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QC/T 942-2021: Test methods of hexavalent chromium in automotive materials---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/QCT942-2021
AUTOMOBILE INDUSTRY STANDARD
ICS 43.020
CCS T 04
Replacing QC/T 942-2013
Test methods of hexavalent chromium in automotive
materials
Issued on: AUGUST 21, 2021
Implemented on: FEBRUARY 01, 2022
Issued by. Ministry of Industry and Information Technology of PRC
Table of Contents
Foreword... 5
1 Scope... 7
2 Normative references... 7
3 Terms and definitions... 7
4 X-ray fluorescence spectroscopy... 8
5 Qualitative test of hexavalent chromium in metal anti-corrosion plating... 11
6 Determination of hexavalent chromium content in metal anti-corrosion plating... 14
7 Determination of hexavalent chromium content in polymer materials and electronic
materials... 18
8 Determination of hexavalent chromium content in leather materials (colorimetric
method)... 26
9 Determination of hexavalent chromium content in leather materials (chromatographic
method)... 32
10 Test report... 35
Appendix A (Informative) Calculation method of surface area of fastener plating... 36
Appendix B (Normative) Determination of recovery and detection limits for the
determination method of hexavalent chromium content in polymer materials and
electronic materials... 42
Appendix C (Normative) Determination of volatile content in leather materials... 45
Appendix D (Normative) Determination of recovery rate of in the determination
method of hexavalent chromium content in leather materials (Colorimetric method) 47
Appendix E (Informative) Chromatographic conditions for direct detection... 49
Appendix F (Informative) Chromatographic conditions for post-column reaction... 52
Appendix G (Normative) Determination of recovery rate of the determination method
of hexavalent chromium content in leather materials (chromatographic method)... 56
1 Scope
This document specifies the terms and definitions of hexavalent chromium detection in
automotive materials, X-ray fluorescence spectroscopy, qualitative test of hexavalent
chromium in metal anti-corrosion plating, determination of hexavalent chromium
content in metal anti-corrosion plating, determination of hexavalent chromium in
polymer materials and electronic materials, determination of hexavalent chromium
content in leather materials (colorimetric method), determination of hexavalent
chromium content in leather materials (chromatographic method), test reports, etc.
This document applies to qualitative and quantitative testing of hexavalent chromium,
in automotive materials.
2 Normative references
The contents of the following documents constitute essential provisions of this
document through normative references in the text. Among them, for dated references,
only the version corresponding to the date applies to this document; for undated
references, the latest version (including all amendments) is applicable to this document.
GB/T 8170 Rules of rounding off for numerical values & expression and judgement
of limiting values
GB/T 30512 Requirements for prohibited substances on automobiles
QB/T 2262 Terms of leather industry
QB/T 2706 Leather - Chemical physical and mechanical and fastness tests -
Sampling location
3 Terms and definitions
The terms and definitions, which are defined in GB/T 30512 and QB/T 2262, as well
as the following terms and definitions, apply to this document.
3.1
Homogeneous material
The material of part or assembly, that cannot be further disassembled by mechanical
means (e.g., unscrewing, cutting, rolling, scraping, grinding, etc.) AND whose parts
have the same composition.
3.2
Equivalent comparison standard solution
A standard solution, that can be replaced by an equivalent value, according to the
requirements of the standard, AND does not affect the detection and analysis results.
3.3
Part
Parts in the initial state, that have not been subject to sample preparation AND
cannot be tested.
3.4
Sample
Parts that have been subject to the processing of the sample preparation and can be
used for testing, OR parts that can be directly tested, without sample preparation.
4 X-ray fluorescence spectroscopy
4.1 Principle
After the part is prepared into a sample, place the sample in the sample chamber of the
X-ray fluorescence spectrometer. Carry out the X-ray fluorescence spectrum analysis,
on the content of hexavalent chromium (calculated as total chromium) in the sample,
according to the selected analysis mode. Whether the content of hexavalent chromium
(calculated as total chromium) in the sample is qualified, AND whether quantitative
detection of hexavalent chromium is required, are judged based on the screening limit
values.
