GB/T 20975.2-2018: Methods for chemical analysis of aluminium and aluminium alloys - Part 2: Determination of arsenic content

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Scope

This Part of GB/T 20975 specifies the method for determination of arsenic
content in aluminium and aluminium alloys.
This Part applies to the determination of arsenic content in aluminium and
aluminium alloys. All coexisting elements in aluminium and aluminium alloys do
not interfere with the determination of arsenic. The measurement range of
Method 1 is. >0.0005%~0.020%. The measurement range of Method 2 is.
0.000002%~0.0005%.
2 Method 1. Molybdenum blue spectrophotometric
method
2.1 Method principle
The test portion is dissolved with a mixed acid of sulfuric acid, hydrochloric acid,
and nitric acid. The iodide of trivalent arsenic is extracted from the hydrochloric
acid solution with carbon tetrachloride, then transferred to the aqueous phase.
The trivalent arsenic is oxidized to pentavalent arsenic with iodine, to form a
colored complex with ammonium molybdate. At a wavelength of 850 nm of a
spectrophotometer, the absorbance of the complex is measured, to calculate
the mass fraction of arsenic.
2.2 Reagents and materials
Unless otherwise stated, in the analysis, only identified guaranteed reagents
and Grade 1 water are used.
2.2.1 Hydrochloric acid (ρ=1.19 g/mL).
2.2.2 Hydrochloric acid (1+1).
2.2.3 Sulfuric acid (1+1).
dilute to volume, and MIX well. PLACE at 20 °C~30 °C for 40 min.
2.5.4.4 Part of the test solution (2.5.4.3) and the blank test solution (2.5.3) are
transferred into a 5 cm absorption cell. With water as a reference, at a
wavelength of 850 nm of the spectrophotometer, the absorbance is measured.
The absorbance of the blank test solution (2.5.3) is subtracted from the
absorbance of the test solution (2.5.4.3), and the corresponding amount of
arsenic is found from the working curve.
2.5.5 Drawing of working curve
2.5.5.1 PIPETTE 0 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL, 5.00 mL, 10.00
mL of arsenic standard solution (2.2.13) into 50 mL volumetric flasks; and
operate as specified in 2.5.4.3.
2.5.5.2 MOVE some of the series of standard solutions (2.5.5.1) into the 5 cm
absorption cell. With water as a reference, at a wavelength of 850 nm of the
spectrophotometer, the absorbance is measured. The arsenic content is taken
as the abscissa; the absorbance, obtained by subtracting the absorbance of the
“zero” concentration solution in the series of standard solutions from the
absorbance of the standard solution, is taken as the ordinate; and the working
curve is drawn.
2.6 Calculation of analytical results
The mass fraction w(As) of arsenic is calculated according to formula (1).
Where.
m1 - The arsenic content found from the working curve, in micrograms (μg);
m0 - The mass of the test portion, in grams (g).
The calculation result retains 2 significant figures.
2.7 Precision
2.7.1 Repeatability
The absolute difference between the two independent determination results
obtained under repeated conditions, within the average range given below,
does not exceed the repeatability limit (r). The situations where the repeatability
limit (r) is exceeded do not exceed 5%. The repeatability limit (r), according to
3.2.5 Mixed acid. Hydrochloric acid (3.2.3) and nitric acid (3.2.4) are mixed in
an equal volume ratio.
3.2.6 Hydrochloric acid (5+95).
3.2.7 Potassium borohydride solution (10 g/L). WEIGH 2.5 g of potassium
borohydride in a beaker; USE sodium hydroxide solution (5 g/L) to dilute to 250
mL and SHAKE well. Prepared when used.
3.2.8 Thiourea-ascorbic acid solution (100 g/L). WEIGH 25 g of thiourea and 25
g of ascorbic acid into a 300 mL beaker; USE water to dissolve and dilute to
250 mL, SHAKE well; and TRANSFER to a brown bottle. Prepared when used.
3.2.9 Standard stock solution of arsenic (1.0 mg/mL). WEIGH 1.320 g of arsenic
trioxide dissolved in 5 mL of sodium hydroxide solution (200 g/L); USE
hydrochloric acid (3.2.3) to acidify until the Congo red paper is blue;
TRANSFER the solution to a 1000 mL volumetric flask; USE water to dilute to
volume, and MIX well. 1 mL of this solution contains 1.0 mg of arsenic.
3.2.10 Arsenic standard solution A (10 μg/mL). PIPETTE 1.00 mL of standard
stock solution of arsenic (3.2.9) into a 100 mL volumetric flask; USE
hydrochloric acid (3.2.6) to dilute to volume, and MIX well. 1 mL of this solution
contains 10 μg of arsenic. Prepared when used.
3.2.11 Arsenic standard solution B (0.1 μg/mL). PIPETTE 1.00 mL of arsenic
standard solution A (3.2.10) into a 100 mL volumetric flask; USE hydrochloric
acid (3.2.6) to dilute to volume, and MIX well. 1 mL of this solution contains 0.1
μg of arsenic. Prepared when used.
3.3 Instrument
Atomic fluorescence spectrometer, with arsenic hollow cathode lamp.
3.4 Sample
The sample is processed into chips having a thickness of no more than 1 mm.
3.5 Analytical procedures
3.5.1 Test portion
Sample (3.4) is weighed according to Table 4, accurate to 0.0001 g.

Basic Data

Standard ID	GB/T 20975.2-2018 (GB/T20975.2-2018)
Description (Translated English)	Methods for chemical analysis of aluminium and aluminium alloys - Part 2: Determination of arsenic content
Sector / Industry	National Standard (Recommended)
Classification of Chinese Standard	H12
Classification of International Standard	77.120.10
Word Count Estimation	9,978
Date of Issue	2018-05-14
Date of Implementation	2019-02-01
Older Standard (superseded by this standard)	GB/T 20975.2-2007
Regulation (derived from)	National Standards Announcement No. 6 of 2018
Issuing agency(ies)	State Administration for Market Regulation, China National Standardization Administration
Summary	This standard specifies the method for the determination of arsenic in aluminum and aluminum alloys. This standard applies to the determination of arsenic in aluminum and aluminum alloys. All coexisting elements in aluminum and aluminum alloys do not interfere with the determination of arsenic. The first method has a measurement range of >0.0005% to 0.020%, and the second method has a detection range of 0.000002% to 0.0005%.