GB/T 13088-2006 English PDF (GBT13088-2006)

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GB/T 13088-2006: Determination of chromium in feeds
GB/T 13088-2006
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 65.120
B 46
Replacing GB/T 13088-1991
Determination of chromium in feeds
ISSUED ON: JUNE 09, 2006
IMPLEMENTED ON: SEPTEMBER 01, 2006
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 Normative references ... 4
3 Method 1: Atomic absorption spectrometry ... 4
4 Method 2: Spectrophotometry ... 9
Determination of chromium in feeds
1 Scope
This Standard specifies two methods for the determination of chromium content in feed
by atomic absorption spectrometer and spectrophotometer.
Method 1 of this Standard is atomic absorption spectrometry. It is applicable to feed
raw materials (including leather powder for feed, hydrolyzed leather powder), trace
element premixes, compound premixes, concentrates and compound feeds. The
minimum detection limit of graphite furnace atomic absorption spectrometry is 0.005
μg/kg. The minimum detection limit of flame atomic absorption spectrometry is 150
μg/kg. Method 2 of this Standard is spectrophotometric method. It is applicable to the
determination of chromium in feed raw materials (including hydrolyzed leather powder)
and compound feed.
2 Normative references
The provisions in following documents become the provisions of this Standard through
reference in this Standard. For dated references, the subsequent amendments (excluding
corrigendum) or revisions do not apply to this Standard, however, parties who reach an
agreement based on this Standard are encouraged to study if the latest versions of these
documents are applicable. For undated references, the latest edition of the referenced
document applies.
GB/T 6682, Water for analytical laboratory use - Specification and test methods
(neq ISO 3696)
GB/T 14699.1, Feeding stuffs - Sampling
3 Method 1: Atomic absorption spectrometry
3.1 Principle
The sample is ashed at high temperature. After dissolving with acid, inject it into the
atomic absorption spectrometer detector. In a certain concentration range, its absorption
value is proportional to the chromium content. Compare with the standard series to
quantify.
3.2 Reagents and solutions
Unless otherwise specified, the reagents used in Method 1 are guaranteed reagents; the
water is ultrapure water or water of corresponding purity, which meets the requirements
of GB/T 6682 for grade one water.
3.2.1 Concentrated nitric acid.
3.2.2 Nitric acid solution: V (nitric acid) +V (water) =2+98.
3.2.3 Nitric acid solution: V (nitric acid) + V (water) =20+80.
3.2.4 Chromium standard solution
3.2.4.1 Chromium standard stock solution (100 mg/L): Weigh 0.2830 g of potassium
dichromate that has been baked at 100°C~110°C to a constant amount. Use water to
dissolve. Move into a 1000 mL volumetric flask. Dilute to the scale. This solution is
equivalent to 0.1 mg of chromium per mL.
3.2.4.2 Chromium standard solution 1 (20 mg/L): Weigh 10.0 mL of chromium standard
stock solution (3.2.4.1) in a 50 mL volumetric flask. Add nitric acid solution (3.2.2) to
dilute to the scale. This solution is equivalent to 20 μg of chromium per mL.
3.2.4.3 Chromium standard solution 2 (2 mg/L): Weigh 1.0 mL of chromium standard
stock solution (3.2.4.1) in a 50 mL volumetric flask. Add nitric acid solution (3.2.2) to
dilute to the scale. This solution is equivalent to 2 μg of chromium per mL.
3.2.4.4 Chromium standard solution 3 (0.2 mg/L): Weigh 10.0 mL of chromium
standard solution 2 (3.2.4.3) in a 100 mL volumetric flask. Add nitric acid solution
(3.2.2) to dilute to the scale. This solution is equivalent to 0.2 μg of chromium per mL.
3.3 Instruments and equipment
All glassware and crucibles are immersed in nitric acid solution (3.2.3) for 24 h or
longer. User pure water to rinse. Dry in the air.
3.3.1 Experimental sample grinder or mortar (chromium-free).
3.3.2 Ultrapure water device (Millipore).
3.3.3 Analytical balance: resolution is 0.0001 g.
3.3.4 Porcelain crucible: 60 mL.
3.3.5 Temperature-controlled electric hob: 600 W.
3.3.6 High temperature electric furnace (muffle furnace).
3.3.7 Volumetric flasks: 20 mL, 50 mL, 100 mL, 1000 mL.
3.3.8 Pipettes: 0.5 mL, 1.0 mL, 2.0 mL, 3.0 mL, 5.0 mL, 10.0 mL, 25.0 mL.
3.3.9 Short-necked funnel: 6 cm in diameter.
3.3.10 Filter paper: 11 cm, quantitative, fast.
3.3.11 Atomic absorption spectrometer.
3.4 Specimen preparation
According to GB/ T 14699.1, collect about 2 kg of representative feed raw materials
(including leather powder for feed, hydrolyzed leather powder), mineral element
premix, compound premix, concentrate and compound feed. Use quartering method to
reduce it to about 250 g. Grind and pass through the 1 mm hole sieve. Mix well. Put in
an airtight container. In order to prevent the specimen from deteriorating, it should be
stored at low temperature for later use.
3.5 Analysis steps
3.5.1 Preparation of specimen solution
Weigh 0.1 g ~ 10.0 g of specimen (accurate to 0.0001 g). Place in the 60 mL porcelain
crucible. Perform complete carbonization on the electric furnace. Place in the muffle
furnace. Starting from room temperature, gradually increase the temperature to 600°C
for 5 h, until the specimen is white or off-white without carbon particles.
Take out after cooling. Use 5 mL of nitric acid (3.2.3) to dissolve. Filter to a 50 mL
volumetric flask. Use pure water to wash repeatedly the crucible and the filter paper.
The washing solution is put into the volumetric flask. Then use pure water to set the
volume constant. Mix it well as the specimen solution. At the same time, prepare the
reagent blank solution.
3.5.2 Determination
3.5.2.1 Determination conditions
Adjust to the best state according to the performance of each instrument.
3.5.2.1.1 Flame method
Light source: Cr hollow cathode lamp.
Wavelength: 359.3 nm.
Lamp current: 7.5 mA.
Slit width: 1.30 nm.
Combustion head height: 7.5 mm.
Flame: air-acetylene.
The calculation result is the arithmetic mean value of two parallel samples of the same
specimen, accurate to two decimal places.
3.7 Repeatability
The same analyst performs two measurements on the same specimen simultaneously or
in rapid succession. The relative deviation of the obtained results:
- When the chromium content is less than 10 mg/kg, the relative deviation shall not
exceed 20%.
- When the chromium content is greater than or equal to 10 mg/kg, the relative
deviation shall not exceed 10%.
4 Method 2: Spectrophotometry
4.1 Principle
Decompose the sample by dry ashing. Chromium ions in it are oxidized to hexavalent
chromium ions in alkaline potassium permanganate solution. Adjust the solution acidic
again. Make hexavalent chromium ion (Cr6+) and diphenylcarbazide
[(C6H5)2·(NH)4·CO] to generate rose red chromium compound. Perform colorimetric
measurement. Calculate the chromium content.
4.2 Reagents and solutions
Unless otherwise specified, the reagents used in this Method 2 are analytically pure; the
water is distilled water or water of corresponding purity, which conforms to the
provisions of GB/T 6682 for grade three water.
4.2.1 Sulfuric acid solution: c (H2SO4) = 0.5 mol/L. Measure 28 mL of concentrated
sulfuric acid. Add it into water slowly. Add water to dilute to 1000 mL.
4.2.2 Pot...