This method is suitable for screening and rapid determination of the content of
hexavalent chromium (calculated as total chromium), in automotive materials, by X-
ray fluorescence spectrometer. However, it is not applicable to the determination of
hexavalent chromium content (calculated as total chromium), in metal anti-corrosion
plating.
4.2 Reagents and materials
4.2.1 Unless otherwise stated, only reagents confirmed to be analytically pure and
distilled or deionized water or water of equivalent purity, are used in the analysis.
4.2.2 Boric acid. Excellent grade pure, which is dried at 105 °C for 1 h, then stored in
a desiccator.
4.2.3 Anhydrous lithium tetraborate. Excellent grade pure, which is calcined at 700 °C
for 4 hours, then stored in a desiccator.
4.2.4 Liquid nitrogen. Industrial grade.
4.2.5 Standard material containing chromium element.
4.2.6 Polyester film.
4.3 Instruments and equipment
4.3.1 X-ray fluorescence spectrometer.
4.3.2 Cutting machine.
4.3.3 Liquid nitrogen cryogenic pulverizer.
4.3.4 Grinding machine. Abrasives with tungsten carbide (WC).
4.3.5 Tablet press. The working pressure is not less than 20 MPa.
4.3.6 Fusion machine. The working temperature is not lower than 1150 °C.
4.4 Samples
4.4.1 Principles of sample preparation
4.4.1.1 The sample, which is used for analysis, must cover the measurement window of
the spectrometer.
4.4.1.2 The irradiated surface of the sample shall be able to represent the whole sample.
4.4.1.3 Care shall be taken, to prevent contamination during sample preparation.
4.4.2 Sample preparation method
4.4.2.1 Solid parts
Homogeneous material part, which has flat surfaces and sizes suitable for X-ray
fluorescence spectrometer requirements, is subject to direct analysis. Small parts, which
have flat surfaces, can be pooled together for analysis. For thin parts, that can be stacked
together to be thick enough (at least 5 mm thick and maintain thickness consistency and
compositional uniformity) for analysis. In order to spread the sample flat, during
analysis, a lining material can be added as a support. It shall select the lining material,
which has a low background, as much as possible.
For various blocks, plates, other indeterminate parts, parts that are too large, cutting
machines and grinders, etc. can also be used to process them to appropriate sizes. For
small parts, which have uneven surfaces (such as plastic particles, etc.), they can be
frozen by liquid nitrogen, pulverized mechanically, then pressed by a tablet press, to
prepare analytical samples. For fragile parts, such as glass and ceramics, they are first
crushed into small pieces; then ground into powders of less than 200 mesh. After mixing
evenly, use boric acid (see 4.2.2) as base, to press it into sample, which has a thickness
of not less than 1 mm. OR use anhydrous lithium tetraborate (see 4.2.3), to prepare glass
melt, for analysis of samples. For heterogeneous parts, which are composed of
heterogeneous materials AND do not require or are difficult to further mechanically
disassemble, cut the parts into pieces; freeze them in liquid nitrogen; use a grinder to
grind the broken samples into powders with a particle size of not more than 1 mm. After
mixing the sample, use boric acid (see 4.2.2) as base to press it, to prepare the sample,
which has a thickness of not less than 1 mm. OR use anhydrous lithium tetraborate (see
4.2.3) to make a glass melt, to analyze the sample.
5 Qualitative test of hexavalent chromium in metal anti-
corrosion plating
5.1 Principle
Under acidic conditions, the hexavalent chromium in the metal anti-corrosion plating
reacts with diphenylcarbazide. The diphenylcarbazide is oxidized to diphenylcarbazone,
whilst the hexavalent chromium is reduced to trivalent chromium. The trivalent
chromium further reacts with diphenylcarbazone, to form a red or purple complex,
which can be used to qualitatively judge whether there is hexavalent chromium in the
metal anti-corrosion plating.
This method is suitable for qualitative determination of hexavalent chromium in
automotive metal anti-corrosion plating.
5.2 Reagents and materials
5.2.1 Unless otherwise stated, only reagents confirmed to be analytically pure and
distilled or deionized water or water of equivalent purity are used, in the analysis.
