GB/T 4325.8-2013 PDF English (GB/T 4325.8-1984: Older version)
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Methods for chemical analysis of molybdenum - Part 8: Determination of cobalt content - 5-CI-PADAB spectrophotometry and flame atomic absorption spectrometry
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| GB/T 4325.8-1984 | English | 199 |
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Methods for chemical analysis of molybdenum--The dimethylglyoxime photometric method for the determination of nickel content
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GB/T 4325.8-2013: PDF in English (GBT 4325.8-2013) GB/T 4325.8-2013
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.120.99
H 63
Replacing GB/T 4325.7-1984
Method for chemical analysis of molybdenum - Part 8:
Determination of cobalt content - 5-CI-PADAB
spectrophotometry and flame atomic absorption
spectrometry
ISSUED ON: MAY 09, 2013
IMPLEMENTED ON: FEBRUARY 01, 2014
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of PRC;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 6
2 Normative references ... 6
3 General ... 6
4 Method 1 - Cobalt reagent spectrophotometry ... 7
5 Method 2 - Flame atomic absorption spectrometry ... 10
6 Test report ... 14
Method for chemical analysis of molybdenum - Part 8:
Determination of cobalt content - 5-CI-PADAB
spectrophotometry and flame atomic absorption
spectrometry
1 Scope
This part of GB/T 4325 specifies the determination method of cobalt in
molybdenum.
This part is suitable for the determination of cobalt in molybdenum powder,
molybdenum bar, molybdenum trioxide and ammonium molybdate. Method 1’s
measurement range: 0.0006% ~ 0.010%; method 2’s measurement range:
0.0010% ~ 0.010%.
2 Normative references
The following documents are essential to the application of this document. For
the dated documents, only the versions with the dates indicated are applicable
to this document; for the undated documents, only the latest version (including
all the amendments) are applicable to this standard.
GB/T 6682 Water for analytical laboratory use - Specification and test
methods (ISO 3696)
GB/T 12806 Laboratory glassware - One-mark volumetric flasks (ISO 1042)
GB/T 12808 Laboratory glassware - One-mark volumetric flasks (ISO 648)
GB/T 12809 Laboratory glassware - Principles of design and construction of
volumetric glassware (ISO 384)
GB/T 12810 Laboratory glassware - Volumetric glassware - Methods for use
and testing of capacity (ISO 4787)
3 General
3.1 Unless otherwise specified, only confirmed analytical reagents are used in
the analysis; the water used is distilled or deionized water or water of equivalent
purity, which shall meet the requirements of GB/T 6682.
3.2 The instruments used shall be within the verification period; their
performance shall meet the technical parameter indicators required by the
verification; the glass container shall use the Class A products as specified in
GB/T 12808, GB/T 12809, GB/T 12806; the specific method of use shall refer
to the requirements of GB/T 12810.
4 Method 1 - Cobalt reagent spectrophotometry
4.1 Method summary
The sample is decomposed with hydrogen peroxide or sodium hydroxide
solution; the main molybdenum is complexed with potassium and sodium
tartrate. The cobalt reagent forms an orange-red complex with cobalt in a
phosphate buffer solution at a pH of 6 ~ 7; the absorbance is measured in a
phosphoric acid medium.
4.2 Reagents
4.2.1 Hydrogen peroxide (ρ = 1.10 g/mL), excellent grade pure.
4.2.2 Nitric acid (1 + 1).
4.2.3 Sulfuric acid (1 + 1).
4.2.4 Phosphoric acid (ρ = 1.70 g/mL), excellent grade pure.
4.2.5 Sodium hydroxide solution (200 g/L), excellent grade pure.
4.2.6 Potassium sodium tartrate solution (400 g/L), excellent grade pure.
4.2.7 4-[(5-Chloro-2-pyridine)azo]-1,3-diaminobenzene (cobalt reagent)
ethanol solution (0.025%), stored in a brown bottle.
4.2.8 Buffer solution (pH 6 ~ 7): Weigh 35.5 g of disodium hydrogen phosphate
and dissolve it in 500 mL of water; weigh 34 g of potassium dihydrogen
phosphate and dissolve it in 500 mL of water; mix the two; prepare for use.
4.2.9 Phenolphthalein ethanol solution (1 g/L).
4.2.10 pH test paper (pH 1 ~ 14).
