using this standard shall have practical experience in standard laboratory work. This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions.
1 Scope
This standard specifies the test principles, reagents or materials, instruments and equipment, samples, test steps, test data processing, detection limits and precision for determining formaldehyde content in water-borne coatings by high performance liquid chromatographic method (HPLC).
This standard is applicable to the determination of formaldehyde content of water-borne coatings. This method is also applicable to the determination of formaldehyde content in the raw material for water-borne coatings.
2 Normative references
The following referenced documents are indispensable for the application of this standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced documents (including any amendments) applies.
GB/T 3186 Paints, varnishes and raw materials for paints and varnishes — Sampling
GB/T 6682-2008 Water for analytical laboratory use — Specification and test methods
GB/T 12807 Laboratory glassware — Graduated pipettes
GB/T 12808 Laboratory glassware — One-mark pipettes
GB/T 23993-2009 Determination of formaldehyde content of waterborne coatings—Spectrophtometric method with acetylacetone
3 Principle
Taking acetonitrile as extraction solvent, the formaldehyde in the sample is extracted by the combination of ultrasonic extraction and centrifugal separation. In acidic conditions, the extraction liquid and 2,4-dinitrophenylhydrazine are derivatized to 2,4-dinitrophenylhydrazone, which may be detected by HPLC or existing effective methods meeting the accuracy requirements (such as liquid chromatography-mass spectrometry, liquid chromatography-tandem mass spectrometry, etc.). The content of formaldehyde in the sample is calculated based on standard working curve.
4 Reagents or materials
Unless otherwise specified, only confirmed analytical reagents, the above chemical reagents and Grade 1 water complying with GB/T 6682-2008 may be used during analysis.
4.1 Acetonitrile: Grade HPLC.
4.2 Phosphoric acid: the content is greater than or equal to 85% (mass fraction).
4.3 Derivatization reagent: weigh about 1g (in dry matter) of 2,4-dinitrophenylhydrazine, put it in a 100mL brown volumetric flask (see 5.5), dilute it to scale with phosphoric acid (see 4.2), and shake it well. Due to its instability, the solution is prepared immediately before use.
Note: 2,4-dinitrophenylhydrazine may be further purified by recrystallization with aqueous solution containing 25% (mass fraction) acetonitrile.
4.4 Formaldehyde solution: the content is approximately 37% (mass fraction).
4.5 Formaldehyde standard stock solution (formaldehyde content is about 1g/L): take 2.8mL of formaldehyde solution (see 4.4) with graduated pipette (see 5.6), put it in a 1,000mL volumetric flask (see 5.5), dilute it to scale with water, and mix it evenly. The accurate concentration shall by calibrated through the method specified in GB/T 23993-2009. Store the formaldehyde standard stock solution under 4℃ in dark place for 3 months.
Note: Certified formaldehyde solution reference materials with known concentration may also be used directly.
4.6 Formaldehyde standard solution (formaldehyde content is about 10mg/L): take 1.0mL of formaldehyde standard stock solution (see 4.5) with one-mark pipette (see 5.7), put it in a 100mL volumetric flask (see 5.5), dilute it to the scale with acetonitrile (see 4.1), and mix it evenly. Due to its instability, the solution is prepared immediately before use.
5 Apparatus
5.1 High performance liquid chromatograph: equipped with ultraviolet detector (UVD) or diode array detector (DAD).
5.2 Analytical balance: with an accuracy of 1mg.
5.3 Ultrasonic extractor.
5.4 High-speed centrifuge: with the rotation speed of 5,000r/min - 20,000r/min, the chamber temperature within 40℃ during operation, and equipped with a centrifuge tube of 10mL or other specifications.
5.5 Volumetric flask: 25mL, 50mL, 100mL, 1,000mL, etc.
5.6 Graduated pipette: 1mL, 5mL, 10mL, reaching Grade A in GB/T 12807.
Note: Other pipetting equipment with satisfactory accuracy, such as piston pipette, may also be used.
5.7 One-mark pipette: 1mL, 2mL, 5mL, 10mL, reaching Grade A in GB/T 12808.
Note: Other pipetting equipment with satisfactory accuracy, such as piston pipette, may also be used.
5.8 Organic-phase microporous membrane: with a hole diameter of 0.22μm.
6 Samples
Take the required amounts of samples either according to the requirements of GB/T 3186, or the agreed method.
7 Test steps
7.1 Parallel test
The two tests shall be conducted in parallel.
7.2 Sample pretreatment
7.2.1 Extraction
Weigh about 2.5g of sample (accurate to 1mg), put it in a 25mL volumetric flask (see 5.5), record the mass m of the sample, dilute it to the scale with acetonitrile (see 4.1), shake it sufficiently to make the sample disperse to the greatest extent, prepare a sample solution, and record the constant volume V. Perform ultrasonic extraction with ultrasonic extractor (see 5.3) for 10 min, then use graduated pipette (see 5.6) to transfer about 7mL of the above solution into centrifuge tube (or volume of the solution to be centrifuged may be adjusted according to the actual situation), and centrifuge for 20min-30min under the condition that the chamber temperature does not exceed 40℃ until supernatant A appears.
Note: If the centrifugation is ineffective to realize effective stratification, the rotating speed or centrifugal time may be appropriately increased.
7.2.2 Derivatization
Use the graduated pipette (see 5.6) to take 4.0mL of supernatant A (see 7.2.1), 4.0mL of water and 0.4mL of derivatization reagent (see 4.3), and mix them evenly in a 10mL centrifuge tube (the amount of supernatant A, water and derivatization reagent and the container used for derivatization may be adjusted according to the actual situation, but the volume ratio of supernatant A, water and derivatization reagent involved in derivatization reaction shall be maintained at 1:1:0.1). Seal the centrifuge tube and place it in a dark environment of (25±5)℃ for 24h for derivazation. Then filter it with 0.22μm organic-phase microporous membrane(see 5.8), and leave the filtrate A for HPLC analysis.
Note: If insoluble substances are generated after derivatization, supernatant may be obtained by centrifugation.
7.3 Blank test
Repeat steps in 7.2 without adding any sample for HPLC analysis. Each batch of samples (less than 20 samples) or every 20 samples shall be subjected to a blank test.
7.4 Chromatographic conditions
Optimal test conditions may be selected according to the property of the adopted high performance liquid chromatograph and the actual conditions of the sample.
As the test result depends on the instruments used, general parameters of chromatographic analysis are impossible to be provided. The following parameters listed in A.1 of Annex A are proved applicable to the test.
The type of detector used for chromatographic analysis shall be specified in the test report.
Foreword ii
1 Scope
2 Normative references
3 Principle
4 Reagents or materials
5 Apparatus
6 Samples
7 Test steps
8 Test data processing
9 Detection limit
10 Precision
Annex A (Informative) Determination conditions of high performance liquid chromatographic method