5.2.2 Diphenylcarbazide.
5.2.3 Potassium dichromate.
5.2.4 Acetone.
5.2.5 Ethanol.
5.2.6 Orthophosphoric acid solution (mass fraction 75%).
5.2.7 Hexavalent chromium stock solution. Weigh 0.1414 g of potassium dichromate
(see 5.2.3), which was dried to constant weight. Dissolve it in water. Transfer it into a
100 mL volumetric flask. Dilute to the mark. The hexavalent chromium content of this
solution is 500 µg/mL. Cap the container tightly. This solution is valid for 12 months.
Or use the national standard solution.
6 Determination of hexavalent chromium content in metal
anti-corrosion plating
6.1 Principle
The hexavalent chromium in the metal anti-corrosion plating is extracted, by boiling
water extraction. Under acidic conditions, the hexavalent chromium reacts with
diphenylcarbazide; the diphenylcarbazide is oxidized to diphenylcarbazone, whilst the
hexavalent chromium is reduced to trivalent chromium; the trivalent chromium and
diphenylcarbazone further react, to form a red or purple complex, which can be
quantitatively determined by a colorimeter at 540 nm; then the content of hexavalent
chromium in the metal plating is quantitatively determined.
This method is suitable for quantitative determination of hexavalent chromium content,
in automotive metal anti-corrosion plating, including no additional covering layers (e.g.,
oil films, water-based or solvent-based polymers or wax films).
Note. For the new off-line metal anti-corrosion plating part, it shall be sealed for at least 5 days,
to make the plating stable, before testing.
6.2 Reagents and materials
6.2.1 Unless otherwise stated, only reagents confirmed to be analytically pure and
distilled or deionized water or water of equivalent purity are used, in the analysis.
6.2.2 Diphenylcarbazide.
6.2.3 Potassium dichromate.
6.2.4 Acetone.
6.2.5 Orthophosphoric acid solution (mass fraction 75%).
6.2.6 Hexavalent chromium stock solution. Weigh 0.113 g of potassium dichromate
(see 6.2.3, dry at 100 °C for 1 h before use) in a glass vessel. Add water to make the
volume reach to 1000 mL. The hexavalent chromium concentration, in this solution, is
40 µg/mL. Cap the container tightly. This solution is valid for 12 months. OR use
national standard solution.
6.2.7 Equivalent standard solution of hexavalent chromium. Pipette 3.3 mL of
hexavalent chromium stock solution (see 6.2.6), into a volumetric flask. Dilute it to
1000 mL. The concentration of this equivalent standard solution of hexavalent
chromium is 0.13 µg/mL, which is equivalent to 0.13 µg/cm2.Cap the container tightly.
This solution is valid for 24 hours. OR use the national standard solution.
6.2.8 Color developing solution B. Weigh 0.5 g of diphenylcarbazide (see 6.2.2).
Dissolve it in 50 mL of acetone (see 6.2.4). Use 50 mL of water to dilute it, under
stirring (quick mixing may produce diphenylcarbazide precipitates). This solution shall
be refrigerated at 7 °C ± 2 °C in brown glass bottles. It shall not be used, if discolored.
7 Determination of hexavalent chromium content in polymer
materials and electronic materials
7.1 Principle
After dissolving or swelling samples of various matrices, by organic solvents, use an
alkaline digestion solution, to extract the hexavalent chromium in the samples. Then
under acidic conditions, diphenylcarbazide reacts with hexavalent chromium;
diphenylcarbazide is oxidized to diphenylcarbazone; hexavalent chromium is reduced
to trivalent chromium. Trivalent chromium and diphenylcarbazone further react, to
form a red or purple complex, which can be quantitatively determined, by a colorimeter,
at 540 nm.
This method is suitable for the determination of hexavalent chromium content, in
automotive polymer materials and electronic materials. The content of hexavalent
chromium in other automotive materials, such as glass, ceramics, fabrics, paints, is
determined with reference to this method.
7.2 Reagents and materials
7.2.1 Unless otherwise stated, only reagents confirmed to be analytically pure and
distilled or deionized water or water of equivalent purity are used, in the analysis.