4.2.11 Cobalt standard storage solution: Weigh 0.1000 g of metallic cobalt
(mass fraction ≥ 99.99%) in a 250 mL beaker; add 10 mL of nitric acid (4.2.2)
to dissolve it; add 10 mL of sulfuric acid (4.2.3); heat until sulfuric acid white
smoke appears; remove and cool it; use water to rinse the watch glass and the
beaker wall; add 30 mL of water; boil it; cool it; use water to transfer it into a
4.5.4.1.2 Add 4 mL of potassium sodium tartrate solution (4.2.6), 1.5 mL of
sulfuric acid (4.2.3); add 1 ~ 2 drops of phenolphthalein ethanol solution (4.2.9);
use sodium hydroxide solution (4.2.5) to neutralize it until the solution is light
purple; add sulfuric acid (4.2.3) to fade the purple (pH 6 ~ 7); use pH test paper
to check it. The solution is transferred to a 50 mL colorimetric tube by a small
amount of water; control the volume within 30 mL.
4.5.4.1.3 Add 1.5 mL of cobalt reagent ethanol solution (4.2.7); mix well; add
2.5 mL of buffer solution (4.2.8); mix well; put the colorimetric tube in a boiling
water bath and heat for 5 min; remove and cool it to room temperature;
accurately add 8 mL of phosphoric acid (4.2.4); use water to dilute to the mark;
mix well.
4.5.4.1.4 Move part of the solution (4.5.4.1.3) into a 2 cm cuvette; along with
the blank solution as a reference, measure its absorbance at a wavelength of
550 nm by a spectrophotometer; find out the corresponding content of cobalt
from the working curve .
4.5.4.2 Molybdenum trioxide, ammonium molybdate
Place the sample (4.5.2) in a 150 mL beaker; add 5 mL of sodium hydroxide
solution (4.2.5); heat to dissolve until the solution is clear; cool it down. The
following shall be carried out according to 4.5.4.1.2 ~ 4.5.4.1.4.
4.5.5 Drawing of working curve
4.5.5.1 Pipette 0 mL, 0.10 mL, 0.20 mL, 0.50 mL, 0.80 mL, 1.00 mL of cobalt
standard solution (4.2.12), respectively, into a set of 50 mL colorimetric tubes.
Add 4 mL of potassium sodium tartrate solution (4.2.6); add 1 ~ 2 drops of
phenolphthalein ethanol solution (4.2.9); add sodium hydroxide solution (4.2.5)
dropwise to neutralize the solution until the solution is light purple; then add
sulfuric acid (4.2 .3) to make the purple fade (pH 6 ~ 7); use pH test paper to
check it. Add water to control the volume within 30 mL. The following shall
proceed according to 4.5.4.1.3.
4.5.5.2 Move part of the solution (4.5.5.1) into a 2 cm cuvette; take the reagent
blank as a reference; measure its absorbance at a wavelength of 550 nm by a
spectrophotometer. Draw a working curve with the content of cobalt as the
abscissa and absorbance as the ordinate.
4.6 Calculation of analysis results
The cobalt content is calculated as the mass fraction of cobalt wCo; the value is
expressed in % and calculated according to formula (1):
5.2 Reagents
5.2.1 Hydrogen peroxide (ρ = 1.10 g/mL), excellent grade pure.
5.2.2 Hydrochloric acid (ρ = 1.19 g/mL), excellent grade pure.
5.2.3 Nitric acid (1 + 1).
5.2.4 Citric acid solution (500 g/L), excellent grade pure.
5.2.5 Cobalt standard storage solution: Weigh 0.1000 g of metallic cobalt (≥
99.99%) in a 250 mL beaker; use a small amount of water to m; add 20 mL of
nitric acid (5.2.3); cover a watch glass; heat it at a low temperature to dissolve
it completely; remove and cool to room temperature; transfer to a 1000 mL
volumetric flask; use water to dilute to the mark; mix it uniformly. This solution
1 mL contains 100 μg of cobalt.
5.2.6 Cobalt standard solution: Pipette 10.00 mL of cobalt standard stock
solution (5.2.5) into a 100 mL volumetric flask; add 10 mL of nitric acid (5.2.3);
use water to dilute to the mark; mix well. 1 mL of this solution contains 10 μg of
cobalt.
5.2.7 Mo matrix: The mass fraction of cobalt contained is less than 0.0001%.
5.3 Apparatus
Atomic absorption spectrometer, which is equipped with cobalt hollow cathode
lamp.
Under the best working conditions of the instrument, those which can achieve
the following indicators can be used:
- Characteristic concentration: In a solution consistent with the measurement
solution matrix, the characteristic concentration of cobalt shall not be
greater than 0.035 μg/mL;
- Precision: Use the highest concentration of standard solution to measure
the absorbance 10 times; the standard deviation shall not exceed 1.0% of
the average absorbance; use the lowest concentration of standard solution
(not the "zero" concentration standard solution) to measure the absorbance
10 times; the standard deviation shall not exceed 0.5% of the average
absorbance of the highest concentration;
- The working curve’s linearity: Divide the working curve into 5 equal
segments according to the concentration, and; the ratio of the absorbance
difference between the highest segment and the lowest segment shall not
be less than 0.7.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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