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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 23973-2009 Determination of formaldehyde in dye products. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 23973-2009:
——The method of determining formaldehyde in dye products by high-performance liquid chromatography (HPLC) has been added (see 3.2).
This standard was proposed by China Petroleum and Chemical Industry Association.
This standard is under the jurisdiction of Technical Committee on Dyestuff of Standardization Administration of China (SAC/TC 134).
The previous edition of this standard is as follows:
——GB/T 23973-2009.
Determination of formaldehyde in dye products
Warning: the personnel using this standard shall have practical experience in laboratory work. This standard does not purport to address all of the safety problems 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 determination method of formaldehyde in dye products.
This standard is applicable to the determination of formaldehyde in dye products.
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 601 Chemical reagent—Preparations of reference titration solutions
GB/T 6682-2008 Water for analytical laboratory use—Specification and test methods (ISO 3696: 1987, MOD).
GB/T 8170-2008 Rules of rounding off for numerical values & expression and judgment of limiting values
3 Test methods
3.1 Spectrophotometry (arbitration method)
3.1.1 Principle
The free formaldehyde in the sample was distilled to prepare an aqueous solution, which was developed with acetylacetone and determined by spectrophotometer colorimetry.
3.1.2 Determination method
3.1.2.1 General
Unless otherwise specified, only recognized analytical reagent and Grade 3 water (specified in GB/T 6682-2008) shall be used. Unless otherwise specified, the standard volumetric solutions used in the test shall be prepared and calibrated according to the requirements of GB/T 601. Judgment of the inspection result shall be carried out according to the rounding-off value by comparison method specified in GB/T 8170-2008, 4.3.3.
3.1.2.2 Reagents and solutions
3.1.2.2.1 Ammonium acetate.
3.1.2.2.2 Acetic acid.
3.1.2.2.3 Acetylacetone.
3.1.2.2.4 Formaldehyde: with a concentration of about 37% (mass fraction).
3.1.2.2.5 Acetylacetone solution: weigh 150 g of ammonium acetate, dissolve it with 800 mL of water, transfer it into a 1,000 mL brown volumetric flask, then add 3 mL of acetic acid and 2 mL of acetylacetone, dilute it to the scale with water, and store it at 0°C ~ 5°C away from light. After 12 h of storage, the color gradually darkens. Therefore, it shall be stored for 12 h before use, and the solution will be effective within 6 ~ 8 weeks. After long-term storage, its sensitivity will change slightly, thus the calibration curve shall be checked weekly, or the absorbance shall be measured at 412 nm with water as the reference solution prior to use and shall be less than 0.015, otherwise it needs to be prepared again.
3.1.2.3 Apparatuses
3.1.2.3.1 500 mL distillation flask, condensing tube and fraction collector.
3.1.2.3.2 Volumetric flasks: 100 mL, 250 mL and 1,000 mL.
3.1.2.3.3 Colorimetric tube with stopper: 25 mL.
3.1.2.3.4 Cuvette: 10 mm.
3.1.2.3.5 Spectrophotometer.
3.1.2.3.6 Water bath with thermostat.
3.1.2.4 Preparation of standard solution and plotting of standard working curve
3.1.2.4.1 Preparation of formaldehyde standard solution
The formaldehyde standard solution is prepared as follows:
a) Preparation of formaldehyde standard stock solution
Pipet 3.8 mL of formaldehyde into a 1,000 mL volumetric flask, dilute it to the scale with water, and the formaldehyde concentration is about 1,500μg/mL; calibrate the accurate concentration of formaldehyde standard solution by Iodine titration method according to Annex A. This is formaldehyde standard solution a.
b) Preparation of formaldehyde standard working solution
Accurately pipet 10 mL of formaldehyde standard solution a, transfer it into a 1,000 mL volumetric flask, and dilute it to the scale with water, and the formaldehyde concentration is about 15 μg/mL. This is formaldehyde standard solution b.
c) Preparation of formaldehyde standard curve solution
According to the preparation requirements listed in Table 1, add formaldehyde standard solution b into 100 mL volumetric flasks, dilute them to the scale with water, and prepare series of formaldehyde standard solutions No.1, No.2, No.3, No.4, No.5 and No.6 for later use.
