GB/T 28019-2011 English PDF (GBT28019-2011)

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GB/T 28019-2011: Adornment -- Determination of Chromium (VI). 1, 5-Diphenylcarbohydrazide spectrophotometric method
GB/T 28019-2011
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 39.060
Y 88
Adornment - Determination of Chromium (VI) - 1,5-
Diphenylcarbohydrazide Spectrophotometric Method
ISSUED ON. OCTOBER 31, 2011
IMPLEMENTED ON. FEBRUARY 1, 2012
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine of the People’s Republic of China
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Method and Principle ... 4
3 Reagents and Materials ... 4
4 Apparatus ... 5
5 Analysis Steps ... 6
6 Representation of the Result ... 7
7 Test Report ... 8
Adornment - Determination of Chromium (VI) - 1,5-
Diphenylcarbohydrazide Spectrophotometric Method
1 Scope
This standard specifies the 1,5-Diphenylcarbohydrazide spectrophotometric method
for Chromium (VI).
This Standard applies to the determination of Chromium (VI) in adornment.
2 Method and Principle
Use alkaline leaching solution to leach the water-soluble and water-insoluble
hexavalent chromium compounds from the sample. In acidic solution, the hexavalent
chromium from the leachate reacts with the diphenylcarbazide and the reaction forms
the purple-red complex. At the wavelength of 540 nm, perform spectrophotometric
determination.
3 Reagents and Materials
Unless otherwise stated, in analysis, it can only use the reagents, which are confirmed
as the analytic reagents and distilled water, or deionized water, or the water with the
equal purity.
3.1 Nitric acid - guarantee reagent.
3.2 Sulfuric acid - guarantee reagent.
3.3 Sodium hydroxide.
3.4 Anhydrous sodium carbonate.
3.5 Dipotassium phosphate.
3.6 Potassium dihydrogen phosphate.
3.7 Potassium dichromate - reference substance.
3.8 Diphenylcarbazide.
5 Analysis Steps
5.1 Sample Preparation
5.1.1 Metal Material
Process the sample into the crumb or strip whose diameter are no more than 1 mm
and whose length are no more than 5 mm.
5.1.2 Other Materials
Use the crushing apparatus, such as electric saw and grinder, etc. to grind the sample
into the powder-like, and the powder’s particle size shall be not more than 1 mm.
5.2 Sample extraction
Accurately weigh and take two 0.3g~1.0g of the processed sample - accuracy. 0.1mg;
place them in a conical flask; add 25.0mL of leaching solution (3.12) and 0.5mL of
buffer solution (3.13). Leaching solution shall completely immerse the sample; shake
it evenly; in a 90°C~95°C water bath kettle [or the oscillating water bath kettle (4.2)],
continuously stir it for 1.5h; take it out; cool it to the room temperature; filter it; use
water to wash the conical flask and sample; collect the filtrate and washing liquid into
a beaker; dropwise-add 5mol/L nitric acid solution (3.11); use the acidity meter (4.3) to
test and control solution’s pH value at 7.5 ± 0.5. If the flocculent precipitate occurs, it
shall be filtered again and shall retain the filtrate. At the same time, perform reagent’s
blank test.
5.3 Color Rendering
Add 2.0mL of diphenylcarbazide (DPC) solution (3.16) into the filtrate (5.2); mix it
evenly; add sulfuric acid solution (3.10); make filtrate’s pH reach 2±0.5; then transfer
the whole filtrate into a 100mL volumetric flask; use water to dilute it until the mark;
shake it evenly; place it for 0.5h.
5.4 Calibration Solution
Respectively pipette 0.0mL, 2.0mL, 4.0mL, 6.0mL, 8.0mL and 10.0mL of standard
solution of hexavalent chromium (3.15) into the 100mL volumetric flask; add 50mL of
water; add 2.0mL of diphenylcarbazide (DPC) solution (3.16); mix it evenly; add 2
drops of sulfuric acid solution (3.10); make filtrate’s pH reach 2±0.5; use water to dilute
it until the mark; shake it evenly; place it for 0.5h.
In this calibration solution series, their hexavalent-chromium’s concentration was
0.0mg/L, 0.1mg/L, 0.2mg/L, 0.3mg/L, 0.4mg/L and 0.5mg/L respectively.