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UDC 661.63 : 543.42
IS0
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
IS0 RECOMMENDATION
R 852
SODIUM TRIPOLYPHOSPHATE AND SODIUM PYROPHOSPHATE
FOR INDUSTRIAL USE
DETERMINATION OF IRON CONTENT
2,2’-BIPYRIDYL SPECTROPHOTOMETRIC METHOD
1st EDITION
October 1968
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
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
The IS0 Recommendation R 852, Sodium tripolyphosphate and sodium pyrophosphate for industrial use -
Determination of iron content - 2,2 Xpvridyl spectrophotometric method, was drawn up by Technical Committee
ISO/TC 47, Chemistry, the Secretariat of which is held by the Ente Nazionale Italian0 di Unificazione (UNI).
Work on this question by the Technical Committee began in 1960 and led, in 1966, to the adoption of a
Draft IS0 Recommendation.
In December 1966, this Draft IS0 Recommendation (No. 1113) 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 :
India
Austria South Africa, Rep. of
Israel
Belgium Spain
Brazil Italy Switzerland
Bulgaria Japan Thailand
Chile Korea, Rep. of Turkey
Czechoslovakia Morocco U.A.R.
France New Zealand United Kingdom
Germany Poland U.S.S.R.
Hungary Romania Yugoslavia
One Member Body opposed the approval of the Draft :
Netherlands
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council, which decided,
in October 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 852-1968(E)
R 852 October 1968
IS0 Recommendation
SODIUM TRIPOLYPHOSPHATE AND SODIUM PYROPHOSPHATE
FOR INDUSTRIAL USE
DETERMINATION OF IRON CONTENT
2,2’-BIPYRIDYL SPECTROPHOTOMETRIC METHOD
1. SCOPE AND FIELD OF APPLICATION
This IS0 Recommendation describes a method for the spectrophotometric determination of the iron
content of sodium tripolyphosphate and sodium pyrophosphate for industrial use, applicable to samples
containing more than 0.001 o/o of iron expressed as Fe.
2. PRINCIPLE
Preliminary hydrolysis of polyphosphates by prolonged boiling in the presence of hydrochloric acid.
Reduction of trivalent iron by means of hydroxylammonium chloride.
Formation of a bivalent iron - 2,2 Lbipyridyl complex in the presence of ammonium acetate at pH 3.1, at a
temperature of 75 “C (under the test conditions, phosphate ions do not interfere).
Spectrophotometric measurement of the coloured complex at a wavelength of about 522 nm.
3. REAGENTS
Distilled water or water of equivalent purity should be used in the test.
Hydrochloric acid, approximately d = 1 .19, 37 o/o (m/m) or 12 N solution.
3.1
3.2 2,2 ‘-bipyridyl, 5 g/l hydrochloric acid solution.
Dissolve 0.50 g of 2,2 Ibipyridyl in 10 ml of approximately d - - 1.19 hydrochloric acid solution and
dilute to 100 ml.
3.3 Ammonium acetate, 300 g/l solution.
Dissolve 300 g of ammonium acetate in water and dilute to l-000 ml.
3.4 Hydroxylammonium chloride, 100 g/l solution.
Dissolve 10 g of hydroxylammonium chloride (NH2 OH.HCl) in water and dilute to 100 ml.
3.5 Iron standard solution, containing 2.00 g/l of Fe.
Weigh, to the nearest 1 mg, 7.022 g of ammonium ferrous sulphate hexahydrate and place in a beaker
of suitable capacity. Add 50 ml of 100 g/l sulphuric acid solution, transfer quantitatively to a 500 ml
one-mark volumetric flask, and dilute to the mark.
1 ml of this standard solution contains 2.0 mg of Fe.
Iron standard solution, containing 0.020 g/l of Fe.
3.6
Transfer 10.0 ml of the iron standard solution (3.5) to a 1000 ml one-mark volumetric flask and dilute
to the mark.
1 ml of this standard solution contains 20 pg of Fe.
The solution should be prepared just before use.
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HO/R 852-1968(E)
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4. APPARATUS
Ordinary laboratory apparatus and
4.1 pH-meter, fitted with glass electrode, sensitivity at least 0.1 pH unit.
4.2 Spectrophotometer, or
4.3 Photoelectric absorptiometer.
5. PROCEDURE
5.1 Test portion
Weigh, to the nearest 1 mg, approximately 10 g of the test sample. If this quantity contains more than
1000 lug of Fe, reduce the quantity of test portion, so as to have a lower iron content, preferably
between 400 and 600 pg.
5.2 Blank test
Place approximately 25 ml of water and 10 ml of the hydrochloric acid solution (3.1) in a conical
flask of approximately 100 ml. Boil until the volume is reduced to about 5 ml.
Cool and transfer the solution to
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