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IS0
I N T ERN AT1 ON A L O RG A N IZ AT1 O N FOR STA N DA RD IZATl ON
IS0 RECOMMEN
DATION
R 793
CHEMICAL ANALYSIS OF ALUMINIUM AND ITS ALLOYS
PHOTOMETRIC DETERMINATION OF IRON
( O rt hop he na nt h ro I i ne met hod
0.05 and 2.50
applicable to iron content between
1st EDITION
July 1968
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore oniy
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
IS0 Recommendation R 793, Chemical analysis of aluminium and its alloys - Photometric
The
determination of iron (Orthophenanthroline method applicable to iron content between 0. 05 and
2.50 'Io), was drawn up by Technical Committee ISOlTC 79, Light metals and their alloys, the
Secretariat of which is held by the Association Française de Normalisation (AFNOR).
Work on this question by the Technical Committee began in 1956 and led, in 1963, to the
adoption of a Draft IS0 Recommendation.
In June 1966, this Draft IS0 Recommendation (NO. 966) was circulated to all the IS0 Member
Bodies for enquiry. It was approved, subject to a few modifications of an editorial nature, by the
following Member Bodies :
Argentina Korea, Rep. of Sweden
Austria India Switzerland
Belgium
Israel Turkey
Brazil Italy U.A.R.
Bulgaria Japan United Kingdom
Canada Netherlands U.S.A.
Chile Norway U.S.S.R.
Czechoslovakia Yugoslavia
Poland
France South Africa,
Germany Rep. of
Hungary Spain
One Member Body opposed the approval of the Draft
Ireland
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which decided, in July 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 793-1968 (E)
~~
IS0 Recommendation R 793 July 1968
CHEMICAL ANALYSIS OF ALUMINIUM AND ITS ALLOYS
PHOTOMETRIC DETERMINATION OF IRON
(Orthophenanthroline method
applicable to iron content between 0.05 and 2.50
1. SCOPE
1.1 This IS0 Recommendation describes a photometric method for the determination of iron in
aluminium and its alloys.
1.2 The method is applicable to the determination of iron content between 0.05 and 2.50 O/'.
1.3 The method does not apply completely to the following special cases for which it should be
modified as described in Annex A and Annex B :
unalloyed aluminium, aluminium-silicon alloys and any other aluminium alloy that
(a)
is not easily attacked with hydrochloric acid (see Annex A);
alloys containing copper (copper content over 5 O/'), zinc (zinc content over 4
(b)
nickel (nickel content over 2 or alloys with a proportional combination of
these elements more than 5 total (see Annex B).
2. PRINCIPLE
2.1
Attack with hydrochloric acid.
2.2 Reduction of ferric iron to bivalent iron by hydroxylammonium chloride.
2.3
Formation in buffered solution between pH 3.5 and pH 4.5 of the orange-red coloured com-
plex, bivalent iron-orthophenanthroline.
2.4 Photometric measurement at a wavelength of about 5 10 nm.*
3. REAGENTS
3.1 Hydrochloric acid, d = 1.1 (approximately 6 N).
Take 500 ml of hydrochloric acid, d = 1.19 (approximately 12 N), and make up the volume to
1000 ml with water.
3.2 Sodium hydroxide solution (5 N)
Dissolve 200g of sodium hydroxide (NaOH) in a nickel basin with about 400 ml of water. After
cooling, transfer the solution to a 1000 ml volumetric flask, rinsing the basin, and make up the
volume to 1000 ml. (Store in polythene containers.)
Hydrochloric acid, d = 1.16 (approximately 10 N)
3.3
Dilute 820 ml of hydrochloric acid, d = 1.19, with water and, after cooling to 20 OC, make up
the volume to 1000 mi. Check the relative density and, if necessasr, adjust the strength of the
solution.
*
Copper, which may interfere if present in appreciable amounts, is largely eliminated in the attack. Of the ele-
ments normally present in aluminium and its alloys, some do not interfere, while others form colourless soluble
complexes with orthophenanthroline, which do not absorb it the wavelength at which the photometric
measurement is performed.
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O/'),
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ISOlR 793 -1968 (1
I
3.4 Mixed reagent
Mix the following solutions in the ratio 1 : 1 :3 by volume :
3.4.1 Hydroxylammonium chloride solution
Dissolve 1 O g of hydroxylammonium chloride (NH2 OH.HC 1) in a little water and make up
the volume to 1000 ml.
3.4.2 ûrthophenan throline soh tion
Dissolve 2.5 g of orthophenanthroline monohydrate (Cl 2H8N2 .H2 O), or 3 g of orthophen-
anthroline hydrocldoride monohydrate (Cl 2HsN2 .HC 1 .H2 O), in water, warm slightly in
order to complete solution, cool and make up the volume to 1000 ml.
3.4.3 Buffer solution
Dissolve 272 g of sodium acetate (CH3COONa.3H20) in about 500 ml of water, filter, add
240 ml of glacial acetic acid (CH3COOH), d = 1.05 (approximately 17.4 N), then make up
the volume to 1000 ml with water.
The mixed reagent should be stored in a dark coloured glass container; it should not be used
after storage for more than four weeks.
3.5 Standard iron solution, 0.2 g per litre (1 ml contains 0.2 mg of iron).
3.5.1 Dissolve 1.4045 g of ferrous ammonium sulphate [(NH,), Fe(SO,), .6H20] in a little water
and add 20 ml of hydrochloric acid (3.1). Transfer the solution to a 1000 ml volumetric flask
and make up the volume to 1000 ml with water.*
Alternatively
3.5.2 Dissolve, by heating, in a 100 ml beaker covered with a watch-glass, 0.2860 g of pure ferric
oxide (Fe203), previously calcined at 600 OC, in 30 ml of hydrochloric acid (3.1). After
cooling, transfer the solution to a 1000 ml volumetric flask and make up the volume to
1000 ml with water.
3.6 Standard iron solution, 0.01 g per litre (1 ml contains 0.01 mg of iron).
Transfer 50.0 ml of the standard iron solution (3.5) to a 1000 ml volumetric flask, then make
up the volume to 1000 ml with water. Prepare the solution just before use.
4. APPARATUS
Ordinary laboratory equipment
4.1
All volumetric apparatus should comply with national standards.
4.2 Electrophotometer or spectrophotometer (wavelength about 5 10 nm).
5. SAMPLING
5.1 Laboratory sample
See the appropriate national standard on sampling.
Test sample
5.2
Chips not more than 1 mm thick should be obtained from the laboratory sample by drilling or
milling. By means of a magnet separate any accidental iron contamination.
*
If the effective strength of the ferrous ammonium sulphate is not known, measure it by titration with potassium
dichromate and correct accordingly the
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