GB/T 223.12-1991 English PDF (GBT223.12-1991)

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GB/T 223.12-1991: Methods for chemical analysis of iron, steel and alloy. The sodium carbonate separation-diphenyl carbazide photometric method for the determination of chromium content
GB/T 223.12-91
GB
NATIONAL STANDARD OF
THE PEOPLE’S REPUBLIC OF CHINA
UDC 223.14.118.821.543.42
H 11
Replacing GB 223.12-82
Methods for chemical analysis of iron, steel and alloy
- The sodium carbonate separation-diphenyl
carbazide photometric method for the
determination of chromium content
ISSUED ON. SEPTEMBER 6, 1991
IMPLEMENTED ON. JUNE 1, 1992
Issued by. China Bureau of Technical Supervision.
Approved by China Bureau of Technical Supervision, September 6, 1991
Table of Contents
Additional Information ... 3 
1 Subject and scope ... 4 
2 Method summary ... 4 
3 Reagents ... 4 
4 Analysis steps ... 5 
5 Calculation of analysis results ... 6 
6 Precisions ... 7 
Annex A (Supplement) Original data for precision test ... 8 
Additional Information
This Standard was proposed by Ministry of Metallurgical Industry of People's
Republic of China.
This Standard shall be under the technical jurisdiction of Metallurgical
Industry Research Institute of Iron and Steel.
Main drafting organization of this Standard. Metallurgical Industry Research
Institute of Iron and Steel.
Main drafter of this Standard. Cao Hongyao.
This Standard level mark. GB 223.12-91 I
Methods for chemical analysis of iron, steel and alloy
- The sodium carbonate separation-diphenyl
carbazide photometric method for the
determination of chromium content
1 Subject and scope
This Standard specifies the sodium carbonate separation-diphenyl carbazide
photometric method for the determination of chromium content.
This Standard is applicable to the determination of chromium content in
carbon steel, low alloy steel and precision alloy. The determination range.
0.005% ~ 0.500%.
2 Method summary
In the sulfuric acid solution, use potassium permanganate to oxidize
chromium to hexavalent. High-price chromium and diphenylcarbazide
generate purple complex. Measure its absorbance. Pre-use sodium
carbonate precipitation to precipitate and separate iron and other elements
coexist.
When 400 mg of iron, 60 mg of nickel, 40 mg of cobalt, 1 mg of copper, 2 mg
of molybdenum, aluminum, 12 mg of tungsten coexist, it shall have no effect
on determination of chromium after separation.
3 Reagents
3.1 Hydrochloric acid (ρ 1.19 g/mL)
3.2 Nitric acid (1+3)
3.3 Sulfuric acid (1+1)
3.4 Sulfuric acid (1+6)
3.5 Potassium permanganate solution (1%)
3.6 Sodium carbonate solution (20%)
3.7 Urea solution (20%)
3.8 Diphenyl carbazide solution (0.25%). weigh 0.25 g of diphenyl carbazide
to dissolve in 94 mL of absolute ethanol and 6 mL of glacial acetic acid (ρ 1.05
g/mL). Store in a brown bottle.
3.9 Sodium nitrite solution (2%)
3.10 Chromium standard solution
3.10.1 Weigh 0.2829 g of potassium dichromate (reference) that have been
dried to constant weight at 150°C. Dissolve in water. Remove to a 1000 mL
volumetric flask. Use water to dilute to scale. Well mix. This solution shall
contain 100 µg of chromium per 1 mL.
3.10.2 Weigh 20.00 mL of chromium standard solution (3.10.1) into a 1000
mL volumetric flask. Use water to dilute to scale. Well mix. This solution shall
contain 2 µg of chromium per 1 mL.
4 Analysis steps
4.1 Sample quantity
Weigh 0.2000 ~ 0.3000 g of sample (when the chromium content in the
sample is less than 0.01%, it shall weigh 0.3000 or 0.4000 g of sample).
4.2 Blank test
Perform the blank test with sample.
4.3 Determination
4.3.1 Sample dissolving
Place the sample (4.1) in to a 200 mL beaker. Add into 10 mL of nitric acid
(3.2) to heat and dissolve [it shall add hydrochloric acid (3.1) to assist
dissolving it is difficult to dissolve]. Add 5 mL of sulfuric acid (3.3). Heat to
evaporate till sulfuric acid smokes. Cool for little while. Add 30 mL of water to
heat and dissolve the salt.
4.3.2 Oxidation and separation
Add 2 mL of potassium permanganate solution (3.5). Boil till manganese
dioxide is completely precipitated. Use water to dilute to 80 ~ 90 mL. While
stirring, slowly add 30 mL of sodium carbonate solution (3.6) (30 mL of
sodium carbonate solution is usually sufficient, but it shall have an excess of
5 mL when sodium carbonate solution precipitates; if 30 mL is not enough,
add a few milliliters). Slowly to heat till it is boiling 2 ~ 3 min. Cool to room
temperature. Move to a 250 mL volumetric flask. Dilute with water to scale
and mix well.
Use double-layer medium-density filter paper to carry out the dry filtration.
Discard the original filtrate. Pipette the filtrate (pipette 50.00 mL when the
chromium content is less than 0.01%, 25.00 mL when it is between 0.01% ~
0.1%, 10.00 mL when it is between 0.1% ~ 0.2%, 5.00 mL when it is more
than 0.2%) into a 100 mL volumetric flask. Add 4.0 mL of sulfuric acid (3.4). At
this point, if the solution is pink, there may be some potassium permanganate
is not decomposed, then add 5 mL of urea solution (3.7). Carefully drop
sodium nitrite solution (3.9) until the test solution is colorless and then an
excess of 1 drop.
4.3.3 Color
Use water to dilute to about 90 mL. Add 3.0 mL of diphenyl carbazide solution
(3.8). Well mix. Use water to dilute to scale. Well mix.
4.3.4 Absorbance measurement
Move the partial solution into a 2 ~ 3 cm absorption dish. Take water as a
reference. Measure its absorbance at a wavelength of 540 nm on
spectrophotometer. Subtract the absorbance of the blank solution along with
the sample, and check the corresponding chromium content in the color
developing solution from the working curve.
4.4 Drawing of working curve
Pipette 0, 1.00, 2.00, 4.00, 7.00, 10.00 mL of chromium standard solution
(3.10.2) into 6 100 mL flasks, respectively. Add 4.0 mL of sulfuric acid (3.4).
The followings shall be carried out according to 4.3.3 and 4.3.4. Use reagent
blank as reference to measure its absorbance. Take absorbance as the
vertical axis, the corresponding chromium content as abscissa to draw the
working curve.
5 Calculation of analysis results
Calculate the percentage of chromium by the following formula.
where,
V1 - volume of sub-test solution, mL;
V - total volume of test solution, mL;
m1 - chromium content checked from working curve, g;
m - sample weighing amount, g.
6 Precisions
The precisions of this Standard were determined in 1989 by a joint test of
eight laboratories at seven levels. The precisions are shown in the following
table.
Level rang, % (m/m) Repeatability r Reproducibility R
0.005 ~ 0.50 lg r = -1.5589 + 0.6552 lg m lg R = -1.3721 + 0.6245 lg m
If the difference between two independent test results exceeds the
repeatability or reproducibility value calculated by the precision function listed
in the table, the two results shall be considered suspicious.
Annex A
(Supplement)
Original data for precision test
Data Level
Laboratory