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IS0
I N TERN AT1 O N A L O R G A N IZ AT1 O N FOR S TA N DA R D I ZATl ON
IS0 RECOMMENDATION
R 792
CHEMICAL ANALYSIS OF MAGNESIUM AND ITS ALLOYS
PHOTOMETRIC DETERMINATION OF IRON
(Orthophenanthroline method
applicable to iron content between 0.002 and 0.05
1st EDITION
July 1968
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belongs to IS0 Member Bodies. Reproduction of these
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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
The IS0 Recommendation R 792, Chemical analysis of magnesium and its dloys - Photometric
determination of iron (Orthophenanthroline method applicable to iron content between O. 002 and
0.05 '/J, was drawn up by Technical Committee ISO/TC 79, Light metals and thcir alloys, the Secret-
ariat 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. 965) 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 Y iigoslavia
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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ISOlR 792-1968 (E
IS0 Recommendation R 792 July 1968
CHEMICAL ANALYSIS OF MAGNESIUM AND ITS ALLOYS
PHOTOMETRIC DETERMINATION OF IRON
(Orthophenanthroline method
applicable to iron content between 0.002 and 0.05
1. SCOPE
This IS0 Recommendation describes a photometric method for the determination of iron in
1.1
magnesium and its alloys.
1.2 The method is applicable to the determination of iron content between 0.002 and 0.05
1.3 The method does not apply to the special case of magnesium alloys containing zirconium. In
this IS0 Recommendation this special case is not treated.
2. PRINCIPLE
2. I Attack with hydrochloric acid.
Reduction of ferric iron to bivalent iron by hydroxylammonium chloride.
2.2
Formation in buffered solution between pH 3.5 and pH 4.5 of the orange-red coloured complex,
2.3
bivalent iron-orthophenanthroline.
2.4 Photometric measurement at a wavelength of about 510 nm.*
3. REAGENTS
3.1 H-vdrochloric acid, d = 1. I (approximately 6 N).
Take 500 mi of hydrochloric acid, d = 1.19 (approximately 12 N), and make up the volume to
1000 mi with water.
3.2 Hydroxylammonium chloride solution, 10 g per litre.
Dissolve 1 O g of hydroxylammonium chloride (NH, OH.HC 1) in water and make up the volume
to 1000 mi.
3.3 Buffer solution.
Dissolve 272 g of sodium acetate (CH3COONa.3H,O) in about 500 mi of water, fdter, add
240 ml of glacial acetic acid (CH, COOH), d = 1 .O5 (approximately 17.4 N), then make up the
volume to 1000 ml with water.
Copper, which may interfere if present in appreciable amounts, is largely eliminated in the attack. Of the elements
normally present in aluminium and its alloys, some do not interfere, while others form colourless soluble com-
plexes with orthophenanthroline, which do not absorb at the wavelength at which the photometric measurement
is performed.
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ISO/R 792-1968 (E
3.4 Orthophenanthroline solution. 1 O g per litre
3.4.1 Aqueous solution of orthophenanthroline hydrochloride monohydrate
Dissolve 1 O g of orthophenanthroline hydrochloride monohydrate (C H, N, . HC 1. H, O) in
water, warm slightly in order to complete the solution, cool and make up the volume to
1000 ml.
Alternatively
3.4.2 Alcoholic solution cif orthophenanthroline monohydrate
Dissolve 10 g of orthophcnanthroline monohydrate iCl ,HEN,. l1,O) in ethanol (95
and
make up the volume to 1000 ml with ethanol from the same source.
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 feirous ammonium sulphate [(NH4)2 Fe(SO,), .6H,O] in a little water
and add 30 ml of hydrochloric acid (3.1). Transfer the sc,liitiiin 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 femc
oxide (Fe,O,), previously calcined at 600 OC, in 30 ml of hydr$acliloric acid (3.1). After
cooling. transfer the solution to a 1000 ml volumetric !!ask and make up the volume to
1000 ml with water.
3.6 Standard iron solution, 0.01 g per litre ( I iiit contains 0.01 mg of iron).
Transfer 50.0 mlofthe standard iron solution (3.5) to a 1000 I il volumetric flask, then make up
the volume to 11>00 ml with water. Prepre the solution just before uîe.
4. AP
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