7.2.2 N-Methylpyrrolidone (NMP). Add 10 g of active molecular sieve, to each 100 mL
of newly opened NMP. Seal it. Store it in a brown bottle. Store it in the dark, at 20 °C
~ 25 °C. Shake it occasionally. It shall be stored for more than 12 hours before first use.
The validity period after opening is 28 days.
7.2.3 Nitric acid (35% by volume fraction). Store it in the dark at 20 °C ~ 25 °C. Do
not use yellow concentrated nitric acid when preparing it, because the contained NO3-
will decompose into NO2- in light, leading to the reduction of hexavalent chromium.
7.2.4 Diphenylcarbazide.
7.2.5 Acetone.
7.2.6 Anhydrous magnesium chloride. 200 mg of MgCl2 is equivalent to 50 mg of Mg2+.
7.2.7 Phosphate buffer solution. Prepare pH = 7 buffer. Use 700 mL of water, to dissolve
87.09 g K2HPO4 and 68.04 g KH2PO4.Transfer it into a 1 L volumetric flask. Dilute it
to the mark. The prepared solution contains K2HPO4 of 0.5 mol/L and KH2PO4 of 0.5
mol/L.
7.2.8 Lead chromate. Excellent grade pure, which is sealed and stored at 20 °C ~ 25 °C.
7.2.9 Digestion solution. Use water to dissolve 20.0 g ± 0.05 g of sodium hydroxide
and 30.0 g ± 0.05 g of anhydrous sodium carbonate. Place it in a 1 L volumetric flask.
Dilute it to the mark. Seal it in polyethylene bottles at 20 °C ~ 25 °C, which is valid for
30 days. Check the pH value of the digestion solution, before use. If the pH value is
less than 11.5, it requires preparing the digestion solution again.
7.2.10 Toluene.
7.2.11 Potassium dichromate stock solution. Dissolve 0.1414 g of K2Cr2O7, which was
dried at 105 °C, in water. Dilute it into a 1 L volumetric flask. The hexavalent chromium
content of this solution is 50 µg/mL. OR use the national standard solution.
7.2.12 Potassium dichromate standard solution. Use water to dilute 10 mL of potassium
dichromate stock solution (see 7.2.11), in a 100 mL volumetric flask. The hexavalent
chromium content of this solution is 5 µg/mL. OR use the national standard solution.
7.2.13 Sulfuric acid (10% by volume fraction). Use water to dilute 10 mL of sulfuric
acid, in a 100 mL volumetric flask.
7.2.14 Color developing solution C. Weigh 0.25 g of diphenylcarbazide (see 7.2.4).
Dissolve it in 50 mL of acetone (see 7.2.5). This solution shall be stored in a brown
glass bottle, which is valid for 14 days. It shall not be used, if discolored.
7.2.15 1000 µg/mL hexavalent chromium standard solution. Dissolve 2.829 g of
K2Cr2O7, which was dried at 105 °C, in water. Dilute it into a 1 L volumetric flask. Seal
and store it under the conditions of 20 ° C ~ 25 ° C, which is valid for 6 months. OR
use the national standard solution.
7.2.16 100 µg/mL hexavalent chromium substrate standard solution. Take 10 mL of
1000 µg/mL hexavalent chromium standard solution (see 7.2.15), in a 100 mL
volumetric flask. Use water to dilute it to the mark.
7.2.17 Molecular sieve (4A). CAS. 70955-01-0, desiccant.
7.3 Instruments and equipment
7.3.1 All reusable containers (glass containers, quartz containers, polyethylene,
polytetrafluoroethylene (PTFE), etc.), including sample containers, shall be immersed
overnight in a laboratory-grade detergent solution. Use water to wash it. Then use HNO3
(the volume fraction is 20%) or mixed acid (volume ratio HNO3.HCl. H2O = 1.2.9),
to soak it in 4 h. Use water to wash it. The cleaning effect can be proved by the method
blank test, OR other cleaning methods can also be used.
