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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces QB/T 1133-1991 Jewellery - Measurement of gold coating thickness - Chemical method.
In addition to a number of editorial changes, the following main technical changes have been made with respect to QB/T 1133-1991:
——the standard name is modified;
——the determination methods are modified.
This standard was proposed by the China National Light Industry Council.
This standard is under the jurisdiction of the National Technical Committee 256 on Jewelry of Standardization Administration of China.
The previous edition of this standard is as follows:
——QB/T 1133-1991.
Jewellery - Determination of gold coatings - Method of spectrometry
1 Scope
This standard specifies the method for measuring the thickness of gold coating on jewellery by inductively coupled plasma emission spectrometer or atomic absorption spectrometer.
This standard is applicable to the determination of gold coating thickness for gold coating jewellery with copper and zinc as substrates.
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.
QB/T 1135 Jewelery - Measurement of gold and silver coating thickness - X-ray fluorescence spectrometric methods
3 Principle
In this standard, leach the specimen with mixed acid, dissolve the gold coating of the specimen, take it out and extract the gold from the test solution using 4-methyl-2-pentanone, then add thiourea to back-extract the gold, and dilute to the scale. Determine the concentration of gold in the test solution by spectrometer, calculate the mass of gold, and then calculate the average thickness of gold coating according to the area of jewelry specimen.
4 Reagents
Unless otherwise specified, only the recognized analytical reagents and distilled water or deionized water (with the electrical conductivity not greater than 1 μS/cm) or water with equivalent purity shall be used during the analysis.
4.1 Hybrochloric acid: with a mass fraction of 36% to 38%.
4.2 Nitric acid: with a mass fraction of 65% to 68%.
4.3 Thiourea: with a mass fraction of 2%.
4.4 Mixed acid: mixture of nitric acid (4.2) and hydrochloric acid (4.1) with a volume ratio of 1:3.
4.5 Hydrochloric acid: 1+9.
4.6 Ethyl acetate.
4.7 Gold standard stock solution: 1,000 mg/mL.
4.8 Gold calibration solution: pipette 10.0 mL gold standard stock solution (4.7) and put it into a 100-mL volumetric flask, then dilute to the scale with water, and 1 mL of such solution contains 100.0 μg gold.
4.9 4-Methyl-2-pentanone.
5 Apparatus
5.1 Analytical balance: with a sensitivity of 0.1mg.
5.2 For analysis spectrometer, inductively coupled plasma emission spectrometer or atomic absorption spectrometer should be used:
a) Inductively coupled plasma emission spectrometer
It is equipped with fixed or scanning channels, with the optical resolution of relevant elements is 0.02 nm, the detection limit is not less than 0.05 mg/L, and it has the function of background correction.
Instruments with the photomultiplier and semiconductor chip (CID, CCD) as the detector may be used for analysis.
b) Atomic absorption spectrometer, equipped with gold hollow cathode lamp
Under the best operating conditions, apparatus with indexes meeting the following requirements may be used:
1) Precision: measure the absorbance in standard solution with the maximum concentration for 10 times, and the standard deviation shall not exceed 1.0% of the average absorbance; measure the absorbance in standard solution with the minimum concentration (not “zero” concentration standard solution) for 10 times, and the standard deviation shall not exceed 0.5% of the average absorbance in standard solution with the maximum concentration.
2) Linearity of working curve: divide the working curve into five sections according to concentration, and the ratio of absorbance difference of the maximum section to that of the minimum section shall not be less than 0.8.
5.3 Micrometer, gauge, etc.
5.4 X-ray fluorescence spectrum thickness gauge.
6 Analysis procedures
6.1 Determination quantity
Whenever possible, use at least two identical samples for parallel determination.
6.2 Determination of area
Remove the oil stain on the surface of the specimen using absorbent cotton with anhydrous ethanol, and measure the jewelry specimen area with micrometer or gauge to the nearest of 0.1 cm2.
6.3 Pre-testing
Determine the thickness of gold coating preliminarily using the methods of QB/T 1135 to estimate the constant volume of sample.
6.4 Inductively coupled plasma emission spectrometer testing
6.4.1 Preparation of sample solution
In the fume hood, leach the specimen repeatedly with 20 mL to 25 mL mixed acid (4.4) to completely dissolve the gold coating of the specimen. Take out the specimen, rinse it clean with deionized water, combine the washing liquor and leaching mixed acid solution, add 10 mL hydrochloric acid (4.1), heat and steam until it is nearly dry, then remove it for cooling. After cooling, add another 10 mL hydrochloric acid (4.1), heat until the residue in the beaker is completely dissolved, remove for cooling, then transfer the solution into a 50-mL volumetric flask, and dilute to the scale with hydrochloric acid (4.5). Pipette 1 mL to 10 mL of solution into a separatory funnel. Add 10 mL of 4-methyl-2-pentanone (4.9) [or ethyl acetate (4.6)] to the separatory funnel, shake it vigorously for 1 min, let it stand for layering, and discard the aqueous phase.
Combine the washing liquors, heat and steam to about 10 mL of the solution, cool it down and diluted to a proper volume. At the same time, prepare the reagent blank.
6.4.2 Working curve
Pipette 0 mL, 1.00 mL, 5.00 mL, 10.00 mL of the gold calibration solution (4.8) into a group of 50-mL volumetric flasks respectively, dilute to the scale with hybrochloric acid (4.5) and mix well. Determine the emission spectral line intensity of gold in the test solution with inductively coupled plasma emission spectrometer [5.2 a)]. Plot the working curve with the gold concentration as the X-coordinate and the emission spectral line intensity as the Y-coordinate.
Foreword i
1 Scope
2 Normative references
3 Principle
4 Reagents
5 Apparatus
6 Analysis procedures
7 Result calculation
8 Test report