Table 1 Preparation of formaldehyde standard curve solution
S.N. The volume of formaldehyde standard solution b /mL Corresponding formaldehyde concentration /(μg/mL)
1 1.00 0.15
2 2.00 0.30
3 5.00 0.75
4 10.00 1.5
5 20.00 3.0
6 40.00 6.0
3.1.2.4.2 Plotting of standard working curve
Pipet 5.0 mL of No.1-6 series formaldehyde standard solutions respectively and add 5.0 mL acetylacetone solution into six 25 mL colorimetric tubes with stoppers, shake well, place in a water bath at (40 ± 2) °C for color development for 30 min, then take it out and cool it to room temperature as soon as possible; determine the absorbance A of No.1-6 series formaldehyde standard solutions at 412 nm with a 10 mm cuvette, using 5.0 mL water and 5.0 mL acetylacetone solution as the reference solution.
Taking absorbance A as ordinate and formaldehyde concentration c (μg/mL) as abscissa, the standard working curve a = KC + a is calculated. This curve is used for all measured values. If the formaldehyde content in the test sample is higher than the test range, dilute the sample solution.
3.1.2.5 Preparation of specimen solutions
Weigh 2g of sample (accurate to 0.001 g), put it in a 500 mL distillation flask, add 250 mL water to dissolve it, and shake it gently. Install the distillation unit, add 50 mL of water into the fraction collector in advance, submerge the fraction outlet, and add ice to cool the external part of the fraction collector. Heat and distill, collect 200 mL of fraction, take off the fraction collector, and put the fraction into a 250 mL volumetric flask. This solution is the fraction solution to be measured.
Note: After some water-insoluble dyes (such as disperse dyes and vat dyes, etc.) are distilled, the distillate will show color with trace dye components, which may be extracted with a proper amount of toluene bath, and then the color can be removed before the following determination.
3.1.2.6 Determination
Accurately pipet 5.0 mL of distillate solution (3.1.2.5) into a 25 mL colorimetric tube, accurately add 5.0 mL of acetylacetone solution, shake it evenly, place it in a water bath at (40±2)°C for 30 min to develop color, take it out and cool it to room temperature as soon as possible; determine the absorbance A of No.1-6 series formaldehyde standard solutions at 412 nm with a 10 mm cuvette, using 5.0 mL water and 5.0 mL acetylacetone solution as the reference solution.
3.1.2.7 Result calculation
The formaldehyde content in dye products which is represented by mass fraction ω1 and expressed in mg/kg is calculated using Equation (1):
(1)
where,
c——the concentration of formaldehyde obtained from the standard working curve, μg/mL;
V——the value of the actual volume of the fraction solution, mL;
m1——the mass of specimen, g.
The calculation result is rounded to one decimal place.
3.1.2.8 Allowed tolerance
The absolute value of the difference between the two parallel determination results of formaldehyde content shall be no more than 10% of the arithmetic mean, and the arithmetic mean thereof is taken as the determination result.
3.1.2.9 Determination lower limit, recovery rate and precision
3.1.2.9.1 Determination lower limit
The lower limit of spectrophotometry of this standard is 20.0 mg/kg.
3.1.2.9.2 Recovery rate
When five formaldehyde standard solutions with different concentrations and known content are treated, measured and calculated according to the spectrophotometry of this standard, the recovery rate is in the range of 85% to 105%.
3.1.2.9.3 Precision.
The absolute difference between the two independent test results obtained from two independent tests performed by the same operator on the same object with the same equipment and the spectrophotometry of this standard in the same laboratory during a short time shall not exceed 10% of the arithmetic average of the determined values.
Foreword i
1 Scope
2 Normative references
3 Test methods
4 Test report
Annex A (Normative) Calibration of formaldehyde standard solution