7.3.2 Vacuum filtration device.
7.3.3 Heating or microwave digestion device. It can keep the digestion temperature at
150 °C ~ 160 °C.
7.3.4 Ultrasonic water bath device. The temperature can be maintained at 60 °C ~ 65 °C.
7.3.5 Calibrated pH meter. The accuracy is ±0.03; the pH measurement range is 0 ~ 14.
7.3.6 Analytical balance. The accuracy is 0.1 mg.
7.3.7 Thermometers, thermistor thermometers or other temperature testers. The
measurement temperature range is greater than 160 °C.
8 Determination of hexavalent chromium content in leather
materials (colorimetric method)
8.1 Principle
The phosphate buffer solution, which has a pH value of 7.0 ~ 8.0, is used as the
extraction solution, to extract hexavalent chromium in the leather sample. When
necessary, the substance that interferes with the test can be removed by solid-phase
extraction. The hexavalent chromium in the extract reacts with diphenylcarbazide,
under acidic conditions; the diphenylcarbazide is oxidized to diphenylcarbazone, whilst
hexavalent chromium is reduced to trivalent chromium. Trivalent chromium and
diphenylcarbazone further react, to form a red or purple complex, which can be
quantitatively determined by a colorimeter, at 540 nm.
This method is suitable for the determination of hexavalent chromium content, in
automotive leather materials.
8.2 Reagents and materials
8.2.1 Unless otherwise stated, only reagents confirmed to be analytically pure and
distilled or deionized water or water of equivalent purity are used, in the analysis.
8.2.2 Diphenylcarbazide.
8.2.3 Acetone.
8.2.4 Methanol. HPLC grade.
8.2.5 Phosphoric acid solution. Take 700 mL of phosphoric acid (ρ = 1.71 g/mL). Dilute
it to 1000 mL.
8.2.6 Phosphate buffer solution (extract). Dissolve 22.8 g of dipotassium hydrogen
phosphate, in 1000 mL of water. Use phosphoric acid solution (see 8.2.5), to adjust the
pH to 8.0 ± 0.1.Then use argon or nitrogen (see 8.2.10), to expel air, OR use ultrasonic
bath. Extracts can be stored at 4 °C ± 3 °C, for 7 days; however, it shall be brought to
room temperature and degassed, before use.
8.2.7 Color developing solution D. Take 1.0 g of diphenylcarbazide (see 8.2.2).
Dissolve it in 100 mL of acetone (see 8.2.3). Add 1 drop of acetic acid to acidify it. This
solution is refrigerated in a brown glass bottle and stored in the dark at 4 °C ± 3 °C. The
validity period is 14 days.
8.2.8 Hexavalent chromium stock solution. Dissolve 2.829 g of potassium dichromate
in water. Use a volumetric flask, to dilute it to 1000 mL. The concentration of
hexavalent chromium in this solution is 1000 µg/mL. OR use the national standard
solution.
8.2.9 Hexavalent chromium standard solution. Pipette 0.5 mL of hexavalent chromium
stock solution (see 8.2.8), into a 100 mL volumetric flask. Use phosphate buffer (see
8.2.6), to make its volume reach to the mark. The valence chromium's concentration of
this solution is 5µg/mL. The solution is stored in a refrigerator at 4 °C ± 3 °C, which
has a valid period of 7 days. However, it shall be brought to room temperature, before
use.
9 Determination of hexavalent chromium content in leather
materials (chromatographic method)
9.1 Principle
Extractable hexavalent chromium is extracted from the sample, by phosphate buffer at
pH 7.0 ~ 8.0.An aliquot of the filtrate extract is analyzed for hexavalent chromium,
using ion exchange chromatography or high performance liquid chromatography.
This method is suitable for the determination of hexavalent chromium content, in
automotive leather materials.
9.2 Reagents and materials
Prepare reagents and materials, as required in 8.2.
9.3 Instruments and equipment
Use the equipment required in 8.3.Meanwhile use an ion exchange chromatograph with
a UV detector OR a high performance liquid chromatograph (HPLC) with an anion
exchange column and a UV detector. A photodiode array detector (DAD) can also be
used.
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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